Mesoscale and Microphysical Characteristics of a Double Rain Belt Event in South China on May 10–13,2022

A second rain belt sometimes occurs ahead of a frontal rain belt in the warm sector over coastal South China,leading to heavy precipitation.We examined the differences in the mesoscale characteristics and microphysics of the frontal and warm sector rain belts that occurred in South China on May 10–13,2022.The southern rain belt occurred in an environment with favorable mesoscale conditions but weak large-scale forcing.In contrast,the northern rain belt was related to low-level horizontal shear and the surface-level front.The interaction between the enhanced southeasterly winds and the rainfall-induced cold pool promoted the persistent growth of convection along the southern rain belt.The convective cell propagated east over the coastal area,where there was a large temperature gradient.The bow-shaped echo in this region may be closely related to the rear-inflow jet.By contrast,the initial convection of the northern rain belt was triggered along the front and the region of low-level horizontal shear,with mesoscale interactions between the enhanced warm-moist southeasterly airflow and the cold dome associated with the earlier rain.The terrain blocked the movement of the cold pool,resulting in the stagnation of the frontal convective cell at an early stage.Subsequently,a meso-γ-scale vortex formed during the rapid movement of the convective cell,corresponding to an enhancement of precipitation.The representative raindrop spectra for the southern rain belt were characterized by a greater number and higher density of raindrops than the northern rain belt,even though both resulted in comparable hourly rainfalls.These results help us better understand the characteristics of double rain belts over South China.

AN OBSERVATIONAL ANALYSIS OF A TORRENTIAL RAINSTORM IN THE WARM SECTOR OF SOUTH CHINA COASTAL AREAS

On May 20 th 2007, a brief but severe downpour rainstorm occurred in the coastal areas of Maoming and Yangjiang with rainfall of 115 mm per hour. Data from NCEP/NCAR reanalysis with 1°×1° resolution, Doppler weather radar, conventional surface observations, high-altitude radiosonde and wind profiler radar were used to analyze characteristics and contributions of synoptic scale and mesoscale systems during this torrential rainstorm. The results showed that:(1) the storm was caused by a quasi-linear mesoscale convective system(MCS) and the slow-movement of this system was the primary trigger of the torrential downpour;(2) water vapor was abundant, nearly saturated and in steady state throughout the atmosphere before the storm; intrusion of the weak dry and cold air in the middle level and a striking "dry above and wet below " structure had increased the atmospheric instability;(3) low-level southwesterly airflow from a low pressure(trough) at the Beibu Gulf provided abundant water vapor at the onset of the rainstorm; a deep dry layer was formed by dry and cold air behind the high-level trough, which facilitated latent heat release;upper-level divergence and low-level convergence circulations also provided vertical uplift for warm and moist air at the lower level;(4) Topography only played a minor role as the MCS developed and strengthened over relatively flat coastal terrain. Low level density flow induced by convection triggered new convective cell generation at the leading edge of the convective system, thereby playing a key role in the change of temperature gradient at lower layers, and resulting in strengthening atmospheric instability.

ANALYSIS OF MESOSCALE CONVECTIVE SYSTEMS ASSOCIATED WITH A WARM-SECTOR RAINSTORM EVENT OVER SOUTH CHINA

With multiple meteorological data, including precipitation from automatic weather stations, integrated satellite-based precipitation (CMORPH), brightness temperature (TBB), radar echoes and NCEP reanalysis, a rainstorm event, which occurred on May 26, 2007 over South China, is analyzed with the focus on the evolution characteristics of associated mesoscale-β convective systems (Mβcss). Results are shown as follows. (1) The rainstorm presents itself as a typical warm-sector event, for it occurs within a surface inverted trough and on the left side of a southwesterly low-level jet (LLJ), which shows no obvious features of baroclinicity. (2) The heavy rainfall event is directly related to at least three bodies of Mβcss with peak precipitation corresponding well to their mature stages. (3) The Mβcss manifest a backward propagation, which is marked with a new form of downstream convection different from the more usual type of forward propagation over South China, i.e., new convective systems mainly form at the rear part of older Mβcss. (4) Rainstorm-causing Mβcss form near the convergence region on the left side of an 850-hPa southwesterly LLJ, over which there are dominantly divergent air flows at 200 hPa. Different from the typical flow pattern of outward divergence off the east side of South Asia High, which is usually found to be over zones of heavy rains during the annually first rainy season of South China, this warm-sector heavy rain is below the divergence region formed between the easterly and southerly flows west of the South Asian High that is moving out to sea. (5) The LLJ transports abundant amount of warm and moist air to the heavy rainfall area, providing advantageous conditions for highly unstable energy to generate and store at middle and high levels, where corresponding low-level warm advection may be playing a more direct role in the development of Mβcss. As a triggering mechanism for organized convective systems, the effect of low-level warm advection deserves more of our attention. Based on the analysis of surface mesoscale airflow in the article, possible triggering mechanisms for Mβcss are also discussed.

Analysis of a Regional Rainstorm Process in South Shaanxi during July 17-18,2010

Based on conventional high-altitude aerial and ground data, regional intensive rainfall data, Doppler weather radar and satellite cloud data, the occurrence and development process of a regional rainstorm in South Shaanxi during July 17 -18, 2010 was discussed deeply. The results showed that the occurrence and development of the mesoscale weather system resulted in the heavy storm directly besides favorable large-scale background, and the the occurrence and development of the system had strong local and sudden characters. In addition, heavily concentrated wa- ter vapor in the troposphere at low and middle altitudes as well as existence of unstable conditions of convection might be favorable to the develop- ment of the system, while dynamic action of terrain, ground weak cold front and disturbance of the low-level jet stream might trigger the occurrence and development of the system.

近62 a华南“龙舟水”气候特征及变化

每年端午节前后龙舟竞渡之时,是华南前汛期降水最多、最为集中的时段,容易引发严重洪涝灾害,并对早稻生产造成严重影响,称之为“龙舟水”。对华南“龙舟水”期间暴雨过程的频次和强度进行研究是当前防灾减灾的迫切需求。利用1961—2022年华南192个国家气象观测站逐日降水资料,采用EOF、线性趋势、M-K突变等方法,分析了华南“龙舟水”期间降水量的时空特征及变化;构建了一个表征华南“龙舟水”暴雨过程的综合强度指数,由此分析华南近62 a“龙舟水”期间暴雨过程频次、强度以及“龙舟水”强度年景指数的特征和变化。结果表明,华南“龙舟水”一致性变化是其最主要的特点。1961—2022年“龙舟水”期间,华南共出现229次暴雨过程,平均每年3.7次。近62 a来华南区域平均“龙舟水”降水量和暴雨过程频次变化趋势不显著,但“龙舟水”强度年景指数以1.2·(10 a)^(-1)的速率显著上升。评估得到近62 a华南“龙舟水”最强暴雨过程出现在2022年6月4—21日,华南“龙舟水”强年有4 a,分别出现在2022年、2020年、2008年和2006年。

“0506”华南持续性暴雨的季风环流背景

提出了确定东亚夏季风活动区域、划分热带季风和副热带季风活动区域的指标,利用大气对流层风速、位势高度、湿度、温度、OLR以及TBB等NCEP/NCAR资料,从月、候和过程平均多种时间尺度,诊断分析了2005年6月(简称“0506”)华南持续性暴雨的季风环流活动变化特征。结果表明:副热带高压强度偏强,西脊点位置偏西偏南,热带西太平洋(130°～140°E)区域越赤道气流偏强,华南处于气旋性低压异常区,无论是月时间尺度还是暴雨过程时间尺度都表现出这些明显特征;暴雨过程水汽除了来源于孟加拉湾和南海外,水汽通量异常部分主要来自南海和热带西太平洋,热带西太平洋水汽随着副高边缘气流经过南海向华南输送,从而为暴雨过程提供了丰富的水汽来源;2005年6月热带季风前沿在华南沿海地区停滞时间比气候平均偏长(2候),该特征是华南暴雨预报值得参考的信号;6月整个南海地区平均季风偏强,主要体现于经向风明显偏强,但华南持续性暴雨过程开始于南海地区夏季风非活跃期,这与热带季风季节内振荡向北传播到华南有关。以上季风活动变化特征为华南强降水提供了有利的动力条件和丰富的水汽来源。

南海夏季风爆发对广西6月暴雨的影响

利用1961—2020年广西地面气象观测站逐日降水资料、NCEP/NCAR再分析资料,研究了南海夏季风爆发对广西6月暴雨的影响。结果表明,当南海夏季风爆发偏早时,东亚大槽显著偏强,中高纬度地区经向环流增强;华南沿海西南风显著偏强,配合中高纬度偏强的经向型环流引导北风南下,南北风在广西上空交汇;印度洋到海洋性大陆热带季节内振荡(MJO)处于对流活跃位相,且向东移动明显,低频对流带在西南季风引导下向广西输送;广西上升气流显著偏强,暴雨日数偏多。反之,暴雨日数偏少。

近30年华南地区“龙舟水”暴雨研究进展

主要综述和回顾近30a来国内外关于华南“龙舟水”暴雨的天气气候研究进展,包括高空槽、切变线、低涡、急流、副热带高压等天气系统的影响,低频振荡、季风等大尺度环流背景,及其对高原积雪、海温等外强迫信号的响应。总结了“龙舟水”暴雨精细化预报中主要存在的问题,对提高“龙舟水”暴雨预报预测能力提出了展望。

华南丘陵区马贵河小流域暴雨山洪灾害强降水特征

降水强度及持续时间是引发山洪灾害的重要气象因素,短时间内高强度的降水极易诱发山洪灾害,研究降水因子时空变化是防范及预警山洪灾害的关键环节。为了探索不同时间尺度的降水与局地山洪灾害之间的潜在联系,本文利用2010—2018年稠密的气象自动站逐小时降水观测数据,统计分析了以马贵河小流域为中心的华南丘陵区多尺度降水特征,重点从短时强降水(降水量≥20 mm/h)的角度揭示了诱发该流域山洪灾害的可能降水成因,并分类建立了该区域典型短时强降水事件的天气学概念模型。研究表明:马贵河小流域并非华南丘陵区的年降水、年暴雨高频中心,但短时强降水发生频次较高,强度较大;山洪灾害频发与时间尺度更短的短时强降水关系更为密切,而非普遍关注的暴雨天气过程;该流域的短时强降水具有双峰型分布特征,华南前汛期(4—6月)短时强降水频次与强度略高于后汛期(7—9月),但后汛期午后的峰值频次更为集中;典型短时强降水过程可分为冷式切变型、低空低涡型、偏南急流型和热带气旋型等4种基本类型,不同环流类型的系统配置与环境条件具有明显差异。该成果一方面加深了对华南丘陵区短时强降水与山洪灾害内在联系的科学认识;另一方面,可为当地短时强降水及山洪灾害预报预警提供技术支持。

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 of the heavy rainfall was in a degree determined by the trumpet-shaped topography of the Zhujiang Delta. It is identified that the topographic effect on precipitation depends on the relative position between the terrain and the mesoscale storm systems. The short distance from the SCS to South China facilitates the moisture transport, which offers ease for the heavy rain to form in South China. Finally, the role played by land-sea contrast in the fast intensification of the MCSs in South China is not yet clear, and the interaction between the MCSs and the mesoscale vortex needs to be clarified as well.

“20.6”华南西部前汛期极端持续性暴雨特征与成因分析

2020年5月底至6月上旬广西出现了12天的严重致灾持续性暴雨过程,由于其形成的极端复杂性,有必要进行深度剖析,揭示其特征和成因。利用欧洲中期天气预报中心(EC)ERA50.25°×0.25°逐小时再分析及实况资料,对该次过程进行了多尺度综合分析。中期天气预报:(1)该次过程具有强降雨持续时间长、范围广、强度强、累积雨量大、多地24 h雨量破历史记录及灾情特别重等特点。(2)该次过程发生在中高纬度环流、副热带高压、孟加拉湾低槽、低空急流及南亚高压有利配置的环流背景下。南亚高压过渡层与副热带高压不形成稳定对峙,中高纬经向型环流重建向纬向型环流转换,冷空气影响华南地区具有波动式特点,造成冷锋、静止锋及暖区交替影响,从而形成局地性、区域性及全省性暴雨交替,具有与以往持续性暴雨明显不同的特点。(3)大气聚积较大能量,锋面和暖区暴雨前聚积巨大能量,能量聚积及有效释放与最大小时降雨量成正相关。低层大气高温高湿且整层大气湿层深厚及较小的CIN和较低的TCL_P有利于能量的积聚和对流触发,暖区和静止锋暴雨具有更易于触发的环境条件。能量、动力及水汽辐合的极端性造成了降雨极端性。(4)锋面暴雨由地面中尺度锋区、切变线及地形触发,系统的合并及低空环境风场的增强,组织了对流发展。暖区暴雨由边界层急流轴左侧气旋性切变、低空急流出口辐合及地形抬升触发,急流的脉动增强组织对流发展。(5)锋面暴雨为移动性云带,暖区暴雨为少动性云团,云顶亮温越低,最大小时雨量越大,云顶亮温低于200 K可作为最大小时雨量大于50 mm/h判据,最大小时雨量出现在最低云顶亮温达最小值之后。强降雨开始于雷达RCS最大值≥45 dBZ,维持期间≥50 dBZ。锋面为高质心冷云回波,暖区为低质心暖云回波。(6)地形对暴雨触发和维持起重要作用,对暖区暴雨作用更明显。(7)观测与再分析资料对弱冷空气的渗透分析存在差异,前者更容易捕捉到对流触发。

Pre‑rainy Season Rainstorms in South China—Risk Perception of the 11 April 2019 Rainstorm in Shenzhen City

With the acceleration of urbanization in South China, rainstorms and floods are threatening the safety of people in urban areas. The 11 April 2019(4·11 hereafter)rainstorm in Shenzhen City was a typical pre-rainy season rainstorm that caused great damage, yet such pre-rainy season events have not attracted sufficient attention in research.Risk perception of the public may indirectly affect their disaster preparedness, which is important for disaster management. In this study, we conducted a questionnaire survey that considered demographic factors and the level of risk perception, knowledge of risk, impact of the 4·11 rainstorm event on public risk perception, and degree of trust in the government. We used a two-factor model of risk perception to evaluate the factors that influenced public risk perception of the 4·11 rainstorm in Shenzhen. The main conclusions are: The 4·11 rainstorm improved public awareness of both risk and impact through the medium term, but the public’s perceived low probability of disaster occurrence and lack of knowledge of the pre-rainy season rainstorm phenomenon led to serious losses during this event. Although the public has high trust in the Shenzhen government, the management of rainstorm disasters in the pre-rainy season needs to be further improved.

华南前汛期区域持续性暴雨的分布特征及分型

利用广东和广西两省共175个台站的日降水观测资料,采用计算机检索的方法,对1961-2005年间华南前汛期区域持续性暴雨进行了定义。对南海夏季风爆发前后区域持续性暴雨的气候分布特征的分析发现,季风爆发前持续性暴雨频数从60年代至今呈现出正态分布的年代际变化特征,而季风爆发后的区域持续性暴雨频数变化则几乎相反;广东省前汛期区域持续性暴雨降水明显比广西强。此外,通过EOF方法和相关分析得到了夏季风爆发前后出现频率较高的几种分布雨型,它们能较好地代表季风爆发前后华南降水分布的特点。

华南暴雨的气候特征及变化

利用华南110个测站1961—2008年逐日降水资料,采用线性趋势分析、Mann-Kendall检验、小波分析、计算趋势系数等统计诊断方法,分析了华南年和前、后汛期的暴雨日数、强度、贡献率等的气候特征及变化。结果表明,近48年来,华南年平均暴雨日数的地理分布总体上呈由沿海向内陆递减的趋势,最多中心在广西东兴(14.9d),最少中心在广西隆林(3.2 d)。华南的暴雨72%发生在汛期,其中前汛期占45%,后汛期占27%。华南平均年和前、后汛期暴雨日数呈微弱上升趋势,但不明显。年和前、后汛期暴雨日数具有明显的年际、年代际变化特征。华南平均年和前汛期的暴雨强度有微弱增加趋势,特别是2005年以来升幅明显,而后汛期暴雨强度有不明显减少趋势。华南年暴雨贡献率增加明显,而前、后汛期暴雨贡献率增加并不明显。小波分析表明:2000年以来,华南年、前、后汛期暴雨日数具有2～3 a和3～4 a准周期振荡。

广东2010年5月一周两次暴雨过程的对比分析

2010年5月中旬,广东省在一周之内连续遭受了两次区域性暴雨过程,其频次之高、雨量之多、强度之大为历史同期所少有。对这两次暴雨过程从水汽输送、动力结构、大气稳定度和雷达特征等方面进行了对比分析。结果表明:两次暴雨过程的环流形势及影响系统不同,水汽输送和辐合强弱与暴雨范围有密切关系,降水强度不但受大气不稳定度影响,动力触发更可能是引发强降水的关键因素;产生暴雨的飑线通过吸收合并其移动前方和沿近地层辐合带新生单体得以维持和发展,飑线上的HP型超级单体是产生降水峰值的主要载体。

华南局地锋生及对流系统发展的模拟分析研究

2009年3月28日一条东西向的锋面出现在华南25°N附近。伴随着锋面的活动,对流降水回波午后开始在广西的梧州附近发展,并在随后几小时向东移动,组织发展成为中尺度对流系统(MCS),为广东中西部及珠三角地区带来了雷暴、暴雨、冰雹等灾害天气。应用地面自动站、雷达回波、卫星云图以及NCEP-FNL再分析资料和WRF模式的模拟结果,对锋面暴雨形成的天气特征进行了诊断分析,考察了中尺度对流系统的发展演变过程及其与局地锋生的相互关系。结果表明,锋面对流系统形成发展于一个东西向水平尺度约200km的地面中尺度辐合线附近,对流起始发展于具有较大对流有效位能(CAPE)和较小对流抑制位能(CIN)的区域。伴随着对流的发展,锋面强度增强。锋生函数的计算发现,非绝热项和倾斜项分别在由对流引起的次级环流的上升运动支和下沉运动支起锋生作用,是引发中尺度锋生的主要影响因子。而相对来说,水平辐合项和形变项的作用却比较小。这与大尺度的锋生过程不同,中尺度锋生更主要的是由热力直接触发的非地转环流所驱动。涡度场的演变分析还发现,沿着850hPa锋区大的正涡度区与500hPa的强上升运动区对应良好,对流系统发展与中尺度锋生之间存在着类似于第二条件不稳定机制的相互作用,对流增强了锋生过程,锋面则对中尺度对流系统的发展起组织作用。中尺度锋生对对流组织发展的作用作为此类灾害天气形成的原因值得关注。

华南地区1961-2008年暴雨事件的气候变化特征

根据华南地区110个气象站1961-2008年逐日降水资料,采用线性趋势法,对华南地区暴雨事件的时空变化特征进行了研究。结果表明:近48 a来,华南年暴雨降水频数呈不显著的上升趋势,上升速率为0.18次/10 a,其中两广地区的东南和西部、海南省呈增加趋势,两广地区中部呈减少趋势;前汛期、后汛期暴雨降水频数均呈不显著的上升趋势,前汛期为0.05次/10 a,后汛期为0.09次/10 a,后汛期上升速率高于前汛期。华南年暴雨降水总量呈不显著的上升趋势,上升速率为16.57 mm/10 a,除粤桂交界地带的中部地区有减少趋势外,其余地方均有不同程度的增加趋势;暴雨降水量上升速率前汛期为4.75 mm/10 a,后汛期为7.59 mm/10 a,均没有通过显著性检验。年暴雨降水平均强度也呈不显著的上升趋势,上升速率为0.19(mm/d)/10 a,其中粤北、海南东部、广西西南以及北部地区年暴雨降水平均强度有增大趋势,其余地区有变小趋势;前汛期暴雨降水平均强度呈不显著的增加趋势,增加速率为0.12(mm/d)/10 a,后汛期暴雨降水平均强度呈不显著的减小趋势,减小速率为0.60(mm/d)/10 a。

2008年华南前汛期致洪暴雨特征及其对比分析

着重对2008年华南前汛期持续性致洪暴雨的降水特征及成因进行了天气尺度的研究,并且对比分析了其与20世纪90年代以来华南前汛期洪灾较为严重的几年(1994、1998和2005年)的降水和环流场特征异同,主要得到以下结果:(1)根据影响系统和雨区分布的不同,将2008年华南前汛期降水过程分为4个阶段。第1阶段(5月26—30日)降水中心分布零星,降水局地性明显。第2阶段(6月7—11日)雨区以带状分布为主,带状雨区上还分布了多个强降水中心。第3阶段(6月12-14日)以片状分布为主,而第4阶段(6月15—19日)雨区既有带状分布,也有片状分布。(2)4个阶段中、低空平均环流场分析表明,环流形势的明显差异决定了雨区分布特点的差异。(3)南海季风涌的频繁活动有力地将水汽一次次地向中国南方地区输送,为暴雨提供了充沛的水汽条件。(4)2008年华南前汛期,500hPa上,中国西南部、华北、华南,华东以及低纬度的孟加拉湾地区均是负的位势高度场异常。华北、华东地区负的异常、青藏高原东部负的异常均有利于冷空气活动,而低纬孟加拉湾地区负的异常又有利于暖湿气流的输送,冷暖气流的活动均非常有利于中国南方地区持续性强降水的发生。(5)对比2008、2005、1998、1994年和气候态的5月15日6月30日总降水分布发现,2008年总降水中心主要位于两广地区及浙赣皖3省交界地区。而浙赣皖3省交界区域的强降水中心位置明显较气候态偏北,被称为"非典型梅雨",而这也是2008年明显不同于另外3年的一个降水分布特点,此外,分析发现,2008年华南前汛期降水强度明显强于另3年。(6)对比4年的500hPa环流及异常场表明,2008年的环流形势相对于另3年要更有利于冷暖空气在中国南方地区交汇,因此,有利于2008年的降水强度大于另外3年。(7)对比4年的850hPa风场异常场分布表明,2008年低层异常风场的偏南风的向北推进得明显偏北,使得总降水量中心原气候态上位于浙闽赣3省交界区域的降水中心向北推进到浙赣皖交界地区,从而出现了华南暴雨与"非典型梅雨"同时出现的特点。

陕西南部地区一次大暴雨过程的干侵入分析(英文)

[Objective] One regional rainstorm weather in the south area of Shaanxi was expounded.[Method] By employing the NCEP/NCAR 1°×1°reanalysis data,routine observation and automatic precipitation station data,the large scale circulation background field of regional precipitation in the south area of Shaanxi province from July 16-18 in 2010 was expounded.By dint of physical quantity such as the meridional wind,relative humidity and false relative temperature,the characteristics of dry intrusion and its role in rainstorm were expounded.[Result] The mild and high latitude at 500 hPa was stable.The continental high pressure and subtropical high pressure were stable.The 700 and 850 hPa shear lines or low vortexes were the main influence system that resulted into large scale of rainstorm in south Shaanxi.The landing typhoon had distinct influences on the importance of storm.The influence of typhoon and subtropical high was mutual.It not only formed and strengthened the torrent in the low air,also transmitted water vapor and energy incessantly to the south area of Shaanxi,playing an important role in augment of rainstorm.There were two distinct dry intrusions in the rainstorm process,showing a dense dry layer in the high layer of convective layer.The existence of dry layer was conductive to the accumulation of convective unstable energy in the low layer.The release of convective unstable energy could transmit warm and wet airstream in the low level to the higher level,being conductive to the occurrence of precipitation.The analysis of θse in the warp direction vertical profile suggested that there was frontal zone in this rainstorm process and the dry air activity in this rainstorm process was very strong.[Conclusion] The study provided theoretical reference to the forecast in future.

局地低矮地形对华南暴雨影响的数值试验

为了探讨华南地区常见的局地喇叭口、迎风坡地形对暴雨的影响,选取云开山地到珠三角平原之间的地理范围为研究区域,利用中尺度气象模式进行三组地形试验,研究了一次特大暴雨过程中局地地形对强降雨的影响。结果表明,移去云开山地,原山地迎风坡的雨带北抬,对应雨量增加带,24h增值超过100mm;增加云开山地的高度,则会出现反"C"形雨量增加带;对于南北向的喇叭口地形,越往北降雨增幅越明显。地形试验表明,华南地区数百米的山地可影响到对流层中上层环流变化;通过改变局地地形,在特定区域将造成近地层辐合与上升运动的增强,有时甚至形成垂直方向的正向闭合环流圈,从而引起局地中尺度对流的发展,造成暴雨增幅;地形的改变将促使近地层风场发生改变,对中尺度而言,先发生变化的风场会引起涡度等要素随之改变,最终导致暴雨落区的变化。