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Original Paper
Precipitation Microphysical Processes in the Inner Rainband of Tropical Cyclone Kajiki (2019) over the South China Sea Revealed by Polarimetric Radar
Hepeng Zheng, Yun Zhang, Lifeng Zhang, Hengchi Lei, Zuhang Wu
, Available online   , Manuscript accepted  16 September 2020, doi: 10.1007/s00376-020-0179-3
Polarimetric radar and 2-D video disdrometer (2DVD) observations provide new insights into the precipitation microphysical processes and characteristics in the inner rainband of tropical cyclone (TC) Kajiki (2019) in the South China Sea for the first time. The precipitation of Kajiki is dominated by high concentrations and small (<3 mm) raindrops, which contribute more than 98% to the total precipitation. The average mass-weighted mean diameter and logarithmic normalized intercept is (1.49 mm, 4.47 log10 mm-1 m-3), indicating a larger mean diameter and a lower concentration compared to the TC landed in eastern China. The ice processes of the inner rainband are dramatically different among different stages. The riming process is dominant during the mature stage, while during the decay stage, the aggregation process is dominant. The vertical profiles of the polarimetric radar variables together with ice and liquid water contents in the convective region indicate that the formation of precipitation is dominated by warm rain processes. Large raindrops collect cloud droplets and other raindrops, causing reflectivity, differential reflectivity, and specific differential phase to increase with decreasing height. That is, accretion and coalescence play a critical role in the formation of heavy rainfall. The melting of different particles generated by the ice process has a great influence on the initial raindrop size distribution (DSD) to further affect the warm rain processes. The aloft DSD above heavy rain with the effect of graupel has a wider spectral width compared with the region without the effect of graupel.
Assimilation of Doppler Radar Data with an Ensemble-3DEnVar Approach to Improve Convective Forecasting
Shibo Gao, Haiqiu Yu, Chuanyou Ren, Limin Liu, Jinzhong Min
, Available online   , Manuscript accepted  16 September 2020, doi: 10.1007/s00376-020-0081-z
An ensemble of three-dimensional ensemble-variational (3DEnVar) data assimilation (E3DA) system was developed within the Weather Research and Forecasting model’s 3DVar framework to assimilate radar data to improve convective forecasting. In this system, ensemble perturbations were updated by an ensemble of 3DEnVar and the ensemble forecasts were used to generate the flow-dependent background error covariance. The performance of the E3DA system was first evaluated against one experiment without radar DA and one radar DA experiment with 3DVar, using a severe storm case over southeastern China on 5 June 2009. Results indicated that E3DA improved the quantitative forecast skills of reflectivity and precipitation, as well as their spatial distributions in terms of both intensity and coverage over 3DVar. The root mean square error of radial velocity from 3DVar was reduced by E3DA, with stronger low-level wind closer to observation. It was also found that E3DA improved the wind, temperature and water vapor mixing ratio, with the lowest errors at the surface and upper levels. The 3DVar showed moderate improvements in comparison with forecasts without radar DA. A diagnoses of the analysis revealed that E3DA increased vertical velocity, temperature, and humidity corresponding to the added reflectivity, while 3DVar failed to produce these adjustments, because of the lack of reasonable cross-variable correlations. The performance of E3DA was further verified using two convective cases over southern and southeastern China, and the reflectivity forecast skill was also improved over 3DVar.
Variations in amplitudes and wave energy along the energy dispersion paths of nonstationary barotropic Rossby waves
Yaokun Li, Jiping CHAO, Yanyan Kang
, Available online   , Manuscript accepted  16 September 2020, doi: 10.1007/s00376-020-0084-9
The variations in the wave energy and the amplitude along the energy dispersion paths of the barotropic Rossby waves in zonally symmetric basic flow are studied by solving the wave energy equation which expresses that the wave energy variability is determined by the divergence of the group velocity and the energy budget from the basic flow. The results suggest that both the wave energy and the amplitude of a leading wave increase significantly in the propagating region that is located south of the jet axis and enclosed by a southern critical line and a northern turning latitude. The leading wave gains the barotropic energy from the basic flow by eddy activities. The amplitude continuously climbs up a peak at the turning latitude due to increasing wave energy and enlarging horizontal scale (shrinking total wavenumber). Both the wave energy and the amplitude eventually decrease when the trailing wave continuously approaches southward to the critical line. The trailing wave decays and its energy is continuously absorbed by the basic flow. Furthermore, both the wave energy and the amplitude oscillate with a limited range in the propagating region that is located near the jet axis and enclosed by two turning latitudes. Both the leading and trailing waves neither develops nor decay significantly. The jet works as a waveguide to allow the waves propagating a long distance.
Profiles and source apportionment of NMVOCs in winter and summer in Xi’an, China, based on Hybrid Environmental Receptor Model
Jian Sun, Zhenxin Shen, Yue Zhang, Wenting Dai, Kun He, Hongmei Xu, Zhou Zhang, Long Cui, Xuxiang Li, Yu Huang, Junji Cao
, Available online   , Manuscript accepted  09 September 2020, doi: 10.1007/s00376-020-0153-0
Summer and winter campaigns for the chemical compositions and sources of nonmethane hydrocarbons (NMHCs) and oxygenated Volatile organic compounds (OVOC) were conducted in Xi’an. Data from 57 photochemical assessment monitoring stations (PAMS) for NMHCs and 20 OVOC species were analyzed. Significant seasonal differences were noted for total VOCs (TVOC, NMHCs and OVOCs) concentrations and compositions. The campaign-average TVOC concentrations in winter (85.3 ± 60.6 ppbv) were almost twice of those in summer (47.2 ± 31.6 ppbv). Alkanes and OVOCs were the most abundant category in winter and summer, respectively. NMHCs but not OVOCs had significantly higher levels on weekends than on weekdays. Total ozone formation potential was higher in summer than in winter (by 50%) because of the high concentrations of alkenes high temperature and solar radiation levels in summer. The hybrid environmental receptor model (HERM) was used to conduct source apportionment for atmospheric TVOCs in winter and summer, with excellent accuracy. The HERM demonstrated its suitability in a situation where only partial source profile data are available. The HERM results indicated significantly different seasonal source contributions to TVOCs in Xi’an. In particular, coal and biomass burning had contributions greater than half in winter (53.4%), whereas traffic sources were prevalent in summer (53.1%). This study’s results underscore the need for targeted and adjustable VOC control measures that account for seasonal differences in Xi’an; such measures should target not only the severe problem with VOC pollution but also the problem of consequent secondary pollution (e.g., from O3 and secondary organic aerosols).
Characterization of organic aerosol at a rural site in North China Plain: sources, volatility and organonitrates
Qiao Zhu, Li-Ming Cao, Meng-Xue Tang, Xiao-Feng Huang, Eri Saikawa, L. -Y. He
, Available online   , Manuscript accepted  09 September 2020, doi: 10.1007/s00376-020-0127-2
The North China Plain (NCP) is the region that experiences serious aerosol pollution. A number of studies focus on aerosol pollution in urban regions in NCP, however, research on characterizing aerosols in rural NCP areas is comparatively limited. In this study, we deployed a thermodenuder high-resolution aerosol mass spectrometer (TD-HR-AMS) system at a rural site in NCP region in summer 2013 to characterize the chemical compositions and volatility of submicron aerosols (PM1). The average PM1 mass concentration was 51.2 ± 48.0µg m-3 and organic aerosol (OA) contributed most (35.4%) to PM1. Positive matrix factorization (PMF) analysis of OA measurements identified four OA factors including hydrocarbon-like OA (HOA, accounting for 18.4%), biomass burning OA (BBOA, 29.4%), less-oxidized oxygenated OA (LO-OOA, 30.8%) and more-oxidized oxygenated OA (MO-OOA, 21.4%). The volatility sequence of the OA factors was HOA > BBOA > LO-OOA > MO-OOA, consistent with their oxygen-to-carbon (O:C) ratios. Additionally, the mean concentration of organonitrates (ON) was 1.48–3.39 µg m-3, contributing 8.1–19% of OA based on cross validation of two estimated methods with the HR-ToF-AMS measurement. The correlation analysis shows that ON were more correlated with BBOA and black carbon emitted from biomass burning but poorly correlated with LO-OOA. And the volatility analysis for ON further confirms that particulate ON formation might be highly associated with primary emissions in rural NCP.
Evaluation of the Arctic sea ice cover and thickness simulated by the MITgcm sea ice-ocean model
Fei Zheng, SUN Yue, Qinghua Yang, MU Longjiang
, Available online   , Manuscript accepted  09 September 2020, doi: 10.1007/s00376-020-9223-6
A regional Arctic Ocean configuration of the Massachusetts Institute of Technology general circulation model (MITgcm) is applied to simulate the Arctic sea ice from 1991 to 2012. The simulations are evaluated by comparing them with the observations from different sources. The results show that MITgcm can reproduce interannual and seasonal variability of the sea ice extent, and underestimates the trend in sea ice extent especially in September. The ice concentration and thickness distributions are comparable to those from the observations with most deviations within the observation uncertainties and less than 0.5m respectively. The simulated sea ice extents are better correlated with observations in September with a correlation coefficient of 0.95, than in March with a correlation coefficient of 0.83. But the distributions of sea ice concentration are better simulated in March with higher pattern correlation coefficients (0.98) than that in September. When the model underestimates the atmospheric influence on the sea ice evolution in March, deviations in the sea ice concentration arise at the ice edges and are higher than those in September. In contrast, when the model underestimates the oceanic boundaries’ influence on the September sea ice evolution, disagreements in the distribution of the sea ice concentration and its trend are found over most marginal seas in the Arctic Ocean. The uncertainties of the model that fails to incorporate the atmospheric information in March and oceanic information in September contribute to varying model errors with the seasons.
Influence of the Eastern Pacific and Central Pacific Types of ENSO on the South Asian Summer Monsoon
Fangxing Fan, Renping Lin, Xiang-Hui Fang, Feng Xue, Fei Zheng, Jiang Zhu
, Available online   , Manuscript accepted  07 September 2020, doi: 10.1007/s00376-020-0055-1
Based on the observational and reanalysis data, the relationships between the eastern Pacific (EP) and central Pacific (CP) types of El Niño-Southern Oscillation (ENSO) during the developing summer and the South Asian summer monsoon (SASM) are examined. The roles of these two types of ENSO on the SASM experienced notable multidecadal modulation in the late 1970s. While the inverse relationship between the EP type of ENSO and SASM has weakened dramatically, the CP type of ENSO plays a far more prominent role in producing anomalous Indian monsoon rainfall after the late 1970s. The drought-producing El Niño warming of both the EP and CP types can excite the anomalous rising motion of the Walker circulation concentrated in the equatorial central Pacific around 160°W to the date line. Accordingly, the compensatory subsidence anomalies are evident from the Maritime Continent to the Indian subcontinent, leading to suppressed convection and decreased precipitation over these regions. Moreover, the anomalously less moisture flux into South Asia associated with the developing EP El Niño and the significant northwesterly anomalies dominating over southern India accompanied by the developing CP El Niño may also be responsible for the Indian monsoon droughts during the pre-1979 and post-1979 sub-periods, respectively. The El Niño events with the same “flavor” may not necessarily produce consistent Indian monsoon rainfall anomalies while the similar Indian monsoon droughts may be induced by different types of El Niño, implying the great sensitivity of monsoonal precipitation to detailed configuration of ENSO forcing imposed on the tropical Pacific.
Water vapor retrievals from near-infrared channels of the advanced MERSI-II instrument onboard Fengyun-3D
Ling Wang, Xiuqing Hu, Na Xu, Lin Chen
, Available online   , Manuscript accepted  07 September 2020, doi: 10.1007/s00376-020-0174-8
Water vapor plays a key role in weather, climate, and environment research on local and global scales. Knowledge about atmospheric water vapor and its spatiotemporal variability is essential for climate and weather research. Because of the advantage of a unique temporal and spatial resolution, satellite observations provide global or regional water vapor distributions. The advanced Medium Resolution Spectral Imager (MERSI) instrument, that is, MERSI-II onboard the Fengyun-3D (FY-3D) meteorological satellite, has been one of the major satellite sensors routinely providing precipitable water vapor (PWV) products to the community using near-infrared (NIR) measurements since June 2018. In this paper, the major updates related to the production of NIR PWV products of MERSI-II are discussed for the first time. In addition, the water vapor retrieval algorithm based on the MERSI-II NIR channels is introduced and derivations are made over clear land areas, clouds, and sun glint areas over the ocean. Finally, the status and samples of the MERSI-II PWV products are presented. The accuracy of MERSI-II PWV products is validated using ground-based global positioning system measurements. The results show that the accuracies of the water vapor products based on the updated MERSI-II are significantly improved compared with those of MERSI, because MERSI-II provides a better channel setting and new calibration method. The root mean square error and relative bias of MERSI-II PWV products are typically 1.8–5.5 mm and -3.0 – -14.3%, respectively, and thus comparable with those of other global remote sensing products of the same type.
Definition of Extensive Cold-Precipitation-Freezing Events in Southern China and their Circulation Characteristics
Jingbei Peng, Cholaw Bueh, Zuowei Xie
, Available online   , Manuscript accepted  03 September 2020, doi: 10.1007/s00376-020-0117-4
Concurrence of low temperature, precipitation and freezing weather in an extensive area would cause devastating impacts on local economy and society. We call such a combination of concurrent disastrous weather events as extensive cold-precipitation-freezing event (ECPFE). In this study, the ECPFEs in southern China ([102-123°E, 15-35°N]) are objectively defined by using daily surface observational data for the period 1951-2013. An ECPFE in southern China is defined if the low temperature area, precipitation area and freezing area concurrently exceed their respective thresholds for at least three consecutive days. The identified ECPFEs are shown to be reasonable and reliable, compared with those in the previous studies. The circulation anomalies in ECPFEs are characterized by a pair of large-scale tilted ridge and trough over mid- and high latitude Eurasia, and the intensified subtropical westerlies along the southern foot of Tibetan Plateau and the anomalous anticyclonic circulation over the subtropical western Pacific. A comparative analysis reveals that the stable cold air from the north and the warm and moist air from the south converge together to be in a confrontation state, facilitating a favorable environment for the concurrence of extensive low-temperature, precipitation and freezing weather.
Observed Long- and Short-Lived North Atlantic Oscillation Events: The Role of the Stratosphere
Jie Song, Jing jing Zhao
, Available online   , Manuscript accepted  02 September 2020, doi: 10.1007/s00376-020-0021-y
Utilizing three different sets of reanalysis data, this study examines the long- and short-lived observed positive North Atlantic Oscillation (NAO) events (referred as NAO+_LE and NAO+_SE) and long- and short-lived observed negative NAO events (referred as NAO-_LE and NAO-_SE). Composite results indicate that the NAO-like circulation anomalies associated with the long-lived NAO events can reach the stratosphere, while, they are primarily confined in the troposphere in the short-lived NAO events. Thus, the coupling/connection of stratospheric and tropospheric circulation anomalies is much better (worse) in the long- (short-) lived NAO events. A series of modified stratospheric initial value experiments conducted by a simplified model indicate that a better (worse) connection between stratospheric and tropospheric circulation anomalies in the initial-value fields tend to gradually induce the NAO-like tropospheric circulation anomalies in the troposphere on the subsequent days, and thus, naturally elongate (reduce) the lifetimes of the original NAO events by altering the tropospheric synoptic eddy vorticity flux over the NA region.
Comparison of ozone and PM2.5 concentrations over urban, suburban, and background sites in China
Lan Gao, Xu Yue, Xiaoyan Meng, Li Du, Yadong Lei, Chenguang Tian, Liang Qiu
, Available online   , Manuscript accepted  01 September 2020, doi: 10.1007/s00376-020-0054-2
Surface ozone (O3) and fine particulate matter (PM2.5) are dominant air pollutants in China. Concentrations of these pollutants can show significant differences between urban and nonurban areas. However, such contrast has never been explored on the country level. This study investigates the spatiotemporal characteristics of urban-to-suburban and urban-to-background differences for O3 (Δ[O3]) and PM2.5 (Δ[PM2.5]) concentrations in China using monitoring data from 1171 urban, 110 suburban, and 15 background sites built by the National Environmental Monitoring Center (NEMC). On the annual mean basis, urban-to-suburban Δ[O3] are -3.7 ppbv in Beijing-Tianjin-Hebei, 1.0 ppbv in Yangtze River Delta, -3.5 ppbv in Pearl River Delta, and -3.8 ppbv in Sichuan Basin. On the contrary, urban-to-suburban Δ[PM2.5] are 15.8, -0.3, 3.5 and 2.4 μg m-3 in those areas. The urban-to-suburban contrast is more significant in winter for both Δ[O3] and Δ[PM2.5]. In eastern China, urban-to-background differences are also moderate during summer, with -5.1~6.8 ppbv for Δ[O3] and -0.1~22.5 μg m-3 for Δ[PM2.5]. However, such contrasts are much larger in winter with -22.2~5.5 ppbv for Δ[O3] and 3.1~82.3 μg m-3 for Δ[PM2.5]. Since the urban region accounts for only 2% of the whole country area, the urban-dominant air quality data from NEMC network may overestimate winter [PM2.5] but underestimate winter [O3] over the vast domain of China. The study suggests that the NEMC monitoring data should be used with cautions for evaluating chemical models and assessing ecosystem health, which require more data outside urban areas.
Spatial and temporal distribution of atmospheric CO2 based on three satellites in East China
BOZHEN LI, Gen Zhang, Lingjun XIA, Ping KONG, Mingjin ZHAN, Rui SU
, Available online   , Manuscript accepted  31 August 2020, doi: 10.1007/s00376-020-0123-6
East China (113.6°E~122.9°E, 23.6°N~38.4°N) is the largest developed region in China. Based on CO2 products retrieved from GOSAT, the temporal and spatial distribution of CO2 mixing ratios in East China during 2014−2017 were discussed, and the retrieved CO2 from AIRS, OCO-2 and WLG (Waliguan) background station observation were compared with that of GOSAT. The annual CO2 retrieved from GOSAT in East China ranged from 398.96±0.24 ppm in 2014 to 407.39±0.20 ppm in 2017, with the growth rate of 2.82±0.15 ppm per year, which were higher than the other six regions in China. The seasonal cycle presented a maximum in spring and a minimum in summer or autumn. Higher values were mainly concentrated in the coastal areas of Zhejiang Province, and lower values were concentrated in Jiangxi and north of Fujian Province. CO2 observed in Fujian and parts of Jiangxi increased less than 1.0 ppm during 2014−2015, but enhanced significantly more than 5.0 ppm during 2015−2016, perhaps influenced by local emissions and global impacts. We calculated year-to-year CO2 enhancements in Yangtze River Delta regions during 2014−2017 that were relatively low and stable, due to its carbon emission control and reduction policies. The annual and seasonal amplitude of CO2 retrieved from AIRS were lower than that from GOSAT in East China, probably owing to CO2 retrieved from AIRS better reflected the characteristics of mid-troposphere, while GOSAT reflected the near-surface CO2 relatively. The spatial and temporal distribution characteristics of CO2 retrieved from OCO-2 were close to that from GOSAT in East China.
Optical, radiative and chemical characteristics of aerosol in Changsha city of Central China
Xiaoyan Wu, Jinyuan Xin, Wenyu Zhang, Chongshui Gong, Yining Ma, Yongjing Ma, Tianxue Wen, Zirui Liu, Shili Tian, Yuesi Wang, Fangkun Wu
, Available online   , Manuscript accepted  21 August 2020, doi: 10.1007/s00376-020-0076-9
Industrial pollution has a significant effect on aerosol properties in Changsha City, a typical city of Central China. Therefore, year-round measurements of aerosol optical, radiative and chemical properties from 2012 to 2014 at an urban site in Changsha were analyzed. During the observation period, the energy structure was continuously optimized, which was characterized by the reduction of coal combustion. The aerosol properties have obvious seasonal variations. The seasonal average aerosol optical depth (AOD) at 500 nm ranged from 0.49 to 1.00, single scattering albedo (SSA) ranged from 0.93 to 0.97 and aerosol radiative forcing at the top of the atmosphere (TOA) ranged from -24.0 to 3.8 W m-2. The chemical components also showed seasonal variations. Meanwhile, the scattering aerosol such as organic carbon (OC), SO42-, NO3-, and NH4%2B showed a decrease and elemental carbon (EC) increased. Compared with the observation in winter 2012, AOD and TOA decreased by 0.14 and -1.49 W m-2 in winter 2014. The scattering components SO42-, NO3- and NH4%2B decreased by 12.8 μg m-3 (56.8%), 9.2 μg m-3 (48.8%) and 6.4 μg m-3 (45.2%) respectively. The atmospheric visibility and pollution diffusion conditions improved. The extinction and radiative forcing of aerosol significantly controlled by the scattering aerosol. The results indicate that Changsha is an industrial city with strong scattering aerosol. The energy structure optimization had a marked effect on controlling pollution, especially in winter (strong scattering aerosol).
Modulation of Madden–Julian Oscillation Activity by the tropical Pacific–Indian Ocean Associated Mode
Lifeng Li, Xin Li, Xiong Chen, Chongyin Li, Jianqi Zhang, Yulong Shan
, Available online   , Manuscript accepted  21 August 2020, doi: 10.1007/s00376-020-0002-1
In this study, the impacts of the tropical Pacific–Indian Ocean associated mode (PIOAM) on Madden–Julian Oscillation (MJO) activity were investigated using reanalysis data. In the positive (negative) phase of PIOAM, the amplitudes of MJO zonal wind and outgoing longwave radiation (OLR) are significantly weakened (enhanced) over the Indian Ocean, while they are pronounced enhanced (weakened) over the central and eastern Pacific. The eastward propagation of MJO can extend to the central Pacific in the positive phase of PIOAM, whereas it is mainly confined to west of 160°E in the negative phase of PIOAM. PIOAM impacts MJO activity by modifying the atmospheric circulation and moisture budget. Anomalous ascending (descending) motion and positive (negative) moisture anomalies occur over the western Indian Ocean and central-eastern Pacific (Maritime Continent and western Pacific) during the positive phase of PIOAM. The anomalous circulation is almost the opposite in the negative phases of PIOAM. These anomalous circulation and moisture can modulate the activity of MJO. The stronger moistening over the Indian Ocean induced by zonal and vertical moisture advection leads to the stronger MJO activity over the Indian Ocean in the negative phase of PIOAM. During the positive phase of PIOAM, MJO propagates further eastward over the central Pacific due to the stronger moistening there, which is mainly attributed to the meridional and vertical moisture advection, especially LFBS moisture advection by MJO meridional and vertical velocities.
Surface Temperature Changes Projected by FGOALS Models under Low Warming Scenarios in CMIP5 and CMIP6
Shang-Min LONG, Kai-Ming HU, Gen LI, Gang HUANG, Xia QU
, Available online   , Manuscript accepted  20 August 2020, doi: 10.1007/s00376-020-0177-5
To meet the low warming targets proposed in the 2015 Paris Agreement, substantial reduction in carbon emissions is needed in the future. It is important to know how surface climates respond under low warming targets. The present study investigates the surface temperature changes under the low-forcing scenario of Representative Concentration Pathways (RCP2.6) and its updated version (Shared Socioeconomic Pathways, SSP1-2.6) by the Flexible Global Ocean–Atmosphere–Land System (FGOALS) models participating in phases 5 and 6 of the Coupled Model Intercomparison Project (CMIP5 and CMIP6, respectively). In both scenarios, radiative forcing (RF) first increases to a peak of 3 W m−2 around 2045 and then decreases to 2.6 W m−2 by 2100. Global mean surface air temperature rises in all FGOALS models when RF increases (RF increasing stage) and declines or holds nearly constant when RF decreases (RF decreasing stage). The surface temperature change is distinct in its sign and magnitude between the RF increasing and decreasing stages over the land, Arctic, North Atlantic subpolar region, and Southern Ocean. Besides, the regional surface temperature change pattern displays pronounced model-to-model spread during both the RF increasing and decreasing stages, mainly due to large intermodel differences in climatological surface temperature, ice-albedo feedback, natural variability, and Atlantic Meridional Overturning Circulation change. The pattern of tropical precipitation change is generally anchored by the spatial variations of relative surface temperature change (deviations from the tropical mean value) in the FGOALS models. Moreover, the projected changes in the updated FGOALS models are generally closer to the multi-model ensemble mean results than their predecessors, suggesting that there are noticeable improvements in the future projections of FGOALS models from CMIP5 to CMIP6.
Statistical modeling with hidden Markov tree and high-resolution interpolation for spaceborne radar reflectivity in wavelet domain
Leilei Kou, Yinfeng Jiang, Aijun Chen, Zhenhui Wang
, Available online   , Manuscript accepted  20 August 2020, doi: 10.1007/s00376-020-0035-5
With the increasing availability of precipitation radar data from space, enhancement of the resolution of spaceborne precipitation observations is important, particularly for hazard prediction and climate modeling at local scales relevant to extreme precipitation intensities and gradients. In this paper, the statistical characteristics of the radar precipitation reflectivity data are studied and modeled using a hidden Markov tree (HMT) in wavelet domain. Then, a high-resolution interpolation algorithm is proposed for spaceborne radar reflectivity using the HMT model as prior information. Owing to the small and transient storm elements embedded in the larger and slowly varying elements, the radar precipitation data exhibits distinct multiscale statistical properties, including the non-Gaussian structure and scale-to-scale dependency. A HMT model can capture well the statistical properties of radar precipitation, where the wavelet coefficients in each subband are characterized as a Gaussian mixture model (GMM), and the wavelet coefficients from the coarse scale to fine scale are described using a multiscale Markov process. The state probabilities of GMM are determined using the expectation maximization (EM) method, and other parameters such as the variance decay parameters in HMT model are learned and estimated from high-resolution ground radar (GR) reflectivity images. Using the prior model, the wavelet coefficients at finer scales are estimated using local Wiener filtering. The interpolation algorithm is validated using the precipitation radar (PR) data on the Tropical Rainfall Measurement Mission (TRMM) satellite, and the reconstruction results are found to be able to enhance the spatial resolution while optimally reproducing the local extremes and gradients.
Opposing Trends of Winter Cold Extremes over Eastern Eurasia and North America under Recent Arctic Warming
Shuangmei MA, Congwen ZHU
, Available online   , Manuscript accepted  14 August 2020, doi: 10.1007/s00376-020-0070-2
Under recent Arctic warming, boreal winters have witnessed severe cold surges over both Eurasia and North America, bringing about serious social and economic impacts. Here, we investigated the changes in daily surface air temperature (SAT) variability during the rapid Arctic warming period of 1988/89–2015/16, and found the daily SAT variance, mainly contributed by the sub-seasonal component, shows an increasing and decreasing trend over eastern Eurasia and North America, respectively. Increasing cold extremes (defined as days with daily SAT anomalies below 1.5 standard deviations) dominated the increase of the daily SAT variability over eastern Eurasia, while decreasing cold extremes dominated the decrease of the daily SAT variability over North America. The circulation regime of cold extremes over eastern Eurasia (North America) is characterized by an enhanced high-pressure ridge over the Urals (Alaska) and surface Siberian (Canadian) high. The data analyses and model simulations show the recent strengthening of the high-pressure ridge over the Urals was associated with warming of the Barents–Kara seas in the Arctic region, while the high-pressure ridge over Alaska was influenced by the offset effect of Arctic warming over the East Siberian–Chukchi seas and the Pacific decadal oscillation (PDO)–like sea surface temperature (SST) anomalies over the North Pacific. The transition of the PDO-like SST anomalies from a positive to negative phase cancelled the impact of Arctic warming, reduced the occurrence of extreme cold days, and possibly resulted in the decreasing trend of daily SAT variability in North America. The multi-ensemble simulations of climate models confirmed the regional Arctic warming as the driver of the increasing SAT variance over eastern Eurasia and North America and the overwhelming effect of SST forcing on the decreasing SAT variance over North America. Therefore, the regional response of winter cold extremes at midlatitudes to the Arctic warming could be different due to the distinct impact of decadal SST anomalies.
Sources of Subseasonal Prediction Skill for Heatwaves over the Yangtze River Basin Revealed from Three S2S Models
Jiehong XIE, Jinhua YU, Haishan CHEN, Pang-Chi HSU
, Available online   , Manuscript accepted  12 August 2020, doi: 10.1007/s00376-020-0144-1
Based on the reforecast data (1999–2010) of three operational models [the China Meteorological Administration (CMA), the National Centers for Environmental Prediction of the U.S. (NCEP) and the European Centre for Medium-Range Weather Forecasts (ECMWF)] that participated in the Subseasonal to Seasonal Prediction (S2S) project, we identified the major sources of subseasonal prediction skill for heatwaves over the Yangtze River basin (YRB). The three models show limited prediction skills in terms of the fraction of correct predictions for heatwave days in summer; the Heidke Skill Score drops quickly after a 5-day forecast lead and falls down close to zero beyond the lead time of 15 days. The superior skill of the ECMWF model in predicting the intensity and duration of the YRB heatwave is attributable to its fidelity in capturing the phase evolution and amplitude of high-pressure anomalies associated with the intraseasonal oscillation and the dryness of soil moisture induced by less precipitation via the land–atmosphere coupling. The effects of 10–30-day and 30–90-day circulation prediction skills on heatwave predictions are comparable at shorter forecast leads (10 days), while the biases in 30–90-day circulation amplitude prediction show close connection with the degradation of heatwave prediction skill at longer forecast leads (> 15–20 days). The biases of intraseasonal circulation anomalies further affect precipitation anomalies and thus land conditions, causing difficulty in capturing extremely hot days and their persistence in the S2S models.
Attribution of the persistent precipitation in the Yangtze–Huaihe River Basin during February 2019
Zhixuan Wang, Jilin SUN, jiancheng Wu, Fangyue Ning, Weiqi Chen
, Available online   , Manuscript accepted  10 August 2020, doi: 10.1007/s00376-020-0107-6
A month-long persistent precipitation happened in Yangtze–Huaihe River Basin during February 2019. The rainfall was mainly caused by the frontogenesis, and the geopotential height factors affecting the duration of rainfall were divided into high latitudes and low latitudes for analysis. The two-wave structure at high latitudes led to quasi-stationary circulation, and the change of blocking high pressure and AO phase caused cold air to invade South China continuously and made the difference in frontal position. The geopotential height in mid-low latitudes was influenced by the quasi‐biweekly oscillation of precipitation. The feedback mechanism of ‘Subtropical High - Precipitation - Anticyclone’ (SHPA) blocked the circulation in the mid-low latitudes and provided a continuous airflow of water vapor for precipitation. As for the effect of sea surface temperature, WNPAC stimulated by El Niño strengthened the intensity of the southerly wind and also provided support for the re-development of the anticyclone system in SHPA. The sea surface temperature anomaly in the South China Sea provides sensible heating for precipitation, and the convergent rising airflow is conducive to the occurrence of precipitation. In addition, the SHPA mechanism provides a reliable basis for the predictability of persistent precipitation in winter for the mid-low latitudes.
Simulated Relationship between Wintertime ENSO and East Asian Summer Rainfall: From CMIP3 to CMIP6
Yuanhai FU, Zhongda LIN, Tao WANG
, Available online   , Manuscript accepted  05 August 2020, doi: 10.1007/s00376-020-0147-y
El Niño–Southern Oscillation (ENSO) events have a strong influence on East Asian summer rainfall (EASR). This paper investigates the simulated ENSO–EASR relationship in CMIP6 models and compares the results with those in CMIP3 and CMIP5 models. In general, the CMIP6 models show almost no appreciable progress in representing the ENSO–EASR relationship compared with the CMIP5 models. The correlation coefficients in the CMIP6 models are relatively smaller and exhibit a slightly greater intermodel diversity than those in the CMIP5 models. Three physical processes related to the delayed effect of ENSO on EASR are further analyzed. Results show that, firstly, the relationships between ENSO and the tropical Indian Ocean (TIO) sea surface temperature (SST) in the CMIP6 models are more realistic, stronger, and have less intermodel diversity than those in the CMIP3 and CMIP5 models. Secondly, the teleconnections between the TIO SST and Philippine Sea convection (PSC) in the CMIP6 models are almost the same as those in the CMIP5 models, and stronger than those in the CMIP3 models. Finally, the CMIP3, CMIP5, and CMIP6 models exhibit essentially identical capabilities in representing the PSC–EASR relationship. Almost all the three generations of models underestimate the ENSO–EASR, TIO SST–PSC, and PSC–EASR relationships. Moreover, almost all the CMIP6 models that successfully capture the significant TIO SST–PSC relationship realistically simulate the ENSO–EASR relationship and vice versa, which is, however, not the case in the CMIP5 models.
Fidelity of the APHRODITE Dataset in Representing Extreme Precipitation over Central Asia
Sheng LAI, Zuowei XIE, Cholaw BUEH, Yuanfa GONG
, Available online   , Manuscript accepted  30 July 2020, doi: 10.1007/s00376-020-0098-3
Using rain-gauge-observation daily precipitation data from the Global Historical Climatology Network (V3.25) and the Chinese Surface Daily Climate Dataset (V3.0), this study investigates the fidelity of the AHPRODITE dataset in representing extreme precipitation, in terms of the extreme precipitation threshold value, occurrence number, probability of detection, and extremal dependence index during the cool (October to April) and warm (May to September) seasons in Central Asia during 1961–90. The distribution of extreme precipitation is characterized by large extreme precipitation threshold values and high occurrence numbers over the mountainous areas. The APHRODITE dataset is highly correlated with the gauge-observation precipitation data and can reproduce the spatial distributions of the extreme precipitation threshold value and total occurrence number. However, APHRODITE generally underestimates the extreme precipitation threshold values, while it overestimates the total numbers of extreme precipitation events, particularly over the mountainous areas. These biases can be attributed to the overestimation of light rainfall and the underestimation of heavy rainfall induced by the rainfall distribution–based interpolation. Such deficits are more evident for the warm season than the cool season, and thus the biases are more pronounced in the warm season than in the cool season. The probability of detection and extremal dependence index reveal that APHRODITE has a good capability of detecting extreme precipitation, particularly in the cool season.
Upper- and Lower-tropospheric Circulation Anomalies Associated with Interannual Variation of Pakistan Rainfall during Summer
Riyu LU, Saadia HINA, Xiaowei HONG
, Available online   , Manuscript accepted  29 July 2020, doi: 10.1007/s00376-020-0137-0
This study investigated the large-scale circulation anomalies, in both the upper and lower troposphere, associated with the interannual variation of rainfall in Pakistan during summer, using the station observation data in this country and circulation data of the NCEP−NCAR reanalysis from 1981 to 2017. Results showed that the upper- and lower-tropospheric circulation anomalies associated with monthly rainfall variability exhibit similar features from June to August, so analyses were performed on June−August circulation and Pakistan rainfall data. The analyzed results indicated that summer rainfall in Pakistan is enhanced when there is an anticyclonic anomaly to the northwest of Pakistan in the upper troposphere and easterly anomalies along the southern foothills of the Himalayas in the lower troposphere, and vice versa. These upper- and lower-tropospheric circulation anomalies were found to be related, but show unique features. The upper-tropospheric anticyclonic anomaly is closely related to the Silk Road Pattern along the Asian westerly jet, while the lower-tropospheric easterly anomalies are related to the cyclonic anomaly to the south of Pakistan, i.e., intensified South Asian monsoon trough. The results presented here suggest that the interannual variability of summer rainfall in Pakistan is a combined result of upper- and lower-tropospheric circulation anomalies, and of extratropical and tropical circulation anomalies.
Characteristics of Feng-Yun-4A Satellite Atmospheric Motion Vectors and Their Impacts on Data Assimilation
Yaodeng CHEN, Jie SHEN, Shuiyong FAN, Deming MENG, Cheng WANG
, Available online   , Manuscript accepted  27 July 2020, doi: 10.1007/s00376-020-0080-0
The high observation efficiency, scanning speed and observation frequency of the Feng-Yun-4A (FY-4A) satellite indicates the progress of Chinese geostationary meteorological satellites. The characteristics of FY-4A atmospheric motion vectors (AMVs) derived from the high-level water vapor (WV-High) channel, mid-level water vapor (WV-Mid) channel, and infrared (IR) channel of FY-4A are analyzed, and their corresponding observation errors estimated. Then, the impacts of single-channel and multi-channel FY-4A AMVs on RMAPS-ST (the Rapid-refresh Multi-scale Analysis and Prediction System—Short Term) are evaluated based on one-month data assimilation cycling and forecasting experiments. Results show that the observation errors of FY-4A AMVs from the three channels have an explicit vertical structure. Results from the cycling experiments indicate that the assimilation of AMVs from WV-High produces more apparent improvement of the wind in the upper layer, while a more positive effect in the lower layer is achieved by the assimilation of AMVs from IR. Furthermore, the assimilation of AMVs from IR is more skillful for medium and moderate precipitation than from other channels owing to the good quality of data in the lower layer in the AMVs from IR. Assimilation of FY-4A AMVs from the three channels could combine the advantages of assimilation from each individual channel to improve the wind in the upper, middle and lower layers simultaneously.
Combined Impacts of Warm Central Equatorial Pacific Sea Surface Temperatures and Anthropogenic Warming on the 2019 Severe Drought in East China
Shuangmei MA, Congwen ZHU, Juan LIU
, Available online   , Manuscript accepted  24 July 2020, doi: 10.1007/s00376-020-0077-8
A severe drought occurred in East China (EC) from August to October 2019 against a background of long-term significant warming and caused widespread impacts on agriculture and society, emphasizing the urgent need to understand the mechanism responsible for this drought and its linkage to global warming. Our results show that the warm central equatorial Pacific (CEP) sea surface temperature (SST) and anthropogenic warming were possibly responsible for this drought event. The warm CEP SST anomaly resulted in an anomalous cyclone over the western North Pacific, where enhanced northerly winds in the northwestern sector led to decreased water vapor transport from the South China Sea and enhanced descending air motion, preventing local convection and favoring a precipitation deficiency over EC. Model simulations in the Community Earth System Model Large Ensemble Project confirmed the physical connection between the warm CEP SST anomaly and the drought in EC. The extremely warm CEP SST from August to October 2019, which was largely the result of natural internal variability, played a crucial role in the simultaneous severe drought in EC. The model simulations showed that anthropogenic warming has greatly increased the frequency of extreme droughts in EC. They indicated an approximate twofold increase in extremely low rainfall events, high temperature events, and concurrently dry and hot events analogous to the event in 2019. Therefore, the persistent severe drought over EC in 2019 can be attributed to the combined impacts of warm CEP SST and anthropogenic warming.
Application and Characteristic Analysis of the Moist Singular Vector in GRAPES-GEPS
Jing WANG, Bin WANG, Juanjuan LIU, Yongzhu LIU, Jing CHEN, Zhenhua HUO
, Available online   , Manuscript accepted  21 July 2020, doi: 10.1007/s00376-020-0092-9
The singular vector (SV) initial perturbation method can capture the fastest-growing initial perturbation in a tangent linear model (TLM). Based on the global tangent linear and adjoint model of GRAPES-GEPS (Global/Regional Assimilation and Prediction System—Global Ensemble Prediction System), some experiments were carried out to analyze the structure of the moist SVs from the perspectives of the energy norm, energy spectrum, and vertical structure. The conclusions are as follows: The evolution of the SVs is synchronous with that of the atmospheric circulation, which is flow-dependent. The moist and dry SVs are located in unstable regions at mid-to-high latitudes, but the moist SVs are wider, can contain more small- and medium-scale information, and have more energy than the dry SVs. From the energy spectrum analysis, the energy growth caused by the moist SVs is reflected in the relatively small-scale weather system. In addition, moist SVs can generate perturbations associated with large-scale condensation and precipitation, which is not true for dry SVs. For the ensemble forecasts, the average anomaly correlation coefficient of large-scale circulation is better for the forecast based on moist SVs in the Northern Hemisphere, and the low-level variables forecasted by the moist SVs are also improved, especially in the first 72 h. In addition, the moist SVs respond better to short-term precipitation according to statistical precipitation scores based on 10 cases. The inclusion of the large-scale condensation process in the calculation of SVs can improve the short-term weather prediction effectively.
Azimuthal Variations of the Convective-scale Structure in a Simulated Tropical Cyclone Principal Rainband
Yue JIANG, Liguang WU, Haikun ZHAO, Xingyang ZHOU, Qingyuan LIU
, Available online   , Manuscript accepted  17 July 2020, doi: 10.1007/s00376-020-9248-x
Previous numerical simulations have focused mainly on the mesoscale structure of the principal rainband in tropical cyclones with a relatively coarse model resolution. In this study, the principal rainband was simulated in a semi-idealized experiment at a horizontal grid spacing of 1/9 km and its convective-scale structure was examined by comparing the convective elements of the simulated principal rainband with previous observational studies. It is found that the convective scale structure of the simulated principal rainband is well comparable to the observation. The azimuthal variations of the convective scale structure were examined by dividing the simulated principal rainband into the upwind, middle and downwind portions. Some new features are found in the simulated principal rainband. First, the overturning updraft contains small-scale rolls aligned along the inward side of the outward-leaning reflectivity tower in the middle portion. Second, the inner-edge downdraft is combined with a branch of inflow from the upper levels in middle and downwind portions, carrying upper-level dry air to the region between the overturning updrafts and eyewall, and the intrusion of the upper-level dry air further limits the altitude of the overturning updrafts in the middle and downwind portions of the principal rainband. Third, from the middle to downwind portions, the strength of the secondary horizontal wind maximum is gradually replaced by a low-level maximum of the tangential wind collocated with the low-level downdraft.
System of Multigrid Nonlinear Least-squares Four-dimensional Variational Data Assimilation for Numerical Weather Prediction (SNAP): System Formulation and Preliminary Evaluation
Hongqin ZHANG, Xiangjun TIAN, Wei CHENG, Lipeng JIANG
, Available online   , Manuscript accepted  17 July 2020, doi: 10.1007/s00376-020-9252-1
A new forecasting system—the System of Multigrid Nonlinear Least-squares Four-dimensional Variational (NLS-4DVar) Data Assimilation for Numerical Weather Prediction (SNAP)—was established by building upon the multigrid NLS-4DVar data assimilation scheme, the operational Gridpoint Statistical Interpolation (GSI)−based data-processing and observation operators, and the widely used Weather Research and Forecasting numerical model. Drawing upon lessons learned from the superiority of the operational GSI analysis system, for its various observation operators and the ability to assimilate multiple-source observations, SNAP adopts GSI-based data-processing and observation operator modules to compute the observation innovations. The multigrid NLS-4DVar assimilation framework is used for the analysis, which can adequately correct errors from large to small scales and accelerate iteration solutions. The analysis variables are model state variables, rather than the control variables adopted in the conventional 4DVar system. Currently, we have achieved the assimilation of conventional observations, and we will continue to improve the assimilation of radar and satellite observations in the future. SNAP was evaluated by case evaluation experiments and one-week cycling assimilation experiments. In the case evaluation experiments, two six-hour time windows were established for assimilation experiments and precipitation forecasts were verified against hourly precipitation observations from more than 2400 national observation sites. This showed that SNAP can absorb observations and improve the initial field, thereby improving the precipitation forecast. In the one-week cycling assimilation experiments, six-hourly assimilation cycles were run in one week. SNAP produced slightly lower forecast RMSEs than the GSI 4DEnVar (Four-dimensional Ensemble Variational) as a whole and the threat scores of precipitation forecasts initialized from the analysis of SNAP were higher than those obtained from the analysis of GSI 4DEnVar.
Impacts of Increased SST Resolution on the North Pacific Storm Track in ERA-Interim
Chao ZHANG, Hailong LIU, Jinbo XIE, Chongyin LI, Pengfei LIN
, Available online   , Manuscript accepted  17 July 2020, doi: 10.1007/s00376-020-0072-0
This study examines the artificial influence of increasing the SST resolution on the storm track over the North Pacific in ERA-Interim. Along with the mesoscale oceanic eddies and fronts resolved during the high-resolution-SST period, the low-level storm track strengthens northward, reaching more than 30% of the maximum values in the low-resolution-SST period after removing the influence of ENSO. The mesoscale structure firstly imprints on the marine atmospheric boundary layer, which then leads to changes in turbulent heat flux and near-surface convergence, forcing a secondary circulation into the free atmosphere, strengthening the vertical eddy heat, momentum and specific humidity fluxes, and contributing to the enhancement of the storm track. Results from a high-resolution atmospheric model further indicate the changes in the storm track due to the mesoscale SST and their relationship.
Bias Correction and Ensemble Projections of Temperature Changes over Ten Subregions in CORDEX East Asia
Chenwei SHEN, Qingyun DUAN, Chiyuan MIAO, Chang XING, Xuewei FAN, Yi WU, Jingya Han
, Available online   , Manuscript accepted  17 July 2020, doi: 10.1007/s00376-020-0026-6
Regional climate models (RCMs) participating in the Coordinated Regional Downscaling Experiment (CORDEX) have been widely used for providing detailed climate change information for specific regions under different emissions scenarios. This study assesses the effects of three common bias correction methods and two multi-model averaging methods in calibrating historical (1980−2005) temperature simulations over East Asia. Future (2006−49) temperature trends under the Representative Concentration Pathway (RCP) 4.5 and 8.5 scenarios are projected based on the optimal bias correction and ensemble averaging method. Results show the following: (1) The driving global climate model and RCMs can capture the spatial pattern of annual average temperature but with cold biases over most regions, especially in the Tibetan Plateau region. (2) All bias correction methods can significantly reduce the simulation biases. The quantile mapping method outperforms other bias correction methods in all RCMs, with a maximum relative decrease in root-mean-square error for five RCMs reaching 59.8% (HadGEM3-RA), 63.2% (MM5), 51.3% (RegCM), 80.7% (YSU-RCM) and 62.0% (WRF). (3) The Bayesian model averaging (BMA) method outperforms the simple multi-model averaging (SMA) method in narrowing the uncertainty of bias-corrected results. For the spatial correlation coefficient, the improvement rate of the BMA method ranges from 2% to 31% over the 10 subregions, when compared with individual RCMs. (4) For temperature projections, the warming is significant, ranging from 1.2°C to 3.5 °C across the whole domain under the RCP8.5 scenario. (5) The quantile mapping method reduces the uncertainty over all subregions by between 66% and 94%.
Contribution of Global Warming and Atmospheric Circulation to the Hottest Spring in Eastern China in 2018
Chunhui LU, Ying SUN, Nikolaos CHRISTIDIS, Peter A. STOTT
, Available online   , Manuscript accepted  08 July 2020, doi: 10.1007/s00376-020-0088-5
The spring of 2018 was the hottest on record since 1951 over eastern China based on station observations, being 2.5°C higher than the 1961−90 mean and with more than 900 stations reaching the record spring mean temperature. This event exerted serious impacts in the region on agriculture, plant phenology, electricity transmission systems, and human health. In this paper, the contributions of human-induced climate change and anomalous anticyclonic circulation to this event are investigated using the newly homogenized observations and updated Met Office Hadley Centre system for attribution of extreme events, as well as CanESM2 (Second Generation Canadian Earth System Model) simulations. Results indicate that both anthropogenic influences and anomalous anticyclonic circulation played significant roles in increasing the probability of the 2018 hottest spring. Quantitative estimates of the probability ratio show that anthropogenic forcing may have increased the chance of this event by ten-fold, while the anomalous circulation increased it by approximately two-fold. The persistent anomalous anticyclonic circulation located on the north side of China blocked the air with lower temperature from high latitudes into eastern China. Without anthropogenic forcing or without the anomalous circulation in northern China, the occurrence probability of the extreme warm spring is significantly reduced.
Establishment of an Objective Standard for the Definition of Binary Tropical Cyclones in the Western North Pacific
Fumin REN, Yanjun XIE, Biwen YIN, Mingyang WANG, Guoping LI
, Available online   , Manuscript accepted  07 July 2020, doi: 10.1007/s00376-020-9287-3
To develop an objective standard for defining binary tropical cyclones (BTCs) in the western North Pacific (WNP), two best-track datasets, from the China Meteorological Administration and the Joint Typhoon Warning Center, were adopted for statistical analyses on two important characteristics of BTCs—two TCs approaching each other, and counterclockwise spinning. Based on the high consistency between the two datasets, we established an objective standard, which includes a main standard for defining BTCs and a secondary standard for identifying typical/atypical BTCs. The main standard includes two requirements: two coexisting TCs are a pair of BTCs if (i) the separation distance is ≤ 1800 km, and (ii) this separation maintains for at least 12 h. Meanwhile, the secondary standard defines a typical BTC as one for which there is at least one observation when the two TCs approach each other and spin counterclockwise simultaneously. Under the standard, the ratio of typical BTCs increases as the BTC duration increases or the minimum distance between the two TCs decreases. Then, using the JTWC dataset, it was found that there are 505 pairs of BTCs during the period 1951−2014, including 328 typical BTCs and 177 atypical BTCs, accounting for 65.0% and 35.0% of the total, respectively. In addition, a study of two extreme phenomena—the maximum approaching speed and the maximum counterclockwise angular velocity in typical BTCs—shows that the configuration of the circulation conditions and the distribution of the BTCs favor the formation of these extreme phenomena.
Insights into the Microwave Instruments Onboard the Feng-Yun 3D Satellite: Data Quality and Assimilation in the Met Office NWP System
Fabien CARMINATI, Nigel ATKINSON, Brett CANDY, Qifeng LU
, Available online   , Manuscript accepted  28 May 2020, doi: 10.1007/s00376-020-0010-1
This paper evaluates the microwave instruments onboard the latest Chinese polar-orbiting satellite, Feng-Yun 3D (FY-3D). Comparing three months of observations from the Microwave Temperature Sounder 2 (MWTS-2), the Microwave Humidity Sounder 2 (MWHS-2), and the Microwave Radiation Imager (MWRI) to Met Office short-range forecasts, we characterize the instrumental biases, show how those biases have changed with respect to their predecessors onboard FY-3C, and how they compare to the Advanced Technology Microwave Sounder (ATMS) onboard NOAA-20 and the Global Precipitation Measurement Microwave Imager (GMI). The MWTS-2 global bias is much reduced with respect to its predecessor and compares well to ATMS at equivalent channel frequencies, differing only by 0.36 ± 0.28 K (1σ) on average. A suboptimal averaging of raw digital counts is found to cause an increase in striping noise and an ascending—descending bias. MWHS-2 benefits from a new calibration method improving the 183-GHz humidity channels with respect to its predecessor and biases for these channels are within ± 1.9 K to ATMS. MWRI presents the largest improvements, with reduced global bias and standard deviation with respect to FY-3C; although, spurious, seemingly transient, brightness temperatures have been detected in the observations at 36.5 GHz (vertical polarization). The strong solar-dependent bias that affects the instrument on FY-3C has been reduced to less than 0.2 K on average for FY-3D MWRI. Experiments where radiances from these instruments were assimilated on top of a full global system demonstrated a neutral to positive impact on the forecasts, as well as on the fit to the background of independent instruments.
Letter and Notes
Seasonal forecast of South China Sea summer monsoon onset disturbed by the cold tongue La Niña in recent decade
Ning Jiang, Congwen Zhu
, Available online   , Manuscript accepted  10 September 2020, doi: 10.1007/s00376-020-0090-y
It has been suggested that a warm (cold) ENSO event in winter is mostly followed by the late (early) onset of the South China Sea (SCS) summer monsoon (SCSSM) in spring. Our results show this positive relationship, which is mainly determined by their phase correlation, has been broken under recent rapid global warming since 2011, due to the disturbance of cold tongue (CT) La Niña events. Different from canonical counterpart, the CT La Niña event is characterized by surface meridional wind divergences in the central-eastern equatorial Pacific, which can delay the SCSSM onset by the enhanced convections in the warming Indian Ocean and the western subtropical Pacific. Owing to the increased Indian-western Pacific warming and the prevalent CT La Niña events, the empirical seasonal forecast of SCSSM onset based on ENSO may be challenged in the future.
News & Views
From Recent Heavy Precipitation in China to a Glocal Hydrometeorological Solution for Flood Risk Prediction
Huan Wu, Xiaomeng Li, Guy J-P. Schumann, Lorenzo Alfieri, yun chen, Hui Xu, Zhifang Wu, Hong Lu, Yamin Hu, Qiang Zhu, Zhijun Huang, Weitian Chen, Ying Hu
, Available online   , Manuscript accepted  10 September 2020, doi: 10.1007/s00376-020-0260-y
The prolonged Meiyu-Baiu system with anomalous precipitation in the year of 2020 has swollen many rivers and lakes, caused flash flooding, urban flooding and landslides, and consistently wreaked havoc across large swathes of China, particularly in Yangtze river basin. Significant precipitation and flooding anomalies have already been seen in magnitude and extension by now for this year, which have been exerting much higher pressure to emergency response in flood control and mitigation than in other years, even though a rainy season with multiple on-going serious flood events in different provinces is not very uncommon in China. Instead of digging into the causations of the uniqueness of this year’s extreme precipitation-flooding situation, which certainly warrants exploration in-depth, we here provide a short view toward a more general hydrometeorological solution to this “annual” nationwide problem. A Glocal (global to local) Hydrometeorological Solution for Floods (GHS-F) is considered to be critical for better preparedness, mitigation, and management of significant precipitation-caused different types of flooding which happen extensively almost every year in many countries such as China, India and USA for examples. Such GHS-F model is necessary from both scientific and operational perspectives with the strength in providing spatially consistent flood definition and spatially distributed flood risk classification considering the heterogeneity in vulnerability and resilience across the entire domain. Priorities in the development of such GHS-F are suggested emphasizing the user’s requirements and needs according to the practical experiences with various flood response agencies.
Data Description Article
Datasets for CMIP6 Scenario Model Intercomparison Project (ScenarioMIP) Simulations with a coupled model CAS FGOALS-f3-L
Shuwen Zhao, Yongqiang Yu, Pengfei LIN, Hailong LIU, Bian He, Qing Bao, Yuyang Guo, Kangjun Chen, Lijuan Hua, Xiaowei Wang
, Available online   , Manuscript accepted  08 September 2020, doi: 10.1007/s00376-020-0112-9
The datasets for the tier-1 Scenario Model Intercomparison Project (ScenarioMIP) experiments from the Chinese Academy of Sciences (CAS) Flexible Global Ocean–Atmosphere–Land System model, finite-volume version 3 (CAS FGOALS-f3-L) are described in this study. ScenarioMIP experiments are ones of the core MIP experiments in the Coupled Model Intercomparison Project Phase 6 (CMIP6). Considering future CO2, CH4, N2O and other gases concentrations and land use, the ScenarioMIP designs eight pathways, included two tiers (tier-1 and tier-2) of priority. The tier-1 includes four Combined Shared Socioeconomic Pathways (SSPs) with radiative forcing, i.e. SSP1-2.6, SSP2-4.5, SSP3-7.0, and SSP5-8.5, in which their globally averaged radiative forcings at the top of the atmosphere around 2100 are approximately 2.6 W/m2, 4.5 W/m2, 7.0 W/m2, 8.5 W/m2, respectively. This study gives overall introduction of the ScenarioMIP datasets of this model, such as the datasets’ storage location, sizes, and variables etc. Preliminary analysis indicates that the surface air temperatures will increase about 1.89°C, 3.07°C, 4.06°C, and 5.17°C around 2100 for these four scenarios, respectively. Meanwhile, some other key climate variables such as sea ice extension, precipitation, heat content, and sea level rise also show significant long term trends associated with the increases of the radiative forcings. These datasets will help us understand how the climate will change under different anthropogenic forcing and radiative forcing.
CAS-ESM2.0 Model Datasets for CMIP6 Ocean Model Intercomparison Project Phase 1 (OMIP1)
Xiao Dong, Jiangbo Jin, Hailong LIU, He Zhang, minghua Zhang, Pengfei LIN, Qing-Cun Zeng, Guangqing Zhou, Yongqiang Yu, Mirong SONG, Zhaohui LIN, Ruxu Lian, Xin Gao, Juanxiong He, Dongling Zhang, Kangjun Chen
, Available online   , Manuscript accepted  04 September 2020, doi: 10.1007/s00376-020-0150-3
As a member of the Chinese modelling groups, the coupled ocean-ice component of the Chinese Academy of Science Earth System Model version 2.0 (CAS-ESM2.0) is taking part in the Ocean Model Intercomparison Project Phase 1 (OMIP1) experiment for the Coupled Model Intercomparison Project Phase 6 (CMIP6). The simulation was conducted, and monthly outputs have been published on the Earth System Grid (ESG) data server. In this paper, the experimental dataset is introduced, and the preliminary performances of the ocean model in simulating the global ocean temperature, salinity, sea surface temperature (SST), sea surface salinity (SSS), sea surface height (SSH), sea ice and Atlantic meridional overturning circulation (AMOC) are evaluated. The results show that the model is at quasi-equilibrium during the integration of 372 years and performances of the model are reasonable compared with observation. This dataset is ready to be downloaded and used by the community in related research, e.g., multi-ocean-sea ice model performance evaluation and inter-annual variation in oceans driven by prescribed atmospheric forcing.
Meeting Summary
The First Fengyun Satellite International User Conference
Di XIAN, Peng ZHANG, Meng FANG, Chang LIU, Xu JIA
, Available online   , Manuscript accepted  09 March 2020, doi: 10.1007/s00376-020-2011-5