孟加拉湾风暴时空分布和活动规律统计特征

利用1945-2006年JTWC公布的孟加拉湾风暴资料,对其进行统计分析.结果表明:孟加拉湾热带气旋(下称孟湾TC)生成个数年平均约为8.12个,全年均有发生,其中2～3月最少,之后开始增加,10月达到峰值;与孟湾TC不同,孟加拉湾热带风暴(下称孟湾TS)呈双峰型分布,峰值为5月和9～10月.从孟湾TS的强度上看,达到H4标准的超级强风暴1971-1986年仅出现1次,而1987-2006年则出现了8次.孟湾TS生成位置、平均维持时间和最长维持时间的月际变化均呈双峰型分布,4～5月和10～11月为峰值.孟湾TS的生成位置10～11月峰值大于4～5月,而平均维持时间和最长维持时间则是4～5月峰值大于10～11月.孟湾TC登陆方向大部分为西北或偏西路径,占56.7%.孟湾TS登陆方向与TC有一些不同,主要差异是西北路径和未登陆次数减少,偏西和东北路径增加.由于4～5月是孟湾TS东北路径登陆的一个峰值,因此,与云南雨季开始期关系密切,对云南初夏降水影响很大.     

The cloud-microphysical cause of torrential rainfall amplification associated with Bilis (0604)

After its landfall in China’s mainland in 2006, Typhoon Bilis brought about torrential rainfall amplification at the edge of Guangdong, Jiangxi, and Hunan provinces, causing severe disasters. From a cloud-microphysical perspective, we discuss the differences of cloud-microphysical processes before and during the precipitation amplification and possible causes of the rainfall amplification by using high-resolution simulation data. The results show that the cloud-microphysical characteristics during the above two periods are significantly different. With the distinct increase in the rainfall intensity, the cloud hydrometeor contents increase markedly, especially those of the ice-phase hydrometeors including ice, snow and graupel, contributing more to the surface rainfall. The clouds develop highly and vigorously. Comparisons of conversion rates of the cloud hydrometeors between the above two periods show that the distinct increases in the cloud water content caused by the distinct enhancement of the water vapor condensation rate contribute to the surface rainfall mainly in two ways. First, the rain water content increases significantly by accretion of cloud water by rain water, which thus contributes to the surface rainfall. Second, the accretion of cloud water by snow increases significantly the content of snow, which is then converted to graupel by accretion of snow by graupel. And then the graupel melts into rain water, which subsequently contributes to the surface rainfall amplification. In summary, a flow chart is given to clarify the cloud-microphysical cause of the torrential rainfall amplification associated with Bilis.     

An Overview of Research and Forecasting on Rainfall Associated with Landfalling Tropical Cyclones

The ability to forecast heavy rainfall associated with landfalling tropical cyclones (LTCs) can be improved with a better understanding of the mechanism of rainfall rates and distributions of LTCs. Research in the area of LTCs has shown that associated heavy rainfall is related closely to mechanisms such as moisture transport, extratropical transition (ET), interaction with monsoon surge, land surface processes or topographic effects, mesoscale convective system activities within the LTC, and boundary layer energy transfer etc.. LTCs interacting with environmental weather systems, especially the westerly trough and mei-yu front, could change the rainfall rate and distribution associated with these mid-latitude weather systems. Recently improved technologies have contributed to advancements within the areas of quantitative precipitation estimation (QPE) and quantitative precipitation forecasting (QPF). More specifically, progress has been due primarily to remote sensing observations and mesoscale numerical models which incorporate advanced assimilation techniques. Such progress may provide the tools necessary to improve rainfall forecasting techniques associated with LTCs in the future.     

登陆粤西的热带气旋降水特征分析

利用1949～2000年《热带气旋年鉴》资料,对51年来登陆粤西的热带气旋在陆地维持时间、不同强度的降水之间的分布、相同量级强降水的分布等进行统计分析,揭示登陆粤西热带气旋降水分布实况和特征。结果表明,登陆粤西的热带气旋在登陆后的维持时间和其造成陆地强降水范围成正相关的关系;热带气旋造成不同强度(暴雨、大暴雨、特大暴雨)的降水在其路径左右侧分布,雨强越大,出现的几率越少;热带气旋登陆后造成的暴雨量级降水在热带气旋路径右侧比左侧产生的几率更大;而大暴雨、特大暴雨落在路径左侧的可能性比落在右侧的可能性大。     

STUDIES ON RELATIONSHIPS BETWEEN ENSO AND LANDFALLING TROPICAL CYCLONES IN CHINA

The data of landfalling tropical cyclones (TCs) in China and ENSO events and the NinoZ index during 1951 to 2005 were used to study the relationships between ENSO and landfalling TCs in China. ENSO events from July to September have obvious effects on landfalling TCs in China. When El Nio persists throughout the months, the frequency of landfalling TCs is less than normal, the season of landfalling TCs is shorter, the annually first landfall is later, the annually last landfall is earlier, and the mean int...     

台风登陆背景下陕西两次大暴雨过程对比分析

采用天气学、动力诊断等方法对2010年7月陕西出现两次大暴雨过程综合分析。目的在于揭示近海台风活动对陕西区域性暴雨作用和影响,结果表明：近海台风活动是影响造成两次大暴雨的一个关键因子。两次暴雨的水汽输送均由登陆后的台风低压环流东侧的偏南急流来实现,且以700hPa表现最为显著。前一次暴雨过程中热力条件和高层抽吸对增强上升运动和对流作用明显。后一次暴雨过程是因持续、深厚和稳定少动的河套低压自身不断发展加深的作用,加剧了上升运动发展,其上升运动区与暴雨区吻合较好。     

An Analysis of the Low Moving Speed of Landfalling Typhoon In-Fa in 2021

The movement speed of Typhoon In-Fa (2021) was notably slow, at 10 km h?1 or less, for over 20 hoursfollowing its landfall in Zhejiang, China, in contrast to other typhoons that have made landfall. This study examines thefactors contributing to the slow movement of Typhoon In-Fa, including the steering flow, diabatic heating, vertical windshear (VWS), and surface synoptic situation, by comparing it with Typhoons Yagi (2018) and Rumbia (2018) whichfollowed similar tracks. The findings reveal that the movement speed of Typhoons Yagi and Rumbia is most closelyassociated with their respective 500 hPa environmental winds, with a steering flow of 10–12 m s ?1. In contrast, Typhoon In Fa’s movement speed is most strongly correlated with the 850 hPa environmental wind field, with a steering flow speed ofonly 2 m s ?1. Furthermore, as Typhoon In-Fa moves northwest after landfall, its intensity is slightly greater than that ofTyphoons Yagi and Rumbia, and the pressure gradient in front of Typhoon In-Fa is notably smaller, leading to its slowmovement. Additionally, the precipitation distribution of Typhoon In-Fa differs from that of the other two typhoons,resulting in a weak asymmetry of wavenumber-1 diabatic heating, which indirectly affects its movement speed. Furtheranalysis indicates that VWS can alter the typhoon’s structure, weaken its intensity, and ultimately impact its movement.     

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.     

登陆台风环流内的一次中尺度强对流过程

2005年05号台风“海棠”登陆福建后,在外围云系里有1个明显发展的中尺度对流云团经过温州东部及北部地区,引起了强降水。通过分析这次中尺度对流系统的环流形势,得到该次中尺度对流系统的垂直结构特征,并对中尺度强对流系统的形成和发展机制进行研究。结果表明:台风东南急流在温州附近冷区边缘处低层受地形影响发生强烈辐合引起的垂直上升运动和冷暖空气相汇产生的对流不稳定性是台风环流内中尺度对流系统的主要形成机制;对流系统在暖湿空气和冷空气中心交汇处发展,西北侧的冷空气堆迫使暖湿东南气流沿西北倾斜的等熵面爬升,有利于倾斜对流系统的发展;低层条件不稳定区与中层条件对称不稳定区叠加,产生对流对称不稳定,在湿等熵面倾斜引起的涡旋发展的强迫机制下在中层产生范围较广的倾斜上升对流;由于等熵面的倾斜,大气水平风垂直切变或湿斜压性增加,进一步加强涡度的发展,使得对流系统向西北方向发展;另外,源于东南沿海,由台风东南气流输送的水汽为特大暴雨的产生提供了有利的热力条件。     

登陆台风与环境因子相互作用对暴雨的影响研究综述

综述登陆台风造成的暴雨强度和范围不仅受台风强度、范围及结构等的影响,还与环境场密切相关。对低空急流、中纬度西风槽及冷空气、季风、大陆高压、台风周围的残涡或小涡、下垫面以及边界层输送等环境因子,与登陆台风相互作用影响暴雨的机理进行了系统全面的综述,并对该领域内存在的问题作了初步讨论。