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1.
In this study,power spectral analysis and bandpass filtering of daily meteorological fields are performed to explore the roles of synoptic to quasi-monthly disturbances in influencing the generation of pre-summer heavy rainfall over South China.Two heavy rainfall episodes are selected during the months of April-June 2008-15,which represent the collaboration between the synoptic and quasi-biweekly disturbances and the synoptic and quasi-monthly disturbances,respectively.Results show that the first heavy rainfall episode takes place in a southwesterly anomalous flow associated with an anticyclonic anomaly over the South China Sea(SCS)at the quasi-biweekly scale with 15.1%variance contributions,and at the synoptic scale in a convergence zone between southwesterly and northeasterly anomalous flows associated with a southeastward-moving anticyclonic anomaly on the leeside of the Yungui Plateau and an eastwardpropagating anticyclonic anomaly from higher latitudes with 35.2%variance contribution.In contrast,the second heavy rainfall episode takes place in southwest-to-westerly anomalies converging with northwest-to-westerly anomalies at the quasi-monthly scale with 23.2%variance contributions to the total rainfall variance,which are associated with an anticyclonic anomaly over the SCS and an eastward-propagating cyclonic anomaly over North China,respectively.At the synoptic scale,it occurs in south-to-southwesterly anomalies converging with a cyclonic anomaly on the downstream of the Yungui Plateau with 49.3%variance contributions.In both cases,the lower-tropospheric mean south-to-southwesterly flows provide ample moisture supply and potentially unstable conditions;it is the above synoptic,quasi-biweekly or quasimonthly disturbances that determine the general period and distribution of persistent heavy rainfall over South China.  相似文献   

2.
Warm-sector heavy rainfalls along the south China coast from April to June during 2009–2014 can be divided into two main types based on their low-level circulations. Type I is the southerly pattern with meridional convergence line at the west of the Pearl River estuary, which is formed by the convergence of southeasterly, southerly, and southwesterly flows. Type II is the southwesterly pattern with a latitudinal convergence line at the east of the Pearl River estuary, which is formed by the convergence of westerly and southwesterly flows. Statistics on 6-hourly heavy rainfall events indicates that, during the afore-mentioned 6 years, there were on average 73.2 occurrences of the southerly pattern and 50.3 occurrences of the southwesterly pattern per year. After the onset of summer monsoon in the South China Sea, the occurrence frequencies of both patterns increase remarkably. The synthetic diagnosis of pattern circulation shows that, at 500 hPa, for the southerly pattern, there is a broad warm high ridge, and a temperature ridge is behind the high ridge, which causes an obvious warm advection at the high ridge area. There is no frontal region. For the southwesterly pattern, the circulation is a weak trough with a temperature trough behind it. The position of the frontal region is near Yangzi River, and the south China coast is in the warm-sector of the frontal region. At the vertical cross-section of each of the two categories of heavy rainfall, there is a strong vertical motion center stretching to 400 hPa, where the convergence layer in the rainfall region is deep and with several vertical convergence centers overlapping one another. Both types of heavy rainfalls are with abundant water vapor, accompanied with deep convective instability energy layers, and with strong release of latent heat caused by condensation of water vapor. The release of latent heat leads to the warming-up and stretching of the air column, thus strengthens deep convergence and vertical velocity upward. There is a stronger latent heat-release in the southwesterly pattern than in the southerly pattern, while in the southerly pattern, the warm advection at middle and upper levels is stronger than the latent head release. To study the thermo-dynamic development mechanisms, weather research and forecasting model (WRF) numerical simulations are made and the results show that, in the two rainstorm regions, latent heat release warms up the air column, hence significantly increase the depth and strength of the vertical velocity. Moreover, the release of latent heat strengthens convergent circulation at lower levels and weakens divergent circulation at middle levels, whose influence can be as strong as 30%–50% of the wind circulation strength of the two types of the warm-sector heavy rainfall over the south China coast, and further enhances deep convection, promoting warm-sector storm development.  相似文献   

3.
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.  相似文献   

4.
This study investigates influencing weather systems for and the effect of Tibetan Plateau （TP）’s surface heating on the heavy rainfall over southern China in June 2010, focusing on the four persistent heavy rainfall events during 14-24 June 2010. The ma jor weather systems include the South Asian high, midlatitude trough and ridge, western Pacific subtropical high in the middle troposphere, and shear lines and eastward-moving vortices in the lower troposphere. An ensemble of convection-permitting simulations （CTL） is carried out with the WRF model for these rainfall events, which successfully reproduce the observed evolution of precipitation and weather systems. Another ensemble of simulations （SEN） with the surface albedo over the TP and its southern slope changed artificially to one, i.e., the surface does not absorb any solar heating, otherwise it is identical to CTL, is also performed. Comparison between CTL and SEN suggests that the surface sensible heating of TP in CTL significantly affects the temperature distributions over the plateau and its surroundings, and the thermal wind adjustment consequently changes atmospheric circulations and properties of the synoptic systems, leading to intensified precipitation over southern China. Specifically, at 200 hPa, anticyclonic and cyclonic anomalies form over the western and eastern plateau, respectively, which enhances the southward cold air intrusion along the eastern TP and the divergence over southern China;at 500 hPa, the ridge over the northern plateau and the trough over eastern China are strengthened, the southwesterly flows along the northwestern side of the subtropical high are intensified, and the positive vorticity propagation from the plateau to its downstream is also enhanced significantly;at 850 hPa, the low-pressure vortices strongly develop and move eastward while the southwesterly low-level jet over southern China strengthens in CTL, leading to increased water vapor convergence and upward motion over the precipitation region.  相似文献   

5.
2010年6月中国南方发生持续性强降水,其强度与2008年6月相当,超过近年来其他年份。但是,与2008年6月相比,2010年6月对流层中低层低值系统活动在青藏高原至长江中下游地区异常频繁,副热带高压(副高)位置异常偏西、强度偏强,导致低层异常风场辐合区及强降水区域相对偏北。分析2010年6月14—24日中国南方连续出现的4次持续性强降水过程,发现南亚高压、对流层中层的中纬度槽脊和西太平洋副高以及低层切变线和东移低涡是造成持续性强降水的主要天气系统。利用WRF模式对2010年6月强降水过程实施显式对流集合模拟试验,在控制试验重现观测到的地面降水和天气系统特征的基础上,在敏感性试验中将青藏高原的地表短波反照率修改为1.0,对比两组模拟试验的结果表明:控制试验中青藏高原的地表感热加热作用使得高原及其周边地区的大气温度发生变化,相应的热成风平衡调整使得对流层低层至高层大气环流和天气系统特征发生显著变化,增强了中国南方的持续性降水。200 hPa青藏高原西部形成反气旋性环流异常,东部形成气旋性环流异常,青藏高原东部南下的冷空气加强,中国南方辐散增强;500 hPa青藏高原北部的脊加强,中国东部的槽加深,副高西北侧的西南风明显增强,从青藏高原向下游传播的正涡度也显著加强;850 hPa的低涡强烈发展并逐步东移,华南沿海的西南低空急流更为强盛,导致降水区的水汽辐合、上升运动及降水强度都增强。  相似文献   

6.
近50年来中国夏季降水及水汽输送特征研究   总被引：15，自引：3，他引：12  
利用1951-2006年中国448站夏季降水资料、NCEP/NCAR VersionⅠ的再分析资料,研究了近50年来中国夏季降水年代际变化特征及其分区,并从季风性水汽输送的变化角度出发,讨论了影响中国一些主要地区降水变化的可能机制.研究发现:(1)从总体上来说,自1951年至今,中国夏季降水存在3个突变时段,即1956-1960年,1980年前后以及1993年以后.且90°E以东突变后的主要变化特征都是多雨区由北向南传播,而90°E以西则是多雨区由南向北传播;2)近56年来就110°E以东的中国东部夏季降水而言,1980年以后多雨区由华北南移到长江中下游,又于1993年以后由长江中下游继续南移至华南;3)中国东部各地区降水和850 hpa风场、整层水汽输送场的相关分布一致表明,中国110°E以东各降水区以南为来自偏东偏南的季风性异常水汽输送,而以北为来自偏北风和相应的异常水汽输送,两者在降水区汇合造成风和水汽输送异常辐合.因而,西太平洋副热带高压南侧的东南季风及其异常水汽输送、北方冷槽的偏北风及其异常水汽输送是中国东部夏季降水异常的主要成员,这和一般认为的这些地区降水异常来自孟加拉湾的季风性异常水汽输送的观点不同,需要作进一步研究.总之,对于中国东部旱涝的形成,应该重点注意来自西北太平洋副热带高压西侧的直接或间接经南海到达的异常四南季风性水汽输送.  相似文献   

7.
The dominant frequency modes of pre-summer extreme precipitation events(EPEs) over South China(SC) between1998 and 2018 were investigated. The 67 identified EPEs were all characterized by the 3–8-d(synoptic) frequency band.However, multiscale combined modes of the synoptic and three low-frequency bands [10–20-d(quasi-biweekly, QBW);15–40-d(quasi-monthly, QM); and 20–60-d(intraseasonal)] accounted for the majority(63%) of the EPEs, and the precipitation intensity on the peak wet day was larger th...  相似文献   

8.
华南前汛期持续暴雨环流分型初步研究   总被引：3，自引：0，他引：3       下载免费PDF全文
采用1961—2010年NCEP/NCAR逐日再分析资料和台站观测降水量资料,按一定标准选取了华南前汛期24个持续暴雨过程;并且按基本判据确定逐年华南夏季风降水开始日期。然后依据南亚高压环流型和相对于该年夏季风降水开始的早晚,将这些暴雨过程划分为夏季风降水前、后南亚高压东部型,夏季风降水后南亚高压带状、西部型共4个类型;其中,夏季风后南亚高压西部型次数最多、平均持续时间最长。所有类型持续暴雨的相同点是:广东东北部附近均为暴雨频率和雨量高值区;暴雨期间华南150 h Pa位势高度增加、500 h Pa位势高度减少;华南处在150 h Pa偏西风急流南侧辐散区中;850 h Pa华南沿海有明显的西南气流,低层辐合在华南东北部最明显;两广沿海为可降水量大值区;华南的整层水汽输送主要呈现西南向。不同点是:夏季风后南亚高压西部型平均雨量较小,夏季风后南亚高压带状型与西部型在印度洋上存在明显的偏东风高空急流;夏季风后南亚高压类型在两广沿海的可降水量数值较大。  相似文献   

9.
The regional climate model （RegCM3）, developed by the Abdus Salam International Centre for Theoretical Physics and nested in one-way mode within the latest version of Community Climate System Model from the National Center for Atmospheric Research, is used to conduct a set of experiments to examine its capability of climate simulation for the past 50 years and to explore possible changes in extreme precipitation （EP） in the next 100 years under the A1B scenario. Compared with the observation from the Climate Research Unit at the University of East Anglia and CPC Merged Analysis of Precipitation, RegCM3 reasonably reproduces the spatiotemporal distributions of precipitation and EP in eastern China. Based on the present-day analysis, this study examines the changes in monsoonal precipitation over eastern China in mid- and late-21st century relative to the reference period of 1970-1999. It is found that the precipitation will increase over the middle and lower reaches of the Yangtze River and areas to its north, and decrease over coastal areas to its south, especially in late-21st century. The various indices reflecting extreme events showed that the EP will enhance 10%-15% over the middle and lower reaches of the Yangtze River and areas to its north, and weaken over the areas to its south. The summer monsoon will strengthen and shift northwards under SERS A1B, bringing more water vapor and energy from the Indian Ocean and South China Sea for precipitation and eventually more precipitation over northern China.  相似文献   

10.
春季中国南方雨带年际变动与大气环流异常   总被引：1，自引：1，他引：0  
蒋品平  赵平 《气象学报》2012,70(4):681-689
利用1960—2008年中国693个站逐日降水资料和NCEP/NCAR日平均再分析资料,采用统计分析方法,分析了中国南方春季降水强度和位置的年际变率及其与大气环流的关系。结果表明:在年代际尺度上,江南春季降水在20世纪60年代中、后期偏少,70年代中期到80年代初偏多,90年代初开始减少;在年际尺度上,当春季西太平洋副热带高压和青藏高原东侧的低层低压系统加强,并且异常中心分别位于20°N以南和30°N以南时,异常西南风主要位于长江以南地区,在异常西南风逐渐减弱区出现明显的辐合,伴随着该地区低层空气质量辐合、对流层上升运动和水汽辐合加强,造成江南地区降水偏多,此时来自西太平洋的异常水汽到达南海后,没有在南海聚集,而是转向北输送到江南;当春季西太平洋副热带高压以及青藏高原东侧低压系统加强且异常中心位于30°N以北时,异常西南风盛行在中国东部大部分地区,此时低层异常空气质量辐合、对流层异常上升运动以及异常水汽通量辐合区都向北移到江淮地区,使江淮地区降水增加,而华南地区为异常空气质量辐散、异常下沉运动以及异常水汽通量辐散,伴随着降水减少,这时异常水汽主要来自西太平洋副热带地区。由于上述观测结果与通过改变东亚和周边海域海-陆热力差异的数值试验结果有很好的一致性,因此,这里观测到的降水和大气环流异常可以被东亚区域热力差异异常激发出来。  相似文献   

11.
During the summer monsoon period in south-east Asia marine airstreams normally prevail at the south China coast. However, when tropical cyclones approach then polluted airmasses from south-eastern China can impart high ionic concentrations and high acidity to rainwater. This is illustrated by two examples and the small-scale horizontal variations in rainwater composition are minor during these episodes. Since long-term quality-assured studies of the composition of rainwater in south-east Asia are scarce, the results at three sampling sites in Hong Kong during summer monsoon periods are compared with previous data from the same season. The results for the mid- to end-1990's show a similar trend to those for the ambient concentrations of sulphate and nitrate in aerosol in Hong Kong, which show flattened trends from 1995 to 1999. A marked increase in acidity is found in the summer monsoon period of 2004 which is attributed to the greater proportion of approaching cyclone weather systems in the dataset, reflecting both the increased local emission sources and the burgeoning economic growth of the Pearl River Delta Region. Comparison of the rainwater composition with that at other south-east Asian cities during the summer monsoon period shows that it is most acidic in Hong Kong.  相似文献   

12.
利用NOAA逐日海表面温度(sea surface temperature,SST)资料、NCEP/NCAR逐日风场和比湿资料以及中国国家气象信息中心提供的逐日降水资料,研究了西北太平洋气候SST的低频周期,进一步分析了夏季西北太平洋SST季节内振荡与中国东部同期降水异常的关系。结果表明:夏季西北太平洋季节内SST异常影响中国东部同期季节内降水最显著的三个区域为:长江中游及华南沿海;江淮流域;华北大部。其影响途径主要是通过西北太平洋季节内海温与850 h Pa环流场之间相互作用,在东亚沿岸自南向北逐渐形成气旋—反气旋—气旋(反气旋—气旋—反气旋)的波列结构,引起东亚沿海局地水汽的辐合辐散,使得中国东部夏季季节内雨带从江淮流域向华北推进(从华北南撤到长江中游及华南沿海地区)。  相似文献   

13.
东亚地区夏季风爆发过程   总被引：72，自引：5，他引：67  
利用中国194站1961～1995年日降水资料及NCEP1979～1997年候格点降水资料,探讨了亚洲地区自春到夏的雨季开始分布。结果表明,东亚地区自春到夏存在副热带季风雨季开始和热带季风雨季开始。前者于4月初开始于华南北部和江南地区,随后向南和向西南扩展,于4月末扩展到华南沿海和中南半岛,这个雨带主要是冷空气和副热带高压西侧转向的SW风以及南亚地区冬春副热带南支西风槽中西风汇合而形成的,是副热带季风雨季开始。后者是南海热带季风爆发后使原来由江南移到华南沿岸的副热带季风雨带随副热带高压北进而北进,前汛期雨季进入盛期,江南出现第二次雨峰,形成梅雨期和江淮及华北雨季。同时,热带季风雨带也自东向西传播到达南亚地区而形成热带季风雨季。还讨论了1998年东亚地区夏季风爆发过程,指出南海夏季风爆发期的季风由副高北侧形成的新生气旋进入南海造成南海中部西风和南海越赤道气流转向的SW季风加强汇合而形成,因而是东亚季风系统中环流系统季节变化造成的,和印度季风无关。在南海季风爆发期阿拉伯海仍由副热带反气旋控制,南亚仍是上述副热带反气旋北侧NW风南下后转向的偏西副热带气流所控制,索马里低空急流仍未爆发,赤道西风并未影响南海。  相似文献   

14.
The relationship between summer rainfall anomalies in northeast China and two types of El Ni?o events is investigated by using observation data and an AGCM. It is shown that, for different types of El Ni?o events, there is different rainfall anomaly pattern in the following summer. In the following year of a typical El Ni?o event, there are remarkable positive rainfall anomalies in the central-western region of northeast China, whereas the pattern of more rainfall in the south end and less rainfall in the north end of northeast China easily appears in an El Ni?o Modoki event. The reason for the distinct differences is that, associated with the different sea surface temperature anomalies (SSTA) along the equatorial Pacific, the large-scale circulation anomalies along east coast of East Asia shift northward in the following summer of El Ni?o Modoki events. Influenced by the anomalous anticyclone in Philippine Sea, southwesterly anomalies over eastern China strengthens summer monsoon and bring more water vapor to Northeast China. Meanwhile, convergence and updraft is strengthened by the anomalous cyclone right in Northeast China in typical El Ni?o events. These moisture and atmospheric circulation conditions are favorable for enhanced precipitation. However, because of the northward shift, the anomalous anticyclone which is in Philippine Sea in typical El Ni?o cases shifts to the south of Japan in Modoki years, and the anomalous cyclone which is in the Northeast China in typical El Ni?o cases shifts to the north of Northeast China, leading to the “dipole pattern” of rainfall anomalies. According to the results of numerical experiments, we further conform that the tropical SSTA in different types of El Ni?o event can give rise to observed rainfall anomaly patterns in Northeast China.  相似文献   

15.
Using the 5-day averaged data from the National Center for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) reanalysis, and precipitation from rain gauge stations in China for the period 1981–2000, we investigated seasonal variations and associated atmospheric circulation and precipitation of the southwesterly wind over eastern China. The southwesterly wind over eastern China begins earliest over southeastern China and strengthens gradually from spring to the early summer, as it extends northward. The strengthening of the spring southwesterly wind, the tropospheric upward motion, and the convergence of low-level water vapor over southeastern China results in the beginning of the local rainy season. The beginning of the Mei-yu (Plum rainfall) is connected with the northward march of the southwesterly wind. The southwesterly wind reaches the valley of the Yangtze River in the early summer and northern China in the middle summer. This signifies an onset of the large-scale southwesterly wind over eastern China. Accordingly, the rain belt over southeastern China moves to the valley of the Yangtze River in the early summer and to northern China in the middle summer. Moreover, the southerly wind extends southward to the South China Sea from the spring to summer, though it does not stretch from the South China Sea to southeastern China at those times. The strengthening of the southerly wind over southeastern China is associated with a weakening/strengthening of the eastward/westward subtropical tropospheric temperature gradient between southwestern China and the western North Pacific. The developments of a low-pressure system over southwestern China and the subtropical high-pressure system over the western North Pacific may contribute to the strengthening of the southwesterly wind. A northward advance of the high-pressure system favors the southwesterly wind stretching from southeastern China to northern China. The onset of the Indian summer monsoon also strengthens the summer southwesterly wind over eastern China.  相似文献   

16.
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.  相似文献   

17.
利用1981—2000年候平均NCEP/NCAR再分析资料和CMAP全球降水资料,分析了从中国东部大陆到西太平洋副热带地区季风和降水季节变化的特征及其与热带季风降水的关系,探讨了季风建立和加强的原因。夏季东亚—西太平洋盛行的西南风开始于江南和西太平洋副热带的春初,并向北扩展到中纬度,热带西南风范围向北扩展的迹象不明显。从冬到夏,中国西部和西太平洋副热带的表面加热季节变化可以使副热带对流层向西的温度梯度反转比热带早,使西南季风在副热带最早开始;从大气环流看,青藏高原东侧低压槽的加强和向东延伸,以及西太平洋副热带高压的加强和向西移动,都影响着副热带西南季风的开始和发展;初夏江南的南风向北扩展与副热带高压向北移动有关,随着高原东侧低压槽向南延伸,槽前的偏南风范围向南扩展。随着副热带季风建立和向北扩展,其最大风速中心前方的低层空气质量辐合和水汽辐合以及上升运动也加强和向北移动,导致降水加强和雨带向北移动。热带季风雨季开始晚,主要维持在热带而没有明显进入副热带,江淮梅雨不是由热带季风雨带直接向北移动而致,而是由春季江南雨带北移而致。在热带季风爆发前,副热带季风区水汽输送主要来自中南半岛北部和中国华南沿海,而在热带季风爆发后,水汽输送来自孟加拉湾和热带西太平洋。  相似文献   

18.
The conventional and intensive observational data of the China Heavy Rain Experiment and Study (CHeRES) are used to specially analyze the heavy rainfall process in the mei-yu front that occurred during 20-21 June 2002, focusing on the meso-β system. A mesoscale convective system (MCS) formed in the warm-moist southwesterly to the south of the shear line over the Dabie Mountains and over the gorge between the Dabie and Jiuhua Mountains. The mei-yu front and shear line provide a favorable synoptic condition for the development of convection. The GPS observation indicates that the precipitable water increased obviously about 2 3 h earlier than the occurrence of rainfall and decreased after that. The abundant moisture transportation by southwesterly wind was favorable to the maintenance of convective instability and the accumulation of convective available potential energy (CAPE). Radar detection reveals that meso-β and -γ systems were very active in the Mα CS. Several convection lines developed during the evolution of the MαCS, and these are associated with surface convergence lines. The boundary outflow of the convection line may have triggered another convection line. The convection line moved with the mesoscale surface convergence line, but the convective cells embedded in the convergence line propagated along the line. On the basis of the analyses of the intensive observation data, a multi-scale conceptual model of heavy rainfall in the mei-yu front for this particular case is proposed.  相似文献   

19.
In this study, the Weather Research and Forecasting (WRF) model and meteorological observation data were used to research the long-distance moisture transport supply source of the extreme rainfall event that occurred on July 21, 2012 in Beijing. Recording a maximum rainfall amount of 460 mm in 24 h, this rainstorm event had two dominant moisture transport channels. In the early stage of the rainstorm, the first channel comprised southwesterly monsoonal moisture from the Bay of Bengal (BOB) that was directly transported to north China along the eastern edge of Tibetan Plateau (TP) by orographic uplift. During the rainstorm, the southwesterly moisture transport was weakened by the transfer of Typhoon Vicente. Moreover, the southeasterly moisture transport between the typhoon and western Pacific subtropical high (WPSH) became another dominant moisture transport channel. The moisture in the lower troposphere was mainly associated with the southeasterly moisture transport from the South China Sea and the East China Sea, and the moisture in the middle troposphere was mainly transported from the BOB and Indian Ocean. The control experiment well reproduced the distribution and intensity of rainfall and moisture transport. By comparing the control and three sensitivity experiments, we found that the moisture transported from Typhoon Vicente and a tropical cyclone in the BOB both significantly affected this extreme rainfall event. After Typhoon Vicente was removed in a sensitivity experiment, the maximum 24-h accumulated rainfall in north China was reduced by approximately 50% compared with that of the control experiment, while the rainfall after removing the tropical cyclone was reduced by 30%. When both the typhoon and tropical cyclone were removed, the southwesterly moisture transport was enhanced. Moreover, the sensitivity experiment of removing Typhoon Vicente also weakened the tropical cyclone in the BOB. Thus, the moisture pump driven by Typhoon Vicente played an important role in maintaining and strengthening the tropical cyclone in the BOB through its westerly airflow. Typhoon Vicente was not only the moisture transfer source for the southwesterly monsoonal moisture but also affected the tropical cyclone in the BOB, which was a key supply source of long-distance moisture transport for the extreme rainfall event on July 21, 2012 in Beijing.  相似文献   

20.
2008年初“低温雨雪冰冻”灾害天气的持续性原因分析   总被引：50，自引：8，他引：50  
从预报角度出发,初步分析了2008年初"低温雨雪冰冻"天气的主要特点和环流特征,对冻雨、暴雪的成因也进行了初步分析:2008年初低温雨雪冰冻期间,大气环流形势稳定,极涡中心偏向于东半球,强而稳定,来自极地的冷气团与来自热带洋面的暖气团长时间在长江中下游地区交汇是主要原因;贝加尔湖以西地区阻塞高压强而稳定,中亚、西亚低槽(涡)位置稳定、发展活跃;对流层700 hPa等压面西南气流稳定,850 hPa低层多切变、低涡活动,为降水提供了非常有利的低空辐合条件;对流层中层高原有低涡发展,高原不断有正涡度向东传播至东部沿海;西太平洋副热带高压(副高)强盛,位置偏西、偏北;副热带锋区强盛,南北温度梯度大;南支槽比较活跃;华南准静止锋、滇黔准静止锋稳定维持;热带洋面上暖气团活跃;逆温层稳定,融化层厚度较厚,是长时间冻雨天气的主要原因之一.2008年初低温雨雪冰冻期间的第1次过程为强冷、暖气流共同作用所致,其后是华南、滇黔准静止锋稳定,扩散冷空气渗透所为;2008年初暴雪天气的主要因四川盆地有正涡度向东传播至中国东部沿海地区,水汽充沛,上升运动强烈所致.  相似文献   

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