COMPARATIVE ANALYSIS OF THE INTENSITY AND DISTRIBUTION OF HEAVY RAINS IN ZHEJIANG PROVINCE CAUSED BY TYPHOONS HAITANG AND MATSA

Study was carried out on two landfall typhoons Haitang and Matsa, which affected Zhejiang province seriously in 2005. Firstly, the similarity and difference between the two typhoon-induced heavy rains were compared and it was pointed out that both of them brought strong large-scale precipitation and the maximum centers of rainfall were located on the north side of the landfall site. Making landfall on Fujian, Haitang was weaker than Matsa in intensity but surpassed it in rainfall. Then with focus on intensity, moving speed, structure of typhoon, circulation and terrain, the two typhoon-related heavy rains were compared and analyzed. Results show that the asymmetrical distribution of rainfall was closely related to the structure of typhoons themselves, moisture transportation and mesoscale terrain. In contrast to the south side, the north side was hotter and wetter and water vapor was also more abundant. The phenomenon of more rainfall induced by Haitang was in connection with the following reasons. Invading cold air led to rainfall increases, weakened dynamic field and slower movement both benefited precipitation. For the last part, the cold characteristic of air mass over Zhejiang was also a favorable factor for the rain.     

ANALYSIS OF RAINSTORMS ASSOCIATED WITH SIMILAR TRACK TROPICAL CYCLONES HAITANG (0505) AND BILIS (0604)

It is generally thought that the influence of comparable track typhoons is approximately similar, but in fact their wind and especially their rainstorm distribution are often very different. Therefore, a contrastive analysis of rainstorms by tropical cyclones (TCs) Haitang (0505) and Bilis (0604), which are of a similar track, is designed to help understand the mechanism of the TC rainstorm and to improve forecasting skills. The daily rainfall of TC Haitang (0505) and Bilis (0604) is diagnosed and compared. The result indicates that these two TCs have similar precipitation distribution before landfall but different precipitation characteristics after landfall. Using NCEP/GFS analysis data, the synoptic situation is analyzed; water vapor transportation is discussed regarding the calculated water vapor flux and divergence. The results show that the heavy rainfall in the Zhejiang and Fujian Provinces associated with Haitang (0505) and Bilis (0604) before landfall results from a peripheral easterly wind, a combination of the tropical cyclone and the terrain. After landfall and moving far inland of the storm, the precipitation of Haitang is caused by water vapor convergence carried by its own circulation; it is much weaker than that in the coastal area. One of the important contributing factors to heavy rainstorms in southeast Zhejiang is a southeast jet stream, which is maintained over the southeast coast. In contrast, the South China Sea monsoon circulation transports large amounts of water vapor into Bilis – when a water-vapor transport belt south of the tropical cyclone significantly strengthens – which strengthens the transport. Then, it causes water vapor flux to converge on the south side of Bilis and diverge on the north side. Precipitation is much stronger on the south side than that on the north side. After Bilis travels far inland, the cold air guided by a north trough travels into the TC and remarkably enhances precipitation. In summary, combining vertical wind shear with water vapor transportation is a good way to predict rainstorms associated with landing tropical cyclones.     

A mesoscale analysis of heavy rain caused by frontal and topographical heterogeneities on Taiwan Island

The prevailing mesoscale model MM5 (V3) is used to simulate a heavy rain case caused by interaction between a move-in front and topographical heterogeneities on Taiwan Island. It is found that both thermodynamic and dynamic fields along the front are heterogeneous in time and space. The heterogeneity becomes more significant as the effect of topography is added on. The heterogeneous distribution of physical variables along the front is the main reason for the heterogeneous frontal rain band; the optimum cooperation of the low level and upper level jet is another reason for the development of the rain band.Topography can strengthen the rainfall and causes extremely heavy rain cells. Updraft induced by topography extends to a rather low level, while the uplifted air by frontal circulation can reach to higher levels.The quasi-steady topographic circulation overlaps the frontal circulation when the front moves over Taiwan Island; the advantageous cooperation of various mesoscale conditions causes the large upward velocity on the windward side of the island.     

ANALYSIS OF THE CHARACTERISTICS OF SUSTAINED TORRENTIAL RAINS IN JUNES DURING 1958-2000

Day-to-day precipitation data of Junes during the 43 years of 1958-2000 from stations to the south of Yangtze River are used to divide regions and run statistical analysis of sustained torrential rainfall processes. A preliminary analysis is then made based on it and the results show that June is the month in which torrential rains in the southern half of China take place frequently and sustained torrential rains occur at the same time in South China and the area to the south of Yangtze River. In addition, the analysis gives the basic features of sustained torrential rains of June in China and their interannual variability patterns, with the suggestion that the amount of these events increases significantly after the 1990s. Lastly, the sustained torrential rains occurring in Junes of 1994, 1998 and 2005 in the southern half of China are taken as examples in the research on the basic patterns and formation mechanisms of the evolution of double rain-bands during the rain season in South China and the area to the south of Yangtze River. The analysis shows that the large scale environment field in which sustained torrential rains occur is related to the stable sustaining of the South Asia High and upper level jet streams.     

IMPACTS OF UPPER-LEVEL COLD VORTEX ON THE RAPID CHANGE OF INTENSITY AND MOTION OF TYPHOON MERANTI (2010)

Typhoon Meranti originated over the western North Pacific off the south tip of the Taiwan Island in 2010.It moved westward entering the South China Sea,then abruptly turned north into the Taiwan Strait,got intensified on its way northward,and eventually made landfall on Fujian province.In its evolution,there was a northwest-moving cold vortex in upper troposphere to the south of the Subtropical High over the western North Pacific(hereafter referred to as the Subtropical High).In this paper,the possible impacts of this cold vortex on Meranti in terms of its track and intensity variation is investigated using typhoon best track data from China Meteorological Administration,analyses data of 0.5×0.5 degree provided by the global forecasting system of National Centers for Environmental Prediction,GMS satellite imagery and Taiwan radar data.Results show as follows:(1)The upper-level cold vortex was revolving around the typhoon anticlockwise from its east to its north.In the early stage,due to the blocking of the cold vortex,the role of the Subtropical High to steer Meranti was weakened,which results in the looping of the west-moving typhoon.However,when Meranti was coupled with the cold vortex in meridional direction,the northerly wind changed to the southerly at the upper level of the typhoon;at the same time the Subtropical High protruded westward and its southbound steering flow gained strength,and eventually created an environment in which the southerly winds in both upper and lower troposphere suddenly steered Meranti to the north;(2)The change of airflow direction above the typhoon led to a weak vertical wind shear,which in return facilitated the development of Meranti.Meanwhile,to the east of typhoon Meranti,the overlapped southwesterly jets in upper and lower atmosphere accelerated its tangential wind and contributed to its cyclonic development;(3)The cold vortex not only supplied positive vorticity to the typhoon,but also transported cold advection to its outer bands.In conjunction with the warm and moist air masses at the lower levels,the cold vortex increased the vertical instability in the atmosphere,which was favorable for convection development within the typhoon circulation,and its warmer center was enhanced through latent heat release;(4)Vertical vorticity budget averaged over the typhoon area further shows that the intensification of a typhoon vorticity column mainly depends on horizontal advection of its high-level vorticity,low-level convergence,uneven wind field distribution and its convective activities.     

STUDY ON THE CAUSE OF HEAVY RAIN 200506 （HR200506） IN GUANGDONG

A continuous heavy rain visited Guangdong province during June 18-25, 2005 (named Heavy Rain 200506, HR200506) and had resulted in enormous economic loss. The ageostropic Q vectors, θse,meridional circulation, computed from the NCEP reanalysis, and TBB are used to study the rainfall processes. The results indicated that a convective system moved northwards from the South China Sea (SCS)and stayed in Guangdong for several days, which was a direct cause of HR200506. The process is a result of the activity of the South China Sea summer monsoon. There were two rainbands of HR200506 in Guangdong. One laid in the north of Guangdong that produced frontal rainfall; another situated on the south of Guangdong which produced monsoon rainfall.     

ANALYSIS OF TYPHOON MATSA （NO.0509） AFFECTING SHANDONG PROVINCE

The characteristics of the moving course of Typhoon Matsa (No.0509), associated heavy rain and physical quantities fields have been analyzed, with the focus on the reason of the typhoon’s abrupt northeastward turn in Anhui Province and heavy rain concentrating in the northeast of typhoon center instead of near it. Meaningful conclusions are as follows. The reasons for typhoon abrupt turning are that the subtropical high pressure was moving southward and divergence fields of 200 hPa were to the right of the typhoon center; there was no obvious cold air invading Shandong after the typhoon entered the westerly belt; the southeasterly jet of typhoon and shear brought heavy rainfall to the Shandong peninsula before the typhoon entered Shandong. But after the typhoon’s movement into Shandong, the typhoon’s inverted trough brought the rainfall to the northern and central Shandong.     

An Extreme Monsoonal Heavy Rainfall Event over Inland South China in June 2023: A Synoptic Causes Analysis

An extreme monsoonal heavy rainfall event lasted for nine days and recurred in the interior of northern south China from June 13 to 21, 2022. Using regional meteorological stations and ERA5 reanalysis data, the causes of this extreme monsoonal rainfall event in south China were analyzed and diagnosed. The results are shown as follows. A dominant South Asian high tended to be stable near the Qinghai-Tibet Plateau, providing favorable upper-level dispersion conditions for the occurrence of heavy rainfall in south China. A western Pacific subtropical high dominated the eastern part of the South China Sea, favoring stronger and more northward transport of water vapor to the northern part of south China at lower latitudes than normal. The continuous heavy precipitation event can be divided into two stages. The first stage (June 13-15) was the frontal heavy rainfall caused by cold air (brought by an East Asian trough) from the mid-latitudes that converged with a monsoonal airflow. The heavy rains occurred mostly in the area near a shear in front of the center of a synoptic-system-related low-level jet (SLLJ), and the jet stream and precipitation were strongest in the daytime. The second stage (June 16-21) was the warm-sector heavy rainfall caused by a South China Sea monsoonal low-level jet penetrating inland. The heavy rainfall occurred on the windward slope of the Nanling Mountains and in the northern part of a boundary layer jet (BLJ). The BLJ experienced five nighttime enhancements, corresponding well with the enhancement of the rainfall center, showing significant nighttime heavy rainfall characteristics. Finally, a conceptual diagram of inland-type warm-sector heavy rainfall in south China is summarized.     

A Diagnostic and Numerical Study on a Rainstorm in South China Induced by a Northward-Propagating Tropical System

A strong cyclonic wind perturbation generated in the northern South China Sea （SCS） moved northward quickly and developed into a mesoscale vortex in southwest Guangdong Province, and then merged with a southward-moving shear line from mid latitudes in the period of 21-22 May 2006, during which three strong mesoscale convective systems （MCSs） formed and brought about torrential rain or even cloudburst in South China. With the 1° ×1° NCEP （National Centers for Environment Prediction） reanalysis data and the Weather and Research Forecast （WRF） mesoscale model, a numerical simulation, a potential vorticity inversion analysis, and some sensitivity experiments are carried out to reveal the formation mechanism of this rainfall event. In the meantime, conventional observations, satellite images, and the WRF model outputs are also utilized to perform a preliminary dynamic and thermodynamic diagnostic analysis of the rainstorm systems. It is found that the torrential rain occurred in favorable synoptic conditions such as warm and moist environment, low lifting condensation level, and high convective instability. The moisture transport by strong southerly winds associated with the rapid northward advance of the cyclonic wind perturbation over the northern SCS provided the warm and moist condition for the formation of the excessive rain. Under the dynamic steering of a southwesterly flow ahead of a north trough and that on the southwest side of the West Pacific subtropical high, the mesoscale vortex （or the cyclonic wind perturbation）, after its genesis, moved northward and brought about enormous rain in most parts of Guangdong Province through providing certain lifting forcing for the triggering of mesoscale convection. During the development of the mesoscale vortex, heavy rainfall was to a certain extent enhanced by the mesoscale topography of the Yunwu Mountain in Guangdong. The effect of the Yunwu Mountain is found to vary under different prevailing wind directions and intensities. The location o     

CLIMATOLOGICAL VARIATION FEATURES OF TYPHOON PRECIPITATION INFLUENCING FUJIAN FOR THE PAST 46 YEARS

The results of an analysis of the temporal and spatial distribution of typhoon precipitation influencing Fujian from 1960 to 2005 show that typhoon precipitation in Fujian province occurs from May to November, with the most in August. There has been a decreasing trend since 1960. Typhoon precipitation gradually decreases from the coastal region to the northwestern mainland of Fujian and the maximum typhoon precipitation occurs in the northeast and the south of Fujian. Typhoon torrential rain is one of the extreme rainfall events in Fujian. High frequencies of typhoon torrential rain occur in the coastal and southwest regions of the province. With the impact of Fujian’s terrain, typhoon precipitation occurs more easily to the east of the mountains than to the west. Atmospheric circulation at 500 hPa over Asia and sea surface temperature anomalies of the equatorial eastern Pacific are analyzed, with the finding that they are closely connected with the anomaly of typhoon precipitation influencing Fujian, possibly mainly by modulating the northbound track of typhoons via changing the atmosphere circulation to lead to the anomaly of typhoon precipitation over the province.     

台风“海棠”特大暴雨数值模拟研究

在福建中北部登陆的台风,往往会严重影响浙江,尤其值得注意的是台风引起特大暴雨经常会发生在浙江东南沿海的南雁荡山区和北雁荡山区,2005年在福建省连江黄歧登陆的台风"海棠"(0505)对浙江东南沿海造成严重影响,是这类台风比较典型个例。文中利用非静力模式MM5模拟"海棠"台风在浙东南沿海造成的特大暴雨,模拟结果与实况对比分析表明,模式较好地模拟了台风降水强度和分布,特别是成功模拟出南雁荡山区特大暴雨中心(南部暴雨区)和雁荡山区特大暴雨中心(北部暴雨区);运用高时空分辨率模拟资料对特大暴雨成因进行诊断分析表明,南部暴雨区涡度低层到高层向西倾斜结构和北部暴雨区高低空强辐散辐合的耦合结构有利于形成暴雨区强烈上升运动,环境风场垂直切变产生次级环流进一步加强暴雨区上升运动;暴雨区持续不稳定层结和特殊水汽输送通道为特大暴雨提供热力条件和水汽条件。最后对浙南闽北地形对台风特大暴雨影响进行数值敏感性试验表明,温州南、北雁荡山脉地形等高线与台风水汽输送路径正交是造成特大暴雨的重要原因,地形使暴雨增幅明显,地形越高对暴雨增幅越明显,降水分布更加不均匀。比较台风造成南、北特大暴雨条件,发现两者既有环境风场垂直切变产生次级环流进一步加强暴雨区上升运动、持续不稳定层结以及地形对暴雨增幅作用等相同之处,又有动力结构、维持持续不稳定层结条件以及水汽输送等不同之处。     

北雁荡山地形对2020年“黑格比”台风暴雨影响的数值模拟

2020年第4号台风“黑格比”在浙南登陆后过境北雁荡山期间在山区引发了特大暴雨。基于中尺度数值模式WRFV4.0.2对台风进行高分辨率数值模拟,分析北雁荡山地形对此次台风暴雨的作用,并设置了升降地形敏感性试验。结果表明:数值试验较好地模拟了台风移动及特大暴雨的落区和强度,台风大风区明显不对称分布,台风登陆后第一、四象限过境山区,其东侧强偏南气流向山区输送了充足水汽。台风登陆前山区低空存在一条由台风内核拖曳出的狭长螺旋辐合带,水汽通量辐合与风场辐合相一致。台风眼墙过境时沿着降水中心的迎风坡有强烈上升运动,动力条件极好,水汽输送带由近地面向对流层低层延展,山区有零星对流单体触发加强。台风后部环流影响时在高海拔山区风速减弱、绕流激发了中尺度低涡,强降水中心迎风坡上出现持续性、停滞不动的强正涡度中心,是特大暴雨发生的主要原因。地形敏感性试验中无地形时降水减幅40%~50%,地形高度翻倍降水增幅超过60%。     

四川盆周山地暖季单站暴雨事件的精细特征

利用四川省2010—2019年2 165个气象站逐小时降水资料,分区统计了四川盆周山地暖季(5—9月)单站暴雨事件的精细特征。结果表明:(1)四川省单站暴雨事件频数在川西山地与川西南山地呈密集的带状分布。川西与川西南山地通常在降水开始不久就达到雨量最大值,而川东北山地的峰值时间集中在暴雨事件中段。(2)盆周山地的暴雨系统整体呈自南向北由前半夜向后半夜传播的特征。川西南山地和川东北山地的暴雨系统分别呈现较弱的自南向北和自西向东传播,而川西山地的暴雨系统则存在明显的自西向东的传播特征。(3)长历时暴雨事件的峰值出现时间略落后于短历时暴雨事件。暴雨持续时间在空间上存在显著的经向差异,大值区主要位于川西山地和川东北山地一带,暴雨雨量、频次和峰值基本不随持续时间变化,但川西南山地的暴雨峰值则随持续时间的加长而推迟。(4)在四川省大部区域,单站暴雨事件的降水量、频次和强度均表现出随海拔高度升高而减小的特征。在成都平原西南部、东部以及川东北山地,夜间暴雨事件持续时间越长,降水量和频次在较高海拔越易出现最大值。     

浙江大暴雨与南海台风“山竹”相关性数值研究

2018年9月17日前后浙江东北部出现了大暴雨,与此同时,1822号台风“山竹”登陆广东并向西移动,为了研究浙江东北部大暴雨是否与“山竹”有关,利用云图资料、ERA-Interim再分析资料和自动站加密资料,先分析了2018年9月17日前后浙江东北部暴雨的天气形势,后通过WRF模式对此次过程进行了数值模拟,并做了将台风“山竹”去掉、增大一倍、缩小一半三个敏感性试验。表明此次暴雨过程出现在台风“山竹”倒槽东北顶端,是对流云系发展引发的。“山竹”的存在使得偏南气流输送到浙江东北部地区,且偏南风输送大小与“山竹”是否存在及其尺度密切相关。同时“山竹”使得浙江东北部区域存在着大范围深厚的高湿区,“山竹”越大,高湿区越深厚。“山竹”使得该区域低层有明显辐合,高层明显辐散,且尺度越大,辐合层高度越高。“山竹”还造成垂直运动旺盛,且尺度越大,上升运动越强。“山竹”使得浙江东北部大气层垂直螺旋度明显增大,且“山竹”越大,中低层垂直螺旋度越大,垂直螺旋度的大小对接下来6小时该区域降水量有很好的指示作用。由此,浙江暴雨预报需考虑同时出现的南海台风活动情况。      

“海棠”台风降水非对称分布特征成因的定量分析

2005年7月19日08时～20日08时“海棠”（Haitang)台风登陆福建省前后24小时期间, 带来一次明显降水过程, 且台风北侧降水较南侧强, 呈明显非对称分布。利用WRF模式对此次降水过程进行了数值模拟, 基于模拟结果, 不仅分析研究了相对湿度、 垂直上升运动场, 同时还进行改进的湿Q矢量诊断分析, 以及计算分析地形抬升和地表摩擦的强迫作用, 定量分析“海棠”台风降水非对称分布特征形成的可能成因。结果表明:（1) WRF模式成功地模拟出了此次降水非对称分布特征、主要降水落区, 以及300 mm以上极端强降水的强度、位置, 模拟效果令人鼓舞。（2) 垂直上升运动条件可能是造成降水非对称分布特征的主要因素。（3) 台风北侧改进的湿Q矢量散度辐合强度明显较其南侧强, 进一步计算分析发现, 改进的湿Q矢量散度强迫产生的降水场也呈明显非对称分布, 且台风北侧强于南侧。（4) 地形因子强迫产生的降水强度约是改进的湿Q矢量散度强迫产生的降水强度的1.6～2.5倍, 且地表摩擦作用强迫产生的降水强度约是地形抬升作用强迫产生的降水强度的2～3倍。     

河北省副热带高压外围降水的特征与预报

应用高空、地面等常规观测资料、NCEP/NCAR再分析资料、京津冀降水量资料,对2000—2013年河北省69次副热带高压(以下简称副高)外围降水个例进行了综合分析,结果表明:(1)69个副高外围降水个例雨量统计表明,暴雨和大暴雨发生频次自西北向东南明显增加,有三个区域较易出现暴雨和大暴雨:燕山南麓的唐山和秦皇岛、太行山东麓的邢台、河北平原东部的沧州和衡水。河北北部的坝上高原和保定西北部山区出现暴雨的概率较低。(2)按照副高型态,将69个副高外围暴雨过程分为三类,分别给出了每类的代表环流型和降水分布特征,并对这三种类型的环流背景场和物理量场进行了合成分析,给出了不同类型的环流特征和物理量特征。(3)统计了多个物理量及气象要素的平均值和极端值,统计结果可作为该类暴雨过程的量级、强度及极端性预报的重要参考指标。(4)在预报副高外围降水过程时,除了关注高空槽和副高的位置、强度、型态外,更要关注中低层及地面辐合系统。强降水多发生在584或586 dagpm等高线外围、低层700和850 hPa的低涡和切变线及地面倒槽或低压附近。     

“苏拉”台风倒槽引发鄂西北特大暴雨的诊断分析

利用常规观测资料、NCEP1°×1°逐6h再分析资料、地面自动站雨量资料,对1209号台风“苏拉”倒槽造成鄂西北特大暴雨天气过程进行诊断分析,结果表明:本次强降水天气过程是在“苏拉”台风倒槽、东南风和东风超低空急流、华北冷锋共同作用下产生的;台风倒槽建立了来自海上的水汽通道,为特大暴雨区提供了源源不断的水汽,降水强度则与水汽通量散度密切对应。      

ANALYSIS OF RAINSTORMS ASSOCIATED WITH SIMILAR TRACK TROPICAL CYCLONES HAITANG (0505) AND BILLS (0604)

It is generally thought that the influence of comparable track typhoons is approximately similar,but in fact their wind and especially their rainstorm distribution are often very different. Therefore,a contrastive analysis of rainstorms by tropical cyclones (TCs) Haitang (0505) and Bilis (0604),which are of a similar track,is designed to help understand the mechanism of the TC rainstorm and to improve forecasting skills. The daily rainthll of TC itaitang (0505) and Bills (0604) is diagnosed and compared.The result indicates that these two TCs have similar precipitation distribution before landtall but different precipitation characteristics after landthll. Using NCEP/GFS analysis data,the synoptic situation is analyzed; water vapor transportation is discussed regarding the calculated water vapor flux and divergence.The results show that the heavy rainfall in the Zhejiang and Fujian Provinces associated with Haitang (0505) and Bitis (0604) before landlhll results ti'om a peripheral easterly wind,a combination of the tropical cyclone and the terrain. After landthll and moving far inland of the storm,the precipitation of Haitang is caused by water vapor convergence carried by its own circulation; it is much weaker than that in the coastal area. One of the important contributing thctors to heavy rainstorms in southeast Zhejiang is a southeast jet stream,which is maintained over the southeast coast. In contrast,the South China Sea monsoon circulation transports large amounts of water vapor into Bills - when a water-vapor transport belt south of the tropical cyclone significantly strengthens - which strengthens the transport. Then,it causes water vapor flux to converge on the south side of Bilis and diverge on the north side. Precipitation is much stronger on the south side than that on the north side. After Bilis travels far inland,the cold air guided by a north trough travels into the TC and remarkably enhances precipitation. In summary,combining vertical wind shear with water vapor transportation is a good way to predict rainstorms associated with landing tropical cyclones.     

湖北一次梅雨大暴雨分析

应用加密探空资料、NCEP再分析资料与自动气象站雨量资料,分析2009年6月29日湖北梅雨大暴雨。结果表明:暴雨期间700hPa江淮较长切变线维持准纬向特性,850hPa低空急流北上到江南北部。700hPa鄂西北等地准东西走向θse锋区有所加强并南移,湖北暴雨区位于θse锋区南侧且θse数值有所增加的地区。垂直积分水汽辐合大值区与强降雨带位置对应比较好,且整层水汽辐合比强降雨发生要早6h以上。恩施、武汉两站暴雨发生除了受低层切变线等较大尺度系统影响外,局地气象要素配合也很重要,尤其是低层较为充足的水汽是降雨维持的条件。当高层低槽移过,高、中层之间出现水平风垂直切变后恩施降雨明显加强。武汉站前期高层或中层干空气向下伸展,中、低层不稳定层结加强后降雨发展,其最强降雨和低层冷式切变线过境同时发生。