台风韦森特对季风水汽流的“转运”效应及其对北京“7·21”暴雨的影响

2012年7月21日北京地区遭受了61年以来最大的暴雨,造成了大量的人员伤亡与巨大的财产损失。资料综合分析表明台风韦森特在暴雨发生过程中的水汽输送起到“枢纽”的作用,夏季季风通过台风韦森特在副高的影响下将水汽“转运”至暴雨区。为了验证北京异常暴雨过程中台风韦森特的“转运”效应,利用中尺度数值模式WRF对暴雨过程进行数值模拟,结果表明模式能够较好的模拟出此次降水过程的强度、落区,且暴雨发生过程中的水汽输送亦能够较好的再现。通过设计剔除台风的敏感性试验发现,剔除台风韦森特之后降水强度仅为控制试验的50%。进一步分析表明低纬季风水汽气流通过处于东南沿海的台风韦森特向暴雨区域输送水汽,在此过程中西南气流直接向北京区域的水汽输送减少,而西南气流向台风的水汽输送增加,台风与东侧副热带高压之间的偏南气流向暴雨区的水汽输送明显增强,从而印证了上述西南季风气流—台风涡旋—暴雨环流三个系统之间水汽的“转运”效应。以上结果表明远距离暴雨的发生是一个复杂的过程,不仅反映了中低纬度系统的相互作用,而且揭示出夏季季风水汽流对台风涡旋的水汽输送持续供应也可能是台风远距离异常暴雨发生的关键因素之一。     

Interaction Between Typhoon Vicente (1208) and the Western Pacific Subtropical High During the Beijing Extreme Rainfall of 21 July 2012

The heaviest rainfall in recent six decades fell in Beijing on 21 July 2012, reaching a record of 460 mm within 18 h. This rainfall was a typical remote precipitation event related to Typhoon Vicente(1208).Observational analysis indicates that Vicente influenced distant heavy rainfall by transporting water vapor northward to the Beijing area. This moisture transport was mainly driven by the interaction between Vicente and the western Pacific subtropical high(WPSH) associated with the formation of a low-level southeasterly moisture channel. A set of numerical sensitivity experiments were performed with prescribed typhoons of different intensities to investigate the interaction between Vicente and the WPSH and its effects on this rainstorm process. The results indicate that the WPSH interacting with typhoons of different intensities may exert varying degrees of influence on the development of a southeasterly moisture channel, resulting in a change in rain rate and location over the Beijing area. Specifically, in the presence of an enhanced typhoon,the WPSH shows remarkable withdrawal to the east, which is favorable for a northward extension of the southeasterly moisture channel, thereby increasing moisture supply for the rainstorm. The WPSH tends to stretch westward in a zonal pattern if the typhoon is weakened or removed, hindering the northward extension of the moisture channel. Thus, the rainfall area may be expected to expand or contract, with corresponding increases or decreases in rain rate over the Beijing area with a strengthened or weakened typhoon, respectively.     

NUMERICAL SIMULATION ON RE-INTENSIFICATION OF TROPICAL REMNANT RE-ENTERING THE SEA: A CASE STUDY

When Typhoon Toraji(2001)reached the Bohai Gulf during 1-2 August 2001,a heavy rainfall event occurred over Shandong province in China along the gulf.The Advanced Research version of the Weather Research and Forecast(WRF-ARW)model was used to explore possible effects of environmental factors,including effects of moisture transportation,upper-level trough interaction with potential vorticity anomalies,tropical cyclone(TC)remnant circulation,and TC boundary-layer process on the re-intensification of Typhoon Toraji,which re-entered the Bohai Gulf after having made a landfall.The National Centers for Environmental Prediction(NCEP)global final(FNL)analysis provided both the initial and lateral boundary conditions for the WRF-ARW model.The model was initialized at 1200 UTC on 31 July and integrated until 1200 UTC on 3 August 2001,during which Toraji remnant experienced the extratropical transition and re-intensification.Five numerical experiments were performed in this study,including one control and four sensitivity experiments.In the control experiment,the simulated typhoon had a track and intensity change similar to those observed.The results from three sensitivity experiments showed that the moisture transfer by a southwesterly lower-level jet,a low vortex to the northeast of China,and the presence of Typhoon Toraji all played important roles in simulated heavy rainfall over Shandong and remnant re-intensification over the sea,which are consistent with the observation.One of the tests illustrated that the local boundary layer forcing played a secondary role in the TC intensity change over the sea.     

A Study on a Heavy Rainfall Event Triggered by an Inverted Typhoon Trough in Shandong Province

A heavy rainfall event that occurred in Shandong Province in 26 28 August 2004 was caused mainly by Typhoon Acre and cold air activities related to a westerly trough. The event was triggered by an inverted typhoon trough, which was closely associated with the intensification of the low-level southeasterly flow and the northward transport of heat and momentum in the periphery of the typhoon low. A numerical simulation of this event is performed using the nonhydrostatic mesoscale model MM5 with two-way interactive and triply-nested grids, and the structure of the inverted typhoon trough is studied. Furthermore, the formation and development mechanism of the inverted typhoon trough and a mesoscale vortex are discussed through a vorticity budget analysis. The results show that the heavy rainfall was induced by the strong convergence between the strong and weak winds within the inverted typhoon trough. Dynamic effects of the low-level jet and the diabatic heating of precipitation played an important role in the development of the inverted typhoon trough and the formation of the mesoscale vortex. The vorticity budget analysis suggests that the divergence term in the low troposphere, the horizontal advection term, and the convection term in the middle troposphere were main contributors to positive vorticity. Nonetheless, at the same pressure level, the effect of the divergence term and that of the adveetion term were opposite to each other. In the middle troposphere, the vertical transport term made a positive contribution while the tilting term made a negative contribution, and the total vorticity tendency was the net result of their counteractions. It is found that the change tendency of the relative vorticity was not uniform horizontally. A strong positive vorticity tendency occurred in the southeast of the mesoscale vortex, which is why the heavy rainfall was concentrated there. The increase of positive vorticity in the low （upper） troposphere was caused by horizontal convergence （upward transport of vorticity from the lower troposphere）. Therefore, the development of the inverted typhoon trough and the formation of the mesoscale vortex were mainly attributed to the vorticity generated in the low troposphere, and also the vertical transport of vorticity from the low and middle troposphere.     

超强台风“威马逊”近海加强与低频水汽输送的关系及前期信号

利用NCEP/NCAR再分析资料以及中国气象局上海台风研究所（简称上海台风所）整编的《热带气旋年鉴》,分析了超强台风“威马逊”在南海加强过程中水汽输送的变化特征,着重探讨台风强度变化与10~30 d低频水汽输送的关系,并从低频场出发寻找台风强度变化的前期信号。研究结果表明:（1）“威马逊”有两条主要的水汽通道,分别为孟加拉湾通道和南海通道,孟加拉湾通道的水汽输送强度大于南海通道;（2）“威马逊”近海加强与10~30 d低频水汽输送有紧密的联系。在热带低频系统作用下,孟加拉湾通道的低频偏西水汽和南海通道的低频偏南水汽在南海汇聚,为“威马逊”的增强提供了有利条件;（3）对于在海南岛东部登陆的台风,其登陆强度与超前5~7 d孟加拉湾通道的低频偏西水汽输送呈现显著的负相关,与南海通道的低频偏南水汽输送有较弱的负相关。若前期从两个通道截面流入的低频水汽输送通量位于低频振荡的谷值时,则有利于其后5~7 d台风在南海加强,反之减弱。      

1617号鲇鱼台风登陆后引发不同性质暴雨的成因对比分析

2016年9月28日1617号台风"鲇鱼"登陆后由台风本体环流和外围环流引发了不同性质的暴雨,这是本次秋季登陆台风暴雨预报的难点。利用常规气象观测资料以及NCEP的1°×1°再分析资料等,对不同性质暴雨的成因进行了诊断对比分析。结果表明:浙江东南部对流性降水和江西南部稳定性降水的大气层结结构具有明显的差异。中高纬度低槽距离台风较远,冷空气主要从低层入侵台风西北侧,破坏台风低层的暖心结构。台风外围中层干冷空气随东南风向浙江东南部输送,并叠加在低层暖湿气流之上,形成上冷下暖的不稳定层结,同时在对流层上层有干冷空气下沉至台风环流中下层(干侵入),导致浙江文成附近出现了局地特大暴雨。江西南部由于低层被湿冷空气占据,层结较为稳定,降水发展平缓。低空东南急流为台风外围环流暴雨提供了充足的水汽,浙江东南部地形对降水起到了增幅作用。不稳定层结及中层冷空气的输送对对流性暴雨的激发作用可以为登陆台风降水性质和强度预报提供参考依据。     

Effects of intraseasonal oscillation on the anomalous East Asian summer monsoon during 1999

The 1999 East Asian summer monsoon was very unusual for its weak northward advance and remarkably anomalous climate conditions. The monsoonal southwesterly airflow and related rain belt in East Asia were blocked south of the Yangtze River Valley. The monsoonal airflow and major moisture transport conduct shifted eastward and turned northward to Japan from the tropical western Pacific rather than to East China from the South China Sea （SCS） as in normal years. Severe and prolonged drought occurred over extensive areas of North China and heavy precipitation in South China and Japan. The investigation on the possible intrinsic mechanisms related to such an anomalous monsoon year has shown that the unique behavior of intraseasonal oscillation may play an essential role during this process. During this year, the northward propagation of 30-60-day anomalous low-level cyclone/anticyclone collapsed in the region around 20°N and did not extend beyond the latitudes of the Yangtze River basin due to the barrier of strong cold air intrusion from the mid-latitudes. The southwesterly moisture flux on the northwestern flank of the anticyclonic moisture transport system in the western North Pacific, which was regulated by the northward shift of 30-60-day cyclonic/anticyclonic moisture transport, also did not reach the region north of 30°N as well. Under this circumstance, the weak northward advance of the monsoon westerlies and associated northward moisture transport could not arrive in North China and led to the severe droughts there in 1999. The SCS and South China were mostly affected by the airflow in the southern and northern flanks of the same 30-60-day cyclones or anticyclones, respectively, and thus controlled by the nearly reverse zonal wind and moisture convergent/divergent conditions. The rainfall in the SCS and South China showed out-of-phase oscillation through the transient local Hadley circulation, with the rainfall maximum occurring in the SCS （South China） when the 30-60-day anticyclone （cyclone） r     

近海台风对“21·7”河南极端暴雨过程水汽通量和动、热力条件影响的模拟

本文利用WRF模式对近海台风“烟花”及“查帕卡”影响2021年7月19日至21日河南极端暴雨的过程进行数值模拟。控制试验（CTL）对台风路径、强度、大尺度环流形势,以及河南暴雨的强度和空间分布型等均给出合理的模拟,基本再现了本次河南极端暴雨的发展过程。敏感性试验表明,在移除台风“烟花”后,副热带高压系统显著南压并在南侧形成东南风急流,河南地区的南风分量减弱、东风增强,东西方向的水汽输送占主导,有利于降水分布型由CTL试验的南—北向转变为东—西向;另一方面,由于低层东南风急流相较于移除“烟花”前的东风急流偏弱,河南降雨区的局地辐合减弱,水汽通量净流入值较CTL试验降低5.81%,且中纬度冷气团西移减慢,引起局地相当位温梯度减弱,最终导致移除台风“烟花”试验的降雨强度偏弱。移除台风“查帕卡”后,大尺度环流形势几乎未受影响,河南南侧的水汽输送略有减弱,因此强降水分布基本与CTL试验类似,降雨强度略有减小。与台风“烟花”相比,“查帕卡”对河南暴雨的影响较弱。     

2021年河南“7.20”极端暴雨动、热力和水汽特征观测分析

利用MICAPS观测降水数据、欧洲气象中心ERA5再分析资料和FY-4A卫星云顶亮温数据,对2021年7月20日河南极端暴雨进行综合分析。结果表明,此次暴雨受200 hPa两槽一脊、大陆高压、副热带高压（副高）西伸北抬和台风“烟花”西移、“查帕卡”台风倒槽等多尺度天气系统共同影响,黄淮气旋的西南气流与副高和“烟花”之间的东南气流稳定控制河南地区,边界层急流供应充沛水汽,在太行山和嵩山迎风坡辐合抬升,致使河南暴雨长时间维持,产生极端降水量。西南气流穿过从广东和广西延伸到河南的高湿带,副高和“烟花”引导东南气流经过从东海洋面延伸到河南的相对较弱湿区,这两条水汽输送带在太行山和嵩山地形阻挡下汇合在河南北部,为暴雨供应水汽。丰富的可降水量、水汽过饱和、深厚暖云层以及降水系统较强的水汽消耗率为郑州高降水效率提供有利条件。郑州低层大气经历多次从强层结不稳定到弱层结不稳定的转化,边界层急流引起的垂直风切变和气流辐合对层结稳定度变化有重要影响。黄淮气旋内部中尺度涡旋对河南暴雨发生发展至关重要,不但提供西南气流,还产生较强的位势高度纬向平流,增强边界层急流。嵩山与太行山余脉构成喇叭口地形,边界层急流在嵩山北侧和东侧爬坡,促使山前水汽堆积,激发和加强暴雨。中尺度云团合并小尺度云团,发展成结构密实的孤立云团,稳定少动,对暴雨有重要影响。降水区上空广义湿位涡异常,由于广义湿位涡能够刻画中尺度系统的垂直风切变、涡度以及大气湿斜压性和层结不稳定等动力和热力因素垂直结构特点,所以对中尺度系统和降水落区有一定指示意义。     

登陆热带气旋研究的进展

随着大气探测技术的发展 ,登陆热带气旋研究已经成为热带气旋研究中一个新的领域。新的探测技术能初步揭示出热带气旋登陆过程中发生的多种改变。近年来 ,国内外科学家实施了一系列外场科学试验 (Fieldscientificexperi ments) ,对登陆热带气旋进行探测和研究 ,旨在提高预报的准确率。登陆热带气旋研究内容包括 :海岸和内陆山脉地形影响 ,结构和强度变化 ,登陆热带气旋的暴雨强度和分布 ,大风强度和分布 ,风暴潮强度和范围 ,登陆热带气旋在陆上的维持机制 ,陆地涡旋的路径和入海加强 ,边界层结构 ,陆面过程和能量交换 ,变性过程等。研究采用外场科学试验与数值模拟相结合的方法。模拟或预报模式中使用同化资料尤其是卫星同化资料来构造初值场 ,取得较好结果。登陆热带气旋的研究目前正在展开 ,并取得了一些重要结果。研究表明 ,潜热释放和斜压位能释放是近海或登陆热带气旋加强或维持的两种主要能源。这两种能量可分别从水汽输送和热带气旋与中纬度环流的相互作用中获得。另外 ,陆面饱和湿地或水面的潜热输送、热带气旋与中尺度涡旋或热带云团的合并以及高空流出气流强辐散也对其加强和维持有利。世界气象组织的热带气象研究计划 (TMRP)正在组织对这一领域的总结和下一步的研究计划。这项研究将对预报和     

Analysis on Precipitation Efficiency of the “21.7” Henan Extremely Heavy Rainfall Event

A record-breaking heavy rainfall event that occurred in Zhengzhou, Henan province during 19–21 July 2021 is simulated using the Weather Research and Forecasting Model, and the large-scale precipitation efficiency(LSPE) and cloud-microphysical precipitation efficiency(CMPE) of the rainfall are analyzed based on the model results. Then, the key physical factors that influenced LSPE and CMPE, and the possible mechanisms for the extreme rainfall over Zhengzhou are explored. Results show that water v...     

华东登陆热带气旋降水不同分布的对比分析

利用CMORPH降水资料，将热带气旋（TC）登陆后的降水分为路径左侧降水（L型）和右侧降水（R型）两类，并针对登陆华东地区TC的 L型和R型降水的大气环流场、环境水平风垂直切变以及台风环流内的动热力条件进行对比分析，结果表明:2005～2014年间登陆华东地区的20例TC中包括12例L型和8例R型。总体来看，大气环流因子对于登陆华东TC降水分布起主要作用。L型降水TC高层南亚高压主要呈纬向带状分布，在登陆过程中路径左侧维持偏东风高空辐散气流，中层西风槽偏东，西太平洋副热带高压（简称副高）偏南，环境水平风垂直切变指向西南。R型降水TC高层南亚高压断裂，呈经向分布。TC路径左侧风场较均匀，右侧东南风高空辐散气流明显。副高的位置偏北呈块状，同时环境水平风垂直切变指向东北，有利于路径右侧降水。台风环流内，低层冷暖平流输送以及水汽辐合与降水落区也有较好对应关系。L型TC低层暖平流的输送使TC西南象限低层增暖，大气稳定度降低。同时水汽辐合区也主要位于西南象限，有利于TC路径左侧降水。而R型TC副高位置偏北可将南侧的东南暖湿气流向台风环流更西部输送，东北象限维持暖平流，有利于路径右侧降水发生。     

江淮区域持续性暴雨过程的水汽源地和输送特征

采用HYSPLIT模式和NCEP/NCAR再分析资料,对中国江淮流域持续性暴雨过程（PHREs）的江南型和江北型过程的水汽源地、输送路径以及干空气路径进行分析。主要结果如下:江南型PHREs的干空气主要通过2条路径进入江淮地区,即源自地中海-欧洲平原的西北路径和来自蒙古高原的东北路径,而江北型PHREs干空气主要有1条路径,即西北路径。干空气是通过对流层中高层的槽脊活动和急流输送至江淮区域。江南型水汽主要由源自印度半岛以南的热带印度洋的西南路径和来自印度尼西亚与中国南海的偏南路径这2条路径输送到江淮流域。江北型的水汽路径有3条,前2条路径与江南型类似,且为主要水汽来源,还有来自西太平洋的东南路径水汽输送。江淮流域的持续性降雨过程中,来自南方的水汽输送主要受索马里越赤道急流、孟加拉湾南部和印度尼西亚群岛附近越赤道气流,以及受西太平洋副热带高压这些系统的影响。      

台风温比亚(1818)降水及环境场极端性分析

利用多种观测及分析资料对台风温比亚（1818）暴雨过程的降水演变、极端降水特点及环境场物理量特征等进行分析。此次台风暴雨日降水量极端性显著,降水主要分为登陆前后、深入内陆并转向以及冷空气作用和变性3个阶段,其中第2阶段为最强降水时段。受其影响,河南、山东等地多个站点的日降水量突破历史极值。温比亚（1818）最大小时降水量达127.7 mm,其中74个站点小时降水量超过80 mm,短时强降水维持时间长达14 h,高降水效率及长持续时间造成极端降水。对流层中、低层存在标准化异常小于-4倍标准差的异常低压环流,造成极端低层辐合,叠加高空急流和高压边缘的极端高空辐散,动力条件极端性显著,200 hPa辐散和850 hPa辐合均接近或远超1988—2017年日降水量排名前30（HT30）降水日的最大值。受台风东侧水汽输送影响,降水区假相当位温、整层大气可降水量和水汽通量散度无论与气候态相比,还是与HT30降水日相比,均具有显著极端性,且极端水汽维持时间长达30 h。     

Maintenance of Tropical Cyclone Bill （1988） after Landfall

The mechanism for the maintenance of Tropical Cyclone Bill （1988） after landfall is investigated through a numerical simulation. The role of the large-scale environmental flow is examined using a scale separation technique, which isolates the tropical cyclone from the environmental flow. The results show that Bill was embedded in a deep easterly-southeasterly environmental flow to the north-northeast of a large-scale depression and to the southwest of the western Pacific subtropical high. The depression had a quasi-barotropic structure in the mid-lower troposphere and propagated northwestward with a speed similar to the northwestward movement of Bill. The moisture budgets associated with both the large-scale and the tropical cyclone scale motions indicate that persistent low-level easterly-southeasterly flow transported moisture into the inner core of the tropical cyclone. The low-level circulation of the tropical cyclone transported moisture into the eyewall to support eyewall convection, providing sufficient latent heating to counteract energy loss due to surface friction and causing the storm to weaken relatively slowly after landfall. Warming and a westward extension of the upper-level easterly flow led to westward propagation of the environmental flow in the mid-lower troposphere. As a result, Bill was persistently embedded in an environment of deep easterly flow with high humidity, weak vertical wind shear, convergence in the lower troposphere, and divergence in the upper troposphere. These conditions are favorable for both significant intensification prior to landfall and maintenance of the tropical cyclone after landfall.     

华北地区持续性极端暴雨过程的分类特征

利用1960—2015年日降水资料,筛选出华北地区56次持续性极端暴雨过程。基于距平相关系数的客观聚类分析方法和天气学检验,将它们进行分类,并使用NCEP（2.5°×2.5°）再分析资料进行分类合成,对比分析不同环流背景下华北地区持续性极端暴雨过程的基本特征。结果表明,这些持续性极端暴雨事件按照环流背景可分为经向型、纬向型、减弱的登陆热带气旋型和初夏型4类。它们一般都与不同天气系统配置结构下的锋面动力学过程有关,由于锋面结构特征、环境大气层结状态以及与低空急流有关的暖湿气流输送通道和强度不同,造成不同环流形势背景下,暴雨日的高频站点与过程平均累计降水量在空间分布上存在差异。（1）纬向型对应的锋区强度明显强于经向型,但是其对应的层结稳定度与整个夏季状态相当,而经向型存在弱的层结不稳定异常,这表明,纬向型的对流活动一般不如经向型强,持续性锋面降水特征更清晰,造成站点上日降水量超过50 mm的最大频率明显低于经向型,但是过程累计平均最大降雨量却比经向型大。（2）从水汽输送通道来看,源于西太平洋副热带高压南侧的水汽通道只在纬向型环流主导下的华北区域持续性极端暴雨过程中起主导作用。初夏型以及减弱的登陆热带气旋与西风带系统相互作用造成的极端暴雨过程中,活跃的印度季风造成25°N以南异常强盛的纬向低空西南气流携带充沛的水汽,穿过中南半岛后以西南低空急流或者通过减弱的登陆热带气旋“中转”,是这两类暴雨区的主要水汽供应方式;经向型环流背景下的水汽输送也与这支源于青藏高原南侧的西风气流异常有关。这可能是华北地区夏季降水与印度季风降水的相关显著强于中国东部其他地区的主要原因。（3）减弱的登陆热带气旋与西风带系统相互作用造成的极端暴雨事件同样由经向型环流主导,但是,更充沛的水汽输送、更强的上升运动和更深厚的大气不稳定层结状态是它比一般的经向型强度更大的直接原因;此外,中高纬度弱冷空气侵入对减弱的登陆热带气旋顶部形成持续性极端暴雨过程非常重要。      

Climatological characteristics of the moisture budget and their anomalies over the joining area of Asia and the Indian-Pacific Ocean

The climatological characteristics of the moisture budget over the joining area of Asia and the Indian-Pacific Ocean (AIPO) and its adjacent regions as well as their anomalies have been estimated in this study. The main results are as follows. In the winter, the northeasterly moisture transport covers the extensive areas at the lower latitudes of the AIPO. The westerly and northerly moisture transport is the major source and the South Indian Ocean (SIO) is the moisture sink. In the summer, influenced by the southwesterly monsoonal wind, the cross-equatorial southwesterly moisture transport across Somali originating from the SIO is transported through the Arabian Sea (AS), the Bay of Bengal (BOB), and the South China Sea (SCS) to eastern China. The AIPO is controlled by the southwesterly moisture transport. The net moisture influx over the AIPO has obvious interannual and interdecadal variations. From the mid- or late 1970s, the influxes over the SIO, the AS, the northern part of the western North Pacific (NWNP), and North China (NC) as well as South China (SC) begin to decrease abruptly, while those over Northeast China (NEC) and the Yangtze River-Huaihe River basins (YHRB) have increased remarkably. As a whole, the net moisture influxes over the BOB and the southern part of the western North Pacific (SWNP) in the recent 50 years take on a linear increasing trend. However, the transition timing for these two regions is different with the former being at the mid- or late 1980s and the latter occurring earlier, approximately at the early stage of the 1970s. The anomalous moisture source associated with the precipitation anomalies is different from the normal conditions of the summer precipitation. For the drought or flood years or the years of El Ni\~no and its following years, the anomalous moisture transport originating from the western North Pacific (WNP) is the vital source of the anomalous precipitation over eastern China, which is greatly related with the variation of the subtropical Pacific high.     

The role of the land surface processes in the rainfall generated by a landfall typhoon: A simulation of the typhoon Sepat (2007)

Landfall tropical cyclones are a major kind of severe weather affecting China. The typhoon Sepat, declassified as tropical storm after its landfalling, caused a continuous heavy rainfall event over China mainland from 19th to 25th August, 2007. The storm cyclone resided over the Hunan province for 60 hours, causing observed accumulated precipitation larger than 300 mm in a large area of the Hunan province and leading severe flood events. This event was simulated using the Weather Research and Forecasting (WRF) model coupled with the surface layer scheme UTOPIA. The model was able to reproduce the main characteristics of the event, including the typhoon track and the rainfall field and timing. In addition, three sets of sensitivity experiments have been performed. In the first one, the effects of different land surface schemes (RUC, NOAH and UTOPIA) coupled with WRF on the precipitation, sensible and latent heat flux fields associated with the Typhoon Sepat (2007) were investigated. The second set of sensitivity experiments analyzed the role of the surface fluxes (sensible and latent heat flux) on the typhoon evolution. The third set of sensitivity experiments regarded the initialization of the soil moisture content. These experiments showed that both latent and sensible heat fluxes sustained this landfalling typhoon, maintaining the spiral structure of rain belt. Among the two fluxes, the latent heat one played a major role in determining the intensity, the track and the rainfall distribution of the typhoon. In addition, the correct initialization of the soil moisture content has reveled a fundamental parameter to be initialized in order to correctly evaluate the distribution and intensity of the rain field. The intercomparison between the three different land surface schemes coupled with WRF showed that the WRF-UTOPIA and WRF-NOAH outputs seem comparable between each other and physically most realistic than those of WRF-RUC. These analyses were helpful to understand the evolution and the development of the landfalling typhoon, and demonstrated that WRF-UTOPIA and WRF-NOAH could be considered a good tool for managing the risk evaluation connected with the occurrence of such events at regional scale.     

Impact of the Monsoonal Surge on Extreme Rainfall of Landfalling Tropical Cyclones

A comparative analysis and quantitative diagnosis has been conducted of extreme rainfall associated with landfalling tropical cyclones(ERLTC) and non-extreme rainfall(NERLTC) using the dynamic composite analysis method.Reanalysis data and the tropical cyclone precipitation dataset derived from the objective synoptic analysis technique were used.Results show that the vertically integrated water vapor transport(Q_(vt)) during the ERLTC is significantly higher than that during the NERLTC.The Q_(vt) reaches a peak 1-2 days before the occurrence of the ERLTC and then decreases rapidly.There is a stronger convergence for both the Q_(vt) and the horizontal wind field during the ERLTC.The Qvt convergence and the wind field convergence are mainly confined to the lower troposphere.The water vapor budget on the four boundaries of the tropical cyclone indicates that water vapor is input through all four boundaries before the occurrence of the ERLTC,whereas water vapor is output continuously from the northern boundary before the occurrence of the NERLTC.The water vapor inflow on both the western and southern boundaries of the ERLTC exceeds that during the NERLTC,mainly as a result of the different intensities of the southwest monsoonal surge in the surrounding environmental field.Within the background of the East Asian summer monsoon,the low-level jet accompanying the southwest monsoonal surge can increase the inflow of water vapor at both the western and southern boundaries during the ERLTC and therefore could enhance the convergence of the horizontal wind field and the water vapor flux,thereby resulting in the ERLTC.On the other hand,the southwest monsoonal surge decreases the zonal mean steering flow,which leads to a slower translation speed for the tropical cyclone associated with the ERLTC.Furthermore,a dynamic monsoon surge index(DMSI) defined here can be simply linked with the ERLTC and could be used as a new predictor for future operational forecasting of ERLTC.     

影响海南岛的台风降水及水汽输送源地分析

利用1986—2016年中国气象局台风最佳路径资料、海南岛区域站降水数据以及基于拉格朗日方法的轨迹模式对近30 a影响海南岛的台风降水和大气环流特征进行分析,并探讨了台风影响降水期间水汽输送通道和源地。结果表明：6—10月是台风影响海南岛的主要时段,也是台风降水主要时段。在台风降水偏多(少)年,长江以南地区冷空气影响偏弱(强),副热带高压偏弱(强),南支槽偏强(弱),低层水汽通量场呈现异常气旋性(反气旋性)环流。降水偏多年,海南岛受到来自西北太平洋异常东北气流与印度洋、孟加拉湾的异常偏强西南气流影响;降水偏少年,水汽主要来自西太平洋的偏东气流和南海较弱的西南气流。海南岛台风降水的四个主要水汽源地分别为西太平洋、孟加拉湾、南海和印度洋,在台风降水偏多年,水汽输送贡献最大的是西太平洋和孟加拉湾,分别为33%和30%,来自东西两路的水汽供应充足,而在偏少年西太平洋水汽输送贡献最大,为38%,其余水汽源地贡献均在30%以下,以110°E以东的水汽输送为主。