“05. 6”华南强降水期间副热带高压活动与加热场的关系

采用NCEP/NCAR再分析逐日资料,根据全型垂直涡度倾向方程,研究2005年6月华南强降水期间西太平洋副热带高压(副高)位置变动特征及其与加热场的关系.结果表明,西太平洋副高位置变化和副热带地区的非绝热加热有密切关系.与气候平均状况相比,2005年6月副高北侧的加热区很强,而南侧赤道辐合带(ITCZ)没有相当强度的对流;伴随着副高北抬,其南侧均有明显的对流潜热加热向北伸展.副高西侧的加热基本上都大于副高纬带内的加热,副高的每一次西伸都伴随着西侧加热的显著增强,并且加热增强先于副高西伸.对流层中层,副高北侧非绝热加热率的垂直变化基本上都大于气候平均值,不利于副高北进;而南侧加热率的垂直变化均小于多年平均,有利于副高南侧反气旋性涡度异常增长,从而有利于副高南退.2005年6月下旬副高西伸之前,副高西侧非绝热加热率的垂直变化基本上都高于气候平均状况,有利于副高两侧反气旋涡度增加,从而诱使副高随后西伸;而东侧加热率的垂直变化大多数时间都低于气候平均状况,使得副高东侧气旋性涡度增加,有利于副高西伸,对流层低层也具有类似特点.因此在南北两侧加热和东西两侧加热的共同作用下,2005年6月副高位置较常年偏南偏西,从而有利于雨带在华南地区维持.     

Relationship Between the Western Pacific Subtropical High and the Subtropical East Asian Diabatic Heating During South China Heavy Rains in June 2005

Based on the daily NCEP/NCAR reanalysis data, the position variation of the western Pacific subtropical high (WPSH) in June 2005 and its relation to the diabatic heating in the subtropical East Asia are analyzed using the complete vertical vorticity equation. The results show that the position variation of the WPSH is indeed associated with the diabatic heating in the subtropical East Asian areas. In comparison with June climatology, stronger heating on the north side of the WPSH and relatively weak ITCZ (intertropical convergence zone) convection on the south side of the WPSH occurred in June 2005. Along with the northward movement of the WPSH, the convective latent heating extended northward from the south side of the WPSH. The heating to the west of the WPSH was generally greater than that inside the WPSH, and each significant enhancement of the heating field corresponded to a subsequent westward extension of the WPSH. In the mid troposphere, the vertical variation of heating on the north of the WPSH was greater than the climatology, which is unfavorable for the northward movement of the WPSH. On the other hand, the vertical variation of heating south of the WPSH was largely smaller than the climatology, which is favorable for the anomalous increase of anticyclonic vorticity, leading to the southward retreat of the WPSH. Before the westward extension of the WPSH in late June 2005, the vertical variation of heating rates to (in) the west (east) of the WPSH was largely higher (lower) than the climatology, which is in favor of the increase of anticyclonic (cyclonic) vorticity to (in) the west (east) of the WPSH, inducing the subsequent westward extension of the WPSH. Similar features appeared in the lower troposphere. In a word, the heating on the north-south, east-west of the WPSH worked together, resulting in the WPSH extending more southward and westward in June 2005, which is favorable to the maintenance of the rainbelt in South China.     

RELATIONSHIPS BETWEEN THE POSITION VARIATION OF THE WEST PACIFIC SUBTROPICAL HIGH AND THE DIABATIC HEATING DURING PERSISTENT INTENSE RAIN EVENTS IN YANGTZE-HUAIHE RIVERS BASIN

By using NCEP/NCAR daily reanalysis data and daily precipitation data of 740 stations in China, relationships between the position variation of the West Pacific subtropical high (WPSH) and the diabatic heating during persistent and intense rains in the Yangtze-Huaihe Rivers basin are studied. The results show that the position variation of WPSH is closely associated with the diabatic heating. There are strong apparent heating sources and moisture sinks in both the basin (to the north of WPSH) and the north of Bay of Bengal (to the west of WPSH) during persistent and intense rain events. In the basin, Q 1z begins to increase 3 days ahead of intense rainfall, maximizes 2 days later and then reduces gradually, but it changes little after precipitation ends, thus preventing the WPSH from moving northward. In the north of Bay of Bengal, 2 days ahead of strong rainfall over the basin, Q 1z starts to increase and peaks 1 day after the rain occurs, leading to the westward extension of WPSH. Afterwards, Q 1z begins declining and the WPSH makes its eastward retreat accordingly. Based on the complete vertical vorticity equation, in mid-troposphere, the vertical variation of heating in the basin is favorable to the increase of cyclonic vorticity north of WPSH, which counteracts the northward movement of WPSH and favors the persistence of rainbands over the basin. The vertical variation of heating in the north of Bay of Bengal is in favor of the increase of anti-cyclonic vorticity to the west of WPSH, which induces the westward extension of WPSH.     

大气加热场影响西太平洋副热带高压短期位置变化的数值模拟

利用江淮2003年和华南1998年夏季持续性强降水典型个例,采用区域气候模式RegCM3模拟了强降水期间江淮、华南及孟加拉湾热源异常分布对西太平洋副热带高压短期位置东西进退及南北变动的影响。模拟证实：西太平洋副热带高压位置的短期变异与大气加热场及其配置有密切的联系。持续性强降水期间,副高西侧较远处孟加拉湾热源是诱导西太平洋副热带高压异常西伸的原因之一;华南强降水期间,华南和孟加拉湾热源的共同存在可使副高在季节性西伸过程中出现短期东撤;江淮强降水期间,江淮和孟加拉湾热源的共同存在会诱导副高异常西伸。但模式在模拟副高位置南北变动上效果并不明显,不能证实华南、江淮热源单独存在时对副高在南北位置变异上的阻碍作用。     

Subseasonal Zonal Oscillation of the Western Pacific Subtropical High during Early Summer

This study examines the features and dynamical processes of subseasonal zonal oscillation of the western Pacific subtropical high (WPSH) during early summer, by performing a multivariate empirical orthogonal function (MVEOF) analysis on daily winds and a diagnosis on potential vorticity (PV) at 500 hPa for the period 1979–2016. The first MV-EOF mode is characterized by an anticyclonic anomaly occupying southeastern China to subtropical western North Pacific regions. It has a period of 10–25 days and represents zonal shift of the WPSH. When the WPSH stretches more westward, the South Asian high (SAH) extends more eastward. Above-normal precipitation is observed over the Yangtze–Huaihe River (YHR) basin. Suppressed convection with anomalous descending motion is located over the subtropical western North Pacific. The relative zonal movement of the SAH and the WPSH helps to establish an anomalous local vertical circulation of ascending motion with upper-level divergence over the YHR basin and descending motion with upper-level convergence over the subtropical western Pacific. The above local vertical circulation provides a dynamic condition for persistent rainfall over the YHR basin. An enhanced southwest flow over the WPSH’s western edge transports more moisture to eastern China, providing a necessary water vapor condition for the persistent rainfall over the YHR basin. A potential vorticity diagnosis reveals that anomalous diabatic heating is a main source for PV generation. The anomalous cooling over the subtropical western Pacific produces a local negative PV center at 500 hPa. The anomalous heating over the YHR basin generates a local positive PV center. The above south–north dipolar structure of PV anomaly along with the climatological southerly flow leads to northward advection of negative PV. These two processes are conducive to the WPSH’s westward extension. The vertical advection process is unfavorable to the westward extension but contributes to the eastward retreat of the WPSH.     

华北夏季降水的年代际变化

利用我国740个测站逐日降水资料和NCEP/NCAR逐日再分析资料,使用合成分析等方法,对华北夏季降水的年代际变化特征进行分析。结果表明:华北夏季降水的年代际变化与华北夏季雨带的年代际变化密不可分。在华北夏季降水偏多阶段,华北地区雨带降水量较大,华北雨带能够向西延伸,雨带位置大多数时间能够越过115°E,并且能够接近华北西部边界110°E,位置偏西;而在华北夏季降水偏少阶段,华北雨带降水量偏小,雨带虽然也能够越过115°E,但维持时间不长,且向西延伸并不明显,雨带位置很难接近华北西部边界110°E,位置偏东。华北雨带发生的年代际变化和东亚地区大气环流以及东亚夏季风的年代际变化有关。     

与2003年梅雨期西太副高东西向运动有关的热带上空东风带扰动的结构和演变特征

利用NCEP/NCAR 1 000～10 hPa 2.5 (×2.5 (的再分析资料,分析了与西太平洋副热带高压(简称西太副高)东西进退相关系的热带对流层上空东风带扰动(简称EV)的结构和演变特征.结果表明:西太副高与其南侧的东风带扰动存在同时西进的过程,当西太副高南、北两侧的东、西风带上的扰动在相向运动中抵达同一经度上时,西太副高出现异常东退.热带对流层上空东风带扰动为中高层天气系统,它从对流层中层伸展到50 hPa高度附近,在200 hPa上表现得最为明显,在热力场上表现出"上暖强下冷弱"的垂直分布特征;在西太副高东退时,东风带扰动东西侧的辐散效应和垂直运动的性质发生了显著变化,东风带扰动中心附近的垂直速度场出现从上升运动到向下下沉运动转化的过程.     

南海夏季风爆发前后华南前汛期降水日变化对比分析

利用华南地区248个国家级地面气象站逐小时降水数据和14个探空站数据,分析了2003—2016年4—6月华南前汛期降水日变化特征。据南海夏季风爆发时间,将降水分为爆发前后两个时段。华南地区主要存在两条大雨带,一个位于云贵高原至南岭山脉以南,另一个位于广东沿海地区。偏北雨带集中发生在后半夜至清晨时段,偏南雨带集中发生在中午至下午时段。南海夏季风爆发前后,降水量不存在明显相关性,相关系数较大时次位于中午至下午时段。前后期年降水标准差在0.5附近,变化幅度明显时段主要集中于凌晨至清晨。午后出现3 h多年降水量变化幅度最大值,最小时段为中午12时。降水量、降水频率和降水强度的经向分布特征明显且相似:降水量和降水频率在112 °E附近出现日变化转折,以西多出现不稳定夜雨,以东白天降水波动较大。在南海夏季风爆发前,降水特征主要表现为西部高频、南部高强,在清晨更多作用于对暴雨系统的增长;季风爆发后则表现为西北-东南南的高频率高强度降水形态,在傍晚更多作用于增加降水发生频率。      

2012年我国夏季降水预测与异常成因分析

本文对2012年我国夏季降水的实况和预测进行简要回顾,发现2012年夏季降水大体呈北方涝、长江旱的分布,主雨带位于黄河流域及其以北,降水异常偏多的区域主要位于西北大部、内蒙古和环渤海湾,黄淮与江淮地区降水偏少,江汉至淮河上游一带干旱严重;预测的主雨带位于华北南部至淮河,较实况偏南。对我国北方降水异常偏多的成因分析表明:2012年夏季欧亚中高纬地区阻塞高压（简称阻高）强盛,同时东北冷涡活动频繁,中高纬500 hPa高度场从西至东呈“+-+”的分布,这种环流形势没有造成长江洪涝是因为东亚夏季风异常偏强,同时西太平洋副热带高压（副高）偏北,冷暖空气对峙于我国北方地区,导致北方降水异常偏多。分析还表明阻高、东北冷涡、东亚夏季风和副高这四个系统的不同配置影响着冷暖气流的对峙位置,进而形成我国夏季的主雨带。最后通过定量和定性判断相结合的方法,选取了2012年夏季降水的最佳相似年和最佳相反年,对比分析了2012年夏季降水与其最佳相似年和最佳相反年的海温演变与东亚夏季风环流系统主要成员的差异:1959年夏季降水作为2012年夏季降水的最佳相似年,虽然海温及东亚夏季风系统关键成员异常不明显,但是和2012年也呈近似相反的特征;而1980年夏季降水作为2012年夏季降水的最佳相反年,海温及东亚夏季风环流系统关键成员和2012年呈显著的反向特征,这些观测事实反映了我国夏季降水与海温及东亚夏季风环流系统关键成员这些主要影响因子之间关系的年代际变化。     

COMPARISON OF THE EFFECTS OF ANOMALOUS CONVECTIVE ACTIVITIES IN THE TROPICAL WESTERN PACIFIC ON TWO PERSISTENT HEAVY RAIN EVENTS IN SOUTH CHINA

The different effects of anomalous convective activities in the tropical western Pacific on two persistent heavy rain events in South China in 2005 and 2006 have been compared in this study. The dataused consist of NOAA Outgoing Longwave Radiation (OLR) data, the NCEP-NCAR reanalysis and precipitation from meteorological stations in South China. Results show that the persistent heavy rain in 2005 was related to the 10-25-day westward propagation of convective activities in the tropical western Pacific from about 150 °E. The physical mechanism is interpreted as a Gill-type response of subtropical anticyclone westward extension during weak convective activities period over the Philippine Sea. Our researches also show that the persistent heavy rain in 2006 has longer period than that in 2005, and the subtropical anticyclone persists westward in the earlier summer which is possibly related to the lasting anomalous strong convective motion in the southern branch of Intertropical Convergence Zone (ITCZ) in the tropic western Pacific. The anomalous convective activities affect the local Hadley circulation over the western Pacific with anomalous ascending motion south of the equator and anomalous descend motion north of it, in favor of the westward extension of the subtropical anticyclone for a long time. Comparison between the two persistent heavy rain events indicates different physical effects of convective activities in the tropical western Pacific, though both effects are helpful to the subtropical anticyclone westward extension as a common character of large-scale circulation backgrounds for persistent heavy rain events in South China.     

水平涡度与夏季风环流变化

在斜压涡度发展理论的基础上，讨论了大尺度大气运动中水平涡度向垂直涡度转化的情况，并用以刻划夏季风变动。将声坐标中涡度方程的有关项在2坐标中分离出水平涡度向垂直涡度转化的主要项，经尺度分析得出，在对流层中、高层，这些转化项中的水平分量是大尺度大气斜压性涡度发展的主要因子。通过对1998年4—8月的GAME(GEWEX Asian Monsoon Experiment，全球能量和水分循环试验(GEWEX)的子试验：亚洲季风试验，简称GAME)再分析资料进行实际计算发现，转化项在东亚夏季风上升支的600 hPa及以上层次对P坐标垂直涡度的局地变化贡献很大，不能忽略。同时发现水平涡度向垂直涡度的转化对南海季风爆发和江淮梅雨入梅及其发展过程均有指示性意义。南海季风爆发以后，在中国东南部地区，转化项的大小与夏季风的活跃和中断等活动吻合，转化项的变化反映了西太平洋副高在中国大陆的活动规律。     

Characteristics of Subtropical Monsoon and Rainfall over Eastern China and Western North Pacific

Using the NCAR/NCEP (National Center for Atmospheric Research/National Centers for Environmental Prediction) reanalysis and the NOAA Climate Prediction Center's merged analysis of precipitation (CMAP)during 1981-2000, we investigated the seasonal evolution of the southwesterly wind and associated precipitation over the eastern China-subtropical western North Pacific area and its relationship with the tropical monsoon and rainfall, and analyzed the reasons responsible for the onset and development of the wind. It was found that the persistent southwesterly wind appears over southern China and the subtropical western Pacific the earliest in early spring, and then expands southwards to the tropics and advances northward to the midlatitudes. From winter to summer, the seasonal variation of surface heating over western China and the subtropical western Pacific may result in an earlier reversal of the westward tropospheric temperature gradient over the subtropics relative to the tropics, which may contribute to the earliest beginning of the subtropical southwesterly wind. Additionally, the strengthening and eastward expanding of the trough near the eastern Tibetan Plateau as well as the strengthening and westward moving of the western Pacific subtropical high also exert positive influences on the beginning and development of the subtropical southwesterly wind.In early summer,the northward expansion of the southwesterly wind over southern China is associated with a northward shift of the subtropical high, while the southward stretch of the southwesterly wind is associated with a southward stretch of the trough in the eastern side of the plateau. With the beginning and northward expansion of the subtropical southwesterly wind (namely southwest monsoon), convergences of the low-level air and water vapor and associated upward motion in front of the strongest southwesterly wind core also strengthen and move northward, leading to an increase in rainfall intensity and a northward shift of the rain belt. Accordingly, the subtropical rainy season occurs the earliest over southern China in spring, moves northward to the Yangtze-Huaihe River valley in early summer, and arrives in North China in mid summer.Compared with the subtropical rainy season, the tropical rainy season begins later and stays mainly over the tropics, not pronouncedly moving into the subtropics. Clearly, the Meiyu rainfall over the Yangtze-Huaihe River valley in early summer results from a northward shift of the spring rain belt over southern China,instead of a northward shift of the tropical monsoon rain belt. Before the onset of the tropical monsoon,water vapor over the subtropical monsoon region comes mainly from the coasts of the northern Indo-China Peninsula and southern China. After the onset, one branch of the water vapor flow comes from the Bay of Bengal, entering into eastern China and the subtropical western Pacific via southwestern China and the South China Sea, and another branch comes from the tropical western North Pacific, moving northwestward along the west edge of the western Pacific subtropical high and entering into the subtropics.     

气候平均场上西太平洋副热带高压双脊线过程可能成因的动力诊断分析

利用NCEP-DOE再分析数据集II,诊断分析了气候平均场上6次西太平洋副热带高压双脊线过程,借助一个两层半大气模式,从动力学上初步揭示了西太平洋热带大气准10天振荡（Quasi Ten-day Oscillation,简称QTO）向西北方向传播与季风槽东伸西撤之间的相互作用过程,探讨了气候平均场上西太副高双脊线可能的形成机制。分析表明季风槽准10天东西振荡是气候平均场上西太副高双脊线形成的主要原因,而季风槽东伸西撤与QTO传播密切相关。进一步分析发现,QTO向西北方向传播,东风切变作用于斜压辐散的经向梯度,在对流中心北侧生成正扰动涡度。QTO在季风槽东侧激发的气旋性扰动涡度,诱导季风槽东伸,侵入副高,造成副高外围变形,形成双脊线。因此,形成西太副高双脊线的主要原因之一可能是西太平洋热带大气QTO。尽管季风槽东伸直接引起副高双脊线发生,但是它只不过是受QTO影响的一种表现。本文仅为诊断结果,其结果还有待于模式敏感性试验的验证。     

DYNAMICAL PREDICTION OF WEST CHINA AUTUMN RAINFALL BY THE NCEP CLIMATE FORECAST SYSTEM

This study investigates the variation and prediction of the west China autumn rainfall (WCAR) and their associated atmospheric circulation features, focusing on the transitional stages of onset and demise of the WCAR. Output from the 45-day hindcast by the National Centers for Environmental Prediction (NCEP) Climate Forecast System version 2 (CFSv2) and several observational data sets are used. The onset of WCAR generally occurs at pentad 46 and decays at pentad 56, with heavy rainfall over the northwestern China and moderate rainfall over the south. Before that, southerly wind changes into southeasterly wind, accompanied by a westward expansion and intensification of the western Pacific subtropical high (WPSH), favoring rainfall over west China. On the other hand, during the decay of WCAR, a continental cold high develops and the WPSH weakens and shifts eastward, accompanied by a demise of southwest monsoon flow, leading to decay of rainfall over west China. The CFSv2 generally well captures the variation of WCAR owing to the high skill in capturing the associated atmospheric circulation, despite an overestimation of rainfall. This overestimation occurs at all time leads due to the overestimated low-level southerly wind. The CFSv2 can pinpoint the dates of onset and demise of WCAR at the leads up to 5 days and 40 days, respectively. The lower prediction skill for WCAR onset is due to the unrealistically predicted northerly wind anomaly over the lower branch of the Yangtze River and the underestimated movement of WPSH after lead time of 5 days.     

华北地区一次黄河气旋发生发展时所引起的暴雨诊断分析

利用NCEP/NCAR的再分析资料和GMS红外黑体亮度温度 (T_BB) 资料等, 对1991年6月9—11日的一次黄河气旋暴雨过程进行了诊断分析。结果表明:黄河气旋的发生发展是大气斜压性强烈发展的结果, 强的高空辐散与正涡度平流共同作用形成了黄河气旋, 对流层低层的暖平流促进了黄河气旋的进一步发展, 并对其移动方向有引导作用; 暴雨出现在黄河气旋的初生、发展阶段, 产生于气旋前部暖区的盾状云系中; 暴雨的水汽有西南和东南两个来源, 其中西南水汽通量大于东南; 暴雨区上空大气具有很强的对流不稳定性, 中尺度对流云团的发生发展, 造成了气旋降水分布的不均匀性和强降水中心; 降水造成的凝结潜热释放对气旋的发展有正反馈作用。     

青藏高原大地形对华南持续性暴雨影响的数值试验

利用新一代中尺度数值预报模式WRF3.2及NCEP/NCAR 逐日4次1°×1°的FNL再分析资料,通过有、无青藏高原以及将高原高度降低到临界高度的数值试验,研究了青藏高原大地形对我国华南地区2010 年5 月一次持续性暴雨过程的影响。试验结果表明:高原大地形对降水的影响显著,随着高原高度的升高,降水增多,高原以东地区的雨带也由北向南移动;高原地形的机械阻挡作用使迎风坡一侧的近地面层附近为强上升运动,背风坡为下沉运动,并分别对应降水的峰值和谷值区;高原对西风气流的爬流、绕流作用明显,高原升高后爬坡作用减弱,以绕流作用为主;高原的加热作用使气流过高原时南支减弱,北支加强,并加强了高原及其东部地区低层的正涡度和高层的负涡度,使高原上空为强烈的上升运动;高原的热力作用使西太平洋副热带高压位置偏南、偏西并稳定维持;高原大地形对形成稳定的高原季风环流圈有重要作用;高原地形高度的作用有利于定常波的形成,波动中心对应强上升运动,形成降水的大值区,稳定维持的定常波使得降水持续集中在同一地区,造成持续性暴雨。     

Changed Relationships Between the East Asian Summer Monsoon Circulations and the Summer Rainfall in Eastern China

In previous statistical forecast models, prediction of summer precipitation along the Yangtze River valley and in North China relies heavily on its close relationships with the western Pacific subtropical high (WPSH), the blocking high in higher latitudes, and the East Asian summer monsoon (EASM). These relationships were stable before the 1990s but have changed remarkably in the recent two decades. Before the 1990s, precipitation along the Yangtze River had a significant positive correlation with the intensity of the WPSH, but the correlation weakened rapidly after 1990, and the correlation between summer rainfall in North China and the WPSH also changed from weak negative to significantly positive. The changed relationships present a big challenge to the application of traditional statistical seasonal prediction models. Our study indicates that the change could be attributed to expansion of the WPSH after around 1990. Owing to global warming, increased sea surface temperatures in the western Pacific rendered the WPSH stronger and further westward. Under this condition, more moisture was transported from southern to northern China, leading to divergence and reduced (increased) rainfall over the Yangtze River (North China). On the other hand, when the WPSH was weaker, it stayed close to its climatological position (rather than more eastward), and the circulations showed an asymmetrical feature between the stronger and weaker WPSH cases owing to the decadal enhancement of the WPSH. Composite analysis reveals that the maximum difference in the moisture transport before and after 1990 appeared over the western Pacific. This asymmetric influence is possibly the reason why the previous relationships between monsoon circulations and summer rainfall have now changed.     

Feature analysis and primary causes of pre-flood season “cumulative effect” of torrential rain over South China

When persistent rainfall occurs frequently over South China, meso-scale and micro-scale synoptic systems persist and expand in space and time and eventually form meso-scale and long-scale weather processes. The accumulation of multiple torrential rain processes is defined as a “cumulative effect” of torrential rain (CETR) event. In this paper, daily reanalysis datasets collected by the National Centers for Environmental Prediction-Department of Energy (NCEP-DOE) during 1979–2014 are used to study the anomalous features and causes of heavy CETR events over South China. The results show that there is a significant difference in the spatial distribution of the heavy CETR events. Based on the center position of the CETR, the middle region displayed middle-region-heavy CETR events while the western region displayed west-region-heavy CETR events. El Niño events in the previous period (December, January, February, March (DJFM)) are major extra-forcing factors of middle-region-heavy CETR events, which is beneficial for the continuous, anomalous Philippine Sea anticyclone and strengthens the West Pacific Subtropical High (WPSH), extending it more westward than normal. The primary water vapor source for precipitation in middle-region-heavy CETR events is the Tropical Western Pacific Ocean. The major extra-forcing factor of a west-region-heavy CETR is the negative anomaly in the southern Tropical Indian Ocean (TIO) during the previous period (DJFM). This factor is beneficial for strengthening the cross-equatorial flow and westerly winds from the Bay of Bengal to the South China Sea (SCS) and early SCS summer monsoon onset. The primary water vapor source of precipitation in the west-region-heavy CETR is the southern TIO.     

“莫拉克”台风螺旋雨带与水平涡度的关系

利用实况资料和WRF模拟资料,分析2009年8月6—10日"莫拉克"台风在台湾地区造成强降水过程中台风螺旋雨带与水平涡度的关系。结果表明:模式较好地模拟出了本次台风暴雨的发生发展过程。在7日00时—9日00时,台风外围有两条螺旋雨带,一支位于台湾的中部偏南,一支位于台湾的南部,暴雨主要位于这两支螺旋雨带上;暴雨出现在环流上升支附近,在中低层,雨带对应着较大的指向东的水平涡度,且随着水平涡度大值区移动而移动,显示出两者较密切的联系;水平涡度的大值区与垂直涡度的大值区也有较好的对应关系,存在水平涡度向垂直涡度的转化;水平涡度的旋度正值区对应上升运动区,其旋度的大值区对应强的螺旋雨带与降水。当水平涡度减小时,若水平涡度的旋度正值区存在,雨带仍然可以维持。     

“05．6”华南特大暴雨过程大尺度水汽输送特征

利用NCEP／NCAR再分析资料、FY-2C卫星逐时云顶亮温TBB资料（0．05°×0．05°分辨率）、自动气象站逐时降水资料、实时地面加密观测资料和实况探空资料等,对“05．6”华南持续性暴雨过程期间大尺度水汽输送特征进行了深入分析。结果表明：南海夏季风的活动与本次暴雨过程水汽输送有密切关系。南亚季风在经过中南半岛后与伸入南海的副高西侧气流汇合,使得西南气流发生“S”形转换,从而演变为副热带季风并持续向华南地区输送水汽。暴雨期间,来自南海中北部和孟加拉湾的水汽输送带一直稳定在18°-27°N,水汽通量大值输送带和水汽通量辐合大值带均随高度向北明显倾斜,显示偏南方向的水汽输送特征,来自南海中北部的水汽是最主要源地,而来自孟加拉湾的输送通道仅对本次过程起到补充作用。过程期间,由于南北向净流入明显大于东西向净流出,故华南地区水汽总收支为净流入,水汽净流入量以低层横向（南北）为主,以行星边界层的水汽输入为最大。