60 heavy rainfall Northeast China Cold Vortex (HR-NCCV) events during 1991–2024 are objectively classified into three types by using K-means clustering, namely the Northern (Cluster-N), Central (Cluster-C), and Southern (Cluster-S) clusters. The differences in structural characteristics and energy conversion associated with dry intrusion during the development of HR-NCCVs are further investigated. Cluster-N originates from a southward splitting polar vortex and have short lifetimes, with precipitation mainly over Heilongjiang and Jilin Provinces. Cluster-C forms to the west of Northeast China and exhibit the greatest persistence in association with a double-blocking circulation pattern. Precipitation is concentrated over Liaoning Province. Cluster-S develops from an eastward-moving short-wave trough originating near Lake Balkhash and evolve into an elongated structure extending offshore, with precipitation over the Shandong Peninsula. Regarding dry intrusion, Cluster-N shows the strongest, fastest and deepest downward penetration but with rapid decay and the shortest duration. Cluster-C exhibits slightly weaker in both intensity and penetration depth but more persistent intrusion than Cluster-N. Cluster-S features the weakest and shallowest intrusion, with limited and short-lived effects on the lower troposphere. Furthermore, all three NCCV types exhibit rapid baroclinic energy conversion (CP), whereas differences in precipitation intensity and duration are primarily governed by efficiency and persistence of anomalous convective heating (CQ). Cluster-N is characterized by efficient CP but delayed CQ, causing rapid but short-lived development. Cluster-C shows the strongest CP–CQ coupling, sustaining unstable energy accumulation to produce the most intense, persistent precipitation. Conversely, Cluster-S has relatively weak CP and CQ, resulting in the weakest precipitation.

Against the backdrop of global warming, East Asian summer temperature exhibits distinct decadal variability, making its reliable prediction crucial for climate adaptation and mitigation; however, current climate models in the Coupled Model Intercomparison Project Phase 6 Decadal Climate Prediction Project are limited in both predictive skills and the representation of physical processes. To address these limitations, this study integrates the decadal increment (DI) method with observational constraint method to improve the decadal predictive skills of the climate models. The critical precursor signals are identified as the preceding 4-year summer DIs of sea surface temperature (SST) in the Kuroshio Extension (KOE) and subtropical western North Pacific for DIs of East Asian summer near-surface air temperature (DI_TAS) during 1941–2023. After correction, the predictive skill of East Asian summer temperature in climate models for 1970–2019 is substantially enhanced. Compared with the raw hindcasts of the multi-model ensemble, the anomaly correlation coefficient of corrected results for the phase prediction of DI_TAS increases from 0.76 to 0.86 (13.16% improvement), while the mean square skill score (MSSS) for amplitude prediction rises from 0.53 to 0.74 (28.38% improvement). For the final 5-year average temperature prediction, the MSSS increases from 0.63 to 0.93 (47.62% improvement), with the associated prediction uncertainty range reduced by approximately 50% on average. Notably, the corrections successfully capture decadal regime shifts with a timing error of less than two years. This study advances decadal climate prediction by mitigating deficiencies in the representation of observed SST-temperature linkages. The proposed correction approach outperforms the conventional climate drift correction method and provides a scalable framework for improving predictions of other climate variables and regions.

Based on the monthly ERA5 and other reanalysis data from 1980 to 2024, this study investigates the physical mechanisms by which Barents Sea ice and the North Atlantic Tripole (NAT) jointly drive drought-flood abrupt alternations (DFAAs) over the Huanghe-Huaihe basin (HHB) during June and July, and discusses how they contribute to the record-breaking DFAA in summer 2024. The key results are as follows: Excessive Barents Sea ice in April can persist until June, triggering upper-level Rossby wave trains via sea ice-atmosphere coupling, which leads to the anomalous anticyclone over northern China alongside a barotropic cyclone over the East China Sea. This process blocks the transportation of cold air and moisture, inducing drought in the HHB. Concurrently, the spring NAT anomalies can persist into July, stimulating upper-level Rossby wave trains that generate the anticyclone over central China, promoting upward atmospheric motion. Additionally, positive tropical sea surface temperature anomalies (SSTAs) associated with the NAT trigger equatorial Rossby wave trains, leading to the Pacific-Japan pattern (PJ) conducive to enhanced precipitation over the HHB. The drought induced by above-average sea ice is predominantly confined to June, whereas the NAT-driven rainfall primarily occurs in July. The sequential influence finally results in DFAAs over the HHB. Notably, in 2024, Barents Sea ice and the NAT attained their second-highest recorded levels since the onset of the twenty-first century and 1980, respectively, thereby contributing to the unprecedented DFAA in the HHB.

In October 2023, northern China experienced a record-breaking extreme high temperature event (EHTE), with monthly mean surface air temperature (SAT) 3℃ above normal, posing a grand threat to crop production and ecological environment. The primary driver of the EHTE was an anomalous large-scale barotropic high-pressure (anticyclone) centered over Lake Baikal. The lower to middle levels northerlies over the southeastern flank of the anomalous anticyclone suppressed air moisture and cloud cover over northern China, which increased downward shortwave radiation and consequently elevated SAT in the region. A comparison of global circulation and sea surface temperature (SST) anomalies in October 2023 with historical anomalies associated with SAT over northern China during 1979–2022 suggests that abnormal North Atlantic tripole (NAT) SST anomalies and the Indo-Pacific zonal SST gradient (IPG) were potential origins of the record-breaking EHTE. Further observations and numerical simulations demonstrated both the NAT and IPG triggered downstream- and poleward-propagating Rossby wave trains. These wave trains contributed to the formation of the anomalous high-pressure over Lake Baikal, leading to reduced cloudiness and elevated SAT over northern China. A physical-based prediction model, utilizing the precursors from the two oceanic origins, outperformed two dynamical models with lead times from zero to three months. It successfully predicted the record-breaking EHTE in 2023, a feat that the dynamical models failed to achieve.

Precipitation data provided by the China Meteorological Administration and ERA5 reanalysis data from 1990 to 2020 are used to analyse the influence of +Silk Road/-East Asia-Pacific (+SR/-EAP) combined pattern on persistent rainfall during the pre-rainy season in South China (PRPSC) and its associated energetic conversion. The results indicate that the typical +SR/-EAP combined pattern is significantly correlated with the PRPSC. The development of the combined pattern results in the southward shift of the western Pacific subtropical high (WPSH), facilitating the transport of water vapour from the western Pacific to South China. Meanwhile, the South Asian high (SAH) intensifies and extends eastward, with its eastern boundary overlapping the western boundary of the WPSH along the East Asian coast, favouring the precipitation in South China. During the persistence of the combined pattern, integrated moisture flux convergence occurs in South China, with positive vorticity in the lower levels and negative vorticity in the upper levels, resulting in increased precipitation. The +SR/-EAP combined pattern develops by extracting energy from the basic flow via both barotropic and baroclinic energy conversions. However, since the barotropic energy conversion is relatively small and inefficient, the maintenance of the combined pattern mainly relies on baroclinic energy conversion to obtain available potential energy from the basic flow. Barotropic and baroclinic energy conversions primarily occur in regions north of 30 degrees N, effectively supporting the anomalous centres of the +SR/-EAP pattern in mid-to-high latitudes. Baroclinic energy conversion is positive in both the upper and lower troposphere. However, the energy conversion in the upper troposphere exceeds that in the lower, which shows that the baroclinic energy conversion contributes more significantly to the maintenance of the +SR pattern.

Extreme winter weather in North America is strongly influenced by atmospheric intraseasonal oscillations (ISOs), yet the dominant modes of intraseasonal variability in this region remain insufficiently documented. Using upper-level meridional winds from the ERA5 reanalysis dataset, this study identifies two leading ISO modes: a quasi-biweekly mode (10–22 days) and a quasi-monthly mode (23–50 days). Both modes share an equivalent barotropic vertical structure and are sustained primarily by baroclinic energy conversion, but they differ markedly in spatial structure, propagation, and climatic impacts. The quasi-biweekly mode manifests as a circumglobal wave train with zonal wave number 6, propagating eastward along the subtropical Asian jet in the Eastern Hemisphere and following a great circle-like pathway in the Western Hemisphere. It produces eastward-propagating precipitation and surface air temperature anomalies across North America. By contrast, the quasi-monthly mode is confined to the Western Hemisphere and exhibits a quasi-stationary Pacific-North America (PNA)-like wave train pattern, originated from westward-propagating precipitation anomalies over the western tropical Pacific. It induces a dipole pattern of precipitation and temperature anomalies between western and eastern North America. Distinguishing between these two modes provides new insights into sources of subseasonal predictability for extreme weather in North America.

The classification of Northeast China Cold Vortex (NCCV) activity paths provides a fundamental framework for understanding their characteristics, but the formation mechanisms of NCCVs with distinct paths remain insufficiently explored. Based on the 6-hourly ERA5 reanalysis data from 1991 to 2022, this study develops an objective identification method for NCCVs during May to July, classifies their activity paths using the K-means clustering method, and investigates their atmospheric circulation configurations and responses to the background flow. The main conclusions are as follows: (1) The NCCV activity paths can be classified into four types: the southern-positioned type (type A) originating over the Mongolian Plateau and moving eastward into the ocean; the northwestward-activity type (type B) primarily occurring between the Greater and Lesser Khingan Mountains with limited propagation distances; the northeastward-activity type (type C) concentrated to east of Northeast China (NEC) and the irregular type (type D) characterized by sparse occurrence and scattered distribution. (2) Differences in the activity paths of NCCVs manifest in the atmospheric circulation features and evolutionary characteristics. Type A and type B NCCVs mainly affect the southern and northern NEC region, respectively, while type C NCCVs impact east of Heilongjiang Province. (3) The background flow modulates wave propagation and eddy generation by regulating Rossby wave energy accumulation and dispersion in different regions. Variations in the double-jet structure’s position, along with differences in the location of zonal wind deceleration and acceleration regions and the intensity of zonal wind anomaly, jointly facilitate local baroclinic eddies formation at different locations, thereby leading to diverse activity paths of NCCVs.

AbstractThe summer monsoon onset over the Bay of Bengal and South China Sea signals the beginning of the Asian summer monsoon, critical for local fisheries, agriculture and livelihoods, so communities are concerned about its potential changes under global warming. Previous projections have suggested a delay, but the extent of this delay remains uncertain, undermining the reliability of the projections. Here, we show a significant correlation between the projected shift in Bay of Bengal/South China Sea monsoon onset and present‐day sea surface temperature (SST) simulation over the western Pacific (WP). This emergent relationship arises from the spread of the precipitation response over the western‐central Pacific to WP SST, as more precipitation induces stronger tropical upper‐tropospheric warming, increasing westerly vertical shear near South Asia, and facilitating the onset delay. The rectified projections indicate that the delayed shift is almost halved compared to raw projections, and the intermodel uncertainty is reduced by 30%.

The co-occurrence of the East Asia–Pacific (EAP) and the Silk-Road (SR) modes is found to have a more pronounced impact on summer rainfall over southern China compared to any single mode, causing huge economic losses. Based on daily ERA5 reanalysis data, this study identifies 25 typical positive EAP (+ EAP) and negative SR (-SR) combination pattern events during the summer of 1979–2023. The + EAP/-SR combination pattern is accompanied by significantly enhanced rainfall over the Yangtze-Huaihe River Basin (YHRB) compared to the other three combination patterns. The coupling of the + EAP and -SR modes contributes to a strengthened western Pacific subtropical high and a deep cyclonic system over northeastern Asia, favoring the maintenance of the Mei-yu front and enhanced rainfall over the YHRB. The energy budget and dynamical mechanisms of the + EAP/-SR combination pattern are further analyzed. The + EAP/-SR combination pattern can efficiently extract available potential energy through baroclinic energy conversion. In addition, the co-occurrence of suppressed convection over the Philippine Sea (SCPS) and enhanced rainfall over southern Europe (ERSE) is conducive to the + EAP/-SR combination pattern. On the one hand, the SCPS and the associated diabatic cooling effect could generate a poleward Rossby wave train, promoting the formation of the + EAP mode. On the other hand, the ERSE enhances divergence anomalies and negative Rossby wave source in the upper troposphere, contributing to the propagation of the -SR mode along the midlatitude westerly jet. The development of the -SR mode also strengthens the anomaly center of the + EAP mode over the Okhotsk region. A linear baroclinic model is applied to verify the above-mentioned physical mechanisms. Model results support the crucial roles of the SCPS and the ERSE and also confirm the contribution of the -SR mode to the + EAP mode over the Okhotsk region. These findings deepen our understanding of the + EAP/-SR combination pattern and have important implications for subseasonal prediction of summer rainfall over the YHRB.

ERA5 reanalysis data, precipitation data from China, and National Oceanic and Atmospheric Administration (NOAA) monthly sea surface temperature (SST) data are used to analyse the impact of the meridional position of the East Asian subtropical jet (EASJ) on summer precipitation in China and its correlation with Atlantic SST. The results indicate that when the EASJ significantly shifts northward, the western North Pacific subtropical high (WNPSH) weakens with an eastward displacement. Upper-level convergence and moisture divergence, corresponding to descending motion, lead to decreased precipitation in the Yangtze River Valley (YRV). Meanwhile, upper-level divergence occurs over South China (SC), the Hexi Corridor (HC), and Northeast China (NEC), where moisture converges and ascends, favouring an increase in precipitation. Conversely, when the EASJ undergoes a significant southward shift, the WNPSH strengthens and expands westward. Opposing atmospheric circulation patterns in these four regions result in reversed precipitation anomalies compared with those observed when the jet shifts northward. The meridional position of the EASJ is closely related to the summer subtropical Atlantic SST. The positive (negative) SST anomaly (SSTA) over the subtropical Atlantic induces negative (positive) geopotential height anomaly in the upper troposphere over the North Atlantic by modulating the atmospheric meridional circulation. Geopotential height anomalies trigger eastward-propagating Rossby waves, generating anomalous cyclones and anticyclones over East Asia. These anomalous cyclones and anticyclones lead to zonal wind anomalies, which alter the strength of the westerlies on both sides of the climatological jet axis, thereby changing the jet's meridional position. Additionally, the difference in the propagation direction of wave activity flux between positive and negative SSTA alters the distribution of wave energy convergence and divergence in the EASJ region, further affecting the intensity of the average westerly winds on both sides of the climatological jet axis, ultimately producing the changes in the meridional position of the EASJ.

The upper and lower-level circulations can be divided into four distinct modes based on ERA5 daily reanalysis data. The impact of these patterns on the summer persistent precipitation (SPP) in the Jianghuai River Basin (JRB) is investigated, with the '-SR (Silk Road)/+EAP (East Asia-Pacific)' mode identified as the most favourable for triggering SPP. The main manifestations are as follows: (1) From 1981 to 2020, 29.4% (30.7%) of extreme precipitation days (the frequencies of persistent extreme precipitation) are related to the '-SR/+EAP' mode, indicating the importance of the '-SR/+EAP' mode to the SPP in the JRB. (2) The '-SR' pattern accelerates the westerly jet, leading to strong divergence over the JRB. Concurrently, the eastward movement of the South Asia High and westward shift of the Western Pacific subtropical high (WPSH) create conditions favourable for SPP in the JRB. (3) Abundant water vapour, facilitated by strong moisture convergence and upward motion, significantly contributes to SPP in the JRB. We classified the teleconnection patterns and analyzed the impact of different circulation patterns on summer persistent precipitation (SPP) in the Jianghuai River Basin (JRB). Results indicate that circulation patterns can be roughly divided into four modes. Among them, the '-SR/+EAP' mode is most conducive to triggering SPP in the JRB.image

In this study, the characteristics of azimuthally asymmetric equivalent potential temperature ( θ e ) distributions in the outer core of tropical cyclones (TCs) encountering weak and strong vertical wind shear are examined using a Lagrangian trajectory method. Evaporatively forced downdrafts in the outer rainbands can transport low-entropy air downward, resulting in the lowest θ e in the downshear-left boundary layer. Quantitative estimations of θ e recovery indicate that air parcels, especially those originating from the downshear-left outer core, can gradually revive from a low entropy state through surface enthalpy fluxes as the parcels move cyclonically. As a result, the maximum θ e is observed in the downshear-right quadrant of a highly sheared TC. The trajectory analyses also indicate that parcels that move upward in the outer rainbands and those that travel through the inner core due to shear make a dominant contribution to the midlevel enhancement of θ e in the downshear-left outer core. In particular, the former plays a leading role in such θ e enhancements, while the latter plays a secondary role. As a result, moist potential stability occurs in the middle-to-lower troposphere in the downshear-left outer core.

South China Sea (SCS) experienced an exceptionally long-lived marine heatwave (MHW) event in summer 2020, which broke the historical records in terms of its time duration since 1982. This long-lasting MHW was primarily attributed to the combined effects of the seasonal cycle (SC) and 30–60-day intraseasonal oscillation (ISO) components of anomalous atmospheric circulations. During the SC developing phase, the superimposed anticyclonic circulation regimes of the SC and 30–60-day ISO jointly contributed to the first warming sea surface temperature (SST) peak over the central SCS in July, via the combined effects of net downward shortwave radiation (SWR) and latent heat flux (LHF) anomalies. In contrast, during the SC decaying phase, the SCS MHW-related warming SST tendency was mostly due to 30–60-day ISO signals. During the growth phase of ISO, the joint warming effect of the SWR and LHF anomalies was the dominant factor maintaining the SCS MHW. In the decaying phase of 30–60-day ISO, however, the second MHW-related warming peak around Beibu Gulf in September was mainly contributed by the sharply reduced LHF loss due to strong southwesterly anomalies over the northern SCS on the 30–60-day timescale. The varying SC component plays a crucial role in the occurrence and maintenance of MHWs, while the 30–60-day ISO can effectively regulate the development and pattern of SCS MHWs. These results suggest that, besides the vital role of the SC component, the 30–60-day ISO should also be considered for fully understanding the extreme MHW events.

江淮流域夏季洪涝灾害主要归因于大气环流异常的稳定维持.不同大气遥相关的低频振荡及其协同变化对江淮流域夏季降水的影响机理是大气科学领域热点问题之一.利用ERA5逐日再分析资料和中国气象局提供的逐日站点降水资料,揭示了"丝绸之路"(SR)型和东亚—太平洋(EAP)型遥相关的低频特征及其对江淮流域夏季降水的影响机理.结果表明:SR型和EAP型遥相关的10～30 d低频周期与江淮流域夏季降水关系密切,SR型和EAP型遥相关各低频系统都经历了正负位相转换并逐渐达到峰值(谷值).其主要表现为:①10～30 d低频200 hPa等压面经向风沿西风急流呈偏北风与偏南风的交替分布,当SR型达到负位相峰值时,江淮流域为偏北风控制,中纬度低频气旋加强,加速西风急流;②10～30 d低频西太平洋副热带高压西伸东退、南亚高压东移西撤,二者相向而行,在峰值位相重叠于对江淮流域降水有利的位置;③由东亚沿岸向西北移动的向外长波辐射异常波列亦表现出显著的10～30 d低频振荡特征,处于峰值位相时,向外长波辐射在江淮流域为负异常,有利于江淮流域降水;④10～30 d低频低层正涡度、高层负涡度的配置有利于低层辐合、高层辐散,导致上升运动增强,进而触发江淮流域低频降水.

Based on a set of hindcast experiments from 2011 to 2020, the prediction skills of the Chinese Academy of Meteorological Science Climate System Model (CAMS‐CSM) climate forecast system (CFS) on the abrupt changes and characteristic processes associated with the South China Sea summer monsoon (SCSSM) establishment are evaluated. We studied predictions for three different lead times, that is, LT1‐30, LT31‐60 and LT61‐90. The CAMS‐CSM CFS captures the climatological SCSSM onset date at all lead times, while the prediction skill of the SCSSM onset index decreases with the increasing lead times. The features of abrupt changes and characteristic processes related to the SCSSM establishment can be generally reproduced in the predictions, but different biases exist at three lead times. Besides, the CAMS‐CSM CFS provides higher skill on the transition of the zonal wind shear (ZWS) than that of meridional temperature difference (MTG). The transition date of MTG can only be accurately predicted at LT1‐30, indicating the limited ability of predicting temperature. Further results confirm that the CFS cannot well capture the eastward withdrawal of the western North Pacific subtropical high on late onset years, thereby leading a poorer prediction skill than early onset years. In addition, skillful prediction on the eastward extension of westerlies from the equatorial Indian Ocean to SCS also contributes to increase predictability of SCSSM onset.

This study evaluated nearly 60 years of spatio-temporal variation in the pan evaporation and identified the correlations between meteorological elements and evaporation and dominant control factors in evaporation variationin in the Badain Jaran Desert.The research findings are: (1) The pan evaporation showed notable spatial differences in distribution and progression. The mean annual evaporation declined from east to west, peaking at 4308.4mm at the desert's northern margin; (2) The annual evaporation displayed significantly varied trends across the desert. At the northwestern and southern margins of the desert, where the evaporation paradox was observed, the annual evaporation showed a gradual downward trend, with decreasing rates of 162mm/10a and 187mm/10a, respectively;The annual evaporation departures at both locations exhibited turning points in 1987, dominated by negative values after this year. In contrast, at the northern and western margins of the desert, the annual evaporation exhibited significantly upward trends, with increasing rates of 132mm/10a and 105mm/10a, respectively. The annual evaporation departures at both locations showed turning points in 1996, dominated by positive values after 1996; (3) In the 20th century, the annual evaporation displayed notable fluctuations coupled with considerably varied trends. In the 21st century, however, the annual evaporation demonstrated roughly uniform trends, increasing from 1999 to 2009, followed by a minor decline from 2009 to 2017. The complete correlation analysis indicated that the evaporation is significantly correlated with the average temperature, wind speed, sunshine duration, and relative humidity. As revealed by the linear regression analysis, at the northern and western margins of the desert, the dominant controlling factor in the increased evaporation is the increase in the average temperature. In contrast, at the northwestern and southern margins of the desert, where the evaporation paradox occurs, the dominant controlling factor in the decreased evaporation is the decrease in the average wind speed.

利用ERA-Interim逐日再分析资料及中国753站逐日降水资料,对2008年3月23-28日的东北冷涡天气过程进行诊断分析,并探讨了冷涡降水的主要影响因子.结果表明:1)与夏季冷涡过程不同,此次初春冷涡过程高层环流场由经向环流向纬向环流转变;冷涡发展初期,经向环流的建立使得冷涡向南移动,而成熟阶段冷涡后部的低槽引导冷空气向冷涡输送,导致了冷涡环流的维持.2)亚欧大陆上空强阻塞形势的发展是初春东北冷涡形成的关键因子;乌拉尔山和鄂霍次克海阻塞高压分别受到前期北大西洋和热带太平洋海温异常的调控,为冷涡向南发展维持提供了有利的环流背景,并影响了高低空急流的配置,有利于冷涡降水的形成.3)涡度场和温度场的高低空配置使得东北冷涡发展成深厚的环流系统,干侵入对冷涡的形成和维持同样有重要作用.冷涡环流的发展为东北地区降水提供了有利的水汽和垂直运动条件,冷暖平流交汇引起的锋面过程则促进大范围降水的形成.

Intimately related to the Asian summer monsoon, the Mei-yu rainfall is also strongly influenced by atmospheric circulation in the middle to high latitudes, especially the Northeast Cold Vortex (NECV), and thus making prediction of the Mei-yu rainfall a challenging issue. The prediction skills of the CAMS-CSM (full name as the Chinese Academy of Meteorological Sciences Climate System Model) for a NECV event at the early onset of 2020 Mei-yu season and the associated Mei-yu rainfall are evaluated. Hindcast experiments with two different horizontal resolutions are employed to assess the climate model in predicting the synoptic system. The ERA5 reanalysis data and the CN05.1 precipitation data are adopted for comparison. Results indicate that both the middle-resolution (T106, ∼1°) and high-resolution (T255, ∼0.47°) version of the CAMS-CSM model are able to capture this NECV event, while showing some biases on its intensity, duration and location. Overpredictions in the strength and duration of the NECV are found in the T106 version, which could be attributed to a stronger dry invasion from higher levels during the development stage, an intensified Okhotsk blocking high, and a weakened upper-level jet at the decaying phase. As for the T255 version, a stronger NECV is predicted further north than the reanalysis, and sources of the biases are identified, including northward displacements of the high-level dry invasion and the westerly jet. Further investigation suggests that the T106 version performs better than the T255 version in predicting the Mei-yu rainfall because of a more accurate prediction on the location of the NECV. Positive biases in the cold advection and Mei-yu front are identified in the T106 version, contributing to a stronger Mei-yu rainfall than the observation. The Mei-yu rainfall is poorly predicted in T255 version due to prediction errors in the location of the NECV-induced cold advection. Therefore, improving the prediction skill of the NECV, not only its intensity but also location, is of vital significance to achieve a better prediction of the Mei-yu rainfall.

为避免直接同化时反射率非线性观测算子线性化带来的线性近似误差问题,目前许多研究和业务中还常采用间接同化方式来同化雷达反射率因子,其通过背景场温度判定水凝物类型及比例.基于一种实时天气背景依赖的雷达反射率因子间接同化方案,进行了4次暴雨过程(2次强对流,2次锋面)的循环同化及预报试验.结果表明:对于强对流暴雨个例,相对于传统温度判定方案,天气背景依赖方案的温度预报误差更小、降水预报评分更高,而对于锋面过程区别不明显;进一步机理分析表明,对于强对流暴雨个例,由于背景依赖方案在同化反射率因子时引入了实时天气背景信息,使得分析场水凝物结构能够更好表征实际对流特征且与其它模式变量更为协调,进而改善了模式预报的热、动力及水汽条件,从而改善了降雨预报效果;而锋面暴雨由浅对流过程占主导,水凝物以低层的雨水为主导,冰相水凝物对于该过程的影响较小,由于两种方案反演的雨水结构和量级均相似,因此降雨预报差异较小.

Long-range transport (LRT) and local accumulation (LA) are key atmospheric physical processes affecting air pollution formation, and their impacts on surface air pollution have been extensively researched. Due to the lack of vertical observations and emphases on model simulations, the characteristics and regional sources of black carbon (BC) aerosol profiles have been relatively understudied. In this study, the chemistry-coupled Weather Research and Forecasting model (WRF-Chem) with a BC source-tagging method was used to quantify BC source contributions (considering 18 geographical regions over east Asia, including 3 subregions over the Yangtze River Delta (YRD)) during a November 2017 pollution event in the YRD, China. In this event, the YRD mainly experienced a uniform pressure field, stable weather and weak wind fields. During the uniform high-pressure period, the dominant contribution to surface BC in each sub-region was from that region itself (70.6 %-98.2 %), with little intra- and inter-regional transport. During the uniform low-pressure period, highly variable contributions to the surface BC from intra-regional transport within the YRD (0.05 %-65.9 %) and inter-regional transport outside the YRD (mostly from Anhui (AH) to the west of the YRD, 0.37 %-23.9 %) were simulated. In the vertical direction, the dominant contributors were local YRD sources (73.8 %-94.2 %) below the atmospheric boundary layer (ABL). The inter-transport contributions increased extensively above the ABL. As a westerly trough crossing, a long-range inter-regional transport from South China (SCHN, 3.3 %) and the North China Plain (NCP, 2.7 %) was simulated above the ABL. We found that when the surface experienced similar stable weather conditions, the weather conditions in the upper air may have been quite different, resulting in significant differences in the regional transport of BC in the upper ABL. This study provides a reference for improving air quality from the local scale to the regional scale.