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CAS FGOALS-f3-L large-ensemble simulations for the CMIP6 Polar Amplification Model Intercomparison Project
Bian He, Xiaoqi Zhang, anmin Duan, Qing Bao, Yimin Liu, Wenting Hu, Jinxiao Li, Guoxiong Wu
, Available online   , Manuscript accepted  24 February 2021, doi: 10.1007/s00376-021-0343-4
Large-ensemble simulations of the atmosphere-only time-slice experiments for the Polar Amplification Model Intercomparison Project (PAMIP) were carried out by the model group of the Chinese Academy of Sciences (CAS) Flexible Global Ocean-Atmosphere-Land System (FGOALS-f3-L). Eight groups of experiments forced by different combinations of the sea surface temperature (SST) and sea ice concentration (SIC) for pre-industrial, present-day and future conditions were performed and published. The time-lag method was used to generate the 100 ensemble members, with each member integrating from 1st April 2000 to 30th June 2001 and the first two months as the spin-up period. The basic model responses of the surface air temperature (SAT) and precipitation were ed. The results indicate that Arctic amplification is mainly caused by Arctic SIC forcing changes. The SAT responses to the Arctic SIC decrease alone show an obvious increase over high latitudes, which is similar to the results from the combined forcing of SST and SIC. However, the change in global precipitation is dominated by the changes in the global SST rather than SIC, partly because tropical precipitation is mainly driven by local SST changes. The uncertainty of the model responses was also investigated through the analysis of the large-ensemble members. The relative roles of SST and SIC, together with their combined influence on Arctic amplification, are also discussed. All these model datasets will contribute to PAMIP multimodel analysis and improve the understanding of polar amplification.
A two-plume convective model for precipitation extremes
Zihan Yin, Panxi Dai, Ji Nie
, Available online   , Manuscript accepted  23 February 2021, doi: 10.1007/s00376-021-0404-8
In the study of diagnosing climate simulations and understanding the dynamics of precipitation extremes, it is an essential step to adopt a simple model to relate water vapor condensation and precipitation, which occur at cloud-microphysical and convective scales, to large-scale variables. Several simple models have been proposed; however, improvement is still needed in both their accuracy and/or the physical basis. Here, we propose a two-plume convective plume model that takes into account the subgrid inhomogeneity of precipitation extremes. The convective model has three components, i.e., cloud condensation, rain evaporation, and environmental descent, and is built upon the zero-buoyancy approximation and guidance from the high-resolution reanalysis. Evaluated against the CMIP5 climate simulations, the convective model shows large improvements in reproducing precipitation extremes compared to previously proposed models. Thus, the two-plume convective model better captures the main physical processes and serves as a useful diagnostic tool for precipitation extremes.
Global freshwater storage capability across time scales in the GRACE satellite era
Enda Zhu, Xing Yuan
, Available online   , Manuscript accepted  22 February 2021, doi: 10.1007/s00376-021-0222-z
Freshwater is mainly recharged by rainfall and stored in land for a period of time, which is directly affected by the storage capability. The storage capability over river basins has different spatiotemporal features that are important for freshwater resources predictability. However, the estimation of freshwater storage capability (FSC) remains challenging due to the lack of observations and quantification index. Here we use a metric that characterizes hydrological “inertia” after rainfalls to analyze FSC over top 194 global major river basins based on the Gravity Recovery and Climate Experiment (GRACE) satellite observation and Community Land Model version 5 (CLM5) simulation. During 2003-2016, the global land can retain 28% of precipitation after one month based on GRACE observation, and the simulation depicts that retained proportions decrease from 42% after one day to 26% after one month, with smaller FSC partly attributing to wetter condition and higher vegetation density. The root zone contributes to about 40% of the global land FSC from daily to monthly time scales. As the time scale increases, the contribution of surface soil decreases from 26% to 14%, while contribution of deep soil increases from 4% to 10%. Snow contributes over 20% of land FSC, especially over high latitude. With six decades of CLM5 long-term simulation, it is found that the change of FSC in most basins is related to internal climate variability. The FSC of river basins which displays the proportion of precipitation retained in land is worthy of more attentions for water resources predictability.
An implementation of full cycle strategy using dynamic blending for rapid refresh short-range weather forecasting in China
Jin Feng, Min Chen, Yanjie Li, jiqing zhong
, Available online   , Manuscript accepted  19 February 2021, doi: 10.1007/s00376-021-0316-7
The partial cycle (PC) strategy has been used in many rapid refresh cycle systems (RRC) for regional short-range weather forecasting. Since the strategy periodically reinitializes the regional model (RM) from the global model (GM) forecasts to correct the large-scale drift, it has replaced the traditional full cycle (FC) strategy in many RRC systems. However, the extra spin-up in the PC strategy increases the computer burden on RRC and generates discontinuous small-scale systems among cycles. This study returns to the FC strategy but with initial fields generated by dynamic blending (DB) and data assimilation (DA). The DB ingests the time-varied large-scale information from the GM to the RM to generate less-biased background fields. Then the DA is performed. We applied the new FC strategy in a series of 7-day batch forecasts with the 3-hour cycle in July 2018, and February, April, and October 2019 over China using a Weather Research and Forecast (WRF) model-based RRC. A comparison shows that the new FC strategy results in less model bias than the PC strategy in most state variables and improves the forecast skills for moderate and light precipitation. The new FC strategy also allows the model to reach a balanced state earlier and gives favorable forecast continuity between adjacent cycles. Hence, this new FC strategy has the potential to be applied in RRC forecast systems to replace the currently used PC strategy.
Aircraft measurements of microphysical properties and the riming process in a mixed–phase cloud system
Tuanjie Hou, Hengchi Lei, Youjiang He, Jiefan Yang, Zhen Zhao, Zhaoxia Hu
, Available online   , Manuscript accepted  10 February 2021, doi: 10.1007/s00376-021-0287-8
The presence of embedded convection in stratiform clouds strongly affects ice microphysical properties and precipitation formation. In situ aircraft measurements, including upward and downward spirals and horizontal penetrations, were performed within both embedded convective cells and stratiform regions of a mixed-phase stratiform cloud system on 22 May 2017. Supercooled liquid water measurements, particle size distributions and particle habits in different cloud regions were discussed with the purpose of characterizing the riming process and determining how particle size distributions vary from convective to stratiform regions. Significant amounts of supercooled liquid water with maxima up to 0.6 g m-3 were observed from -3 to -6°C in the embedded convective cells while the peak liquid water content was generally less than 0.1 g m-3 in the stratiform regions. There are two distinct differences in particle size distributions between convective and stratiform regions. One difference is the significant shift toward large particles from -15°C to -10°C in the convective region, with the particle maximum dimensions increasing from less than 6000 μm to over 1 cm. This effect is due to habit variations from broad-branched crystals to large dendrites and their aggregates. The other difference is the large concentrations of small particles (25-205 μm) at temperatures between -3 and -5°C in the convective region, where rimed ice particles and needles coexist. Needle regions are observed from three of the five spirals, but only cloud conditions within the convective region fit into the Hallett-Mossop criteria.
Different Configurations of Interannual Variability in the Western North Pacific Subtropical High and East Asian Westerly Jet in Summer
Xinyu Li, Ri-Yu LU, Gen Li
, Available online   , Manuscript accepted  10 February 2021, doi: 10.1007/s00376-021-0339-0
This study investigates the circulation and precipitation anomalies associated with different configurations of the western North Pacific subtropical high (WNPSH) and the East Asian westerly jet (EAJ) in summer on the interannual timescale. The in-phase configuration of the WNPSH and EAJ is characterized by the westward (eastward) extension of the WNPSH and the southward (northward) shift of the EAJ, which is consistent with the general correspondence between their variations. The out-of-phase configuration includes the residual cases. It is found that the in-phase configuration manifests as a typical meridional teleconnection. For instance, there is an anticyclonic (cyclonic) anomaly over the tropical WNP and a cyclonic (anticyclonic) anomaly over mid-latitude East Asia in the lower troposphere. These circulation anomalies are more conductive to rainfall anomalies over the Yangtze River basin and south Japan than the individual WNPSH or EAJ. By contrast, for the out-of-phase configuration, the mid-latitude cyclonic (anticyclonic) anomaly is absent, and the lower-tropospheric circulation anomalies are featured with an anticyclonic (cyclonic) anomaly with large meridional extension. Correspondingly, significant rainfall anomalies move northward to North China and northern Korean Peninsula. Further results indicate that the out-of-phase configuration is associated with the developing phase of ENSO, with strong and significant sea surface temperature (SST) anomalies in the tropical central and eastern Pacific in simultaneous summer and following winter. This is sharply different from the in-phase configuration, for which the tropical SSTs are not a necessity.
Natural climate solutions for China: The last mile to carbon neutrality
Zhangcai Qin, Xi Deng, Bronson Griscom, Yao Huang, Tingting Li, Pete Smith, Wenping Yuan, Wen Zhang
, Available online   , Manuscript accepted  07 February 2021, doi: 10.1007/s00376-021-1031-0
There is no shortcut to a carbon neutral society; solutions are urgently required from both energy & industrial sectors and global ecosystems. While the former is often held accountable and emphasized in terms of its emissions reduction capability, the latter (recently termed natural climate solutions) should also be assessed for potential and limitations by the scientific community, the public, and policy makers.
Convective/large-scale rainfall partitions of tropical heavy precipitation in CMIP6 atmospheric models
Jing Yang, Sicheng He, Qing Bao
, Available online   , Manuscript accepted  04 February 2021, doi: 10.1007/s00376-021-0238-4
Convective/large-scale (C/L) precipitation partitions are crucial for achieving realistic rainfall modeling, which are classified in 16 CMIP6 atmospheric models. Only 4 models capture the feature that convective rainfall significantly exceeds the large-scale rainfall component in tropics while the other 12 models show 50%-100% large-scale rainfall component in heavy rainfall. Increased horizontal resolution generally increases the convective rainfall percentage, but not in all models. The former 4 models can realistically reproduce two peaks of moisture vertical distribution, respectively located in the upper and the lower troposphere. In contrast, the latter 12 models correspond to three types of moisture vertical profile biases: (1) whole mid-to-lower tropospheric wet biases (60–80% large-scale rainfall); (2) mid-tropospheric wet peak (50% convective/large-scale rainfall); and (3) lower-tropospheric wet peak (90–100% large-scale rainfall). And the associated vertical distribution of unique clouds potentially causes different climate feedback, suggesting accurate C/L rainfall components are necessary to reliable climate projection.
Rainfall Microphysical Properties of Landfalling Typhoon Yagi Based on the Observations of Micro Rain Radar and Cloud Radar in Shandong, China
Hong Wang, Wenqing Wang, Jun Wang, Dianli Gong, Dianguo Zhang, Ling Zhang, Qiuchen Zhang
, Available online   , Manuscript accepted  03 February 2021, doi: 10.1007/s00376-021-0062-x
The development and evolution of precipitation microphysical parameters and the vertical structure characteristics associated with Typhoon Yagi (201814) are analyzed in the city of Jinan, Shandong Province based on the observations of micro rain radar (MRR), cloud radar, disdrometer, etc. The precipitation process is further subdivided into four types: convective, stratiform, mixed and light precipitation according to the ground disdrometer data, which is in agreement with the vertical profile of the radar reflectivity detected by MRR. Vertical wind may be the main source of MRR retrieval error during convective precipitation. Convective precipitation has the shortest duration but the largest contribution to the cumulative precipitation. Collision-coalescence is the main microphysical process of stratiform precipitation and light precipitation below the bright band observed by MRR. It is worth noting that while typhoon Yagi transforms into extratropical cyclones, its raindrop size distributions no longer have the characteristics of maritime precipitation, but typical characteristics of continental precipitation, a very different raindrop size distribution from that normally observed in landfalling typhoon.
Projection of the Future Changes in Tropical Cyclones Activity Affecting East Asia over the Western North Pacific based on Multi-RegCM4 Simulations
Jie Wu, Xue-Jie Gao, Yingmo Zhu, Ying Shi, Filippo Giorgi
, Available online   , Manuscript accepted  03 February 2021, doi: 10.1007/s00376-021-0286-9
Future changes in tropical cyclone (TC) activity over the western North Pacific (WNP) under the representative concentration pathway RCP4.5 are investigated based on a set of 21st century climate change simulations over East Asia with the regional climate model RegCM4 driven by 5 global models. The RegCM4 reproduces the major features of the observed TC activity over the region in the present day period, although with an overestimation of the number of TC genesis and an underestimation of TC intensity. A low number of TCs making landfall over China is also simulated. By the end of the 21st century, the annual mean frequency of TC genesis and occurrence are projected to increase over the WNP by ~10%. The increase in frequency of TC occurrence is in good agreement among the simulations, with the largest increase over the ocean around the Taiwan Island and south of Japan. The TCs tend to be stronger in the future compared to the present day, with a large increase in the frequency of strong TCs. In addition, more TCs landings are projected over most of the China coast, with an increase of ~13% over the whole Chinese territory.
Assimilation of GPM Microwave Imager Radiance for Track Prediction of Typhoon Cases with the WRF Hybrid En3DVAR System
Dongmei Xu, Feifei Shen, jinzhong min, aiqing shu
, Available online   , Manuscript accepted  29 January 2021, doi: 10.1007/s00376-021-0252-6
The impact of assimilating radiance data from the advanced satellite sensor GMI (GPM microwave imager) for typhoon analyses and forecasts was investigated using both a three-dimensional variational (3DVAR) and a Hybrid ensemble-3DVAR method. The interface of assimilating the radiance for the sensor GMI was established in the Weather Research and Forecasting (WRF) model. The GMI radiance data are assimilated for Typhoon Matmo (2014), Typhoon Chan-hom (2015), Typhoon Meranti (2016), and Typhoon Mangkhut (2018) in the Pacific before their landing. The results show that after assimilating the GMI radiance data under the clear sky condition with 3DVAR method, the wind, temperature, and humidity fields are effectively adjusted, leading improved forecast skills of the typhoon track with GMI radiance assimilation. The hybrid DA method is able to further adjust the location of the typhoon systematically. Moreover, the improvement of the track forecast is even more obvious for later forecast hours. In addition, the contents of water vapor and hydrometer are enhanced to some extent especially with the hybrid method.
The relationship between melt season sea-ice over Bering Sea and summer precipitation over mid-latitude East Asia
Yurun Tian, Yongqi Gao, Dong Guo
, Available online   , Manuscript accepted  28 January 2021, doi: 10.1007/s00376-021-0348-z
The understanding of linkage between spring Bering sea ice and East Asian summer precipitation remains controversial, in terms of both impact regions and mechanisms behind. In this study, we use four sea ice (HadISST1, HadISST2.2, ERA-Interim and NOAA/NSIDC) and two global precipitation datasets (CRU V4.01 and GPCP V2.3) to investigate co-variations between melt season (March-April-May-June, MAMJ) Bering sea ice cover (BSIC) and summer (June-July-August, JJA) East Asian precipitation. All datasets demonstrate a significant correlation between the MAMJ BSIC and the JJA rainfall in Lake Baikal-Northeastern China (Baikal-NEC). Based on the reanalysis datasets and our numerical sensitivity experiments using Community Atmospheric Model version 5 (CAM5), we suggest a mechanism to understand how the MAMJ BSIC influences the JJA Baikal-NEC rainfall. More MAMJ BSIC triggers a wave train and causes a positive sea level pressure (SLP) anomaly over the North Atlantic during MAMJ. The high SLP anomaly, associated with an anti-cyclonic wind stress circulation anomaly, favors the appearance of Sea Surface Temperature (SST) anomalies in a zonal dipole-pattern in North Atlantic during summer. The dipole SST anomaly drives a zonally-orientated wave train, which causes a high anomaly geopotential height at 500hPa over the Sea of Japan. As a result, the mean East Asian trough moves westward and a low geopotential height anomaly occurs over Baikal-NEC. This prevailed regional low pressure anomaly together with enhanced moisture transport from the western North Pacific and converging over the Baikal-NEC, benefits the increased rainfall in summer.
Assessment of FY-4A and Himawari-8 Cloud Top Height Retrieval through Comparison with Ground-Based Millimeter Radar at Sites in Tibet and Beijing
Bo LIU, Juan Huo, Daren Lu, Xin Wang
, Available online   , Manuscript accepted  19 January 2021, doi: 10.1007/s00376-021-0337-2
The accuracy of passive satellite cloud top height (CTH) retrieval shows regional dependence. This paper assesses the CTH derived from the FY-4A and Himawari-8 satellites through comparison with those from the ground-based millimeter radar at two sites: Yangbajing, Tibet, China (YBJ), and the Institute of Atmospheric Physics, Beijing, China (IAP). Comparison shows that Himawari-8 missed more CTHs at night than FY-4A, especially at YBJ. It is found that the CTH difference (CTHD; radar CTH minus satellite CTH) for FY-4A and Himawari-8 is 0.06 ± 1.90 km and −0.02 ± 2.40 km at YBJ respectively, and that is 0.93 ± 2.24 km and 0.99 ± 2.37 km at IAP respectively. The discrepancy between the satellites and radar at IAP is larger than that at YBJ. Both satellites show better performance for mid- and low-level clouds than high-level clouds at the two sites. The retrievals from FY-4A agree well with those from Himawari-8, with mean differences of 0.08 km at YBJ and 0.06 km at IAP. It is found that the CTHD decreases as the cloud depth increases at both sites. However, the CTHD has no obvious dependence on cloud layers and fractions. Investigations show that aerosol has little impact on the CTHD. For high and thin clouds, the CTHD increases gradually with the increase of the surface temperature, which might be a key factor causing the regional discrepancy between IAP and YBJ.
Background error covariance statistics of hydrometeor control variables based on Gaussian transform
Tao Sun, Yaodeng Chen, Deming Meng, Haiqin Chen
, Available online   , Manuscript accepted  19 January 2021, doi: 10.1007/s00376-021-0271-3
Using data assimilation technique to initialize hydrometeors plays a vital role in the numerical weather prediction (NWP).To directly analyze hydrometeors in data assimilation systems from cloud-sensitive observations, the hydrometeor control variables is necessary. The common data assimilation systems theoretically require that the probability density functions (PDFs) of analysis, background, and observation errors should satisfy Gaussian unbiased assumptions, while the distribution of hydrometeors is greatly non-Gaussian. In this study, a Gaussian transform method, named as the Quasi-Softmax transform, is proposed to transform hydrometeors to more Gaussian control variables. The Quasi-Softmax transform method then is compared to some other existing transform methods, and the spatial distribution, the non-Gaussianity of the background errors, and the characteristics of the background errors of hydrometeors before and after transformation are studied. Compared to the original hydrometeors, the vertical distribution of the transformed hydrometeors is greatly changed except for the newly constructed Quasi-Softmax method. The results of the D’Agostin test show that the hydrometeors transformed by the Quasi-Softmax method are more Gaussian when compared to the other methods. The characteristics of the hydrometeor background errors are reasonable for the Quasi-Softmax method. The transformed hydrometeors using the Quasi-Softmax transform meet the Gaussian unbiased assumptions of the data assimilation system, and they are promising to be the control variables of the data assimilation systems.
ROx budgets and O3 formation during summertime at Xianghe suburban site in the North China Plain
Min Xue, Jianzhong Ma, Guiqian Tang, Shengrui Tong, Bo Hu, Xingran Zhang, Xingru Li, Yuesi wang
, Available online   , Manuscript accepted  19 January 2021, doi: 10.1007/s00376-021-0327-4
Photochemical smog characterized by high concentrations of O3 is a main air pollution issue in the North China Plain (NCP) region, especially in summer and autumn. To better understand the photochemical process about O3 formation and optimal way to control ozone pollution, we measured O3, NOx, VOCs, CO and HONO and key physical parameters at Xianghe suburban site in the NCP region in summer 2018. Here we investigate the radical chemistry and ozone photochemical budget based on measurement data from 1 to 23 July using a chemical box model. For daytime (06:00-18:00) average, the primary ROx (OH%2BHO2%2BRO2) production rate is 3.9 ppbv h-1. HONO photolysis is the largest primary ROx source (41%). Reaction of NO2%2BOH is the largest contributor to radical termination (41%), followed by reactions of RO2%2BNO2 (26%). The average diurnal maximum O3 production and loss rates are 32.9 ppbv h-1 and 4.3 ppbv h-1, respectively. Sensitivity results without HONO constrain leads to decreases in daytime average primary ROx production by 55%, and O3 photochemical production by 42%, highlighting the importance of measuring HONO for quantifying ROx budget and O3 photochemical production. Considering heterogeneous reactions of trace gases and radicals on aerosols, aerosol uptake of HO2 contribute 11% to ROx sink, and the daytime average F(O3) decreases by 14%. The O3-NOx-VOCs sensitivity shows that the ozone production is mainly controlled by VOCs at Xianghe during the investigated period.
CMIP6 Evaluation and Projection of Temperature and Precipitation over China
Xiaoling Yang, Botao Zhou, Ying Xu, Zhen-Yu HAN
, Available online   , Manuscript accepted  18 January 2021, doi: 10.1007/s00376-021-0351-4
This article evaluates the performance of 20 Coupled Model Intercomparison Project phase 6 (CMIP6) models in simulating temperature and precipitation over China through comparisons with gridded observation data for the period of 1995–2014, with a focus on spatial pattern and interannual variability. The evaluations show that the CMIP6 models perform well in reproducing the climatological spatial distribution of temperature and precipitation, with better performance for temperature than for precipitation. Their interannual variability can also be reasonably captured by most models but with poor performance for the interannual variability of winter precipitation. Based on the comprehensive performance for the above two aspects, the “highest ranked” models are selected as an ensemble (BMME). The BMME outperforms the ensemble of all models (AMME) in simulating annual and winter temperature and precipitation, particularly for those subregions with complex terrain but it shows little improvement for summer temperature and precipitation. The AMME and BMME projections indicate increases in annual temperature and precipitation across China by the end of the 21st century, with larger increases under the scenario of the Shared Socioeconomic Pathway 5/Representative Concentration Pathway 8.5 (SSP585) than under scenario of the Shared Socioeconomic Pathway 2/Representative Concentration Pathway 4.5 (SSP245). The greatest increases in annual temperature are projected for higher latitudes and higher elevations and the larger percentage increases in annual precipitation are projected to occur in northern and western China, especially under SSP585. However, the BMME, which generally shows better performance over those regions, projects lower changes in annual temperature and larger variations in annual precipitation when compared to the AMME projection.
Parameterized Forward Operators for Simulation and Assimilation of Polarimetric Radar Data with Numerical Weather Predictions
Guifu Zhang, Jidong Gao, Muyun Du
, Available online   , Manuscript accepted  14 January 2021, doi: 10.1007/s00376-021-0289-6
Many weather radar networks in the world have now provided polarimetric radar data (PRD) that have the potential to improve our understanding of cloud and precipitation microphysics, and numerical weather prediction (NWP). To realize this potential, an accurate and efficient set of polarimetric observation operators are needed to simulate and assimilate the PRD with an NWP model for an accurate analysis of the model state variables. For this purpose, a set of parameterized observation operators are developed to simulate and assimilate polarimetric radar data from an NWP model-predicted water mixing ratios and number concentrations of rain, snow, hail and graupel. The polarimetric radar variables are calculated based on the T-matrix calculation of wave scattering and integrations of the scattering weighted by the particle size distribution. The calculated polarimetric variables are then fitted to simple functions of water content and volume-weighted mean diameter of the hydrometeor particle size distribution. The parameterized PRD operators are applied to an ideal case and a real case predicted by the weather research and forecasting (WRF) model to have simulated PRD and compared them with existing operators and real observations to show their validity and applicability. The new PRD operators use less than one percent of the computing time of the old operators to complete the same simulations, making it efficient in PRD simulation and assimilation usage.
Three-year observations of ozone columns over polar vortex edge area above West Antarctica
Yuanyuan Qian, Yuhan Luo, Fuqi Si, Taiping Yang, Dongshang Yang
, Available online   , Manuscript accepted  12 January 2021, doi: 10.1007/s00376-021-0243-7
The ozone vertical column densities (VCDs) were retrieved by Zenith Scattered Light-Differential Optical Absorption Spectroscopy (ZSL-DOAS) from January 2017 to February 2020 over Fildes Peninsula, West Antarctica (62.22S, 58.96W). The retrieved ozone VCDs started to decline around July with a comparable gradient (around 1.4 DU/day), then dropped to the lowest level in September and October, when the ozone holes appeared (less than 220 DU). The daily mean values of ozone columns were compared with OMI and GOME-2 satellite observations and MERRA-2 reanalysis dataset, with the correlation coefficients (R^2) of 0.86, 0.94 and 0.90 respectively. To better understand the causes of ozone depletion, the retrieved ozone columns, temperature and potential vorticity (PV) at certain altitude were analyzed. The profiles of ozone and PV showed positive correlation during the fluctuations, which indicates that polar vortex has great influence on stratospheric ozone depletion during Antarctic spring. Located at the edge of polar vortex, the observed data will provide a basis for further analysis and prediction of the inter-annual variation of stratospheric ozone in future.
The Record-breaking Meiyu in 2020 and Associated Atmospheric Circulation and Tropical SST Anomalies
Yihui Ding, Yunyun Liu, Zeng-zhen Hu
, Available online   , Manuscript accepted  11 January 2021, doi: 10.1007/s00376-021-0361-2
The record-breaking Meiyu in the Yangtze-Huaihe River valley (YHRV) in 2020 is characterized by early onset, delayed retreat, long duration, wide meridional rainbelt, abundant precipitation, and frequent heavy rainstorm processes. It is noted that the East Asian monsoon circulation system presents a significant quasi-biweekly oscillation (QBWO) during the Meiyu season of 2020. That is associated with the onset and retreat of Meiyu, the northward shift and stagnation of the rainbelt, and the occurrence and persistence of heavy rainstorm processes. Correspondingly during the Meiyu season, the monsoon circulation subsystems, including the western Pacific subtropical high (WPSH), the East Asian westerly jet in the upper level, and the southwesterly jet in the lower level, experience periodic oscillations linked with the QBWO. Especially, the repeated establishment of the large southerly center with relatively stable latitude leads to moisture convergence and ascending developed repeatedly, and the long-term duration of the Meiyu rainfall in YHRV, with frequent occurrences of the rainstorm processes. Moreover, two blocking highs present in the mid-high latitudes over Eurasia, and the low trough along the East Asian coast is also active, which is conducive to the cold air activities moving southward through the northwestern and/or northeastern paths, and frequently merging with the warm and wet moisture from the low latitudes and converging over YHRV. The persistent warming in the tropical Indian Ocean is an important external contributor to an EAP/PJ-like teleconnection pattern over East Asia and the intensified and southward displaced WPSH, which is favorable to excessive rainfall over YHRV.
An experiment on the prediction of the surface wind speed in Chongli based on the WRF model: evaluation and calibration
Na Li, Lingkun Ran, Dongdong Shen, Baofeng Jiao
, Available online   , Manuscript accepted  11 January 2021, doi: 10.1007/s00376-021-0201-4
An experiment was conducted in this paper to evaluate the ability of the Weather Research and Forecasting (WRF) model to generate accurate near-surface wind speed forecasts at the kilometer- to subkilometer-scale resolution along race tracks (RTs) in Chongli during the wintertime. The performance of two postprocessing methods, including the decaying-averaging (DA), and analogy-based (AN) methods, is tested to calibrate the near-surface wind speed forecasts. It is found that great uncertainties exist in the model’s raw forecasts of the near-surface wind speed in Chongli. The improvement of the forecast accuracy due to the refinement of the horizontal resolution from the kilometer to subkilometer scale is limited and not systematic. The RT sites tend to have large bias and centered root mean square error (CRMSE) values and also exhibit notable underestimation of high-wind speeds, notable overestimation or underestimation of the near-surface wind speed at high altitudes and notable underestimation during daytime. These problems are not resolved by increasing the horizontal resolution and are even exacerbated, which leads to great challenges in the accurate forecasting of the near-surface wind speed in the competition areas in Chongli. The application of postprocessing methods can greatly improve the forecast accuracy of near-surface wind speed. Both methods have comparable abilities in reducing the (positive or negative) bias, while AN method is also capable of decreasing the random error reflected by CRMSE. In particular, the large bias for high-wind speed, at high-altitude stations and during daytime in RT stations can be evidently reduced.
Vertical Profiles of Volatile Organic Compounds in suburban Shanghai
Yuhan Liu, Hongli Wang, Shengao Jing, Ming Zhou, Shengrong Lou, Kun Qu, Wanyi Qiu, Qian Wang, Shule Li, Yaqin Gao, Yusi Liu, Xiaobing Li, Zhong-Ren Peng, Junhui Chen, Keding Lu
, Available online   , Manuscript accepted  07 January 2021, doi: 10.1007/s00376-021-0126-y
As Volatile Organic Compounds (VOCs) is one of the precursors of ozone, its distribution and concentrations variation are highly related to local ozone pollution control. In this study, we obtained vertical profiles of VOCs in Shanghai’s Jinshan district on September 8 and September 9 in 2016 to investigate their distribution and impact on local atmospheric oxidation in near surface layer. Vertical samples were collected from heights of between 50 m and 400 m by summa canisters using an unmanned aerial vehicle (UAV). Concentrations of VOCs (VOCs refers to the 52 species measured in this study) varied less below 200 m, and decreased by 21.2% from 100 m to 400 m. The concentrations of VOCs above 200 m reduced significantly in comparison to those below 200 m. The proportions of alkanes and aromatics increased from 55.2% and 30.5% to 57.3% and 33.0%, respectively. And the proportion of alkenes decrease from 13.2% to 8.4%. Toluene and m/p-xylene were the key species in the formation of SOA and ozone. Principal component analysis (PCA) revealed that VOCs measured in this study were mainly originated from industrial emissions.
Correlation Structures Between Satellite All-Sky Infrared Brightness Temperatures and the Atmospheric State at Storm Scales
Yunji Zhang, David Stensrud, Eugene Clothiaux
, Available online   , Manuscript accepted  06 January 2021, doi: 10.1007/s00376-021-0352-3
This study explores the structures of the correlations between infrared brightness temperatures (BTs) from the three water vapor channels of the Advanced Baseline Imager (ABI) onboard the GOES-16 satellite and the atmospheric state. Ensemble-based data assimilation techniques such as the ensemble Kalman filter (EnKF) rely on correlations to propagate innovations of BTs to increments of model state variables. Because the three water vapor channels are sensitive to moisture in different layers of the troposphere, the heights of the strongest correlations between these channels and moisture in clear-sky regions are closely related to the peaks of their respective weighting functions. In cloudy regions, the strongest correlations appear at the cloud tops of deep clouds, and ice hydrometeors generally have stronger correlations with BT than liquid hydrometeors. The magnitudes of the correlations decrease from the peak value in a column with both vertical and horizontal distance. Just how the correlations decrease depend on both the cloud scenes and the cloud structures, as well as the model variables. Horizontal correlations between BTs and moisture, as well as hydrometeors, in fully cloudy regions decrease to almost 0 at about 30 km. The horizontal correlations with atmospheric state variables in clear-sky regions are broader, maintaining non-zero values out to ~100 km. The results in this study provide information on the proper choice of cut-off radii in horizontal and vertical localization schemes for the assimilation of BTs. They also provide insights on the most efficient and effective use of the different water vapor channels.
Impact of the Monsoon Surge on Landfalling Tropical Cyclone Extreme Rainfall Events
Dajun Zhao, Yubin YU, Lianshou CHEN
, Available online   , Manuscript accepted  06 January 2021, doi: 10.1007/s00376-021-0281-1
We carried out a comparative analysis and quantitative diagnosis of landfalling tropical cyclone extreme rainfall (LTCER) and non-extreme rainfall (NLTCER) events using the dynamic composite analysis method. Results show that the vertically integrated water vapor transport (IVT) during an LTCER event is significantly higher than that during an NLTCER event. There is a stronger convergence for both the IVT and the horizontal wind field during an LTCER event, which are mainly contributed by the lower troposphere. The water vapor budget on the four boundaries of the tropical cyclone indicates that the water vapor inflow on both the western and southern boundaries of an LTCER event exceeds that during an NLTCER event, although there is no significant difference on the eastern boundary, mainly as a result of the different intensities of the southwest monsoon surge in the environmental field of the tropical cyclone. The low-level jet accompanying the southwest monsoon surge can increase the inflow of water vapor at both the western and southern boundaries during an LTCER event and lead to the convergence of the horizontal wind field and the water vapor flux, thereby resulting in the LTCER event. On the other hand, the southwest monsoon surge can decreases the mean steering flow, which leads to a slower translation speed for the tropical cyclone associated with the LTCER event. Furthermore, a dynamic monsoon surge index defined here can be simply linked with the LTCER event and could be used as a new predictor in the operational forecasting of LTCER events.
Particulate amines in the background atmosphere of Yangtze River Delta, China: concentration, size distribution, and sources
Wei Du, Gehui Wang, Can Wu, shaojun lv, Fanglin Wang, fengqin Yang, Kaixu Bai, shijie Liu, jinze Wang, xinpei wang, xiaoyong chen, Wenliang liu, lujun wang, yubao chen
, Available online   , Manuscript accepted  03 January 2021, doi: 10.1007/s00376-021-0274-0
Amines are important for new particle formation and growth in the atmosphere, thus getting increasing concern in recent years. In this study, a field observation was conducted to investigate the atmospheric particulate amines at a background site in Yangtze River Delta (YRD) in the summer of 2018. Four amines in PM2.5, i.e., methylamine (MA), dimethylamine (DMA), diethylamine (DEA), and trimethylamine (TMA), were detected based on a semidiurnal duration. During the campaign concentrations of MA, DMA, DEA, and TMA were 15.0±15.0, 6.3±6.9, 20.4±30.1, and 4.0±5.9 ng/m3, respectively, and the four amines correlated with each other. The measured amines did not show a significantly difference between night and day concentrations, apart from DMA. MA and DMA exhibited a bimodal size distribution and maximized between 0.67 and 1.1 μm, suggesting amines preferably distribute on submicron particles. Boundary layer height (BLH), relative humility, and pH of aerosols were found have negative relationship with amines, while aerosol liquid water content (ALWC) were found to have a positive relationship with amines. The PMF source apportionment results showed that the main source of amines in Chongming Island was anthropogenic sources such as industrial and biomass emission, followed by marine sources including sea salt and marine biogenic source. Given the YRD region is still suffering from complex atmospheric pollution and the knowledge on aerosol amines is still limited, more field studies are in urgent need for a better understanding of the pollution characteristics of amines.
Impacts of Aerosol-Radiation Interactions on the Wintertime Particulate Pollution under Different Synoptic Patterns in the Guanzhong Basin, China
Naifang BEI, Xia LI, Qiyuan WANG, Suixin LIU, Jiarui WU, Jiayi LIANG, Lang LIU, Ruonan WANG, Guohui LI
, Available online   , Manuscript accepted  29 December 2020, doi: 10.1007/s00376-020-0329-7
The effects of aerosol–radiation interactions (ARI) are not only important for regional and global climate, but they can also drive particulate matter (PM) pollution. In this study, the ARI contribution to the near-surface fine PM (PM2.5) concentrations in the Guanzhong Basin (GZB) is evaluated under four unfavorable synoptic patterns, including “north-low”, “transition”, “southeast-trough”, and “inland-high”, based on WRF-Chem model simulations of a persistent heavy PM pollution episode in January 2019. Simulations show that ARI consistently decreases both solar radiation reaching down to the surface (SWDOWN) and surface temperature (TSFC), which then reduces wind speed, induces sinking motion, and influences cloud formation in the GZB. However, large differences under the four synoptic patterns still exist. The average reductions of SWDOWN and daytime TSFC in the GZB range from 15.2% and 1.04°C in the case of the “transition” pattern to 26.7% and 1.69°C in the case of the “north-low” pattern, respectively. Furthermore, ARI suppresses the development of the planetary boundary layer (PBL), with the decrease of PBL height (PBLH) varying from 18.7% in the case of the “transition” pattern to 32.0% in the case of the “north-low” pattern. The increase of daytime near-surface PM2.5 in the GZB due to ARI is 12.0%, 8.1%, 9.5%, and 9.7% under the four synoptic patterns, respectively. Ensemble analyses also reveal that when near-surface PM2.5 concentrations are low, ARI tends to lower PM2.5 concentrations with decreased PBLH, which is caused by enhanced divergence or a transition from divergence to convergence in an area. ARI contributes 15%–25% toward the near-surface PM2.5 concentrations during periods of severe PM pollution under the four synoptic patterns.
Characteristics of chemical speciation in PM1 in six representative regions in China
Kaixu Bai, Can Wu, Jianjun Li, Ke Li, Jianping Guo, Gehui Wang
, Available online   , Manuscript accepted  21 December 2020, doi: 10.1007/s00376-020-0224-2
A better knowledge of aerosol properties is critical for elucidating the complex mechanism behind frequently occurred haze pollution events. In this study, we examined the temporal and spatial variations in PM1 and major chemical compositions using three-year field measurements that were collected in six representative regions in China between 2012 and 2014. Both PM1 and its chemical compositions varied significantly in space and time, with high PM1 loadings mainly observed in the winter due to significant increases in organic matter (OM) and inorganic salts like sulfate, nitrate, and ammonium (SNA). Comparisons of chemical components during clean and polluted episodes indicated that the significant increase in OM and SNA was the primary reason for the elevated PM1 loading, revealing the critical role of primary emissions and secondary aerosols in elevating PM1 pollution levels. The PM1 to PM2.5 ratios were generally high in Shanghai and Guangzhou while relatively low in Xi’an and Chengdu, indicating anthropogenic components were more likely to accumulate in smaller particles. According to the relative importance of chemical components and meteorological factors that was resolved via statistical modeling practices, we found that primary emissions and secondary aerosols were still two dominant factors modulating PM1 pollution levels, though meteorological factors also played important roles in regulating the dispersion of atmospheric PM.
On the Mechanism of a Terrain-Influenced Snow Burst Event during Midwinter in Northeast China
Na LI, Baofeng JIAO, Lingkun RAN, Xinyong SHEN, Yanbin QI
, Available online   , Manuscript accepted  15 December 2020, doi: 10.1007/s00376-020-0104-9
Short-duration snow bursts with heavy snow represent one type of hazardous weather in winter which can be easily missed by the winter weather warnings but often results in great hazards. In this paper, the mechanism for the occurrence of such events was investigated with the aid of a localized terrain-influenced snow burst event in Northeast China. The snow burst was produced by an eastward-moving cold-frontal snowband which encountered the downstream complex terrain of the Changbai Mountains and intensified. To ascertain the role of orography on the snow burst, numerical experiments, together with a parallel sensitivity experiment removing Changbai Mountains, were performed to attempt to distinguish the contributions of cold-frontal system and orographic effects to produce the heavy snow. Diagnosis showed that without the influence of Changbai Mountains, the release of conditional instability (CI) and inertial instability (II) within a weak frontogenetical environment was responsible for the snowband maintenance. Orographic effects played important roles in enhancing the snowband and increasing the snowfall intensities. The enhancement mechanism was related to the interactions of the cold-frontal snowband and the topography. On one hand, orographic frontogenesis and persistent ascent, created by orographic gravity waves over the terrain, greatly enhanced the orographic lifting. The intensification of the lifting promoted the release of CI and thus enhanced the snowfall. On the other hand, pre-existing orographic instabilities were released due to the passing of the cold-frontal snowband, which could also serve to intensify the snowband over terrain and thus increase the snowfall.
The Asymmetric Atmospheric Response to the Decadal Variability of Kuroshio Extension during Winter
Jianqi ZHANG, Chongyin LI, Xin LI, Chao ZHANG, Jingjing CHEN
, Available online   , Manuscript accepted  14 December 2020, doi: 10.1007/s00376-020-0264-7
The Kuroshio extension (KE) exhibits interdecadal variability, oscillating from a stable state to an unstable state. In this paper, ERA-Interim reanalysis data are used to discuss the possible reasons for the asymmetric response of the atmosphere to symmetric sea surface temperature anomalies (SSTAs) during periods of differential KE states. The analysis has the following results: the SSTA presents a nearly symmetrical distribution with opposite signs during the KE stable and unstable periods. During the KE stable period, the storm track is located north of 40°N and is significantly enhanced in the northeast Pacific Ocean. The atmospheric response is similar to the West Pacific/North Pacific Oscillation teleconnection (WP/NPO like pattern) and presents a barotropic structure. The inversion results of the potential vorticity equation show that the feedback of transient eddy vorticity manifests a WP/NPO like pattern and presents a barotropic structure, which is the main reason for bringing about the response of the WP/NPO like pattern. The magnitude of the feedbacks of both diabatic heating and transient eddy heating is small, which can offset one another. During the KE unstable period, the main body of the storm track is located to the south of 40°N, and there is no significant response signal in the atmosphere, except near the west coast of North America. Compared with the KE stable period, the asymmetry of response of the transient eddy vorticity is the main reason for the asymmetric response of the atmosphere.
Characteristics of Lake Breezes and Their Impacts on Energy and Carbon Fluxes in Mountainous Areas
Lujun XU, Huizhi LIU, Qun DU, Yang LIU, Jihua SUN, Anlun XU, Xiaoni MENG
, Available online   , Manuscript accepted  14 December 2020, doi: 10.1007/s00376-020-0298-x
In mountainous lake areas, lake–land and mountain–valley breezes interact with each other, leading to an “extended lake breeze”. These extended lake breezes can regulate and control energy and carbon cycles at different scales. Based on meteorological and turbulent fluxes data from an eddy covariance observation site at Erhai Lake in the Dali Basin, southwest China, characteristics of daytime and nighttime extended lake breezes and their impacts on energy and carbon dioxide exchange in 2015 are investigated. Lake breezes dominate during the daytime while, due to different prevailing circulations at night, there are two types of nighttime breezes. The mountain breeze from the Cangshan Mountain range leads to N1 type nighttime breeze events. When a cyclonic circulation forms and maintains in the southern part of Erhai Lake at night, its northern branch contributes to the formation of N2 type nighttime breeze events. The prevailing wind directions for daytime, N1, and N2 breeze events are southeast, west, and southeast, respectively. Daytime breeze events are more intense than N1 events and weaker than N2 events. During daytime breeze events, the lake breeze decreases the sensible heat flux (Hs) and carbon dioxide flux ( Fco2 ) and increases the latent heat flux (LE). During N1 breeze events, the mountain breeze decreases Hs and LE and increases Fco2 . For N2 breeze events, the southeast wind from the lake surface increases Hs and LE and decreases Fco2 . Results indicate that lakes in mountainous areas promote latent heat mixing but suppress carbon dioxide exchange.
A Case Study of the Initiation of Parallel Convective Lines Back-Building from the South Side of a Mei-yu Front over Complex Terrain
Qiwei WANG, Yi ZANG, Kefeng ZHU, Zhemin TAN, Ming XUE
, Available online   , Manuscript accepted  10 December 2020, doi: 10.1007/s00376-020-0216-2
Parallel back-building convective lines are often observed extending to the southwest of some mesoscale convective systems (MCSs) embedded in the mei-yu front in China. The convective lines with echo training behavior can quickly develop into a stronger convective group of echoes, resulting in locally heavy rainfall within the mei-yu front rainband. The initiation mechanism of the back-building convective lines is still unclear and is studied based on high-resolution numerical simulation of a case that occurred during 27−28 June 2013. In the present case, the new convection along the convective lines was found to be forced by nonuniform interaction between the cold outflow associated with the mei-yu front MCSs and the warm southerly airflow on the south side of the mei-yu front, which both are modified by local terrain. The mei-yu front MCSs evolved from the western to the eastern side of a basin surrounded by several mesoscale mountains and induced cold outflow centered over the eastern part of the basin. The strong southwest airflow ahead of the mei-yu front passed through the Nanling Mountains and impacted the cold outflow within the basin. The nonuniform interaction led to the first stage of parallel convective line formation, in which the low mountains along the boundary of the two airflows enhanced the heterogeneity of their interaction. Subsequently, the convective group quickly developed from the first stage convective lines resulted in apparent precipitation cooling that enhanced the cold outflow and made the cold outflow a sharp southward windshift. The enhanced cold outflow pushed the warm southerly airflow southward and impacted the mountains on the southeast side of the basin, where the roughly parallel mountain valleys or gaps play a controlling role in a second stage formation of parallel convective lines.
Iterative Methods for Solving the Nonlinear Balance Equation with Optimal Truncation
Qin XU, Jie CAO
, Available online   , Manuscript accepted  10 December 2020, doi: 10.1007/s00376-020-0291-4
Two types of existing iterative methods for solving the nonlinear balance equation (NBE) are revisited. In the first type, the NBE is rearranged into a linearized equation for a presumably small correction to the initial guess or the subsequent updated solution. In the second type, the NBE is rearranged into a quadratic form of the absolute vorticity with the positive root of this quadratic form used in the form of a Poisson equation to solve NBE iteratively. The two methods are rederived by expanding the solution asymptotically upon a small Rossby number, and a criterion for optimally truncating the asymptotic expansion is proposed to obtain the super-asymptotic approximation of the solution. For each rederived method, two iterative procedures are designed using the integral-form Poisson solver versus the over-relaxation scheme to solve the boundary value problem in each iteration. Upon testing with analytically formulated wavering jet flows on the synoptic, sub-synoptic and meso-α scales, the iterative procedure designed for the first method with the Poisson solver, named M1a, is found to be the most accurate and efficient. For the synoptic wavering jet flow in which the NBE is entirely elliptic, M1a is extremely accurate. For the sub-synoptic wavering jet flow in which the NBE is mostly elliptic, M1a is sufficiently accurate. For the meso-α wavering jet flow in which the NBE is partially hyperbolic so its boundary value problem becomes seriously ill-posed, M1a can effectively reduce the solution error for the cyclonically curved part of the wavering jet flow, but not for the anti-cyclonically curved part.
Distinctive MJO Activity during the Boreal Winter of the 2015/16 Super El Niño in Comparison with Other Super El Niño Events
Xuben LEI, Wenjun ZHANG, Pang-chi HSU, Chao LIU
, Available online   , Manuscript accepted  10 December 2020, doi: 10.1007/s00376-020-0261-x
Many previous studies have demonstrated that the boreal winters of super El Niño events are usually accompanied by severely suppressed Madden-Julian oscillation (MJO) activity over the western Pacific due to strong descending motion associated with a weakened Walker Circulation. However, the boreal winter of the 2015/16 super El Niño event is concurrent with enhanced MJO activity over the western Pacific despite its sea surface temperature anomaly (SSTA) magnitude over the Niño 3.4 region being comparable to the SSTA magnitudes of the two former super El Niño events (i.e., 1982/83 and 1997/98). This study suggests that the MJO enhanced over western Pacific during the 2015/16 super El Niño event is mainly related to its distinctive SSTA structure and associated background thermodynamic conditions. In comparison with the previous super El Niño events, the warming SSTA center of the 2015/16 super El Niño is located further westward, and a strong cold SSTA is not detected in the western Pacific. Accordingly, the low-level moisture and air temperature (as well as the moist static energy, MSE) tend to increase in the central-western Pacific. In contrast, the low-level moisture and MSE show negative anomalies over the western Pacific during the previous super El Niño events. As the MJO-related horizontal wind anomalies contribute to the further westward warm SST-induced positive moisture and MSE anomalies over the western tropical Pacific in the boreal winter of 2015/16, stronger moisture convergence and MSE advection are generated over the western Pacific and lead to the enhancement of MJO convection.
Diurnal Variations of Precipitation over the Steep Slopes of the Himalayas Observed by TRMM PR and VIRS
Xiao PAN, Yunfei FU, Sen YANG, Ying GONG, Deqin LI
, Available online   , Manuscript accepted  08 December 2020, doi: 10.1007/s00376-020-0246-9
This study investigates diurnal variations of precipitation during May–August, 1998–2012, over the steep slopes of the Himalayas and adjacent regions (flat Gangetic Plains–FGP, foothills of the Himalayas–FHH, the steep slope of the southern Himalayas–SSSH, and the Himalayas-Tibetan Plateau tableland–HTPT). Diurnal variations are analyzed at the pixel level utilizing collocated TRMM precipitation radar and visible infrared data. The results indicate that rain parameters (including rain frequency, rain rate, and storm top altitude) are predominantly characterized by afternoon maxima and morning minima at HTPT and FGP, whereas, maximum rain parameters at FHH typically occur in the early morning. Rain parameters at SSSH are characterized by double peaks; one in the afternoon and one at midnight. Over HTPT and FGP, convective activity is strongest in the afternoon with the thickest crystallization layer. Over FHH, the vertical structure of precipitation develops most vigorously in the early morning when the most intense collision and growth of precipitation particles occurs. Over SSSH, moist convection is stronger in the afternoon and at midnight with strong mixing of ice and water particles. The results of harmonic analysis show that rain bands move southward from lower elevation of SSSH to FHH with apparent southward propagation of the harmonic phase from midnight to early morning. Moreover, the strongest diurnal harmonic is located at HTPT, having a diurnal harmonic percentage variance of up to 90%. Large-scale atmospheric circulation patterns exhibit obvious diurnal variability and correspond well to the distribution of precipitation.
Diversity of the Coupling Wheels in the East Asian Summer Monsoon on the Interannual Time Scale: Challenge of Summer Rainfall Forecasting in China
Congwen ZHU, Boqi LIU, Kang XU, Ning JIANG, Kai LIU
, Available online   , Manuscript accepted  03 December 2020, doi: 10.1007/s00376-020-0199-z
Two types of three-dimensional circulation of the East Asian summer monsoon (EASM) act as the coupling wheels determining the seasonal rainfall anomalies in China during 1979–2015. The first coupling mode features the interaction between the Mongolian cyclone over North Asia and the South Asian high (SAH) anomalies over the Tibetan Plateau at 200 hPa. The second mode presents the coupling between the anomalous low-level western Pacific anticyclone and upper-level SAH via the meridional flow over Southeast Asia. These two modes are responsible for the summer rainfall anomalies over China in 24 and 7 out of 37 years, respectively. However, the dominant SST anomalies in the tropical Pacific, the Indian Ocean, and the North Atlantic Ocean fail to account for the first coupling wheel’s interannual variability, illustrating the challenges in forecasting summer rainfall over China.
Which Features of the SST Forcing Error Most Likely Disturb the Simulated Intensity of Tropical Cyclones?
Jiawei YAO, Wansuo DUAN, Xiaohao QIN
, Available online   , Manuscript accepted  03 December 2020, doi: 10.1007/s00376-020-0073-z
Among all of the sources of tropical cyclone (TC) intensity forecast errors, the uncertainty of sea surface temperature (SST) has been shown to play a significant role. In the present study, we determine the SST forcing error that causes the largest simulation error of TC intensity during the entire simulation period by using the WRF model with time-dependent SST forcing. The SST forcing error is represented through the application of a nonlinear forcing singular vector (NFSV) structure. For the selected 12 TC cases, the NFSV-type SST forcing errors have a nearly coherent structure with positive (or negative) SST anomalies located along the track of TCs but are especially concentrated in a particular region. This particular region tends to occur during the specific period of the TCs life cycle when the TCs present relatively strong intensity, but are still intensifying just prior to the mature phase, especially within a TC state exhibiting a strong secondary circulation and very high inertial stability. The SST forcing errors located along the TC track during this time period are verified to have the strongest disturbing effect on TC intensity simulation. Physically, the strong inertial stability of TCs during this time period induces a strong response of the secondary circulation from diabatic heating errors induced by the SST forcing error. Consequently, this significantly influences the subsidence within the warm core in the eye region, which, in turn, leads to significant errors in TC intensity. This physical mechanism explains the formation of NSFV-type SST forcing errors. According to the sensitivity of the NFSV-type SST forcing errors, if one increases the density of SST observations along the TC track and assimilates them to the SST forcing field, the skill of TC intensity simulation generated by the WRF model could be greatly improved. However, this adjustment is most advantageous in improving simulation skill during the time period when TCs become strong but are still intensifying just prior to reaching full maturity. In light of this, the region along the TC track but in the time period of TC movement when the NFSV-type SST forcing errors occur may represent the sensitive area for targeting observation for SST forcing field associated with TC intensity simulation.
Assimilating All-sky Infrared Radiances from Himawari-8 using the 3DVar Method for the Prediction of a Severe Storm over North China
Dongmei XU, Zhiquan LIU, Shuiyong FAN, Min CHEN, Feifei SHEN
, Available online   , Manuscript accepted  02 December 2020, doi: 10.1007/s00376-020-0219-z
Although radar observations capture storm structures with high spatiotemporal resolutions, they are limited within the storm region after the precipitation formed. Geostationary satellites data cover the gaps in the radar network prior to the formation of the precipitation for the storms and their environment. The study explores the effects of assimilating the water vapor channel radiances from Himawari-8 data with Weather Research and Forecasting model data assimilation system (WRFDA) for a severe storm case over north China. A fast cloud detection scheme for Advanced Himawari imager (AHI) radiance is enhanced in the framework of the WRFDA system initially in this study. The bias corrections, the cloud detection for the clear-sky AHI radiance, and the observation error modeling for cloudy radiance are conducted before the data assimilation. All AHI radiance observations are fully applied without any quality control for all-sky AHI radiance data assimilation. Results show that the simulated all-sky AHI radiance fits the observations better by using the cloud dependent observation error model, further improving the cloud heights. The all-sky AHI radiance assimilation adjusts all types of hydrometeor variables, especially cloud water and precipitation snow. It is proven that assimilating all-sky AHI data improves hydrometeor specifications when verified against the radar reflectivity. Consequently, the assimilation of AHI observations under the all-sky condition has an overall improved impact on both the precipitation locations and intensity compared to the experiment with only conventional and AHI clear-sky radiance data.
Satellite Observations of Reflectivity Maxima above the Freezing Level Induced by Terrain
Aoqi ZHANG, Weibiao LI, Shumin CHEN, Yilun CHEN, Yunfei FU
, Available online   , Manuscript accepted  02 December 2020, doi: 10.1007/s00376-020-0221-5
Previous studies have recognized reflectivity maxima above the freezing level (RMAF) within stratiform precipitation over mountain slopes, however, quantitative studies are limited due to the lack of adequate identification criteria. Here, we establish an identification method for RMAF precipitation and apply it to the Tropical Rainfall Measuring Mission (TRMM) Precipitation Radar (PR) observations. Using the TRMM 2A25 product from 1998 to 2013, we show that the RMAF structure in reflectivity profiles can be effectively identified. RMAF exists not only in stratiform precipitation but also in convective precipitation. RMAF frequency is positively correlated with elevation, which is thought to be caused by enhanced updrafts in the middle layers of stratiform precipitation, or in the low to middle layers of convective precipitation over mountains. The average RMAF heights in stratiform and convective precipitation were 1.35 and 2.01 km above the freezing level, respectively, which is lower than previous results. In addition, our results indicate that the RMAF structure increased the echo top height and enhanced precipitation processes above the RMAF height, but it suppressed the downward propagation of ice particles and the near-surface rain rate. Future studies of orographic precipitation should take into account the impact of the RMAF structure and its relevant dynamic triggers.
Morphological Characteristics of Precipitation Areas over the Tibetan Plateau Measured by TRMM PR
Yilun CHEN, Aoqi ZHANG, Yunfei FU, Shumin CHEN, Weibiao LI
, Available online   , Manuscript accepted  24 November 2020, doi: 10.1007/s00376-020-0233-1
The multidimensional morphological characteristics (including scale, horizontal shape and 3D morphology) of precipitation areas over the Tibetan Plateau in summer were studied using 15 years (1998–2012) of observational data from the precipitation radar onboard the Tropical Rainfall Measuring Mission satellite. As the scale of the precipitation area increased from 20 to 150 km, the near-surface rain rate (RRav) of the precipitation area increased by up to 78% (from ~1.12 to ~2 mm h−1). Linear precipitation areas had the lowest median RRav (~1 mm h−1 over the eastern Tibetan Plateau), whereas square-shaped precipitation areas had the highest median RRav (~1.58 mm h−1 over the eastern Tibetan Plateau). The 3D morphology was defined as the ratio of the average vertical scale to the average horizontal scale, where a large value corresponds to thin and tall, and a small value corresponds to plump and short. Thin-and-tall precipitation areas and plump-and-short precipitation areas had a greater median RRav, whereas the precipitation areas with a moderate 3D morphology had the lowest median RRav. The vertical structure of the precipitation-area reflectivity was sensitive to both size and 3D morphology, but was not sensitive to the horizontal shape. The relationship between RRav and the morphological characteristics was most significant over the southern slopes of the Tanggula Mountains and the Tibetan Plateau east of 100°E. The morphological characteristics of precipitation areas are therefore closely related to the intensity of precipitation and could potentially be used to forecast precipitation and verify numerical models.
Rainfall Algorithms Using Oceanic Satellite Observations from MWHS-2
Ruiyao CHEN, Ralf Bennartz
, Available online   , Manuscript accepted  13 November 2020, doi: 10.1007/s00376-020-0258-5
This paper describes three algorithms for retrieving precipitation over oceans from brightness temperatures (TBs) of the Micro-Wave Humidity Sounder-2 (MHWS-2) onboard Fengyun-3C (FY-3C). For algorithm development, scattering-induced TB depressions (ΔTBs) of MWHS-2 at channels between 89 and 190 GHz were collocated to rain rates derived from measurements of the Global Precipitation Measurement’s Dual-frequency Precipitation Radar (DPR) for the year 2017. ΔTBs were calculated by subtracting simulated cloud-free TBs from bias-corrected observed TBs for each channel. These ΔTBs were then related to rain rates from DPR using (1) multilinear regression (MLR); the other two algorithms, (2) range searches (RS) and (3) nearest neighbor searches (NNS), are based on k-dimensional trees. While all three algorithms produce instantaneous rain rates, the RS algorithm also provides the probability of precipitation and can be understood in a Bayesian framework. Different combinations of MWHS-2 channels were evaluated using MLR and results suggest that adding 118 GHz improves retrieval performance. The optimal combination of channels excludes high-peaking channels but includes 118 GHz channels peaking in the mid and high troposphere. MWHS-2 observations from another year were used for validation purposes. The annual mean 2.5° × 2.5° gridded rain rates from the three algorithms are consistent with those from the Global Precipitation Climatology Project (GPCP) and DPR. Their correlation coefficients with GPCP are 0.96 and their biases are less than 5%. The correlation coefficients with DPR are slightly lower and the maximum bias is ~8%, partly due to the lower sampling density of DPR compared to that of MWHS-2.
Properties of High-Order Finite Difference Schemes and Idealized Numerical Testing
Daosheng XU, Dehui CHEN, Kaixin WU
, Available online   , Manuscript accepted  10 November 2020, doi: 10.1007/s00376-020-0130-7
Construction of high-order difference schemes based on Taylor series expansion has long been a hot topic in computational mathematics, while its application in comprehensive weather models is still very rare. Here, the properties of high-order finite difference schemes are studied based on idealized numerical testing, for the purpose of their application in the Global/Regional Assimilation and Prediction System (GRAPES) model. It is found that the pros and cons due to grid staggering choices diminish with higher-order schemes based on linearized analysis of the one-dimensional gravity wave equation. The improvement of higher-order difference schemes is still obvious for the mesh with smooth varied grid distance. The results of discontinuous square wave testing also exhibits the superiority of high-order schemes. For a model grid with severe non-uniformity and non-orthogonality, the advantage of high-order difference schemes is inapparent, as shown by the results of two-dimensional idealized advection tests under a terrain-following coordinate. In addition, the increase in computational expense caused by high-order schemes can be avoided by the precondition technique used in the GRAPES model. In general, a high-order finite difference scheme is a preferable choice for the tropical regional GRAPES model with a quasi-uniform and quasi-orthogonal grid mesh.
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
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.
Vertical Evolution of Boundary Layer Volatile Organic Compounds in Summer over the North China Plain and the Differences with Winter
Shuang WU, Guiqian TANG, Yinghong WANG, Rong MAI, Dan YAO, Yanyu KANG, Qinglu WANG, Yuesi WANG
, Available online   , Manuscript accepted  06 November 2020, doi: 10.1007/s00376-020-0254-9
The vertical observation of volatile organic compounds (VOCs) is an important means to clarify the mechanisms of ozone formation. To explore the vertical evolution of VOCs in summer, a field campaign using a tethered balloon during summer photochemical pollution was conducted in Shijiazhuang from 8 June to 3 July 2019. A total of 192 samples were collected, 23 vertical profiles were obtained, and the concentrations of 87 VOCs were measured. The range of the total VOC concentration was 41–48 ppbv below 600 m. It then slightly increased above 600 m, and rose to 58 ± 52 ppbv at 1000 m. The proportion of alkanes increased with height, while the proportions of alkenes, halohydrocarbons and acetylene decreased. The proportion of aromatics remained almost unchanged. A comparison with the results of a winter field campaign during 8–16 January 2019 showed that the concentrations of all VOCs in winter except for halohydrocarbons were more than twice those in summer. Alkanes accounted for the same proportion in winter and summer. Alkenes, aromatics, and acetylene accounted for higher proportions in winter, while halohydrocarbons accounted for a higher proportion in summer. There were five VOC sources in the vertical direction. The proportions of gasoline vehicular emissions + industrial sources and coal burning were higher in winter. The proportions of biogenic sources + long-range transport, solvent usage, and diesel vehicular emissions were higher in summer. From the surface to 1000 m, the proportion of gasoline vehicular emissions + industrial sources gradually increased.
Monthly Variations of Atmospheric Circulations Associated with Haze Pollution in the Yangtze River Delta and North China
Xinyu ZHANG, Zhicong YIN, Huijun WANG, Mingkeng DUAN
, Available online   , Manuscript accepted  05 November 2020, doi: 10.1007/s00376-020-0227-z
Haze pollution in early winter (December and January) in the Yangtze River Delta (YRD) and in North China (NC) are both severe; however, their monthly variations are significantly different. In this study, the dominant large-scale atmospheric circulations and local meteorological conditions were investigated and compared over the YRD and NC in each month. Results showed that the YRD (NC) is dominated by the so-called Scandinavia (East Atlantic/West Russia) pattern in December, and these circulations weaken in January. The East Asian December and January monsoons over the YRD and NC have negative correlations with the number of haze days. The local descending motion facilitates less removal of haze pollution over the YRD, while the local ascending motion facilitates less removal of haze pollution over NC in January, despite a weaker relationship in December. Additionally, the monthly variations of atmospheric circulations showed that adverse meteorological conditions restrict the vertical (horizontal) dispersion of haze pollution in December (January) over the YRD, while the associated local weather conditions are similar in these two months over NC.
Growing Operational Use of FY-3 Data in the ECMWF System
Niels BORMANN, David DUNCAN, Stephen ENGLISH, Sean HEALY, Katrin LONITZ, Keyi CHEN, Heather LAWRENCE, Qifeng LU
, Available online   , Manuscript accepted  04 November 2020, doi: 10.1007/s00376-020-0207-3
This paper reviews the data quality and impact of observations from the FY-3 satellite series used operationally in the ECMWF system. This includes data from the passive microwave radiometers MWHS-1, MWHS-2 and MWRI, as well as observations from the radio occultation receiver GNOS. Evaluations against background equivalents show that the quality of the observations is broadly comparable to that of similar instruments on other polar-orbiting satellites, even though biases for the passive microwave observations can be somewhat larger and more complex for some channels. An observing system experiment shows that the FY-3 instruments jointly contribute significantly to the forecast skill in the ECMWF system. Positive impact of up to 2% is seen for most variables out to the day-2 forecasts over hemispheric scales, with significant benefits for total column water vapor or for temperature and wind in the stratosphere out to day 4.
Characterization of Organic Aerosol at a Rural Site in the North China Plain Region: Sources, Volatility and Organonitrates
Qiao ZHU, Li-Ming CAO, Meng-Xue TANG, Xiao-Feng HUANG, Eri SAIKAWA, Ling-Yan HE
, Available online   , Manuscript accepted  09 September 2020, doi: 10.1007/s00376-020-0127-2
The North China Plain (NCP) is a region that experiences serious aerosol pollution. A number of studies have focused on aerosol pollution in urban areas in the NCP region; however, research on characterizing aerosols in rural NCP areas is comparatively limited. In this study, we deployed a TD-HR-AMS (thermodenuder high-resolution aerosol mass spectrometer) system at a rural site in the NCP region in summer 2013 to characterize the chemical compositions and volatility of submicron aerosols (PM1). The average PM1 mass concentration was 51.2 ± 48.0 μg 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 estimation methods with the high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS) measurement. Correlation analysis shows that ON were more correlated with BBOA and black carbon emitted from biomass burning but poorly correlated with LO-OOA. Also, volatility analysis for ON further confirmed that particulate ON formation might be closely associated with primary emissions in rural NCP areas.
Water Vapor Retrievals from Near-infrared Channels of the Advanced Medium Resolution Spectral Imager Instrument onboard the Fengyun-3D Satellite
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 environmental 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 the 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 GPS measurements. The results show that the accuracies of the water vapor products based on the updated MERSI-II instrument 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% to −14.3%, respectively, and thus comparable with those of other global remote sensing products of the same type.
Insights into the Microwave Instruments Onboard the Fengyun 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, Fengyun 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.
News & Views
IAP’s Solar-Powered Unmanned Surface Vehicle Actively Passes Through the Center of Typhoon Sinlaku(2020)
Hongbin CHEN, Jun LI, Wenying HE, Shuqing MA, Yingzhi WEI, Jidong PAN, Yu ZHAO, Xuefen ZHANG, Shuzhen HU
, Available online   , Manuscript accepted  19 February 2021, doi: 10.1007/s00376-021-1006-1
The solar-powered marine unmanned surface vehicle (USV) developed by the USV team of the Institute of Atmospheric Physics is a rugged, long-duration, and autonomous navigation vessel designed for the collection of long-range, continuous, real-time, meteorological and oceanographic measurements, especially under extreme sea conditions (sea state 6–7). These solar-powered USVs completed a long-term continuous navigation observation test over 26 days. During this time, they coordinated double-USV observations and actively navigated into the path of Typhoon Sinlaku (2020) before collecting data very close to its center during the 2020 USV South China Sea Typhoon Observation Experiment. Detailed high temporal resolution (1 min) real-time observations collected by the USV on the typhoon were used for operational typhoon forecasting and warning for the first time. As a mobile meteorological and oceanographic observation station capable of reliable, automated deployment, data collection, and transmission, such solar-powered USVs can replace traditional observation platforms to provide valuable real-time data for research, forecasting, and early warnings for potential marine meteorological disasters.
The 2020/21 Extremely Cold Winter in China Influenced by the Synergistic Effect of La Niña and Warm Arctic
Fei ZHENG, Yuan YUAN, Yihui DING, Kexin LI, Xianghui FANG, Yuheng ZHAO, Yue SUN, Jiang ZHU, Zongjian KE, Ji WANG, Xiaolong JIA
, Available online   , Manuscript accepted  01 February 2021, doi: 10.1007/s00376-021-1033-y
In the first half of winter 2020/21, China has experienced an extremely cold period across both northern and southern regions, with record-breaking low temperatures set in many stations of China. Meanwhile, a moderate La Niña event which exceeded both oceanic and atmospheric thresholds began in August 2020 and in a few months developed into its mature phase, just prior to the 2020/21 winter. In this report, the mid−high-latitude large-scale atmospheric circulation anomalies in the Northern Hemisphere, which were forced by the negative phase of Arctic Oscillation, a strengthened Siberian High, an intensified Ural High and a deepened East Asian Trough, are considered to be the direct reason for the frequent cold surges in winter 2020/21. At the same time, the synergistic effect of the warm Arctic and the cold tropical Pacific (La Niña) provided an indispensable background, at a hemispheric scale, to intensify the atmospheric circulation anomalies in middle-to-high latitudes. In the end, a most recent La Niña prediction is provided and the on-coming evolution of climate is discussed for the remaining part of the 2020/21 winter for the purpose of future decision-making and early warning.
Upper Ocean Temperatures Hit Record High in 2020
Lijing CHENG, John ABRAHAM, Kevin E. TRENBERTH, John FASULLO, Tim BOYER, Ricardo LOCARNINI, Bin ZHANG, Fujiang YU, Liying WAN, Xingrong CHEN, Xiangzhou SONG, Yulong LIU, Michael E. MANN, Franco RESEGHETTI, Simona SIMONCELLI, Viktor GOURETSKI, Gengxin CHEN, Alexey MISHONOV, Jim REAGAN, Jiang ZHU
, Available online   , Manuscript accepted  09 January 2021, doi: 10.1007/s00376-021-0447-x
Comprehensive Marine Observing Experiment Based on High-Altitude Large Unmanned Aerial Vehicle (South China Sea Experiment 2020 of the “Petrel Project”)
Xuefen ZHANG, Liangxu LI, Rongkang YANG, Ran GUO, Xia SUN, Jianping LUO, Hongbin CHEN, Daxin LIU, Kebing TANG, Wenwu PENG, Xiaodong HAN, Qiyun GUO, Xiaoxia LI, Xikun FEI
, Available online   , Manuscript accepted  03 December 2020, doi: 10.1007/s00376-020-0314-1
In collaboration with 12 other institutions, the Meteorological Observation Center of the China Meteorological Administration undertook a comprehensive marine observation experiment in the South China Sea using the Yilong-10 high-altitude large unmanned aerial vehicle (UAV). The Yilong-10 UAV carried a self-developed dropsonde system and a millimeter-wave cloud radar system. In addition, a solar-powered unmanned surface vessel and two drifting buoys were used. The experiment was further supported by an intelligent, reciprocating horizontal drifting radiosonde system that was deployed from the Sansha Meteorological Observing Station, with the intent of producing a stereoscopic observation over the South China Sea. Comprehensive three-dimensional observations were collected using the system from 31 July to 2 August, 2020. This information was used to investigate the formation and development processes of Typhoon Sinlaku (2020). The data contain measurements of 21 oceanic and meteorological parameters acquired by the five devices, along with video footage from the UAV. The data proved very helpful in determining the actual location and intensity of Typhoon Sinlaku (2020). The experiment demonstrates the feasibility of using a high-altitude, large UAV to fill in the gaps between operational meteorological observations of marine areas and typhoons near China, and marks a milestone for the use of such data for analyzing the structure and impact of a typhoon in the South China Sea. It also demonstrates the potential for establishing operational UAV meteorological observing systems in the future, and the assimilation of such data into numerical weather prediction models.
Letter and Notes
Partition of Forecast Errors into Positional and Structural Components
Isidora Jankov, Scott Gregory, Sai Ravela, Zoltan Toth, Malaquia Pena-Mendez
, Available online   , Manuscript accepted  18 February 2021, doi: 10.1007/s00376-021-0251-7
Weather manifests in spatiotemporally coherent structures. Weather forecasts hence are affected by both positional and structural or amplitude errors. This has been long recognized by practicing forecasters (cf., e.g., Tropical Cyclone track and intensity errors). Despite the emergence in recent decades of various objective methods for the diagnosis of positional forecast errors, most routine verification or statistical post-processing methods implicitly assume that forecasts have no positional error. The Forecast Error Decomposition (FED) method proposed in this study uses the Field Alignment technique which aligns a gridded forecast with its verifying analysis field. The total error is then partitioned into three orthogonal components: (a) large scale positional, (b) large scale structural, and (c) small scale error variance. The use of FED is demonstrated over a month-long MSLP data set. As expected, positional errors are often characterized by dipole patterns related to the displacement of features, while structural errors appear with single extrema, indicative of magnitude problems. The most important result of this study is that over the test period, more than 50% of the total mean sea level pressure forecast error variance is associated with large scale positional error. The importance of positional error in forecasts of other variables and over different time periods remain to be explored.
What drives the decadal variability of global tropical storm days from 1965 to 2019
Yifei Dai, Bin Wang, Weiyi Sun
, Available online   , Manuscript accepted  26 January 2021, doi: 10.1007/s00376-021-0354-1
The tropical storm day (TSD) is a combined measure of genesis and lifespan. It reflects tropical cyclone (TC) overall activity, yet its variability has rarely been studied, especially globally. Here we show that the global total TSDs exhibit pronounced interannual (3-6 years) and decadal (10 years) variations over the past five-to-six decades without a significant trend. The leading modes of the interannual and decadal variability of global TSD feature similar patterns in the western Pacific and Atlantic but different patterns in the Eastern Pacific and the Southern Indian Ocean. The interannual and decadal leading modes are primarily linked to El Niño-Southern Oscillation (ENSO) and Pacific Decadal Oscillation (PDO), respectively. The TSDs-ENSO relationship has been steady during the entire 55-year period, but the TSDs-PDO relationship has experienced a breakdown in the 1980s. We find that the decadal variation of TSD in the Pacific is associated with the PDO sea surface temperature (SST) anomalies in the tropical eastern Pacific (PDO-E) while that in the Atlantic and the Indian Ocean is associated with the PDO SST anomalies in the western Pacific (PDO-W). However, the PDO-E and PDO-W SST anomalies are poorly coupled in the 1980s, and this “destructive PDO” pattern results in a breakdown of the TSDs-PDO relationship. The results here have an important implication for seasonal to decadal predictions of global TSD.
Data Description Article
Fengyun Meteorological Satellite Products for Earth System Science Applications
Di Xian, Peng Zhang, Ling Gao, Ruijing Sun, Haizhen Zhang, Xu JIA
, Available online   , Manuscript accepted  03 February 2021, doi: 10.1007/s00376-021-0425-3
With the progress of satellite data assimilation in the 1990s, a combination of meteorological satellites and numerical models has changed the way scientists understand the earth. With the evolution of the numerical weather prediction models to the earth system models, meteorological satellites will play a more important role in the Earth sciences in the future. As part of the space-based infrastructure, the Fengyun (FY) meteorological satellites have contributed to Earth science sustainably studies through an open data policy and a stable data quality since the first launch of the FY-1A satellite in 1988. The capability of earth system monitoring was greatly enhanced after the second-generation polar orbiting FY-3 satellites and geostationary orbiting FY-4 satellites were developed. Meanwhile, the quality of the products generated from the FY-3 and FY-4 satellites are comparable to the well-known MODIS products.FY satellite data have been utilized broadly in weather forecasting, climate and climate change investigations, environmental disaster monitoring, etc. This article reviewed the instruments mounted on the FY satellites. Sensor-dependent level 1 products (radiance data) and inversion algorithm-dependent level 2 products (geophysical parameters) have been introduced. As an example, some typical geophysical parameters, such as wild fires, lightning, vegetation indices and aerosol products, have been demonstrated and validated by in situ observations and other well-known satellite products. To help users access the FY products, a set of data sharing systems have been developed and operated. The newly developed data sharing system based on cloud technology has been illustrated to improve the efficiency of data delivery.
The Assessment of Global Surface Temperature Change from 1850s: The C-LSAT2.0 Ensemble and the CMST-Interim Datasets
Wenbin SUN, Qingxiang LI, Boyin HUANG, Jiayi CHENG, Zhaoyang SONG, Haiyan LI, Wenjie DONG, Panmao ZHAI, Phil JONES
, Available online   , Manuscript accepted  14 January 2021, doi: 10.1007/s00376-021-1012-3
Based on C-LSAT2.0, using high- and low-frequency components reconstruction methods, combined with observation constraint masking, a reconstructed C-LSAT2.0 with 756 ensemble members from the 1850s to 2018 has been developed. These ensemble versions have been merged with the ERSSTv5 ensemble dataset, and an upgraded version of the CMST-Interim dataset with 5° × 5° resolution has been developed. The CMST-Interim dataset has significantly improved the coverage rate of global surface temperature data. After reconstruction, the data coverage before 1950 increased from 78%−81% of the original CMST to 81%−89%. The total coverage after 1955 reached about 93%, including more than 98% in the Northern Hemisphere and 81%−89% in the Southern Hemisphere. Through the reconstruction ensemble experiments with different parameters, a good basis is provided for more systematic uncertainty assessment of C-LSAT2.0 and CMST-Interim. In comparison with the original CMST, the global mean surface temperatures are estimated to be cooler in the second half of 19th century and warmer during the 21st century, which shows that the global warming trend is further amplified. The global warming trends are updated from 0.085 ± 0.004°C (10 yr)–1 and 0.128 ± 0.006°C (10 yr)–1 to 0.089 ± 0.004°C (10 yr)–1 and 0.137 ± 0.007°C (10 yr)–1, respectively, since the start and the second half of 20th century.
Western North Pacific Tropical Cyclone Database Created by the China Meteorological Administration
Xiaoqin LU, Hui YU, Ming YING, Bingke ZHAO, Shuai ZHANG, Limin LIN, Lina BAI, Rijin WAN
, Available online   , Manuscript accepted  22 October 2020, doi: 10.1007/s00376-020-0211-7
This paper describes the access to, and the content, characteristics, and potential applications of the tropical cyclone (TC) database that is maintained and actively developed by the China Meteorological Administration, with the aim of facilitating its use in scientific research and operational services. This database records data relating to all TCs that have passed through the western North Pacific (WNP) and South China Sea (SCS) since 1949. TC data collection has expanded over recent decades via continuous TC monitoring using remote sensing and specialized field detection techniques, allowing collation of a multi-source TC database for the WNP and SCS that covers a long period, with wide coverage and many observational elements. This database now comprises a wide variety of information related to TCs, such as historical or real-time locations (i.e., best track and landfall), intensity, dynamic and thermal structures, wind strengths, precipitation amounts, and frequency. This database will support ongoing research into the processes and patterns associated with TC climatic activity and TC forecasting.
CAS-LSM Datasets for the CMIP6 Land Surface Snow and Soil Moisture Model Intercomparison Project
Binghao JIA, Longhuan WANG, Yan WANG, Ruichao LI, Xin LUO, Jinbo XIE, Zhenghui XIE, Si CHEN, Peihua QIN, Lijuan LI, Kangjun CHEN
, Available online   , doi: 10.1007/s00376-021-0293-x
The datasets of the five Land-offline Model Intercomparison Project (LMIP) experiments using the Chinese Academy of Sciences Land Surface Model (CAS-LSM) of CAS Flexible Global Ocean-Atmosphere-Land System model version g3 (CAS FGOALS-g3) are presented in this study. These experiments were forced by five global meteorological forcing datasets, which contributed to the framework of the Land Surface Snow and Soil Moisture Model Intercomparison Project (LS3MIP) of CMIP6. These datasets have been released on the Earth System Grid Federation node. In this paper, the basic descriptions of the CAS-LSM and the five LMIP experiments are shown. The performance of the soil moisture, snow, and land-atmosphere energy fluxes was preliminarily validated using satellite-based observations. Results show that their mean states, spatial patterns, and seasonal variations can be reproduced well by the five LMIP simulations. It suggests that these datasets can be used to investigate the evolutionary mechanisms of the global water and energy cycles during the past century.
News & Views (invited)
Koo Chen-Chao and the Early Numerical Weather Prediction Experiments in China
Jianhua Lu
, Available online   , Manuscript accepted  26 January 2021, doi: 10.1007/s00376-021-0268-y
While the first successful numerical weather prediction (NWP) project led by Charney and von Neumann has been widely known, little is known by the international community about the development of NWP during the 1950s in China. Here, a detailed historical perspective on the early NWP experiments in China is provided. The leadership in NWP of the late Prof. KOO Chen-chao, a protégé of C. G. Rossby in University of Stockholm during the late 1940s and a key leader of modern meteorology (particularly in atmospheric dynamics and physics) in China during the 1950s-1970s, is highlighted. The unique contributions to NWP by Koo and his students, such as the ideas of formulating NWP as an “evolution” problem, in which the past data over multiple time steps are utilized, rather than an initial-value problem, and on cybernetic aspect of atmospheric processes, i.e., regarding the motion of atmosphere at various time scales as an optimal control system, are also emphasized.
Invited Review
Spatial and temporal distributions and sources of anthropogenic NMVOCs in the atmosphere of China: a review
Fanglin Wang, Wei Du, shaojun lv, Zhijian DING, Gehui Wang
, Available online   , Manuscript accepted  19 January 2021, doi: 10.1007/s00376-021-0317-6
As the key precursors of O3, anthropogenic non-methane volatile organic compounds (NMVOCs) have been studied intensively. This paper performed a meta-analysis on the spatial and temporal variations, roles in the photochemical reactions and their sources of NMVOCs in China, based on published researches. The results showed that both non-methane hydrocarbons (NMHCs) and oxygenated VOCs (OVOCs) in China have higher mixing ratios in the east developed cities than those in the central and western areas, with a decreasing trend in the developed cities such. Alkanes are the most abundant NMHCs species in all reported sites while formaldehyde is the most abundant OVOCs. OVOCs have the highest mixing ratios in summer and the lowest in winter, being opposite to NMHCs. Among all NMVOCs, the top eight species account for 50 ~ 70% of the total ozone formation potential (OFP) with different compositions and contributions in different areas. In devolved regions, OFP-NMHCs are the highest in winter while OFP-OVOCs are the highest in summer. Based on PMF analysis, vehicle exhaust, industrial, and solvent usage in China are the main sources for NMHCs. However, the emission trend analysis showed that solvent usage and industrial will exceed vehicle exhausts and become the two major sources of NMVOCs in near future. Based on the meta-analysis conducted by this work, we believe that the oxidation mechanisms of atmospheric OVOCs as well as high spatial resolution of emission inventories of NMVOCs should be considered preferentially for the future studies on NMVOCs in China
Anthropogenic Effects on Biogenic Secondary Organic Aerosol Formation
Li XU, Lin DU, Narcisse T. TSONA, Maofa GE
, Available online   , Manuscript accepted  17 November 2020, doi: 10.1007/s00376-020-0284-3
Anthropogenic emissions alter biogenic secondary organic aerosol (SOA) formation from naturally emitted volatile organic compounds (BVOCs). We review the major laboratory and field findings with regard to effects of anthropogenic pollutants (NOx, anthropogenic aerosols, SO2, NH3) on biogenic SOA formation. NOx participate in BVOC oxidation through changing the radical chemistry and oxidation capacity, leading to a complex SOA composition and yield sensitivity towards NOx level for different or even specific hydrocarbon precursors. Anthropogenic aerosols act as an important intermedium for gas–particle partitioning and particle-phase reactions, processes of which are influenced by the particle phase state, acidity, water content and thus associated with biogenic SOA mass accumulation. SO2 modifies biogenic SOA formation mainly through sulfuric acid formation and accompanies new particle formation and acid-catalyzed heterogeneous reactions. Some new SO2-involved mechanisms for organosulfate formation have also been proposed. NH3/amines, as the most prevalent base species in the atmosphere, influence biogenic SOA composition and modify the optical properties of SOA. The response of SOA formation behavior to these anthropogenic pollutants varies among different BVOCs precursors. Investigations on anthropogenic–biogenic interactions in some areas of China that are simultaneously influenced by anthropogenic and biogenic emissions are summarized. Based on this review, some recommendations are made for a more accurate assessment of controllable biogenic SOA formation and its contribution to the total SOA budget. This study also highlights the importance of controlling anthropogenic pollutant emissions with effective pollutant mitigation policies to reduce regional and global biogenic SOA formation.
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