In Press

Articles in press have been peer-reviewed and accepted, which are not yet assigned to volumes/issues, but are citable by Digital Object Identifier (DOI).
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Original Paper
A statistic linkage between extreme cold wave events in southern China and the sea ice extent in Barents-Kara seas from 1289 to 2017
Cunde Xiao, Qi Zhang, Jiao Yang, Zhiheng Du, Minghu Ding, Tingfeng Dou, Binhe Luo
, Available online   , Manuscript accepted  02 February 2023, doi: 10.1007/s00376-023-2227-2
Abstract:
Arctic sea ice loss and the associated enhanced warming has been related to mid-latitude weather and climate changes through modulate meridional temperature gradients linked to circulation. However, contrasting lines of evidence results in low confidence in the influence of Arctic warming on mid-latitude climate. This study examines the additional perspectives that palaeoclimate evidence provides on the decadal relationship between the autumn sea ice extent (SIE) in Barents-Kara (B-K) seas and the extreme cold wave events (ECWEs) occurred in southern China. Reconstruction of winter Cold Index and SIE in B-K seas from 1289 to 2017 show that the significant anti-phase relationship occurred in most periods of SIE decreasing, performing with the cold winter occurred more likely in the low SIE years, associated with the “bridge” role of North Atlantic Oscillation and Siberian High. It is confirmed that the recent frequently occurrence of the ECWEs in southern China is closely related to the sea ice decline in B-K seas. However, our results investigated the linkage is unstable, especially in the high SIE periods, which is probably modulated by the atmospheric internal variability.
The Remarkable Life History of Super Typhoon Hinnamnor (2022) with a record-breaking lifespan over the Western North Pacific
Qian Wang, Dajun Zhao, Duan Yihong, Shoude GUAN, Lin DONG, Hongxiong XU, Hui WANG
, Available online   , Manuscript accepted  01 February 2023, doi: 10.1007/s00376-023-2336-y
Abstract:
Super Typhoon Hinnamnor (2022) was rare and unique in the record over the western North Pacific as throughout its lifespan it featured all of the major frontier issues in typhoon research currently. Specifically, in different stages of its lifespan, it had a sudden change of track, underwent rapid intensification, interacted and merged with another vortex, expanded in size, underwent rapid weakening and had a strong cold wake, eyewall replacement, and extratropical transition. Therefore, a timely identification and review of these typical features of Hinnamnor (2022), as reported in this article, will help update and enrich the case sets for each of these scientific issues and provide a background for more in-depth mechanistic studies of typhoon track, intensity, and structural changes in the future. We believe that Hinnamnor can serve as an excellent benchmark to quickly evaluate the overall performance of different typhoon numerical models in predicting its track, intensity, and structural changes.
Prediction of Seasonal Tropical Cyclone Activity in the NUIST-CFS1.0 forecast system
Ke Peng, Jing-Jia Luo, Yan Liu
, Available online   , Manuscript accepted  31 January 2023, doi: 10.1007/s00376-023-2213-8
Abstract:
Prediction skill of the seasonal tropical cyclone (TC) activity in the Northern Hemisphere is investigated using the coupled climate forecast system (version 1.0) of Nanjing University of Information Science and Technology (NUIST CFS1.0). This assessment is based on the 7-month (May to November) hindcasts consisting of 9 ensemble members during 1982–2019. The simulation results are compared with the Japanese 55-year Reanalysis and observed tropical storms in the Northern Hemisphere. The results show that the overall distributions of the TC genesis and track densities in model hindcasts agree well with the observations, although the seasonal mean TC frequency and accumulated cyclone energy (ACE) are underestimated in all basins due to the low resolution (T106) of the atmospheric component in the model. NUIST CFS1.0 well predicts the interannual variations of TC frequency and ACE in the North Atlantic (NA) and eastern North Pacific (ENP), which have a good relationship with indexes based on the sea surface temperature. In the western North Pacific (WNP), the NUIST CFS1.0 can well capture the ACE that is significantly correlated with the El Niño-Southern Oscillation (ENSO), while it is difficult to forecast the interannual variation of TC frequency in this area. When the WNP is further divided into the eastern and western subregions, the model displays improved TC activities. Additionally, it is found that the bias in the predicted TC genesis location leads to inaccurate TC-environment relationship, which may affect the capability of model in well reproducing the interannual variations of TC activities.
Processes-based attribution of four major surface melting events over the Antarctic Ross Ice Shelf
Wenyi LI, Yuting WU, Xiaoming Hu
, Available online   , Manuscript accepted  31 January 2023, doi: 10.1007/s00376-023-2287-3
Abstract:
Ross-Amundsen sector is experiencing accelerating warming trend and more intensive advective influx of marine air streams, massive surface melting prone to occur more frequently in ice shelf and put the West Antarctica Ice Sheet at greater risk of degradation. This study shows the connection between surface melting and prominent intrusion of warm and humid air flows from lower latitudes. By applying Climate Feedback-Response Analysis Method (CFRAM), the temporal surge of the downward longwave (LW) surface radiative fluxes over the Ross Ice Shelf (RIS) and adjacent regions during four historically massive RIS surface melting events are decomposed to identify the main contributor. It is found that the intrusion of warm and humid air flows from lower latitude conduces to warm air temperature and more water vapor anomalies, as well as the clouds development. These changes make cooperative impact on abnormal enhancement of the downward LW surface radiative fluxes, contributing significantly the surface warming and causing massive ice melting.
Seasonal prediction skill and biases in GloSea5 relating to the East Asia winter monsoon
Daquan Zhang, lijuan chen, Gill Martin, zongjian ke
, Available online   , Manuscript accepted  31 January 2023, doi: 10.1007/s00376-023-2258-8
Abstract:
The simulation and prediction of the climatology, interannual variability of East Asia winter monsoon (EAWM) and associated atmospheric circulation was investigated, using the hindcast data from Global Seasonal Forecast System version 5 (GloSea5), with a focus on the evolution of model bias among different forecast lead times. While GloSea5 well reproduces the climatological mean of large scale circulation systems related to EAWM, systematic biases exist, including a cold bias for most mainland China, especially for North and Northeast China. GloSea5 shows robust skill in predicting the EAWM intensity index 2 months ahead, which can be attributed to the performance in representing the leading modes of surface air temperature and associated circulation background. GloSea5 realistically reproduces the synergistic effect of El Niño-Southern Oscillation (ENSO) and Arctic Oscillation (AO) on EAWM, especially for the western North Pacific anticyclone (WNPAC). Compared with North Pacific and North America, the representation of circulation anomalies over Eurasia is poor, especially for the sea level pressure (SLP), which limits the the prediction skill of surface air temperature of East Asia. The representation of SLP anomalies might be associated with the model performance in simulating the interaction between atmospheric circulations and underlying surface conditions.
Hybrid seasonal prediction of meridional temperature gradient associated with “Warm Arctic-Cold Eurasia”
tianbao xu, Zhicong Yin, Xiaoqing MA, Yanyan Huang, Hui-Jun WANG
, Available online   , Manuscript accepted  31 January 2023, doi: 10.1007/s00376-023-2226-3
Abstract:
The meridional gradient of surface air temperature associated with “Warm Arctic-Cold Eurasia” (GradTAE) is closely related to climate anomalies and weather extremes in the mid-low latitudes. However, the Climate Forecast System Version 2 (CFSv2) shows a poor capability for the GradTAE prediction. Based on the year-to-year increment approach, a hybrid seasonal prediction model for GradTAE in winter (HMAE) is conducted with observed September sea ice over the Barents-Kara Sea, October sea surface temperature over the North Atlantic, September soil moisture in southern North America and CFSv2 forecasted winter sea ice over the Baffin Bay, Davis Strait and Labrador Sea. The HMAE model demonstrates a good capability for predicting GradTAE with a significant correlation coefficient of 0.84 and the percentage of the same sign is 88% in cross-validation during 1983−2015. The HMAE also maintains high accuracy and robustness during independent predictions of 2016−2020. Meanwhile, the HMAE model can well predict the GradTAE in 2021 as an experiment of routine operation. Moreover, the well-predicted GradTAE is useful in the prediction of the large-scale pattern of “Warm Arctic-Cold Eurasia” and has potentials to enhance the skill of surface air temperature occurrences in east of China.
Linkage of the Decadal Variability of Extreme Summer Heat in North China with the IPOD since 1981
Tiejun Xie, Ji Wang, Taichen FENG, Ting Ding, Liang Zhao
, Available online   , Manuscript accepted  28 January 2023, doi: 10.1007/s00376-023-2304-6
Abstract:
Extreme summer heat can have serious impacts on human health and economic life in North China. Here, we explore the decadal variability and mechanism of the number of the extreme heat days in early-mid summer (June and July) of the heat major occurrence period in North China (NCSH). Observational analysis shows that there is a significant decadal variability in NCSH during the period 1981–2021 and it is potentially linked to the Indo-Pacific warm pool and Northwest Pacific Ocean dipole (IPOD) in early-mid summer. The analyses of dynamical diagnostics and linear baroclinic model (LBM) show that the positive IPOD in early-mid summer can excite upward vertical wind anomalies in the South China-East China Sea region, shifting the position of western Pacific subtropical high (WPSH) to the east or weakening its control intensity in the South China-East China Sea region, thus generating a positive geopotential height quadrupole (EAWPQ) pattern in the East Asia-Northwest Pacific region. And then the EAWPQ can cause the compression of the air over North China by regulating the tropospheric thickness anomalies in North China, thus increasing the decadal NCSH, and vice versa. Finally, the empirical model adding a linear trend can better simulate the decadal NCSH than the empirical model solely by the IPOD index, suggesting that the decadal variability of NCSH may be a combined contribution of the decadal IPOD and external linear forcing.
Assessing Performances of CMIP6 Models in Simulating Droughts across Global Drylands
Xiaojing YU, Lixia Zhang, Tian-Jun ZHOU, Jianghua Zheng
, Available online   , Manuscript accepted  28 January 2023, doi: 10.1007/s00376-023-2278-4
Abstract:
Both historical change attribution and future projection of droughts rely heavily on climate models. However, a reasonable simulation of drought has been a challenge and the performances of the current state-of-the-art Coupled Model Intercomparison Project phase 6 (CMIP6) models remain unknown. Here, both the strengths and weaknesses of CMIP6 models in simulating droughts and corresponding hydrothermal conditions in drylands are assessed. While the general patterns of simulated meteorological elements in drylands resemble the observations, the annual precipitation is overestimated by ~33% (with model spread 2.3–77.2%), along with an underestimation of potential evapotranspiration (PET) by ~32%(5.8–69.3%). The water deficit condition, measured by the difference between precipitation and PET, is 50%(20.2–94.5%) weaker than observation. The CMIP6 models show weaknesses in capturing the climate mean drought characteristics in drylands, particularly with occurrence and duration largely underestimated in the hyperarid Afro-Asian areas. Nonetheless, the drought-associated meteorological anomalies, including less precipitation, warmer temperature, higher evaporative demand and increased water deficit conditions, are reasonably reproduced. The magnitude of precipitation (water deficit) associated with dryland droughts is overestimated by 28%(24%) than observation. The observed increasing trends in drought fraction area and occurrence and corresponding meteorological anomalies during 1980–2014 are reasonably reproduced. But the increasing in drought characteristics and associated precipitation and water deficit are obviously underestimated after the late 1990s, especially for mild and moderate droughts, indicating a weaker responses of dryland drought changes to global warming in CMIP6 models. Our results suggest that it is imperative to employ bias correction approaches in drought-related studies over drylands.
Dynamical Predictability of Leading Interannual Variability Modes of Asian-Australian Monsoon in Climate Models
Lin Wang, Hongli Ren, Fang ZHOU, Nick Dunstone, Xu Xiangde
, Available online   , Manuscript accepted  28 January 2023, doi: 10.1007/s00376-023-2288-2
Abstract:
Dynamical prediction of the Asian-Australian monsoon (AAM) has been an important and long-standing issue in climate science. In this study, predictability of the first two leading modes of the AAM is studied using retrospective prediction datasets from the seasonal forecasting models in four operational centers worldwide. Results show that model predictability of the leading AAM modes is sensitive to their definitions in terms of different seasonal sequences, especially for the second mode. The first AAM mode, from various seasonal sequences, concur with the El Niño phase transition in the eastern-central Pacific. The second mode initialized from boreal summer and autumn lead the El Niño by about 1 year but can be during the decay phase of El Niño when initialized from boreal winter and spring. Our findings hint that ENSO, as an early signal, is conducive to better performance of model predictions in capturing spatiotemporal variations of the leading AAM modes, but the persistence barrier of ENSO in spring leads to a poor skill in spatial features. The multi-model ensemble (MME) mean show some advantages in capturing spatiotemporal variations of the AAM modes but has not contributed apparent improvement compared to the best individual model in predicting temporal features. The BCC_CSM1.1M shows promising skill in predicting the two AAM indices associated with two leading AAM modes. The predictability demonstrated in this study is potentially useful for the AAM prediction in operational and climate services.
Rainfall Monitoring Using a Microwave Links Network: A Long-term Experiment in East China
Xichuan Liu, Kun Zhao, Mingzhong ZOU, Kang Pu, Kun Song
, Available online   , Manuscript accepted  28 January 2023, doi: 10.1007/s00376-023-2104-z
Abstract:
The first long-term rainfall monitoring experiment using commercial microwave links (CMLs) network in East China is introduced. It is located in Jiangyin, Jiangsu Province, and there are 49 links with frequencies ranging from 15 GHz to 26 GHz and lengths from 1.14 km to 4.78 km. An OTT PARSIVEL disdrometer is deployed to modify the local rain-induced attenuation relationship, and the CML observations are compared simultaneously with five rain gauges. The inversion parameters of the CML are optimized by minimizing the accumulated rainfall of historical rainfall events. The inversion results show that the daily accumulated rainfall retrieved by the CMLs is in good agreement with the rain gauge measurements. As an opportunistic approach to monitor near-surface rainfall with high spatial-temporal representativeness and accuracy, the CML can be used to monitor and forecast urban flood disasters, especially in regions where conventional meteorological instruments are difficult to deploy widely.
A Lagrangian Trajectory Analysis of Azimuthally Asymmetric Equivalent Potential Temperature in the Outer Core of Sheared Tropical Cyclones
Yufan Dai, Qingqing Li, Xinhang Liu, Lijuan Wang
, Available online   , Manuscript accepted  28 January 2023, doi: 10.1007/s00376-023-2245-0
Abstract:
In this study, the characteristics of azimuthally asymmetric equivalent potential temperature (θ_e) distributions in the outer core of tropical cyclones (TCs) encountering weak and strong vertical wind shear are examined using a Lagrangian trajectory method. Evaporatively forced downdrafts in the outer rainbands can transport low-entropy air downward, resulting in the lowest θ_e in the downshear-left boundary layer. Quantitative estimations of θ_e recovery indicate that air parcels, especially originating from the downshear-left outer core, can gradually revive from low entropy through surface enthalpy fluxes as the parcels move cyclonically. As a result, the maximum θ_e is observed in the downshear-right quadrant of the highly sheared TC. The trajectory analyses also indicate that parcels that move upward in the outer rainbands and those that travel through the inner core due to shear contribute dominantly to the midlevel enhancement of θ_e in the downshear-left outer core. In particular, the former plays an overarching role in such an increase in θ_e, while the latter plays a secondary role. As a result, moist potential stability occurs in the middle-to-lower troposphere in the downshear-left outer core.
Evaluation of long-term performance of microwave radiometers onboard Chinese Fengyun satellites
Wenying He, Hongbin Chen, Xiang-Ao XIA, Shengli Wu, Peng Zhang
, Available online   , Manuscript accepted  10 January 2023, doi: 10.1007/s00376-023-2199-2
Abstract:
Accurate brightness temperature (BT) is a top priority for retrievals of atmospheric and surface properties. Microwave Radiation Imagers (MWRI) on Chinese Fengyun-3 (FY-3) serial polar-orbiting satellites have been providing abundant BT data since 2008, showing great potential for retrievals of atmospheric parameters and surface properties. Much work has been done to evaluate short-term MWRI observations, but it remains unclear on the long-term performance of MWRI. In this paper, the operational MWRI BT during 2012-2019 was carefully examined by using the simultaneous Advanced Microwave Scanning Radiometer 2 (AMSR2) BTs as the reference. A significant correlation between BTs from MWRI and AMSR2 was found. The BT difference between MWRI/FY3B and AMSR2 during 2012-2019 increased gradually over time. As compared with MWRI/FY3B, MWRI/FY3D BTs over land were much closer to those of AMSR2. The ascending and descending orbit difference for MWRI/FY3D is also much smaller than that for MWRI/FY3B. Both suggest the improvement of MWRI/FY3D over MWRI/FY3B. A substantial BT difference between AMSR2 and MWRI was found over water, even exceeding 5 K at the vertical polarization channels. A similar BT difference was found over polar water based on the simultaneous conical overpassing (SCO) method. Radiative transfer model simulations suggested the substantial BT differences at the vertical polarization channels of MWRI and AMSR2 over water were partly accounted for by their difference in the incident angle; however, the underestimation of the operational MWRI BT over the water was still a very important issue.
Asymmetry of Salinity Variability in the Tropical Pacific during Interdecadal Pacific Oscillation Phases
hai zhi, Zihui YANG, Rong-Hua ZHANG, Pengfei LIN, Jifeng QI, Huang Yu, Dong Meng
, Available online   , Manuscript accepted  06 January 2023, doi: 10.1007/s00376-022-2284-y
Abstract:
It has been recognized that salinity variability in the tropical Pacific is closely related to the Interdecadal Pacific Oscillation (IPO). Model simulations during 1900–2017 are used to illustrate an obvious asymmetry of salinity variability in the tropical Pacific during positive and negative IPO phases. During positive IPO phases, the salinity variability amplitude in the tropical Pacific is larger than that during negative IPO phases, with a more westward shift of large sea surface salinity (SSS) anomaly along the equator. Salinity budget analyses show that the asymmetry of salinity variability during positive and negative IPO phases is dominated by the difference in the surface forcing associated with the freshwater flux (FWF, precipitation (P) minus evaporation (E)), with its contribution of 40–50% near the dateline on the equator. Moreover, the relationships between the salinity variability and its budget terms also show differences in their lead-lag correlations during positive and negative IPO phases. These differences in salinity variability during different IPO phases act to produce asymmetric effects on density which reduce or enhance upper-ocean stratification. Therefore, the salinity effects may modulate the intensity of El Niño-Southern Oscillation (ENSO), with enhanced (reduced) El Niño but reduced (enhanced) La Niña during positive (negative) IPO phases by 1.6°C psu−1 (1.3°C psu−1), respectively. It suggested that the asymmetry of salinity variability may be related to the recent change in ENSO amplitude associated with the IPO, which can help explain and represent ENSO diversity.
Interannual Meridional Displacement of Upper-tropospheric Westerly Jet over the Western East Asia in Summer
Si-Ning LING, Ri-Yu LU, Hao Liu, Yali Yang
, Available online   , Manuscript accepted  28 December 2022, doi: 10.1007/s00376-022-2279-8
Abstract:
The interannual meridional displacement of upper-tropospheric westerly jet over the eastern East Asia in summer has been well ed. This study investigates the interannual meridional displacement of westerly jet over the western East Asia in summer, which is distinct from its eastern counterpart. The results show that the meridional displacement of western East Asian jet shows a clear asymmetric feature, that is, there are remarkable differences between the southward and northward displacement of jet. The southward displacement of jet corresponds to the suppressed convection in the tropical western North Pacific and Maritime Continent, and enhanced convection in the equatorial Pacific, which can be explained by the warming in the northern Indian Ocean and equatorial eastern Pacific. These tropical anomalies resemble somewhat those associated with the eastern East Asian jet variability. However, the northward displacement of western East Asia does not correspond to significant convection and SST anomalies in the tropics. It is found that the northward displacement of jet corresponds well to the positive phase of Arctic Oscillation. Furthermore, the meridional displacement of the western jet has asymmetric impacts on rainfall and surface air temperatures in East Asia. When the western jet shifts northward, more precipitation is found over South China and Northeast China, and higher temperatures appear in northern China. By contrast, when the jet shifts southward, more precipitation appears over the East Asian rainy belt, including the Yangtze River valley, South Korea, and southern and central Japan, and higher temperatures occur in Southeast Asia and South Asia.
Characteristics of PM2.5 and its reactive oxygen species in heating energy transition and estimation of its impact on the environment and health in China – A case study in the Fenwei Plain
Zexuan WANG, Hongmei Xu, Rong FENG, Yunxuan GU, Jian SUN, Suixin Liu, Ningning Zhang, Dan LI, Tao WANG, Linli QU, Steven Sai Hang Ho, Zhenxing SHEN, Junji CAO
, Available online   , Manuscript accepted  28 December 2022, doi: 10.1007/s00376-022-2249-1
Abstract:
To reduce the adverse effects of traditional domestic solid fuel, the central government has begun to implement a clean heating policy in northern China in 2017. Clean coal is an alternative low-cost fuel for rural households at the present stage. In this study, 18 households that used lump coal, biomass, and clean coal as the main fuel were selected to evaluate the benefits of clean heating transformation in Tongchuan, an energy city in the Fenwei Plain, China. Both indoor and personal exposure (PE) samples of fine particulate matter (PM2.5) were synchronically collected. Compared with the lump coal and biomass groups, the indoor PM2.5 concentration in the clean coal group is 43.6% and 20.0%, respectively, lower, while the values are 16.8% and 21.3% lower in the personal exposure samples. PM2.5-bound elements Cd, Ni, Zn, and Mn strongly correlated with reactive oxygen species (ROS) levels in all fuel groups, indicating that transition metals are the principal components to generate oxidative stress. Using a reliable estimation method, it is predicted that after the substitution of clean coal as a household fuel, the all-cause, cardiovascular, and respiratory disease that caused female death per year could be reduced by 16, 6, and 3, respectively, in the lump coal group, and 22, 8, and 3, respectively, in the biomass group. Even though the promotion of clean coal gained impressive environmental and health benefits, the efficiencies are still limited. More environmental-friendly energy sources must be promoted in the rural regions of China.
Asymmetric drying and wetting trends in eastern and western China
Wen Wu, Fei Ji, Shujuan Hu, Yongli He
, Available online   , Manuscript accepted  23 December 2022, doi: 10.1007/s00376-022-2216-x
Abstract:
As an important factor that directly affects agricultural production, the social economy and policy implementation, the changes in dry/wet conditions have caused widespread concern. However, previous research has always concentrated on the long-term linear changes of dry/wet conditions, while the detection and evolution of dry/wet changes along a nonlinear trend have received less attention. The findings in nonlinear trend of annual aridity index obtained by ensemble empirical mode decomposition (EEMD) method reveal that the change in dry/wet conditions in China is asymmetric and can be characterized by contrasting features in both time and space in China. Spacially, most areas in western China have experienced the transitions from drying to wetting, while opposite changes have occurred in most areas of eastern China. In terms of time, the transitions occurred earlier in western China than that in eastern China. Research of the asymmetric spatial characteristics on dry/wet conditions make up for the inadequacy of the previous studies focusing only on the temporal evolution. At the same time, it is a remedy for the inadequacy of traditional research on linear trend of century scale. Also, research of nonlinear trend has maken our understanding of the drying/wetting changes in China more comprehensive.
Impact of a revised trigger-closure of the double-plume convective parameterization on precipitation simulation over East Asia
Xiaohan Li, Yi Zhang, Yanluan Lin, Xindong Peng, Baiquan ZHOU, Panmao Zhai, Jian Li
, Available online   , Manuscript accepted  16 December 2022, doi: 10.1007/s00376-022-2225-9
Abstract:
A double-plume convective parameterization scheme is revised to improve the precipitation simulation of a global model (Global-to-Regional Integrated Forecast System; GRIST). The improvement is achieved by considering the effect of large‐scale dynamic processes on the trigger of deep convection. The closure based on dynamic CAPE is improved accordingly to allow other processes to consume CAPE under the more restricted convective trigger condition. The revised convective parameterization is evaluated with a variable-resolution model setup (110-35 km, refined over East Asia). AMIP-type simulations demonstrate that the revised convective parameterization substantially delays the daytime precipitation peaks over most land areas, leading to an improved diurnal cycle. This corresponds to a delay and reduction of the frequency of precipitation in the afternoon. Meanwhile, changes in the threshold of trigger function show a small impact on the diurnal amplitude of precipitation because of the consistent setting of dCAPE-based trigger and closure. The mean precipitation remains reasonable, with some improvements seen in the southern slope of the Tibetan Plateau. The revised scheme increases convective precipitation at the low levels of the windward slope and reduces the large-scale precipitation over the upper slope. It shifts the rainfall peak southward, leading to a better agreement with the observation.
Fluorescence Properties and Chemical Composition of Fine Particles in the Background Atmosphere of North China
Ping Li, Siyao Yue, Xiaoyang Yang, Di Liu, Qiang Zhang, Wei Hu, Shengjie Hou, Wanyu Zhao, Hong Ren, Gang Li, Yuanguan Gao, Junjun Deng, Qiaorong Xie, Yele Sun, Zifa Wang, Pingqing Fu
, Available online   , Manuscript accepted  13 December 2022, doi: 10.1007/s00376-022-2208-x
Abstract:
To understand the aerosol characteristics in a regional background environment, we collected fine particle (PM2.5, n = 228) samples over a one-year period at the Shangdianzi (SDZ) station, which is a Global Atmospheric Watch regional background station in North China. The chemical and optical characteristics of PM2.5 were analyzed, including organic carbon, elemental carbon, water-soluble organic carbon, water-soluble inorganic ions, and fluorescent components of water-soluble organic matter. We apportion the source factors of major aerosol components and further analyze the sources of the fluorescent chromophores. The major chemical components of PM2.5 at SDZ were NO3-, organic matter, SO42-, and NH4%2B. Annually, water-soluble organic carbon contributed 48 ± 15% to the total organic carbon. Secondary formation (52%) and fossil fuel combustion (63%) are the largest sources of water-soluble organic matter and water-insoluble organic matter, respectively. In addition, three humic-like and one protein-like matter were identified via parallel factor analysis for excitation-emission matrices. The fluorescence intensities of the components were highest in winter and lowest in summer, indicating the main impact of burning sources. This study contributes to understanding the chemical and optical characteristics of ambient aerosols in the background atmosphere.
Black carbon size in snow of Chinese Altai Mountain in Central Asia
Yulan Zhang, Shichang Kang, Tanguang GAO, Michael SPRENGER, Wei ZHANG, Zhaoqing WANG
, Available online   , Manuscript accepted  07 December 2022, doi: 10.1007/s00376-022-2141-z
Abstract:
Black carbon (BC) in snow plays on important role to enhance snow melting. However, current studies mostly focused on BC concentrations, few on their size distributions in snow which affected BC’s effect on albedo changes. Here we presented refractory BC (rBC) concentrations and size distributions in snow collected from Chinese Altai Mountains in Central Asia from November 2017 to April 2018. The results revealed that the average rBC concentrations were 5.77 and 2.82 ng g−1 for the surface snow and sub-surface snow, which were relatively higher in the melting season (April) than that in winter (November-January). The mass median volume-equivalent diameter of rBC size in surface snow was approximately at 120−150 nm, which was typically smaller than that in the atmosphere (about 200 nm for urban atmosphere). However, there existed no specific mass median volume-equivalent diameter of BC size for sub-surface snow in winter. While during the melting season, the median mass size of refractory BC in sub-surface snow was similar to that in surface snow. Backward trajectories indicated that anthropogenic sourced BC dominated rBC in snow (70−85%) of this study. This study will enhance our understanding on BC size distributions in snow, and highlight the possible impact of BC size on climate effect.
Raindrop Size Distribution Measurements at High Altitudes in the Northeastern Tibetan Plateau during Summer
Han Huibang, Yuxin Zhang, Tian Jianbing, Xiaoyan Kang
, Available online   , Manuscript accepted  01 December 2022, doi: 10.1007/s00376-022-2186-z
Abstract:
Characteristics of raindrop size distribution during summer are studied by using the data from six Parsivel disdrometers located in the northeastern Tibetan Plateau. The analysis focuses on convective and stratiform precipitation at high altitudes from 2434 m to 4202 m. The results show that the contribution of the stratiform and convective precipitation with the rain rate of 1–5 mm h−1 to total precipitation increases with the altitude, and the raindrop scale and number concentration of convective precipitation were larger than stratiform precipitation. The droplet size spectra of both stratiform and convective precipitation show a single peak with a peak particle size was between 0.31-0.50 mm, and they have essentially the same peak particle size and number concentration at the same altitude. The maximum spectral widths of stratiform clouds are between 4 mm and 5 mm, while those of convective clouds range from 4 mm to 8 mm. The Gamma distribution is more suitable than the Marshall-Palmer distribution in terms of the actual raindrop spectrum distribution. The stratiform precipitation particles are smaller with higher number concentration, while the opposite is true for the convective precipitation particles. The convective precipitation particles drop faster than stratiform precipitation particles when the particle size exceeds 2 mm, and the falling velocity of raindrops after standard curve fitting is underestimated during the observation period. Moreover, conventional radar estimation methods would underestimate the precipitation in the northeastern Tibetan Plateau.
The Warm Arctic–Cold Eurasia Pattern and Its Key Region in Winter in CMIP6 Model Simulations
Liang ZHAO, Yunwen LIU, Yihui DING, Qingquan LI, Wei DONG, Xinyong SHEN, Wei CHENG, Haoxin YAO, Ziniu XIAO
, Available online   , Manuscript accepted  29 November 2022, doi: 10.1007/s00376-022-2201-4
Abstract:
An enhanced Warm Arctic–Cold Eurasia (WACE) pattern has been a notable feature in recent winters of the Northern Hemisphere. However, divergent results between model and observational studies of the WACE still remain. This study evaluates the performance of 39 climate models participating in the Coupled Model Intercomparison Project Phase 6 (CMIP6) in simulating the WACE pattern in winter of 1980–2014 and explores the key factors causing the differences in the simulation capability among the models. The results show that the multimodel ensemble (MME) can better simulate the spatial distribution of the WACE pattern than most single models. Models that can/cannot simulate both the climatology and the standard deviation of the Eurasian winter surface air temperature well, especially the latter, usually can/cannot simulate the WACE pattern well. This mainly results from the different abilities of the models to simulate the range and intensity of the warm anomaly in the Barents Sea–Kara seas (BKS) region. Further analysis shows that a good performance of the models in the BKS area is usually related to their ability to simulate location and persistence of Ural blocking (UB), which can transport heat to the BKS region, causing the warm Arctic, and strengthen the westerly trough downstream, cooling central Eurasia. Therefore, simulation of UB is key and significantly affects the model’s performance in simulating the WACE.
An interdecadal change in the influence of NAO on Atlantic-induced Arctic daily warming around the mid-1980s
Cen Wang, Baohua Ren, Gen Li, Jianqiu Zheng, Linwei Jiang, Di Xu
, Available online   , Manuscript accepted  28 November 2022, doi: 10.1007/s00376-022-2218-8
Abstract:
After approaching 0 °C owing to an Atlantic storm at the end of 2015, the Arctic temperature approached 0 °C again in 2022, indicating that the Arctic daily warming event remains a concern. The NCEP/NCAR Reanalysis dataset was used to investigate the influence of NAO on the Arctic winter daily warming event induced by the Atlantic storm, known as the Atlantic pattern-Arctic rapid tropospheric daily warming (Atlantic-RTDW) event. Atlantic-RTDW events are triggered by Atlantic storms with warm and humid air masses moving into the Arctic. Furthermore, an interdecadal change in the influence of NAO on the Atlantic-RTDW events frequency around the mid-1980s was observed. Specifically, before the mid-1980s (pre-transition period), 500 hPa southerly (northerly) wind anomalies occupied the North Atlantic (NA) in the positive (negative) phase of NAO, which increased (decreased) the Atlantic-RTDW events occurrence by steering Atlantic storms into (away from) the Arctic; thus, NAO could influence the Atlantic-RTDW events frequency. However, the relationship between the NAO and the Atlantic-RTDW events frequency has weakened since the mid-1980s (post-transition period). In the post-transition period, such 500 hPa southerly (northerly) wind anomalies over the NA hardly existed in the positive (negative) phase of NAO, which was attributed to the stronger Atlantic storm track (AST) activity intensity than that in the pre-transition period. During this period, the strong AST induced an enhanced NAO-related cyclone via transient eddy-mean flow interactions, resulting in the disappearance of southerly and northerly wind anomalies over the NA.
Seasonal Prediction of Extreme High Temperature Days in Southwestern China based on the Physical Precursors
Zhiyi Zhou, Juan Li, Haishan Chen, Zhiwei Zhu
, Available online   , Manuscript accepted  24 November 2022, doi: 10.1007/s00376-022-2075-5
Abstract:
Extreme high temperatures are occurring more frequently in southwestern China, causing huge impacts upon the local ecological system and economic development. However, accurate prediction of extreme high temperature days (EHDs) in this region is still an unsolved challenge. Based on spatial-temporal characteristic of the EHDs over China, a domain-averaged EHDs index over southwestern China (SWC-EHDs) during April-May is defined. The simultaneous dynamic and thermodynamic fields associated with the increased SWC-EHDs are a local upper-level anticyclonic (high-pressure) anomaly and wavy geopotential height anomaly patterns over Eurasia. Tracking back the origins of the lower boundary anomalies, two physically meaningful precursors are detected for SWC-EHDs, i.e., the tripolar SST change tendency from December-January to February-March in the northern Atlantic and the February-March mean snow depth in central Asia. Using these two selected predictors, a physics-based empirical model is conducted in training period of 1961–2005 and obtain a skillful prediction of EHDs index with correlation coefficient of 0.76 in independent forecast period (2006–2019), suggesting that 58% of total SWC-EHDs variability is predictable. This study provides an estimate for the lower bound of the seasonal predictability of EHDs as well as the hydrological drought over southeastern China.
Phosphorus limitation on carbon sequestration in China under RCP8.5
Jing Peng, Li Dan, xiba tang
, Available online   , Manuscript accepted  23 November 2022, doi: 10.1007/s00376-022-2195-y
Abstract:
Currently, there is a lack of understanding regarding carbon (C) sequestration in China arising as a result of phosphorus (P) limitation. In this study, a global land-surface model (CABLE) was used to investigate the response of C uptake to P limitation after 1901. In China, P limitation resulted in reduced net primary production (NPP), heterotrophic respiration, and net ecosystem production (NEP) in both the 2030s and the 2060s. The reductions in NEP in the period 2061–2070 varied from 0.32 Pg C yr−1 in China to 5.50 Pg C yr−1 at the global scale, translating to a decrease of 15.0% for China and 7.6% globally in the period 2061–2070, relative to the changes including C and nitrogen cycles. These ranges reflect variations in the magnitude of P limitation on C uptake (or storage) at the regional and global scales. Both in China and at the global scale, these differences can be attributed to differences in soil nutrient controls on C uptake, or positive feedback between NPP and soil deposition rates, or both. Our results highlight the strong ability of P limitation to influence the pattern, response and magnitude of C uptake under future conditions (2030s–2060s), which may help to clarify the potential influence of P limitation when projecting C uptake in China.
The Climate Response to Global Forest Area Changes under Different Warming Scenarios in China
Ying HUANG, Anning HUANG, Jie TAN
, Available online   , Manuscript accepted  21 November 2022, doi: 10.1007/s00376-022-2230-z
Abstract:
Human activities have notably affected the Earth’s climate through greenhouse gases (GHG), aerosol, and land use/land cover change (LULCC). To investigate the impact of forest changes on regional climate under different shared socioeconomic pathways (SSPs), changes in surface air temperature and precipitation over China under low and medium/high radiative forcing scenarios from 2021 to 2099 are analyzed using multimodel climate simulations from the Coupled Model Intercomparison Project Phase 6 (CMIP6). Results show that the climate responses to forest changes are more significant under the low radiative forcing scenario. Deforestation would increase the mean, interannual variability, and the trend of surface air temperature under the low radiative forcing scenario, but it would decrease those indices under the medium/high radiative forcing scenario. The changes in temperature show significant spatial heterogeneity. For precipitation, under the low radiative forcing scenario, deforestation would lead to a significant increase in northern China and a significant decrease in southern China, and the effects are persistent in the near term (2021–40), middle term (2041–70), and long term (2071–99). In contrast, under the medium/high radiative forcing scenario, precipitation increases in the near term and long term over most parts of China, but it decreases in the middle term, especially in southern, northern, and northeast China. The magnitude of precipitation response to deforestation remains comparatively small.
Bias Analysis in the Simulation of the Western North Pacific Tropical Cyclone Characteristics by Two High-Resolution Global Atmospheric Models
Qiyang LIU, Fengxue QIAO, Yongqiang YU, Yiting ZHU, Shuwen ZHAO, Yujia LIU, Fulin JIANG, Xinyu HU
, Available online   , Manuscript accepted  17 November 2022, doi: 10.1007/s00376-022-2159-2
Abstract:
This study compares the atmosphere-only HighResMIP simulations from FGOALS-f3-H (FGOALS) and MRI-AGCM3-2-S (MRI) with respect to tropical cyclone (TC) characteristics over the Western North Pacific (WNP) for the July–October months of 1985–2014. The focus is on investigating the role of the tropical easterly jet over the Western Pacific (WP_TEJ) in modulating the simulation biases in terms of their climatological distribution and interannual variability of WNP TC genesis frequency (TCGF) based on the analysis of the genesis potential index (GPI). Results show that the two models reasonably capture the main TC genesis location, the maximum center of frequency, and track density; however, their biases mainly lie in simulating the intense TCs and TCGF distributions. The MRI better simulates the wind-pressure relationship (WPR) but overestimates the proportion of super typhoons (SSTYs). At the same time, FGOALS underestimates the WPR and the proportion of SSTYs but better simulates the total WNP TC precipitation. In particular, FGOALS overestimates the TCGF in the northeastern WNP, which is strongly tied to an overestimated WP_TEJ and the enhanced vertical circulation to the north of its entrance region. In contrast, the MRI simulates a weaker WP_TEJ and vertical circulation, leading to a negative TCGF bias in most of the WNP. Both models exhibit comparable capability in simulating the interannual variability of WP_TEJ intensity, but the composite difference of large-scale atmospheric factors between strong and weak WP_TEJ years is overestimated, resulting in larger interannual anomalies of WNP TCGF, especially for FGOALS. Therefore, accurate simulations of the WP_TEJ and the associated oceanic and atmospheric factors are crucial to further improving WNP TC simulations for both models.
Different Turbulent Regimes and Vertical Turbulence Structures of the Urban Nocturnal Stable Boundary Layer
Yu SHI, Qingcun ZENG, Fei HU, Weichen DING, Zhe ZHANG, Kang ZHANG, Lei LIU
, Available online   , Manuscript accepted  09 November 2022, doi: 10.1007/s00376-022-2198-8
Abstract:
Turbulence in the nocturnal boundary layer (NBL) is still not well characterized, especially over complex underlying surfaces. Herein, gradient tower data and eddy covariance data collected by the Beijing 325-m tower were used to better understand the differentiating characteristics of turbulence regimes and vertical turbulence structure of urban the NBL. As for heights above the urban canopy layer (UCL), the relationship between turbulence velocity scale (VTKE) and wind speed (V) was consistent with the “HOckey-Stick” (HOST) theory proposed for a relatively flat area. Four regimes have been identified according to urban nocturnal stable boundary layer. Regime 1 occurs where local shear plays a leading role for weak turbulence under the constraint that the wind speed V<VT (threshold wind speed). Regime 2 is determined by the existence of strong turbulence that occurs when V>VT and is mainly driven by bulk shear. Regime 3 is identified by the existence of moderate turbulence when upside-down turbulence sporadic bursts occur in the presence of otherwise weak turbulence. Regime 4 is identified as buoyancy turbulence, when V>VT, and the turbulence regime is affected by a combination of local wind shear, bulk shear and buoyancy turbulence. The turbulence activities demonstrated a weak thermal stratification dependency in regime 1, for which within the UCL, the turbulence intensity was strongly affected by local wind shear when V<VT. This study further showed typical examples of different stable boundary layers and the variations between turbulence regimes by analyzing the evolution of wind vectors. Partly because of the influence of large-scale motions, the power spectral density of vertical velocity for upside-down structure showed an increase at low frequencies. The upside-down structures were also characterized by the highest frequency of the stable stratifications in the higher layer.
Variability of Raindrop Size Distribution during a Regional Freezing Rain Event in the Jianghan Plain of Central China
Jingjing LÜ, Yue ZHOU, Zhikang FU, Chunsong LU, Qin HUANG, Jing SUN, Yue ZHAO, Shengjie NIU
, Available online   , Manuscript accepted  09 November 2022, doi: 10.1007/s00376-022-2131-1
Abstract:
The characteristics of the raindrop size distribution (DSD) during regional freezing rain (FR) events that occur throughout the phase change (from liquid to solid) are poorly understood due to limited observations. We investigate the evolution of microphysical parameters and the key formation mechanisms of regional FR using the DSDs from five disdrometer sites in January 2018 in the Jianghan Plain (JHP) of Central China. FR is identified via the size and velocity distribution measured from a disdrometer, the discrete Fréchet distancemethod, surface temperature, human observations, and sounding data. With the persistence of precipitation, the emergence of graupel or snowflakes significantly reduces the proportion of FR. The enhancement of this regional FR event is mainly dominated by the increase in the number concentration of raindrops but weakly affected by the diameters. To improve the accuracy of quantitative precipitation estimation for the FR event, a modified second-degree polynomial relation between the shape μ and slope Λ of gamma DSDs is derived, and a new Z-R (radar reflectivity to rain rate) relationship is developed. The mean values of mass-weighted mean diameters (Dm) and generalized intercepts (log10Nw) in FR are close to the stratiform results in the northern region of China. Both the melting of tiny-rimed graupels and large-dry snowflakes are a response to the formation of this regional FR process in the JHP, dominated by the joint influence of the physical mechanism of warm rain, vapor deposition, and aggregation/riming coupled with the effect of weak convective motion in some periods.
Subseasonal Prediction of Early-summer Northeast Asian Cut-off Lows by BCC-CSM2-HR and GloSea5
Yu NIE, Jie WU, Jinqing ZUO, Hong-Li REN, Adam A. SCAIFE, Nick DUNSTONE, Steven C HARDIMAN
, Available online   , Manuscript accepted  08 November 2022, doi: 10.1007/s00376-022-2197-9
Abstract:
Northeast Asian cut-off lows are crucial cyclonic systems that can bring temperature and precipitation extremes over large areas. Skillful subseasonal forecasting of Northeast Asian cut-off lows is of great importance. Using two dynamical forecasting systems from the Beijing Climate Center (BCC-CSM2-HR) and one from the Met Office (GloSea5),this study assesses simulation ability and subseasonal prediction skill for early-summer Northeast Asian cut-off lows. Both models are shown to have good ability in representing the spatial structure of cut-off lows, but they underestimate the intensity. The skillful prediction time scales for cut-off low intensity are about 10.2 days in advance for BCC-CSM2-HR and 11.4 days in advance for GloSea5. Further examination shows that both models can essentially capture the initial Rossby wave train,rapid growth and decay processes responsible for the evolution of cut-off lows, but the models show weaker amplitudes for the three stages processes. The underestimated simulated strength of both the Eurasian midlatitude and East Asian subtropical jets may lead to the weaker local eddy-mean flow interaction responsible for the cut-off low evolution.
Evaluation of the Added Value of Probabilistic Nowcasting Ensemble Forecasts on Regional Ensemble Forecasts
Lu YANG, Cong-Lan CHENG, Yu XIA, Min CHEN, Ming-Xuan CHEN, Han-Bin ZHANG, Xiang-Yu HUANG
, Available online   , Manuscript accepted  26 October 2022, doi: 10.1007/s00376-022-2056-8
Abstract:
Ensemble forecasting systems have become an important tool for estimating the uncertainties in initial conditions and model formulations and they are receiving increased attention from various applications. The Regional Ensemble Prediction System (REPS), which has operated at the Beijing Meteorological Service (BMS) since 2017, allows for probabilistic forecasts. However, it still suffers from systematic deficiencies during the first couple of forecast hours. This paper presents an integrated probabilistic nowcasting ensemble prediction system (NEPS) that is constructed by applying a mixed dynamic-integrated method. It essentially combines the uncertainty information (i.e., ensemble variance) provided by the REPS with the nowcasting method provided by the rapid-refresh deterministic nowcasting prediction system (NPS) that has operated at the Beijing Meteorological Service (BMS) since 2019. The NEPS provides hourly updated analyses and probabilistic forecasts in the nowcasting and short range (0–6 h) with a spatial grid spacing of 500 m. It covers the three meteorological parameters: temperature, wind, and precipitation. The outcome of an evaluation experiment over the deterministic and probabilistic forecasts indicates that the NEPS outperforms the REPS and NPS in terms of surface weather variables. Analysis of two cases demonstrates the superior reliability of the NEPS and suggests that the NEPS gives more details about the spatial intensity and distribution of the meteorological parameters.
Predecessor Rain Events in the Yangtze River Delta Region Associated with South China Sea and Northwest Pacific Ocean (SCS-WNPO) Tropical Cyclones
Huiyan XU, Xiaofan LI, Jinfang YIN, Dengrong ZHANG
, Available online   , Manuscript accepted  26 October 2022, doi: 10.1007/s00376-022-2069-3
Abstract:
Predecessor rain events (PREs) in the Yangtze River Delta (YRD) region associated with the South China Sea and Northwest Pacific Ocean (SCS-WNPO) tropical cyclones (TCs) are investigated during the period from 2010 to 2019. Results indicate that approximately 10% of TCs making landfall in China produce PREs over the YRD region; however, they are seldom forecasted. PREs often occur over the YRD region when TCs begin to be active in the SCS-WNPO with westward paths, whilst the cold air is still existing or beginning to be present. PREs are more likely to peak in June and September. The distances between the PRE centers and the parent TC range from 900 to 1700 km. The median value of rain amounts and the median lifetime of PREs is approximately 200 mm and 24 h, respectively. Composite results suggest that PREs form in the equatorward jet-entrance region of the upper-level westerly jet (WJ), where a 925-hPa equivalent potential temperature ridge is located east of a 500-hPa trough. Deep moisture is transported from the TC vicinity to the remote PREs region. The ascent of this deep moist air in front of the 500-hPa trough and frontogenesis beneath the equatorward entrance region of the WJ is advantageous for the occurrence of PREs in the YRD region. The upper-level WJ may be affected by the subtropical high and westerly trough in the Northwest Pacific Ocean, and the occurrence of PREs may favor the maintenance of the upper-level WJ. The upper-level outflow of TCs in the SCS plays a secondary role.
Predictor Selection for CNN-based Statistical Downscaling of Monthly Precipitation
Dangfu YANG, Shengjun LIU, Yamin HU, Xinru LIU, Jiehong XIE, Liang ZHAO
, Available online   , Manuscript accepted  24 October 2022, doi: 10.1007/s00376-022-2119-x
Abstract:
Convolutional neural networks (CNNs) have been widely studied and found to obtain favorable results in statistical downscaling to derive high-resolution climate variables from large-scale coarse general circulation models (GCMs). However, there is a lack of research exploring the predictor selection for CNN modeling. This paper presents an effective and efficient greedy elimination algorithm to address this problem. The algorithm has three main steps: predictor importance attribution, predictor removal, and CNN retraining, which are performed sequentially and iteratively. The importance of individual predictors is measured by a gradient-based importance metric computed by a CNN backpropagation technique, which was initially proposed for CNN interpretation. The algorithm is tested on the CNN-based statistical downscaling of monthly precipitation with 20 candidate predictors and compared with a correlation analysis-based approach. Linear models are implemented as benchmarks. The experiments illustrate that the predictor selection solution can reduce the number of input predictors by more than half, improve the accuracy of both linear and CNN models, and outperform the correlation analysis method. Although the RMSE (root-mean-square error) is reduced by only 0.8%, only 9 out of 20 predictors are used to build the CNN, and the FLOPs (Floating Point Operations) decrease by 20.4%. The results imply that the algorithm can find subset predictors that correlate more to the monthly precipitation of the target area and seasons in a nonlinear way. It is worth mentioning that the algorithm is compatible with other CNN models with stacked variables as input and has the potential for nonlinear correlation predictor selection.
The Subsurface and Surface Indian Ocean Dipoles and Their Association with ENSO in CMIP6 models
Ge SONG, Rongcai REN
, Available online   , Manuscript accepted  24 October 2022, doi: 10.1007/s00376-022-2086-2
Abstract:
This study assesses the reproducibility of 31 historical simulations from 1850 to 2014 in the Coupled Model Inter-comparison Project phase 6 (CMIP6) for the subsurface (Sub-IOD) and surface Indian Ocean Dipole (IOD) and their association with El Niño-Southern Oscillation (ENSO). Most CMIP6 models can reproduce the leading east-west dipole oscillation mode of heat content anomalies in the tropical Indian Ocean (TIO) but largely overestimate the amplitude and the dominant period of the Sub-IOD. Associated with the much steeper west-to-east thermocline tilt of the TIO, the vertical coupling between the Sub-IOD and IOD is overly strong in most CMIP6 models compared to that in the Ocean Reanalysis System 4 (ORAS4). Related to this, most models also show a much tighter association of Sub-IOD and IOD events with the canonical ENSO than observations. This explains the more (less) regular Sub-IOD and IOD events in autumn in those models with stronger (weaker) surface-subsurface coupling in TIO. Though all model simulations feature a consistently low bias regarding the percentage of the winter–spring Sub-IOD events co-occurring with a Central Pacific (CP) ENSO, the linkage between a westward-centered CP-ENSO and the Sub-IOD that occurs in winter–spring, independent of the IOD, is well reproduced.
Urban Impact on Landfalling Tropical Cyclone Precipitation: A Numerical Study of Typhoon Rumbia (2018)
Xinguan DU, Haishan CHEN, Qingqing LI, Xuyang GE
, Available online   , Manuscript accepted  20 October 2022, doi: 10.1007/s00376-022-2100-8
Abstract:
Coastal urban areas are prone to serious disasters caused by landfalling tropical cyclones (TCs). Despite the crucial role of urban forcing in precipitation, how fine-scale urban features impact landfalling TC precipitation remains poorly understood. In this study, high-resolution ensemble simulations of Typhoon Rumbia (2018), which crossed the Yangtze River Delta urban agglomeration, were conducted to analyze the potential urban impact on TC precipitation. Results show that the inner-core rainfall of Rumbia is strengthened by approximately 10% due to the urban impact near the landfall, whereas minor differences in outer-core rainfall are found when the urban impact is excluded. Further diagnostic analyses indicate that low-level upward motion is crucial for precipitation evolution, as both co-vary during landfall. Moreover, the frictionally induced upward motion plays a decisive role in enhancing the rainfall when the urban impacts are included. Urban surface friction can decelerate the tangential wind and therefore destroy the gradient balance and strengthen the radial wind within the boundary layer and thus can enhance upward motion. This study demonstrates that urban surface friction and related physical processes make the most significant contribution to landfalling TC rainfall enhancement.
Marine Boundary Layer Heights in the Tropical and Subtropical Oceans Derived from COSMIC-2 Radio Occultation Data
Xiaohua XU, Yadi LI, Jia LUO
, Available online   , Manuscript accepted  19 October 2022, doi: 10.1007/s00376-022-2052-z
Abstract:
Using the global navigation satellite system (GNSS) and radio occultation (RO) refractivity data from the Constellation Observing System for Meteorology Ionosphere and Climate-2 (COSMIC-2) mission from January 2020 to December 2021, the spatial and temporal variability of Marine Boundary Layer Heights (MBLHs) over the tropical and subtropical oceans are investigated. The MBLH detection method is based on the wavelet covariance transform (WCT) algorithm, while the distinctness (DT) parameter, which reflects the significance of the maximum WCT function values, is introduced. For the refractivity profiles with indistinct maximum WCT function values, the available surrounding RO-derived MBLHs are used as auxiliary information, which helps to improve the objectiveness of the inversion process. The RO-derived MBLHs are validated with the MBLHs derived from the collocated high-vertical-resolution radiosonde observations, and the seasonal distributions of the RO-derived MBLHs are presented. Further comparisons of the magnitudes and the distributions of the RO-derived MBLHs with those derived from two model datasets, the European Centre for Medium-Range Weather Forecasts (ECMWF) analyses and the National Centers for Environmental Prediction (NCEP) Aviation (AVN) 12-hour forecast data, reveal that although high correlations exist between the RO-derived and the model-derived MBLHs, the model-derived ones are generally lower than the RO-derived ones in most parts of the tropics and sub-tropic ocean areas during different seasons, which should be partially attributed to the limited vertical resolutions of the model datasets. The correlation analyses between the MBLHs and near-surface wind speeds demonstrate that over the Pacific Ocean, near-surface wind speed is an important factor that influences the variations of the MBLHs.
Separation of Atmospheric Circulation Patterns Governing Regional Variability of Arctic Sea Ice in Summer
Shaoyin WANG, Jiping LIU, Xiao CHENG, Richard J. GREATBATCH, Zixin WEI, Zhuoqi CHEN, Hua LI
, Available online   , Manuscript accepted  19 October 2022, doi: 10.1007/s00376-022-2176-1
Abstract:
In recent decades, Arctic summer sea ice extent (SIE) has shown a rapid decline overlaid with large interannual variations, both of which are influenced by geopotential height anomalies over Greenland (GL-high) and the central Arctic (CA-high). In this study, SIE along coastal Siberia (Sib-SIE) and Alaska (Ala-SIE) is found to account for about 65% and 21% of the Arctic SIE interannual variability, respectively. Variability in Ala-SIE is related to the GL-high, whereas variability in Sib-SIE is related to the CA-high. A decreased Ala-SIE is associated with decreased cloud cover and increased easterly winds along the Alaskan coast, promoting ice–albedo feedback. A decreased Sib-SIE is associated with a significant increase in water vapor and downward longwave radiation (DLR) along the Siberian coast. The years 2012 and 2020 with minimum recorded ASIE are used as examples. Compared to climatology, summer 2012 is characterized by a significantly enhanced GL-high with major sea ice loss along the Alaskan coast, while summer 2020 is characterized by an enhanced CA-high with sea ice loss focused along the Siberian coast. In 2012, the lack of cloud cover along the Alaskan coast contributed to an increase in incoming solar radiation, amplifying ice–albedo feedback there; while in 2020, the opposite occurs with an increase in cloud cover along the Alaskan coast, resulting in a slight increase in sea ice there. Along the Siberian coast, increased DLR in 2020 plays a dominant role in sea ice loss, and increased cloud cover and water vapor both contribute to the increased DLR.
Precipitation Microphysical Characteristics of Typhoon Ewiniar (2018) before and after Its Final Landfall Over Southern China
Lu FENG, Hui XIAO, Xiantong LIU, Sheng HU, Huiqi LI, Liusi XIAO, Xiao HAO
, Available online   , Manuscript accepted  13 October 2022, doi: 10.1007/s00376-022-2135-x
Abstract:
In this paper, the evolution of the microphysical characteristics in different regions (eyewall, inner core, and outer rainbands) and different quadrants [downshear left (DL), downshear right (DR), upshear left (UL), and upshear right (UR)] during the final landfall of Typhoon Ewiniar (2018) is analyzed using two-dimensional video disdrometer and S-band polarimetric radar data collected in Guangdong, China. Due to the different types of underlying surfaces, the periods before landfall (mainly dominated by underlying sea surface) and after landfall (mainly dominated by underlying land surface) are also analyzed. Both before landfall and after landfall, the downshear quadrants had the dominate typhoon precipitation. The outer rainbands had more graupel than the inner core, resulting in a larger radar reflectivity, differential reflectivity, specific differential phase shift, and mass-weighted mean diameter below the melting layer. Compared with other regions, the eyewall region had the smallest mean logarithmic normalized intercept parameter before landfall and the smallest mean mass-weighted mean diameter and the largest mean logarithmic normalized intercept parameter after landfall. The hydrometeor size sorting was obvious in the eyewall and inner core (especially in the eyewall) after landfall. A high concentration of large raindrops fell in the DL quadrant, and more small raindrops fell in the UR quadrant. Although the ice-phase process and warm rain process were both important in the formation of tropical cyclone precipitation, the warm rain process (ice-phase process) contributed more liquid water before landfall (after landfall). This investigation provides a reference for improving the microphysical parameterization scheme in numerical models.
Radar Quantitative Precipitation Estimation Based on the Gated Recurrent Unit Neural Network and Echo-Top Data
Haibo ZOU, Shanshan WU, Miaoxia TIAN
, Available online   , Manuscript accepted  09 October 2022, doi: 10.1007/s00376-022-2127-x
Abstract:
The Gated Recurrent Unit (GRU) neural network has great potential in estimating and predicting a variable. In addition to radar reflectivity (Z), radar echo-top height (ET) is also a good indicator of rainfall rate (R). In this study, we propose a new method, GRU_Z-ET, by introducing Z and ET as two independent variables into the GRU neural network to conduct the quantitative single-polarization radar precipitation estimation. The performance of GRU_Z-ET is compared with that of the other three methods in three heavy rainfall cases in China during 2018, namely, the traditional Z-R relationship (Z=300R1.4), the optimal Z-R relationship (Z=79R1.68) and the GRU neural network with only Z as the independent input variable (GRU_Z). The results indicate that the GRU_Z-ET performs the best, while the traditional Z-R relationship performs the worst. The performances of the rest two methods are similar. To further evaluate the performance of the GRU_Z-ET, 200 rainfall events with 21882 total samples during May–July of 2018 are used for statistical analysis. Results demonstrate that the spatial correlation coefficients, threat scores and probability of detection between the observed and estimated precipitation are the largest for the GRU_Z-ET and the smallest for the traditional Z-R relationship, and the root mean square error is just the opposite. In addition, these statistics of GRU_Z are similar to those of optimal Z-R relationship. Thus, it can be concluded that the performance of the GRU_Z-ET is the best in the four methods for the quantitative precipitation estimation.
Analysis of the Characteristics of the Low-level Jets in the Middle Reaches of the Yangtze River during the Mei-yu Season
Chunguang CUI, Wen ZHOU, Hao YANG, Xiaokang WANG, Yi DENG, Xiaofang WANG, Guirong XU, Jingyu WANG
, Available online   , Manuscript accepted  09 October 2022, doi: 10.1007/s00376-022-2107-1
Abstract:
Here, we analyze the characteristics and the formation mechanisms of low-level jets (LLJs) in the middle reaches of the Yangtze River during the 2010 mei-yu season using Wuhan station radiosonde data and the fifth generation of the European Centre for Medium-Range Weather Forecasts (ERA5) reanalysis dataset. Our results show that the vertical structure of LLJs is characterized by a predominance of boundary layer jets (BLJs) concentrated at heights of 900–1200 m. The BLJs occur most frequently at 2300 LST (LST=UTC+ 8 hours) but are strongest at 0200 LST, with composite wind velocities >14 m s–1. Synoptic-system-related LLJs (SLLJs) occur most frequently at 0800 LST but are strongest at 1100 LST, with composite wind velocities >12 m s−1. Both BLJs and SLLJs are characterized by a southwesterly wind direction, although the wind direction of SLLJs is more westerly, and northeasterly SLLJs occur more frequently than northeasterly BLJs. When Wuhan is south of the mei-yu front, the westward extension of the northwest Pacific subtropical high intensifies, and the low-pressure system in the eastern Tibetan Plateau strengthens, favoring the formation of LLJs, which are closely related to precipitation. The wind speeds on rainstorm days are greater than those on LLJ days. Our analysis of four typical heavy precipitation events shows the presence of LLJs at the center of the precipitation and on its southern side before the onset of heavy precipitation. BLJs were shown to develop earlier than SLLJs.
The Role of Ozone Depletion in the Lack of Cooling in the Antarctic Upper Stratosphere During Austral Winter
Xuan MA, Lei WANG
, Available online   , Manuscript accepted  09 October 2022, doi: 10.1007/s00376-022-2047-9
Abstract:
Temperature trends in the upper stratosphere are investigated using satellite measurements from Stratospheric Sounding Unit (SSU) outputs and simulations from chemistry–climate models (CCMs) and the Coupled Model Intercomparison Project Phase 6 (CMIP6). Observational evidence shows a lack of cooling in the Antarctic, in contrast to strong cooling at other latitudes, during austral winter over 1979–1997. Analysis of CCM simulations for a longer period of 1961–1997 also shows a significant contrast in the upper stratospheric temperature trends between the Antarctic and lower latitudes. Results from two sets of model integrations with fixed ozone-depleting substances (ODSs) and fixed greenhouse gases (GHGs) at their 1960 levels suggest that the ODSs have made a major contribution to the lack of cooling in the Antarctic upper stratosphere. Results from CMIP6 simulations with prescribed GHGs and ozone confirm that changes in the dynamical processes associated with observed ozone depletion are largely responsible for the lack of cooling in the Antarctic upper stratosphere. The lack of cooling is found to be dynamically induced through increased upward wave activity into the upper stratosphere, which is attributed mainly to ODSs forcing. Specifically, the radiative cooling caused by the ozone depletion results in a stronger meridional temperature gradient between middle and high latitudes in the upper stratosphere, allowing more planetary waves propagating upward to warm the Antarctic upper stratosphere. These findings improve our understanding of the chemistry–climate coupling in the southern upper stratosphere.
The Concurrent Record-breaking Rainfall over Northwest India and North China in September 2021
Ying NA, Riyu LU
, Available online   , Manuscript accepted  27 September 2022, doi: 10.1007/s00376-022-2187-y
Abstract:
Extremely heavy rainfall occurred over both Northwest India and North China in September 2021. The precipitation anomalies were 4.1 and 6.2 times interannual standard deviation over the two regions, respectively, and broke the record since the observational data were available, i.e., 1901 for India and 1951 for China. In this month, the Asian upper-tropospheric westerly jet was greatly displaced poleward over West Asia, and correspondingly, an anomalous cyclone appeared over India. The anomalous cyclone transported abundant water vapor into Northwest India, leading to the heavy rainfall there. In addition, the Silk Road pattern, a teleconnection pattern of upper-level meridional wind over the Eurasian continent and fueled by the heavy rainfall in Northwest India, contributed to the heavy rainfall in North China. Our study emphasizes the roles of atmospheric teleconnection patterns in concurrent rainfall extremes in the two regions far away from each other, and the occurrence of rainfall extremes during the post- or pre-monsoon period in the northern margins of monsoon regions.
Contrasting Regional Responses of Indian Summer Monsoon Rainfall to Exhausted Spring and Concurrently Emerging Summer El Niño Events
E. K. KRISHNA KUMAR, S. ABHILASH, SANKAR SYAM, P. VIJAYKUMAR, K. R. SANTOSH, A.V. SREENATH
, Available online   , Manuscript accepted  22 September 2022, doi: 10.1007/s00376-022-2114-2
Abstract:
The inverse relationship between the warm phase of the El Niño Southern Oscillation (ENSO) and the Indian Summer Monsoon Rainfall (ISMR) is well established. Yet, some El Niño events that occur in the early months of the year (boreal spring) transform into a neutral phase before the start of summer, whereas others begin in the boreal summer and persist in a positive phase throughout the summer monsoon season. This study investigates the distinct influences of an exhausted spring El Niño (springtime) and emerging summer El Niño (summertime) on the regional variability of ISMR. The two ENSO categories were formulated based on the time of occurrence of positive SST anomalies over the Niño-3.4 region in the Pacific. The ISMR's dynamical and thermodynamical responses to such events were investigated using standard metrics such as the Walker and Hadley circulations, vertically integrated moisture flux convergence (VIMFC), wind shear, and upper atmospheric circulation. The monsoon circulation features are remarkably different in response to the exhausted spring El Niño and emerging summer El Niño phases, which distinctly dictate regional rainfall variability. The dynamic and thermodynamic responses reveal that exhausted spring El Niño events favor excess monsoon rainfall over eastern peninsular India and deficit rainfall over the core monsoon regions of central India. In contrast, emerging summer El Niño events negatively impact the seasonal rainfall over the country, except for a few regions along the west coast and northeast India.
Assessment of ERA5 and ERA-Interim in Reproducing Mean and Extreme Climates over West Africa
Imoleayo Ezekiel GBODE, Toju Esther BABALOLA, Gulilat Tefera DIRO, Joseph Daniel INTSIFUL
, Available online   , Manuscript accepted  22 September 2022, doi: 10.1007/s00376-022-2161-8
Abstract:
In situ data in West Africa are scarce, and reanalysis datasets could be an alternative source to alleviate the problem of data availability. Nevertheless, because of uncertainties in numerical prediction models and assimilation methods, among other things, existing reanalysis datasets can perform with various degrees of quality and accuracy. Therefore, a proper assessment of their shortcomings and strengths should be performed prior to their usage. In this study, we examine the performance of ERA5 and ERA-interim (ERAI) products in representing the mean and extreme climates over West Africa for the period 1981–2018 using observations from CRU and CHIRPS. The major conclusion is that ERA5 showed a considerable decrease in precipitation and temperature biases and an improved representation of inter-annual variability in much of western Africa. Also, the annual cycle is better captured by ERA5 in three of the region’s climatic zones; specifically, precipitation is well-reproduced in the Savannah and Guinea Coast, and temperature in the Sahel. In terms of extremes, the ERA5 performance is superior. Still, both reanalyses underestimate the intensity and frequency of heavy precipitations and overestimate the number of wet days, as the numerical models used in reanalyses tend to produce drizzle more often. While ERA5 performs better than ERAI, both datasets are less successful in capturing the observed long-term trends. Although ERA5 has achieved considerable progress compared to its predecessor, improved datasets with better resolution and accuracy continue to be needed in sectors like agriculture and water resources to enable climate impact assessment.
A Statistical Algorithm for Retrieving Background Value of Absorbing Aerosol Index Based on TROPOMI Measurements
Fuying TANG, Weihe WANG, Fuqi SI, Haijin ZHOU, Yuhan LUO, Dongshang YANG, Yuanyuan QIAN
, Available online   , Manuscript accepted  22 September 2022, doi: 10.1007/s00376-022-2093-3
Abstract:
The ultraviolet aerosol index (UVAI) is essential for monitoring the absorbing aerosols during aerosol events. UVAI depends on the absorbing aerosol concentration, the viewing geometry, and the temporal drift of radiometric sensitivity. To efficiently detect absorbing aerosols with the highest precision and to improve the accuracy of long-term UVAI estimates, the background UVAI must be examined through the UVAI retrieval. This study presents a statistical method that calculates the background value of UVAI using TROPOspheric Monitoring Instrument (TROPOMI) observation data over the Pacific Ocean under clear-sky scenes. Radiative transfer calculations were performed to simulate the dependence of UVAI on aerosol type and viewing geometry. We firstly applied the background UVAI to reducing the effects of viewing geometry and the degradation of the TROPOMI irradiance measurements on the UVAI. The temporal variability of the background UVAI under the same viewing geometry and aerosol concentration was identified. Radiative transfer calculations were performed to study the changes in background UVAI using Aerosol Optical Depth from the Moderate Resolution Imaging Spectroradiometer (MODIS) and reflectance measurements from TROPOMI as input. The trends of the temporal variations in the background UVAI agreed with the simulations. Alterations in the background UVAI expressed the reflectance variations driven by the changes in satellite state. Decreasing trends in solar irradiance at 340 and 380 nm due to instrument degradation were identified. Our findings are valuable because they can be applied to future retrievals of UVAI from the Environmental Trace Gases Monitoring Instrument (EMI) onboard the Chinese GaoFen-5 satellite.
The Arctic sea ice thickness change in CMIP6’s historical simulations
Lanying Chen, Renhao Wu, Qi Shu, Chao Min, Qinghua Yang, Bo Han
, Available online   , Manuscript accepted  14 September 2022, doi: 10.1007/s00376-022-1460-4
Abstract:
This study assesses sea ice thickness (SIT) from the historical run of the Coupled Model Inter-comparison Project Phase 6 (CMIP6). The SIT reanalysis from the Pan-Arctic Ice Ocean Modeling and Assimilation System (PIOMAS) product is chosen as the validation reference data. Results show that most models can adequately reproduce the climatological mean, seasonal cycle, and long-term trend of Arctic Ocean SIT during 1979 - 2014, but significant inter-model spread exists. Differences in simulated SIT patterns among the CMIP6 models may be related to model resolution and sea ice model components. By comparing the climatological mean and trend for SIT among all models, we evaluate the Arctic SIT change in different seas during 1979 - 2014. Under the scenario of historical radiative forcing, the Arctic SIT will probably exponentially decay at -18 %/decade and plausibly reach its minimum (equilibrium) of 0.48 m since the 2070s.
The Arctic Sea Ice Thickness Change in CMIP6’s Historical Simulations
Lanying CHEN, Renhao WU, Qi SHU, Chao MIN, Qinghua YANG, Bo HAN
, Available online   , Manuscript accepted  14 September 2022, doi: 10.1007/s00376-022-1460-4
Abstract:
This study assesses sea ice thickness (SIT) from the historical run of the Coupled Model Inter-comparison Project Phase 6 (CMIP6). The SIT reanalysis from the Pan-Arctic Ice Ocean Modeling and Assimilation System (PIOMAS) product is chosen as the validation reference data. Results show that most models can adequately reproduce the climatological mean, seasonal cycle, and long-term trend of Arctic Ocean SIT during 1979–2014, but significant inter-model spread exists. Differences in simulated SIT patterns among the CMIP6 models may be related to model resolution and sea ice model components. By comparing the climatological mean and trend for SIT among all models, the Arctic SIT change in different seas during 1979–2014 is evaluated. Under the scenario of historical radiative forcing, the Arctic SIT will probably exponentially decay at –18% (10 yr)–1 and plausibly reach its minimum (equilibrium) of 0.47 m since the 2070s.
Improvement and Evaluation of the Latest Version of WRF-Lake at a Deep Riverine Reservoir
Shibo GUO, Dejun ZHU, Yongcan CHEN
, Available online   , Manuscript accepted  13 September 2022, doi: 10.1007/s00376-022-2180-5
Abstract:
The WRF-lake vertically one-dimensional (1D) water temperature model, as a submodule of the Weather Research and Forecasting (WRF) system, is being widely used to investigate water–atmosphere interactions. But previous applications revealed that it cannot accurately simulate the water temperature in a deep riverine reservoir during a large flow rate period, and whether it can produce sufficiently accurate heat flux through the water surface of deep riverine reservoirs remains uncertain. In this study, the WRF-lake model was improved for applications in large, deep riverine reservoirs by parametric scheme optimization, and the accuracy of heat flux calculation was evaluated compared with the results of a better physically based model, the Delft3D-Flow, which was previously applied to different kinds of reservoirs successfully. The results show: (1) The latest version of WRF-lake can describe the surface water temperature to some extent but performs poorly in the large flow period. We revised WRF-lake by modifying the vertical thermal diffusivity, and then, the water temperature simulation in the large flow period was improved significantly. (2) The latest version of WRF-lake overestimates the reservoir–atmosphere heat exchange throughout the year, mainly because of underestimating the downward energy transfer in the reservoir, resulting in more heat remaining at the surface and returning to the atmosphere. The modification of vertical thermal diffusivity can improve the surface heat flux calculation significantly. (3) The longitudinal temperature variation and the temperature difference between inflow and outflow, which cannot be considered in the 1D WRF-lake, can also affect the water surface heat flux.
Investigating the Changes in Air Pollutant Emissions over the Beijing-Tianjin-Hebei Region in February from 2014 to 2019 through an Inverse Emission Method
Xuechun LUO, Xiao TANG, Haoyue WANG, Lei KONG, Huangjian WU, Weiguo WANG, Yating SONG, Hongyan LUO, Yao WANG, Jiang ZHU, Zifa WANG
, Available online   , Manuscript accepted  09 September 2022, doi: 10.1007/s00376-022-2039-9
Abstract:
In recent years, China has implemented several measures to improve air quality. The Beijing-Tianjin-Hebei (BTH) region is one area that has suffered from the most serious air pollution in China and has undergone huge changes in air quality in the past few years. How to scientifically assess these change processes remain the key issue in further improving the air quality over this region in the future. To evaluate the changes in major air pollutant emissions over this region, this paper employs ensemble Kalman filtering (EnKF) for integrating the national ground monitoring pollutant observation data and the Nested Air Quality Prediction Modeling System (NAQPMS) simulation data to inversely estimate the emission rates of SO2, NOX, CO, and primary PM2.5 over BTH region in February from 2014 to 2019. The results show that SO2, NOX, CO, and primary PM2.5 emissions in the BTH region decreased in February from 2014 to 2019 by 83%, 37%, 41%, and 42%, while decreases in Beijing during this period were 86%, 67%, 59%, and 65%, respectively. Compared with the prior emission inventory, the inversion emission inventory reduces the uncertainty of multi-pollutant simulation in the BTH region, with simulated root mean square errors of the monthly average concentrations of SO2, NOX, PM2.5, and CO reduced by 41%, 30%, 31%, and 22%, respectively. The average uncertainties of SO2, NOX, PM2.5, and CO inversion emissions in 2014–19 are ±14.03% yr–1, ±28.91% yr–1, ±126.15% yr–1, and ±43.58% yr–1. Compared with the uncertainty of MEIC emission, the uncertainties of all species changed by +2% yr–1, –2% yr–1, –26% yr–1, and –4% yr–1, respectively. The spatial distribution results illustrate that air pollutant emissions are mainly distributed over the eastern and southern BTH regions. The spatial gap between the inversion emissions and MEIC emissions was further closed in 2019 compared to 2014. The results of this paper can provide a new reference for assessing changes in air pollution emissions over the BTH region in recent years and validating a bottom-up emission inventory.
Convective Storm VIL and Lightning Nowcasting Using Satellite and Weather Radar Measurements Based on Multi-Task Learning Models
Yang LI, Yubao LIU, Rongfu SUN, Fengxia GUO, Xiaofeng XU, Haixiang XU
, Available online   , Manuscript accepted  31 August 2022, doi: 10.1007/s00376-022-2082-6
Abstract:
Convective storms and lightning are among the most important weather phenomena that are challenging to forecast. In this study, a novel multi-task learning (MTL) encoder-decoder U-net neural network was developed to forecast convective storms and lightning with lead times for up to 90 min, using GOES-16 geostationary satellite infrared brightness temperatures (IRBTs), lightning flashes from Geostationary Lightning Mapper (GLM), and vertically integrated liquid (VIL) from Next Generation Weather Radar (NEXRAD). To cope with the heavily skewed distribution of lightning data, a spatiotemporal exponent-weighted loss function and log-transformed lightning normalization approach were developed. The effects of MTL, single-task learning (STL), and IRBTs as auxiliary input features on convection and lightning nowcasting were investigated. The results showed that normalizing the heavily skew-distributed lightning data along with a log-transformation dramatically outperforms the min-max normalization method for nowcasting an intense lightning event. The MTL model significantly outperformed the STL model for both lightning nowcasting and VIL nowcasting, particularly for intense lightning events. The MTL also helped delay the lightning forecast performance decay with the lead times. Furthermore, incorporating satellite IRBTs as auxiliary input features substantially improved lightning nowcasting, but produced little difference in VIL forecasting. Finally, the MTL model performed better for forecasting both lightning and the VIL of organized convective storms than for isolated cells.
CMIP6 Evaluation and Projection of Precipitation over Northern China: Further Investigation
Xiaoling Yang, Botao Zhou, Ying Xu, Zhen-Yu HAN
, Available online   , Manuscript accepted  31 August 2022, doi: 10.1007/s00376-022-2092-4
Abstract:
Based on 20 Coupled Model Intercomparison Project phase 6 (CMIP6) models, this article explored possible reasons for differences in simulation biases and projected changes of precipitation in northern China among all-model ensemble (AMME), "highest-ranked" model ensemble (BMME) and "lowest-ranked" model ensemble (WMME), from the perspective of atmospheric circulations and moisture budget. The results show that the BMME and AMME reproduce the East Asian winter circulations better than the WMME. Compared with the AMME and WMME, the BMME reduces the overestimation of evaporation, thereby improving the simulation of winter precipitation. The three ensemble simulated biases for the East Asian summer circulations are generally similar, featured with a stronger zonal pressure gradient between the mid-latitudes of the North Pacific and East Asia and a northward displacement of the East Asian westerly jet. However, the simulation of vertical moisture advection is improved in the BMME, contributing to slightly higher performance of the BMME than the AMME and WMME on summer precipitation in North and Northeast China. Concerning future changes, the BMME projects larger increases in precipitation in northern China during both seasons by the end of the 21st century under the Shared Socioeconomic Pathway 5-8.5 (SSP5-8.5) as compared to the AMME and WMME projections. One of the reasons is that the increase in evaporation projected by the BMME is larger. The BMME projected greater dynamic contribution also plays a role. In addition, larger changes of the nonlinear component in the BMME projection contribute to the larger increase in winter precipitation in northern China.
CMIP6 Evaluation and Projection of Precipitation over Northern China: Further Investigation
Xiaoling YANG, Botao ZHOU, Ying XU, Zhenyu HAN
, Available online   , Manuscript accepted  31 August 2022, doi: 10.1007/s00376-022-2092-4
Abstract:
Based on 20 models from phase 6 of the Coupled Model Intercomparison Project (CMIP6), this article explored possible reasons for differences in simulation biases and projected changes in precipitation in northern China among the all-model ensemble (AMME), “highest-ranked” model ensemble (BMME), and "lowest-ranked" model ensemble (WMME), from the perspective of atmospheric circulations and moisture budgets. The results show that the BMME and AMME reproduce the East Asian winter circulations better than the WMME. Compared with the AMME and WMME, the BMME reduces the overestimation of evaporation, thereby improving the simulation of winter precipitation. The three ensemble simulated biases for the East Asian summer circulations are generally similar, characterized by a stronger zonal pressure gradient between the mid-latitudes of the North Pacific and East Asia and a northward displacement of the East Asian westerly jet. However, the simulated vertical moisture advection is improved in the BMME, contributing to the slightly higher performance of the BMME than the AMME and WMME on summer precipitation in North and Northeast China. Compared to the AMME and WMME, the BMME projects larger increases in precipitation in northern China during both seasons by the end of the 21st century under the Shared Socioeconomic Pathway 5-8.5 (SSP5-8.5). One of the reasons is that the increase in evaporation projected by the BMME is larger. The projection of a greater dynamic contribution by the BMME also plays a role. In addition, larger changes in the nonlinear components in the BMME projection contribute to a larger increase in winter precipitation in northern China.
Summer Extreme Precipitation in the Key Region of the Sichuan-Tibet Railway
Jiali MA, Xiuping YAO
, Available online   , Manuscript accepted  29 August 2022, doi: 10.1007/s00376-022-2133-z
Abstract:
The Sichuan-Tibet Railway, mainly located in the southeastern Qinghai-Tibet Plateau, is affected by summertime extreme precipitation (SEP). Using daily rain-gauge observations and ERA5 reanalysis data for the summers of 1979–2020, the spatiotemporal distribution characteristics of SEP in the key region of the Sichuan-Tibet Railway (28°–33°N, 90°–105°E, hereafter KR) are revealed, and the mechanism for SEP amount (SEPA) variation in the KR is investigated. The results show that SEPA in the KR contributes nearly 30% to the total summer precipitation. Regional differences are evident in SEP, justifying thresholds higher in the plateau-dominated central-western KR (CWKR) and lower in the basin-dominated eastern KR (EKR). In addition, SEP in the CWKR is less intense but more frequent than SEP in the EKR. During 1979–2020, the SEPA in the KR increased slightly while the SEPA in the CWKR increased significantly and peaked in the last decade. When anticyclonic circulation (AC) anomalies dominate the 500 hPa pattern over the Bay of Bengal and Mongolia, the southerly flow and cyclonic shear over the southeastern plateau will be strengthened, favoring more SEPA in the CWKR. When an AC anomaly dominates the 500 hPa pattern over the Bohai Sea, the low-level easterly wind over the basin will be strengthened, favoring more SEPA in the EKR. The strengthening of the ascent, water vapor convergence, and convective instability is conducive to more SEPA in the KR. Our results deepen the understanding of the characteristics and the physical mechanisms responsible for extreme precipitation in the KR.
The Initial Mesoscale Vortexes Leading to the Formation of Tropical Cyclones in the Western North Pacific
Shenglan WU, Juan FANG
, Available online   , Manuscript accepted  22 August 2022, doi: 10.1007/s00376-022-2029-y
Abstract:
A statistical analysis of the initial vortexes leading to tropical cyclone (TC) formation in the western North Pacific (WNP) is conducted with the ECMWF ERA5 reanalysis data from 1999 to 2018. It is found that TCs in the WNP basically originate from three kinds of vortexes, i.e., a mid-level vortex (MV), a low-level vortex (LV), and a relatively deep vortex with notable vorticity in both the lower and middle troposphere (DV). Among them, LV and DV account for 47.9% and 24.2% of tropical cyclogenesis events, respectively, while only 27.9% of TCs develop from the MV, which is much lower than that which occurs in the North Atlantic and eastern Pacific. Such a difference might be ascribed to the active monsoon systems in the WNP all year round. Due to the nearly upright structure of mid-level convergence in the early pre-genesis stage, TC genesis efficiency is the highest in DV. Compared with MV, LV generally takes a shorter time to intensify to a TC because of the higher humidity and the stronger low-level cyclonic circulation, which is related to air-sea interaction and boundary-layer convergence. Further examination of the relationship between tropical cyclogenesis and large-scale flow patterns indicate that the TC genesis events associated with LV are primarily related to the monsoon shear line, monsoon confluence region, and monsoon gyre, while those associated with MV are frequently connected with easterly waves and wave energy dispersion of preexisting TC. Compared with other flow patterns, tropical cyclones usually form and intensify faster in the monsoon confluence region.
The Influence of Meridional Variation in North Pacific Sea Surface Temperature Anomalies on the Arctic Stratospheric Polar Vortex
Tao WANG, Qiang FU, Wenshou TIAN, Hongwen LIU, Yifeng PENG, Fei XIE, Hongying TIAN, Jiali LUO
, Available online   , Manuscript accepted  16 August 2022, doi: 10.1007/s00376-022-2033-2
Abstract:
This study examines the dependence of Arctic stratospheric polar vortex (SPV) variations on the meridional positions of the sea surface temperature (SST) anomalies associated with the first leading mode of North Pacific SST. The principal component 1 (PC1) of the first leading mode is obtained by empirical orthogonal function decomposition. Reanalysis data, numerical experiments, and CMIP5 model outputs all suggest that the PC1 events (positive-minus-negative PC1 events), located relatively northward (i.e., North PC1 events), more easily weaken the Arctic SPV compared to the PC1 events located relatively southward (i.e., South PC1 events). The analysis indicates that the North PC1-related Aleutian low anomaly is located over the northern North Pacific and thus enhances the climatological trough, which strengthens the planetary-scale wave 1 at mid-to-high latitudes and thereby weakens the SPV. The weakened stratospheric circulation further extends into the troposphere and favors negative surface temperature anomalies over Eurasia. By contrast, the South PC1-related Aleutian low anomaly is located relatively southward, and its constructive interference with the climatological trough is less efficient at high latitudes. Thus, the South PC1 events could not induce an evident enhancement of the planetary-scale waves at high latitudes and thereby a weakening of the SPV on average. The Eurasian cooling associated with South PC1 events (positive-minus-negative PC1 events) is also not prominent. The results of this study suggest that the meridional positions of the PC1 events may be useful for predicting the Arctic SPV and Eurasian surface temperature variations.
Effects of Dropsonde Data in Field Campaigns on Forecasts of Tropical Cyclones over the Western North Pacific in 2020 and the Role of CNOP Sensitivity
Xiaohao QIN, Wansuo DUAN, Pak-Wai CHAN, Boyu CHEN, Kang-Ning HUANG
, Available online   , Manuscript accepted  12 August 2022, doi: 10.1007/s00376-022-2136-9
Abstract:
Valuable dropsonde data were obtained from multiple field campaigns targeting tropical cyclones, namely Higos, Nangka, Saudel, and Atsani, over the western North Pacific by the Hong Kong Observatory and Taiwan Central Weather Bureau in 2020. The conditional nonlinear optimal perturbation (CNOP) method has been utilized in real-time to identify the sensitive regions for targeting observations adhering to the procedure of real-time field campaigns for the first time. The observing system experiments were conducted to evaluate the effect of dropsonde data and CNOP sensitivity on TC forecasts in terms of track and intensity, using the Weather Research and Forecasting model. It is shown that the impact of assimilating all dropsonde data on both track and intensity forecasts is case-dependent. However, assimilation using only the dropsonde data inside the sensitive regions displays unanimously positive effects on both the track and intensity forecast, either of which obtains comparable benefits to or greatly reduces deterioration of the skill when assimilating all dropsonde data. Therefore, these results encourage us to further carry out targeting observations for the forecast of tropical cyclones according to CNOP sensitivity.
A Precursory Signal of June–July Precipitation over the Yangtze River Basin: December–January Tropospheric Temperature over the Tibetan Plateau
Xiaying ZHU, Mingzhu YANG, Ge LIU, Yanju LIU, Weijing LI, Sulan NAN, Linhai SUN
, Available online   , Manuscript accepted  04 August 2022, doi: 10.1007/s00376-022-2079-1
Abstract:
The prediction of summer precipitation over the Yangtze River basin (YRB) has long been challenging, especially during June–July (JJ), when the mei-yu generally occurs. This study explores the potential signal for the YRB precipitation in JJ and reveals that the Tibetan Plateau tropospheric temperature (TPTT) in the middle and upper levels during the preceding December–January (DJ) is significantly correlated with JJ YRB precipitation. The close connection between the DJ TPTT anomaly with JJ YRB precipitation may be due to the joint modulation of the DJ ENSO and spring TP soil temperatures. The lagged response to an anomalously cold TPTT during the preceding DJ is a TPTT that is still anomalously cold during the following JJ. The lower TPTT can lead to an anomalous anticyclone to the east of Lake Baikal, an anomalous cyclone at the middle latitudes of East Asia, and an anomalous anticyclone over the western North Pacific. Meanwhile, the East Asian westerly jet shifts southward in response to the meridional thermal gradient caused by the colder troposphere extending from the TP to the east of Lake Baikal. The above-mentioned circulation anomalies constitute the positive anomaly of the East Asia-Pacific pattern, known to be conducive to more precipitation over the YRB. Since the DJ TPTT contains both the land (TP soil temperature) and ocean (ENSO) signals, it has a closer relationship with the JJ precipitation over the YRB than the DJ ENSO alone. Therefore, the preceding DJ TPTT can be considered an alternative predictor of the JJ YRB precipitation.
Toward Quantifying the Increasing Accessibility of the Arctic Northeast Passage in the Past Four Decades
Chao MIN, Xiangying ZHOU, Hao LUO, Yijun YANG, Yiguo WANG, Jinlun ZHANG, Qinghua YANG
, Available online   , Manuscript accepted  04 August 2022, doi: 10.1007/s00376-022-2040-3
Abstract:
Sea ice, one of the most dominant barriers to Arctic shipping, has decreased dramatically over the past four decades. Arctic maritime transport is hereupon growing in recent years. To produce a long-term assessment of trans-Arctic accessibility, we systematically revisit the daily Arctic navigability with a view to the combined effects of sea ice thickness and concentration throughout the period 1979−2020. The general trends of Navigable Windows (NW) in the Northeast Passage show that the number of navigable days is steadily growing and reached 89±16 days for Open Water (OW) ships and 163±19 days for Polar Class 6 (PC6) ships in the 2010s, despite high interannual and interdecadal variability in the NWs. More consecutive NWs have emerged annually for both OW ships and PC6 ships since 2005 because of the faster sea ice retreat. Since the 1980s, the number of simulated Arctic routes has continuously increased, and optimal navigability exists in these years of record-low sea ice extent (e.g., 2012 and 2020). Summertime navigability in the East Siberian and Laptev Seas, on the other hand, varies dramatically due to changing sea ice conditions. This systematic assessment of Arctic navigability provides a reference for better projecting the future trans-Arctic shipping routes.
Role of Ocean Dynamics in the Seasonal Hadley Cell: A Response to Idealized Arctic Amplification
Haijin DAI, Qiang YAO
, Available online   , Manuscript accepted  18 July 2022, doi: 10.1007/s00376-022-2057-7
Abstract:
How atmospheric and oceanic circulations respond to Arctic warming at different timescales are revealed with idealized numerical simulations. Induced by local forcing and feedback, Arctic warming appears and leads to sea-ice melting. Deep-water formation is inhibited, which weakens the Atlantic Meridional Overturning Circulation (AMOC). The flow and temperature in the upper layer does not respond to the AMOC decrease immediately, especially at mid-low latitudes. Thus, nearly uniform surface warming in mid-low latitudes enhances (decreases) the strength (width) of the Hadley cell (HC). With the smaller northward heat carried by the weaker AMOC, the Norwegian Sea cools significantly. With strong warming in Northern Hemisphere high latitudes, the long-term response triggers the “temperature-wind-gyre-temperature” cycle, leading to colder midlatitudes, resulting in strong subsidence and Ferrel cell enhancement, which drives the HC southward. With weaker warming in the tropics and stronger warming at high latitudes, there is a stronger HC with decreased width. A much warmer Southern Hemisphere appears due to a weaker AMOC that also pushes the HC southward. Our idealized model results suggest that the HC strengthens under both warming conditions, as tropical warming determines the strength of the HC convection. Second, extreme Arctic warming led by artificially reduced surface albedo decreases the meridional temperature gradient between high and low latitudes, which contracts the HC. Third, a warmer mid-high latitude in the Northern (Southern) Hemisphere due to surface albedo feedback (weakened AMOC) in our experiments pushes the HC northward (southward). In most seasons, the HC exhibits the same trend as that described above.
Comparative Analysis of the Generalized Omega Equation and Generalized Vertical Motion Equation
Baofeng JIAO, Lingkun RAN, Na LI, Ren CAI, Tao QU, Yushu ZHOU
, Available online   , Manuscript accepted  04 May 2022, doi: 10.1007/s00376-022-1435-5
Abstract:
Research on vertical motion in mesoscale systems is an extraordinarily challenging effort. Allowing for fewer assumptions, a new form of generalized vertical motion equation and a generalized Omega equation are derived in the Cartesian coordinate system (nonhydrostatic equilibrium) and the isobaric coordinate system (hydrostatic equilibrium), respectively. The terms on the right-hand side of the equations, which comprise the Q vector, are composed of three factors: dynamic, thermodynamic, and mass. A heavy rain event that occurred from 18 to 19 July 2021 in southern Xinjiang was selected to analyze the characteristics of the diagnostic variable in the generalized vertical motion equation (\begin{document}$ {Q_z} $\end{document}) and the diagnostic variable in the generalized Omega equation (\begin{document}${Q_p}$\end{document}) using high-resolution model data. The results show that the horizontal distribution of the \begin{document}${Q_z}$\end{document}-vector divergence at 5.5 km is roughly similar to the distribution of the \begin{document}${Q_p}$\end{document}-vector divergence at 500 hPa, and that both relate well to the composite radar reflectivity, vertical motion, and hourly accumulated precipitation. The \begin{document}${Q_z}$\end{document}-vector divergence is more effective in indicating weak precipitation. In vertical cross sections, regions with alternating positive and negative large values that match the precipitation are mainly concentrated in the middle levels for both forms of Q vectors. The temporal evolutions of vertically integrated \begin{document}${Q_z}$\end{document}-vector divergence and \begin{document}${Q_p}$\end{document}-vector divergence are generally similar. Both perform better than the classical quasigeostrophic Q vector and nongeostrophic Q vector in indicating the development of the precipitation system.
The asymmetric connection of SST in the Tasman Sea with respect to the opposite phases of ENSO in austral summer
Xueqian Sun, Shuanglin Li, Stefan Liess
, Available online   , Manuscript accepted  11 February 2022, doi: 10.1007/s00376-022-0421-y
Abstract:
Using linear regression and composite analyses, this study identifies a pronounced asymmetric connection of sea surface temperature (SST) in the Tasman Sea with the two opposite phases of El Niño-Southern Oscillation (ENSO) during austral summer. In El Niño years, the SST anomalies (SSTAs) in the Tasman Sea exhibit a dipolar pattern with weak warmth in the northwest and modest cooling in the southeast, while during La Niña years the SSTAs exhibit a basin-scale warmth with greater amplitude. Investigations on the underlying mechanism suggest that this asymmetry arises from the oceanic heat transport, especially the anomalous Ekman meridional heat fluxes induced by the zonal wind stress anomalies, rather than the surface heat fluxes on the air-sea interface. A further analysis demonstrates that the asymmetry of oceanic heat transport between El Niño and La Niña years is driven by the asymmetric atmospheric circulation over the Tasman Sea stimulated by the asymmetric diabatic heating in the tropical Pacific between the two opposite ENSO phases.
Microphysical Characteristics of Extreme-Rainfall Convection over the Pearl River Delta Region, South China from Polarimetric Radar Data during the Pre-summer Rainy Season
Hao HUANG, Kun ZHAO, Johnny C. L. CHAN, Dongming HU
, Available online   , Manuscript accepted  09 February 2022, doi: 10.1007/s00376-022-1319-8
Abstract:
During the pre-summer rainy season, heavy rainfall occurs frequently in South China. Based on polarimetric radar observations, the microphysical characteristics and processes of convective features associated with extreme rainfall rates (ERCFs) are examined. In the regions with high ERCF occurrence frequency, sub-regional differences are found in the lightning flash rate (LFR) distributions. In the region with higher LFRs, the ERCFs have larger volumes of high reflectivity factor above the freezing level, corresponding to more active riming processes. In addition, these ERCFs are more organized and display larger spatial coverage, which may be related to the stronger low-level wind shear and higher terrain in the region. In the region with lower LFRs, the ERCFs have lower echo tops and lower-echo centroids. However, no clear differences of the most unstable convective available potential energy (MUCAPE) exist in the ERCFs in the regions with different LFR characteristics. Regardless of the LFRs, raindrop collisional coalescence is the main process for the growth of raindrops in the ERCFs. In the ERCFs within the region with lower LFRs, the main mechanism for the rapid increase of liquid water content with decreasing altitude below 4 km is through the warm-rain processes converting cloud drops to raindrops. However, in those with higher LFRs, the liquid water content generally decreases with decreasing altitude.
Assimilation of the FY-4A AGRI Clear-Sky Radiance Data in a Regional Numerical Model and Its Impact on the Forecast of the “21·7” Henan Extremely Persistent Heavy Rainfall
Lan XU, Wei CHENG, Zhongren DENG, Juanjuan LIU, Bin WANG, Bin LU, Shudong WANG, Li DONG
, Available online   , Manuscript accepted  14 January 2022, doi: 10.1007/s00376-022-1380-3
Abstract:
Assimilation of the Advanced Geostationary Radiance Imager (AGRI) clear-sky radiance in a regional model is performed. The forecasting effectiveness of the assimilation of two water vapor (WV) channels with conventional observations for the “21·7” Henan extremely heavy rainfall is analyzed and compared with a baseline test that assimilates only conventional observations in this study. The results show that the 24-h cumulative precipitation forecast by the assimilation experiment with the addition of the AGRI exceeds 500 mm, compared to a maximum value of 532.6 mm measured by the national meteorological stations, and that the location of the maximum precipitation is consistent with the observations. The results for the short periods of intense precipitation processes are that the simulation of the location and intensity of the 3-h cumulative precipitation is also relatively accurate. The analysis increment shows that the main difference between the two sets of assimilation experiments is over the ocean due to the additional ocean observations provided by FY-4A, which compensates for the lack of ocean observations. The assimilation of satellite data adjusts the vertical and horizontal wind fields over the ocean by adjusting the atmospheric temperature and humidity, which ultimately results in a narrower and stronger WV transport path to the center of heavy precipitation in Zhengzhou in the lower troposphere. Conversely, the WV convergence and upward motion in the control experiment are more dispersed; therefore, the precipitation centers are also correspondingly more dispersed.
Assimilation of FY-3D MWTS-II Radiance with 3D Precipitation Detection and the Impacts on Typhoon Forecasts
Luyao QIN, Yaodeng CHEN, Gang MA, Fuzhong WENG, Deming MENG, Peng ZHANG
, Available online   , Manuscript accepted  07 January 2022, doi: 10.1007/s00376-022-1252-x
Abstract:
Precipitation detection is an essential step in radiance assimilation because the uncertainties in precipitation would affect the radiative transfer calculation and observation errors. The traditional precipitation detection method for microwave only detects clouds and precipitation horizontally, without considering the three-dimensional distribution of clouds. Extending precipitation detection from 2D to 3D is expected to bring more useful information to the data assimilation without using the all-sky approach. In this study, the 3D precipitation detection method is adopted to assimilate Microwave Temperature Sounder-2 (MWTS-II) onboard the Fengyun-3D, which can dynamically detect the channels above precipitating clouds by considering the near-real-time cloud parameters. Cycling data assimilation and forecasting experiments for Typhoons Lekima (2019) and Mitag (2019) are carried out. Compared with the control experiment, the quantity of assimilated data with the 3D precipitation detection increases by approximately 23%. The quality of the additional MWTS-II radiance data is close to the clear-sky data. The case studies show that the average root-mean-square errors (RMSE) of prognostic variables are reduced by 1.7% in the upper troposphere, leading to an average reduction of 4.53% in typhoon track forecasts. The detailed diagnoses of Typhoon Lekima (2019) further show that the additional MWTS-II radiances brought by the 3D precipitation detection facilitate portraying a more reasonable circulation situation, thus providing more precise structures. This paper preliminarily proves that 3D precipitation detection has potential added value for increasing satellite data utilization and improving typhoon forecasts.
Multiscale Combined Action and Disturbance Characteristics of Pre-summer Extreme Precipitation Events over South China
Hongbo LIU, Ruojing YAN, Bin WANG, Guanghua CHEN, Jian LING, Shenming FU
, Available online   , Manuscript accepted  08 September 2021, doi: 10.1007/s00376-021-1172-1
Abstract:
The dominant frequency modes of pre-summer extreme precipitation events (EPEs) over South China (SC) between 1998 and 2018 were investigated. The 67 identified EPEs were all characterized by the 3–8-d (synoptic) frequency band. However, multiscale combined modes of the synoptic and three low-frequency bands (10 20-d (quasi-biweekly, QBW); 15–40-d (quasi-monthly, QM); and 20–60-d (intraseasonal)) accounted for the majority (63%) of the EPEs, and the precipitation intensity on the peak wet day was larger than that of the single synoptic mode. It was found that EPEs form within strong southwesterly anomalous flows characterized by either lower-level cyclonic circulation over SC or a deep trough over eastern China. Bandpass-filtered disturbances revealed the direct precipitating systems and their life cycles. Synoptic-scale disturbances are dominated by mid–high latitude troughs, and the cyclonic anomalies originate from downstream of the Tibetan Plateau (TP). Given the warm and moist climate state, synoptic-scale northeasterly flows can even induce EPEs. At the QBW and QM scales, the disturbances originate from the tropical Pacific, downstream of the TP, or mid–high latitudes (QBW only). Each is characterized by cyclonic–anticyclonic wave trains and intense southwesterly flows between them within a region of large horizontal pressure gradient. The intraseasonal disturbances are confined to tropical regions and influence SC by marginal southwesterly flows. It is concluded that low-frequency disturbances provide favorable background conditions for EPEs over SC and synoptic-scale disturbances ultimately induce EPEs on the peak wet days. Both should be simultaneously considered for EPE predictions over SC.
Estimations of Land Surface Characteristic Parameters and Turbulent Heat Fluxes over the Tibetan Plateau Based on FY-4A/AGRI Data
Nan GE, Lei ZHONG, Yaoming MA, Yunfei FU, Mijun ZOU, Meilin CHENG, Xian WANG, Ziyu HUANG
, Available online   , Manuscript accepted  10 November 2020, doi: 10.1007/s00376-020-0169-5
Abstract:
Accurate estimates of land surface characteristic parameters and turbulent heat fluxes play an important role in the understanding of land–atmosphere interaction. In this study, Fengyun-4A (FY-4A) Advanced Geostationary Radiation Imager (AGRI) satellite data and the China Land Data Assimilation System (CLDAS) meteorological forcing dataset CLDAS-V2.0 were applied for the retrieval of broadband albedo, land surface temperature (LST), radiation flux components, and turbulent heat fluxes over the Tibetan Plateau (TP). The FY-4A/AGRI and CLDAS-V2.0 data from 12 March 2018 to 30 April 2018 were first used to estimate the hourly turbulent heat fluxes over the TP. The time series data of in-situ measurements from the Tibetan Observation and Research Platform were divided into two halves—one for developing retrieval algorithms for broadband albedo and LST based on FY-4A, and the other for the cross validation. Results show the root-mean-square errors (RMSEs) of the FY-4A retrieved broadband albedo and LST were 0.0309 and 3.85 K, respectively, which verifies the applicability of the retrieval method. The RMSEs of the downwelling/upwelling shortwave radiation flux and downwelling/upwelling longwave radiation flux were 138.87/32.78 W m−2 and 51.55/17.92 W m−2, respectively, and the RMSEs of net radiation flux, sensible heat flux, and latent heat flux were 58.88 W m−2, 82.56 W m−2 and 72.46 W m−2, respectively. The spatial distributions and diurnal variations of LST and turbulent heat fluxes were further analyzed in detail.
Evaluation of a Regional Ensemble Data Assimilation System for Typhoon Prediction
Lili Lei, Yangjinxi Ge, Zhe-Min Tan, Yi Zhang, Kekuan Chu, Xin Qiu, Qifeng Qian
, Available online  
Abstract:
An ensemble Kalman filter (EnKF) combined with the Advanced Research Weather Research and Forecasting model (WRF) is cycled and evaluated for western North Pacific (WNP) typhoons of year 2016. Conventional in-situ data, radiance observations, and tropical cyclone (TC) minimum sea level pressure (SLP) are assimilated every 6 h using an 80-member ensemble. For all TC categories, the 6-h ensemble priors from the WRF/EnKF system have appropriate amount of variance for TC tracks, but have insufficient variance for TC intensity. The 6-h ensemble priors from the WRF/EnKF system tend to overestimate the intensity for weak storms, but underestimate the intensity for strong storms. The 5-d deterministic forecasts launched from the ensemble mean analyses of WRF/EnKF are compared to the NCEP and ECMWF operational control forecasts. Results show that the WRF/EnKF forecasts generally have larger track errors than the NCEP and ECMWF forecasts for all TC categories, because the regional simulation cannot better represent the large-scale environment than the global simulation. The WRF/EnKF forecasts produce smaller intensity errors and biases than the NCEP and ECMWF forecasts for typhoons, but the opposite is true for tropical storms and severe tropical storms. The 5-d ensemble forecasts from the WRF/EnKF system for seven typhoon cases show appropriate variance for TC track and intensity with short forecast lead times, but have insufficient spread with long forecast lead times. The WRF/EnKF system provides better ensemble forecasts and higher predictability for TC intensity than the NCEP and ECMWF ensemble forecasts.
Invited Review
A Review of Atmospheric Electricity Research in China from 2019 to 2022
Weitao Lyu, Dong Zheng, zhang yang, Wen Yao, Rubin Jiang, Shanfeng Yuan, Dongxia Liu, Fanchao Lyu, Baoyou Zhu, Gaopeng Lu, Qilin Zhang, Yongbo Tan, Xuejuan Wang, Yakun Liu, Shaodong Chen, LuWen Chen, Qingyong Li, Yijun Zhang
, Available online   , Manuscript accepted  10 January 2023, doi: 10.1007/s00376-023-2280-x
Abstract:
Atmospheric electricity is composed of a series of electric phenomena in the atmosphere. Significant advances in atmospheric electricity research in China have been achieved in recent years. In this paper, the research progress on atmospheric electricity in China during 2019-2022 is reviewed mainly in the following aspects: (1) lightning detection and location techniques, (2) thunderstorm electricity, (3) lightning forecasting methods and techniques, (4) physical processes of lightning discharge, (5) high energy emissions and effects of thunderstorms on the upper atmosphere, and (6) effect of aerosol on lightning.
Parameterization and Explicit Modeling of Cloud Microphysics: Approaches, Challenges and Future Directions
Yangang Liu, Man-Kong Yau, Shin-Ichiro Shima, Lu Chunsong, Sisi chen
, Available online   , Manuscript accepted  23 December 2022, doi: 10.1007/s00376-022-2077-3
Abstract:
Cloud microphysical processes occur at the smallest end of scales among cloud-related processes, and thus must be parameterized not only in large scale global circulation models (GCMs) but also in various higher-resolution limited-area models such as cloud-resolving models (CRMs), and large eddy simulation (LES) models. Instead of having a comprehensive review of existing microphysical parameterizations that have been developed over the years, this study concentrates purposely on several topics that we believe, are understudied, but hold great potentials for further advancing bulk microphysics parameterizations: multi-moment bulk microphysics parameterizations and the role of the spectral shape of hydrometeor size distributions; discrete vs “continuous” representation of hydrometeor types; turbulence-microphysics interactions including turbulent entrainment-mixing processes and stochastic condensation; theoretical foundations for the mathematical expressions used to describe hydrometeor size distributions and hydrometeor morphology; and approaches for developing bulk microphysics parameterizations. Also presented are the spectral bin scheme and particle-based scheme (esp., super-droplet method) for representing explicit microphysics. Their advantages and disadvantages are elucidated for constructing cloud models with detailed microphysics that are essential to developing processes understanding and bulk microphysics parameterizations. Particle-resolved direct numerical simulation (DNS) models are described as an emerging technique to investigate turbulence-microphysics interactions at the most fundamental level by tracking individual particles and resolving the smallest turbulent eddies in turbulent clouds. Outstanding challenges and future research directions are explored as well.
Data Description Article
Homogenised Monthly and Daily Temperature and Precipitation Time Series in China and Greece since 1960
Athanassios A. ARGIRIOU, Zhen LI, Vasileios ARMAOS, Anna MAMARA, Yingling SHI, Zhongwei YAN
, Available online   , Manuscript accepted  20 December 2022, doi: 10.1007/s00376-022-2246-4
Abstract:
In this paper, we describe and analyze two datasets entitled “Homogenised monthly and daily temperature and precipitation time series in China during 1960–2021” and “Homogenised monthly and daily temperature and precipitation time series in Greece during 1960–2010”. These datasets provide the homogenised monthly and daily mean (TG), minimum (TN), and maximum (TX) temperature and precipitation (RR) records since 1960 at 366 stations in China and 56 stations in Greece. The datasets are available at the Science Data Bank repository and can be downloaded from https://doi.org/10.57760/sciencedb.01731 and https://doi.org/10.57760/sciencedb.01720. For China, the regional mean annual TG, TX, TN, and RR series during 1960–2021 showed significant warming or increasing trends of 0.27°C (10 yr)−1, 0.22°C (10 yr)−1, 0.35°C (10 yr)−1, and 6.81 mm (10 yr)−1, respectively. Most of the seasonal series revealed trends significant at the 0.05 level, except for the spring, summer, and autumn RR series. For Greece, there were increasing trends of 0.09°C (10 yr)−1, 0.08°C (10 yr)−1, and 0.11°C (10 yr)−1 for the annual TG, TX, and TN series, respectively, while a decreasing trend of –23.35 mm (10 yr)−1 was present for RR. The seasonal trends showed a significant warming rate for summer, but no significant changes were noted for spring (except for TN), autumn, and winter. For RR, only the winter time series displayed a statistically significant and robust trend [–15.82 mm (10 yr)−1]. The final homogenised temperature and precipitation time series for both China and Greece provide a better representation of the large-scale pattern of climate change over the past decades and provide a quality information source for climatological analyses.
Value-Added Products Derived from 15 Years of High-Quality Surface Solar Radiation Measurements at Xianghe, a Suburban Site in the North China Plain
Mengqi LIU, Xuehua FAN, Xiang’ao XIA, Jinqiang ZHANG, Jun LI
, Available online   , Manuscript accepted  02 November 2022, doi: 10.1007/s00376-022-2205-0
Abstract:
Surface solar radiation (SSR) is a key component of the energy budget of the Earth’s surface, and it varies at different spatial and temporal scales. Considerable knowledge of how and why SSR varies is crucial to a better understanding of climate change, which surely requires long-term measurements of high quality. The objective of this study is to introduce a value-added SSR dataset from Oct 2004 to Oct 2019 based on measurements taken at Xianghe, a suburban site in the North China Plain; two value-added products based on the 1-minute SSR measurements are developed. The first is clear sky detection by using a machine learning model. The second is cloud fraction estimation derived from an effective semi-empirical method. A “brightening” of global horizontal irradiance (GHI) was revealed and found to occur under both clear and cloudy conditions. This could likely be attributed to a reduction in aerosol loading and cloud fraction. This dataset could not only improve our knowledge of the variability and trend of SSR in the North China Plain, but also be beneficial for solar energy assessment and forecasting.
Dataset of Comparative Observations for Land Surface Processes over the Semi-Arid Alpine Grassland against Alpine Lakes in the Source Region of the Yellow River
Xianhong MENG, Shihua LYU, Zhaoguo LI, Yinhuan AO, Lijuan WEN, Lunyu SHANG, Shaoying WANG, Mingshan DENG, Shaobo ZHANG, Lin ZHAO, Hao CHEN, Di MA, Suosuo LI, Lele SHU, Yingying AN, Hanlin NIU
, Available online   , Manuscript accepted  14 September 2022, doi: 10.1007/s00376-022-2118-y
Abstract:
Thousands of lakes on the Tibetan Plateau (TP) play a critical role in the regional water cycle, weather, and climate. In recent years, the areas of TP lakes underwent drastic changes and have become a research hotspot. However, the characteristics of the lake-atmosphere interaction over the high-altitude lakes are still unclear, which inhibits model development and the accurate simulation of lakeclimate effects. The source region of the Yellow River (SRYR) has the largest outflow lake and freshwater lake on the TP and is one of the most densely distributed lakes on the TP. Since 2011, three observation sites have been set up in the Ngoring Lake basin in the SRYR to monitor the lake-atmosphere interaction and the differences among water-heat exchanges over the land and lake surfaces. This study presents an eight-year (2012–19), half-hourly, observation-based dataset related to lake–atmosphere interactions composed of three sites. The three sites represent the lake surface, the lakeside, and the land. The observations contain the basic meteorological elements, surface radiation, eddy covariance system, soil temperature, and moisture (for land). Information related to the sites and instruments, the continuity and completeness of data, and the differences among the observational results at different sites are described in this study. These data have been used in the previous study to reveal a few energy and water exchange characteristics of TP lakes and to validate and improve the lake and land surface model. The dataset is available at National Cryosphere Desert Data Center.
News & Views
Can Eurasia Experience a Cold Winter under a Third-Year La Niña in 2022/23?
Fei ZHENG, Bo WU, Lin WANG, Jingbei PENG, Yao YAO, Haifeng ZONG, Qing BAO, Jiehua MA, Shuai HU, Haolan REN, Tingwei CAO, Renping LIN, Xianghui FANG, Lingjiang TAO, Tianjun ZHOU, Jiang ZHU
, Available online   , Manuscript accepted  14 November 2022, doi: 10.1007/s00376-022-2331-8
Abstract:
The Northern Hemisphere (NH) often experiences frequent cold air outbreaks and heavy snowfalls during La Niña winters. In 2022, a third-year La Niña event has exceeded both the oceanic and atmospheric thresholds since spring and is predicted to reach its mature phase in December 2022. Under such a significant global climate signal, whether the Eurasian Continent will experience a tough cold winter should not be assumed, despite the direct influence of mid- to high-latitude, large-scale atmospheric circulations upon frequent Eurasian cold extremes, whose teleconnection physically operates by favoring Arctic air invasions into Eurasia as a consequence of the reduction of the meridional background temperature gradient in the NH. In the 2022/23 winter, as indicated by the seasonal predictions from various climate models and statistical approaches developed at the Institute of Atmospheric Physics, abnormal warming will very likely cover most parts of Europe under the control of the North Atlantic Oscillation and the anomalous anticyclone near the Ural Mountains, despite the cooling effects of La Niña. At the same time, the possibility of frequent cold conditions in mid-latitude Asia is also recognized for this upcoming winter, in accordance with the tendency for cold air invasions to be triggered by the synergistic effect of a warm Arctic and a cold tropical Pacific on the hemispheric scale. However, how the future climate will evolve in the 2022/23 winter is still subject to some uncertainty, mostly in terms of unpredictable internal atmospheric variability. Consequently, the status of the mid- to high-latitude atmospheric circulation should be timely updated by medium-term numerical weather forecasts and sub-seasonal-to-seasonal prediction for the necessary date information and early warnings.
Negligible Warming Caused by Nord Stream Methane Leaks
Xiaolong CHEN, Tianjun ZHOU
, Available online   , Manuscript accepted  04 November 2022, doi: 10.1007/s00376-022-2305-x
Abstract:
Unanticipated sabotage of two underwater pipelines in the Baltic Sea (Nord Stream 1 and 2) happened on 26 September 2022. Massive quantities of natural gas, primarily methane, were released into the atmosphere, which lasted for about one week. As a more powerful greenhouse gas than CO2, the potential climatic impact of methane is a global concern. Using multiple methods and datasets, a recent study reported a relatively accurate magnitude of the leaked methane at 0.22 ± 0.03 million tons (Mt), which was lower than the initial estimate in the immediate aftermath of the event. Under an energy conservation framework used in IPCC AR6, we derived a negligible increase in global surface air temperature of 1.8 × 10−5 °C in a 20-year time horizon caused by the methane leaks with an upper limit of 0.25 Mt. Although the resultant warming from this methane leak incident was minor, future carbon release from additional Earth system feedbacks, such as thawing permafrost, and its impact on the methane mitigation pathways of the Paris Agreement, warrants investigation.
Perspectives
A Perspective on the Evolution of Atmospheric Blocking Theories: From Eddy-Mean flow Interaction to Nonlinear Multiscale Interaction
Dehai LUO, Binhe LUO, Wenqi ZHANG
, Available online   , Manuscript accepted  14 September 2022, doi: 10.1007/s00376-022-2194-z
Abstract:
In this paper, we first review the research advancements in blocking dynamics and highlight the merits and drawbacks of the previous theories of atmospheric blocking. Then, the dynamical mechanisms of atmospheric blocking are presented based on a nonlinear multi-scale interaction (NMI) model. Previous studies suggested that the eddy deformation (e.g., eddy straining, wave breaking, and eddy merging) might lead to the formation and maintenance of atmospheric blocking. However, the results were speculative and problematic because the previous studies, based on the time-mean eddy-mean flow interaction model, cannot identify the causal relationship between the evolution of atmospheric blocking and the eddy deformation. Based on the NMI model, we indicate that the onset, growth, maintenance, and decay of atmospheric blocking is mainly produced by the spatiotemporal evolution of pre-existing upstream synoptic-scale eddies, whereas the eddy deformation is a concomitant phenomenon of the blocking formation. The lifetime of blocking is mainly determined by the meridional background potential vorticity gradient (PVy) because a small PVy favors weak energy dispersion and strong nonlinearity to sustain the blocking. But the zonal movement of atmospheric blocking is associated with the background westerly wind, PVy, and the blocking amplitude. Using this NMI model, a bridge from the climate change to sub-seasonal atmospheric blocking and weather extremes might be established via examining the effect of climate change on PVy. Thus, it is expected that using the NMI model to explore the dynamics of atmospheric blocking and its change is a new direction in the future.
Electronic Supplementary Materials to: The Combined Effects of the Tropical and Extratropical Quasi-biweekly Oscillations on the Record-setting Mei-yu Rainfall in the Summer of 2020*
Zhen HUANG, Shuanglin LI, Jianying LI, Chao ZHANG
, Available online   , Manuscript accepted  25 August 2022, doi: 10.1007/s00376-022-2050-1
Abstract: