Variations of the Summer Somali and Australia Cross-Equatorial Flows and the Implications for the Asian Summer Monsoon

The temporal variations during 1948-2010 and vertical structures of the summer Somali and Australia cross-equatorial flows （CEFs） and the implications for the Asian summer monsoon were explored in this study. The strongest southerly and northerly CEFs exist at 925 hPa and 150 hPa level, respectively. The low-level Somali （LLS） CEFs were significantly connected with the rainfall in most regions of India （especially the monsoon regions）, except in a small area in southwest India. In comparison to the climatology, the low- level Australia （LLA） CEFs exhibited stronger variations at interannual time scale and are more closely connected to the East Asian summer monsoon circulation than to the LLS CEFs. The East Asian summer monsoon circulation anomalies related to stronger LLA CEFs were associ- ated with less water vapor content and less rainfall in the region between the middle Yellow River and Yangtze River and with more water vapor and more rainfall in southern China. The sea-surface tempera- ture anomalies east of Australia related to summer LLA CEFs emerge in spring and persist into summer, with implications for the seasonal prediction of summer rainfall in East Asia. The connection between the LLA CEFs and East Asian summer monsoon rainfall may be partly due to its linkage with E1 Nino-Southern Oscillation. In addition, both the LLA and LLS CEFs .exhibited interdecadal shifts in the late 1970s and the late 1990s, consistent with the phase shifts of Pacific Decadal Oscillation （PDO）.

苏南两次回流天气过程形势特征和降水相态分析

利用常规观测资料、0.25°×0.25°FNL资料、微波辐射计资料和风廓线雷达资料,对发生在苏南的两次回流天气过程的环流特征、大气层结特征等进行分析。结果表明:高纬度地区500 hPa是两槽一脊的环流形势,近地面层持续受东北风影响,西南暖湿气流在底层冷垫上爬升,是回流降雪天气形势;从东北平原回流南下的冷空气湿度小,在降水中只起到了“冷垫”的作用。中低层西南暖湿气流差异导致两次降雪强度存在差异;近地面层的降温在雨和雪的区分判别上影响更大,统计2012—2022年初苏南地区8个降雪个例发现,苏南地区,满足T_(850)≤-4℃,T_(925)≤-3℃,T_(1000)≤1℃,T_(2 m)≤2℃这样的温度阈值条件时开始雨转降雪;当1515 gpm≤H_(700-850)≤1575 gpm,1289 gpm≤H_(850-1000)≤1317 gpm时,相态易由雨转雪。中低层西南气流、底层东北风的加强,2000 m左右高度风场的转变,短波槽(或切变线)触发了不稳定能量的释放,导致降雪发生;当中低层西南气流减弱转为西北气流后,大气水汽含量降低,降雪结束。

New Evidences on the Climatic Causes of the Formation of the Spring Persistent Rains over Southeastern China

The spring persistent rains（SPR）over southeastern China（SEC）are a unique synoptic and climatic phenomenon in East Asia.A former study has found that the southwesterly flow which lies on the southeastern flank of the Tibetan Plateau（TP）is one of the deflected westerly flows of the TP,and it is suggested to be the direct climatic cause of SPR.This study found that the southwesterly flow is also highly correlated with the sensible heating of the southeastern TP in interannual variability,in addition to having a high correlation in seasonal variability.These facts suggest that the thermal forcing of the TP is another important climatic cause of SPR.Numerical sensitivity experiments further prove that the mechanical and thermal forcings of the TP are the climatic causes of the formation of the SPR.On the other hand,the Nanling Mountains and Wuyi Mountains（NWM）over southeastern China not only increase the SPR precipitation amount evidently,but also make the SPR rain belt move to the south by blocking the strong southwesterly flow.

The Record-breaking Mei-yu in 2020 and Associated Atmospheric Circulation and Tropical SST Anomalies

The record-breaking mei-yu in the Yangtze-Huaihe River valley(YHRV)in 2020 was characterized by an early onset,a delayed retreat,a long duration,a wide meridional rainbelt,abundant precipitation,and frequent heavy rainstorm processes.It is noted that the East Asian monsoon circulation system presented a significant quasi-biweekly oscillation(QBWO)during the mei-yu season of 2020 that was associated with the onset and retreat of mei-yu,a northward shift and stagnation of the rainbelt,and the occurrence and persistence of heavy rainstorm processes.Correspondingly,during the mei-yu season,the monsoon circulation subsystems,including the western Pacific subtropical high(WPSH),the upper-level East Asian westerly jet,and the low-level southwesterly jet,experienced periodic oscillations linked with the QBWO.Most notably,the repeated establishment of a large southerly center,with relatively stable latitude,led to moisture convergence and ascent which was observed to develop repeatedly.This was accompanied by a long-term duration of the mei-yu rainfall in the YHRV and frequent occurrences of rainstorm processes.Moreover,two blocking highs were present in the middle to high latitudes over Eurasia,and a trough along the East Asian coast was also active,which allowed cold air intrusions to move southward through the northwestern and/or northeastern paths.The cold air frequently merged with the warm and moist air from the low latitudes resulting in low-level convergence over the YHRV.The persistent warming in the tropical Indian Ocean is found to be an important external contributor to an EAP/PJ-like teleconnection pattern over East Asia along with an intensified and southerly displaced WPSH,which was observed to be favorable for excessive rainfall over YHRV.

一次季风潮爆发引致的区域性大暴雨过程分析

利用气象观测资料、卫星云图、雷达图以及其它物理量等,对2012年6月21至23日区域性暴雨天气过程进行分析,得出如下结论:这次暴雨过程发生在热带气旋东北移及南海季风槽北抬的背景下,沿海西南急流是这次大暴雨的直接影响系统;这次过程水汽主要来源是南海,降水主要发生在水汽通量大值中心的右边及右前方,本次大暴雨降水强弱与水汽通量、急流及地形等有极为吻合的对应关系。

Analysis of Rainfall Weather Process in Most of China from 3-6 October, 2021

Heavy rain is a common abnormal weather in China, which is prone to major natural disasters such as floods. By using China National Climate Center’s DERF2.0 (the second-generation product of monthly dynamic extended ensemble prediction) models and NCEP (National Centers for Environmental Prediction) data, and using synoptic and dynamic methods and other research methods, the rainfall weather process in most of China from October 3-6, 2021 is analyzed. The results show that: 1) this process had a long duration, large cumulative rainfall and strong extreme. 2) The warm and wet flow and the cold air intersected in the central and western regions of China and Northeast China, which resulted in a regional rainstorm process within ten days. 3) There was a low-level jet moving from Guizhou and Hunan to the south of Northeast China, bringing a lot of water vapor. To sum up, the rainfall process of this round has a certain relationship with the adjustment of atmospheric circulation.

DYNAMIC STUDY ON INFLUENCE OF INERTIAL GRAVITY WAVES INDUCED BY UNBALANCED FLOW ON MEIYU FRONT HEAVY RAIN

The Meiyu front heavy rain process in 1-3 June 2000 is numerically simulated in this paper, and results are then analyzed to show the effects of geostrophic balance collapse,unbalanced flow occurrence,low level jet (LLJ) development,and gravity waves genesis and propagation on the rainstorm.Analyses indicate that the sudden northwest movement of subtropical high may destruct the local geostrophic balance,leading to an increase in the local pressure gradient and the occurrence of ageostrophic flow,and meanwhile the adjustment of circulation starts to build a new balance.During the process,an LLJ and gravity waves appear correspondingly.The dispersion of unbalanced energy through the divergence/convergence of the geostrophic departure winds, promotes the propagation of strong wind cores along the LLJ,and the dispersion direction is influenced by the steering flow and the moisture concentration area.The development of LLJ is one of important conditions,which induces the heavy rain especially in the left front part of the jet where the convergence and shear of winds occur.It is also found that the genesis of disturbance, meso-vortex,and meso-convective system provides a favorable condition for the rainstorm.The above results are clearly illustrated by the high spatial and temporal resolution simulation data from a mesoscale numerical model.

SymPas:Symbolic Program Slicing

Program slicing is a technique for simplifying programs by focusing on selected aspects of their behavior.Current mainstream static slicing methods operate on dependence graph PDG(program dependence graph)or SDG(system dependence graph),but these friendly graph representations may be a bit expensive for some users.In this paper we attempt to study a light-weight approach of static program slicing,called Symbolic Program Slicing(SymPas),which works as a dataflow analysis on LLVM(low-level virtual machine).In our SymPas approach,slices are stored in symbolic forms,not in procedures being re-analyzed(cf.procedure summaries).Instead of re-analyzing a procedure multiple times to find its slices for each callling context,we calculate a single symbolic slice which can be instantiated at call sites avoiding re-analysis;SymPas is implemented with LLVM to perform slicing on LLVM intermediate representation(IR).For comparison,we systematically adapt IFDS(interprocedural finite distributive subset)analysis and the SDG-based slicing method(SDGIFDS)to statically slice IR programs.Evaluated on open-source and benchmark programs,our backward SymPas shows a factor-of-6 reduction in time cost and a factor-of-4 reduction in space cost,compared with backward SDG-IFDS,thus being more efficient.In addition,the result shows that after studying slices from 66 programs,ranging up to 336800 IR instructions in size,SymPas is highly size-scalable.