During the Heavy Rainfall Experiment in South China （HUAMEX） of 1998, a record heavy rainfall event occurred in the delta of the Pearl River during the 24 hours from 1200 UTC 8 June to 1200 UTC 9 June, 1998, and a 2...During the Heavy Rainfall Experiment in South China （HUAMEX） of 1998, a record heavy rainfall event occurred in the delta of the Pearl River during the 24 hours from 1200 UTC 8 June to 1200 UTC 9 June, 1998, and a 24-hour precipitation maximum of 574 mm was reported in Hong Kong. In this paper, some mesoscale characteristics of this heavy rainfall event are studied using data from satellites, Doppler radar, wind profilers, and automatic meteorological stations collected during HUAMEX. The following conclusions are drawn： （1） During this heavy rainfall event, there existed a favorable large-scale environment, that included a front with weak baroclinity in the heavy rain area and with an upward motion branch ahead of the front. （2） Unlike most extratropical or subtropical systems, the closed low in the geopotential height field does not exited. The obvious feature was that a southerly branch trough in the westerlies existed and Hong Kong was located ahead of the trough. （3） The rainfall areas were located in the warm sector ahead of the front, rather than in the frontal zone, which is one of the characteristics of heavy rainfalls during the pre-rainy season of South China. A southerly warm and moist current contributed to the heavy rainfall formation, including the transportation of rich water vapor and the creation of strong horizontal wind convergence. （4） The observations show that the heavy rainfall in Hong Kong was directly caused by a series of meso β systems rather than a mesoscale convective complex （MCC）. These meso β systems moved with the steering current in the lower-mid troposphere, their life cycles were 3-6 hours, and their horizontal sizes were 10-100 km. （5） The disturbances in the lower and mid troposphere, especially that in the planetary boundary layer （PBL） were very shallow. However, they are a possible trigger mechanism for the occurrence and development of the mesoscale convective systems and related heavy rainfalls. Finally, a conceptual model of the heavy rainfall in the warm sector ahead of the front in South China is proposed.展开更多
In this paper,by carrying out sensitivity tests of initial conditions and diagnostic analysis of physical fields,the impact factors and the physical mechanism of the unusual track of Morakot in the Taiwan Strait are d...In this paper,by carrying out sensitivity tests of initial conditions and diagnostic analysis of physical fields,the impact factors and the physical mechanism of the unusual track of Morakot in the Taiwan Strait are discussed and examined based on the potential vorticity(PV)inversion.The diagnostic results of NCEP data showed that Morakot's track was mainly steered by the subtropical high.The breaking of a high-pressure zone was the main cause for the northward turn of Morakot.A sensitivity test of initial conditions showed that the existence of upper-level trough was the leading factor for the breaking of the high-pressure zone.When the intensity was strengthened of the upper-level trough at initial time,the high-pressure zone would break ahead of time,leading to the early northward turn of Morakot.Conversely,when the intensity was weakened,the breaking of the high-pressure zone would be delayed.Especially,when the intensity was weakened to a certain extent,the high-pressure zone would not break.The typhoon,steered by the easterly flow to the south of the high-pressure zone,would keep moving westward,with no turn in the test.The diagnostic analysis of the physical fields based on the sensitivity test revealed that positive vorticity advection and cold advection associated with the upper-level trough weakened the intensity of the high-pressure zone.The upper-level trough affected typhoon's track indirectly by influencing the high-pressure zone.展开更多
Predecessor rain events(PREs) in the Yangtze River Delta(YRD) region associated with the South China Sea and Northwest Pacific Ocean(SCS-WNPO) tropical cyclones(TCs) are investigated during the period from 2010 to 201...Predecessor rain events(PREs) in the Yangtze River Delta(YRD) region associated with the South China Sea and Northwest Pacific Ocean(SCS-WNPO) tropical cyclones(TCs) are investigated during the period from 2010 to 2019.Results indicate that approximately 10% of TCs making landfall in China produce PREs over the YRD region;however,they are seldom forecasted. PREs often occur over the YRD region when TCs begin to be active in the SCS-WNPO with westward paths, whilst the cold air is still existing or beginning to be present. PREs are more likely to peak in June and September. The distances between the PRE centers and the parent TC range from 900 to 1700 km. The median value of rain amounts and the median lifetime of PREs is approximately 200 mm and 24 h, respectively. Composite results suggest that PREs form in the equatorward jet-entrance region of the upper-level westerly jet(WJ), where a 925-hPa equivalent potential temperature ridge is located east of a 500-hPa trough. Deep moisture is transported from the TC vicinity to the remote PREs region. The ascent of this deep moist air in front of the 500-hPa trough and frontogenesis beneath the equatorward entrance region of the WJ is advantageous for the occurrence of PREs in the YRD region. The upper-level WJ may be affected by the subtropical high and westerly trough in the Northwest Pacific Ocean, and the occurrence of PREs may favor the maintenance of the upper-level WJ. The upper-level outflow of TCs in the SCS plays a secondary role.展开更多
针对2007年6-7月的淮河致洪暴雨,采用NCEP资料、卫星TBB（Temperature of Black Body）资料、地面加密资料和1 h的降水资料对此次暴雨过程进行了详细的分析,得到结果如下：1）2007年6-7月主汛期的暴雨带主要位于淮河流域,而不是像通常...针对2007年6-7月的淮河致洪暴雨,采用NCEP资料、卫星TBB（Temperature of Black Body）资料、地面加密资料和1 h的降水资料对此次暴雨过程进行了详细的分析,得到结果如下：1）2007年6-7月主汛期的暴雨带主要位于淮河流域,而不是像通常那样集中在长江中下游。时间长达30余天,超过2003年（持续20余天）。2）整个汛期从6月19日开始至7月26日结束,根据影响系统和雨区分布的不同,可将降水分为3个阶段。其中,第2阶段（6月29日-7月10日）降水最强,影响最大,与梅雨的降水有更多相似。在第2阶段中又有4次降水过程,其中第4次过程（7月7-9日）降水最强,导致10日在王家坝开闸泄洪。3）高纬度的阻塞形势（西阻型）有利于环流的稳定维持和暴雨的持续发生。4）副热带高压稳定在26°N,有利于雨带维持在32°N,另外南海季风涌沿副高西侧将大量水汽输送至淮河流域。5）在阻高和副高之间的西风带上,巴尔喀什湖为低槽区,不断有小股冷空气经我国西北和黄河上游沿偏西路径移至淮河流域,西风槽加深甚至在中国大陆出现切断低压,这在过去淮河暴雨期间不太多见,表明存在明显的中低纬度的相互作用。与此同时,在7月8日高空急流入口区（右侧）与低空急流出口区（左侧）相迭置耦合,非常有利于垂直运动的加强和暴雨的发生。6）在暴雨期间有中尺度低压（扰动）的发生发展,并有与之相关的中尺度云团、雨团甚至更小的中尺度对流系统出现,致使8日寿县24h降水量达262 mm之多。该次强暴雨与淮河流域前期多场强降水形成的高水位“遭遇”,引发了严重的洪水,其影响超过了2003年,成为了1954年以来淮河流域最严重的洪涝。展开更多
基金National Key Basic Research and Development Project of China （Project No. 2004CB418301） the National Natural Science Foundation of China under Grant No. 40405008.
文摘During the Heavy Rainfall Experiment in South China （HUAMEX） of 1998, a record heavy rainfall event occurred in the delta of the Pearl River during the 24 hours from 1200 UTC 8 June to 1200 UTC 9 June, 1998, and a 24-hour precipitation maximum of 574 mm was reported in Hong Kong. In this paper, some mesoscale characteristics of this heavy rainfall event are studied using data from satellites, Doppler radar, wind profilers, and automatic meteorological stations collected during HUAMEX. The following conclusions are drawn： （1） During this heavy rainfall event, there existed a favorable large-scale environment, that included a front with weak baroclinity in the heavy rain area and with an upward motion branch ahead of the front. （2） Unlike most extratropical or subtropical systems, the closed low in the geopotential height field does not exited. The obvious feature was that a southerly branch trough in the westerlies existed and Hong Kong was located ahead of the trough. （3） The rainfall areas were located in the warm sector ahead of the front, rather than in the frontal zone, which is one of the characteristics of heavy rainfalls during the pre-rainy season of South China. A southerly warm and moist current contributed to the heavy rainfall formation, including the transportation of rich water vapor and the creation of strong horizontal wind convergence. （4） The observations show that the heavy rainfall in Hong Kong was directly caused by a series of meso β systems rather than a mesoscale convective complex （MCC）. These meso β systems moved with the steering current in the lower-mid troposphere, their life cycles were 3-6 hours, and their horizontal sizes were 10-100 km. （5） The disturbances in the lower and mid troposphere, especially that in the planetary boundary layer （PBL） were very shallow. However, they are a possible trigger mechanism for the occurrence and development of the mesoscale convective systems and related heavy rainfalls. Finally, a conceptual model of the heavy rainfall in the warm sector ahead of the front in South China is proposed.
基金National Public Benefit(Meteorology)Research Foundation of China(GYHY201106004)National Basic Research Program"973"of China(2009CB421502)National Nature Science Foundation of China (40730948,41005029)
文摘In this paper,by carrying out sensitivity tests of initial conditions and diagnostic analysis of physical fields,the impact factors and the physical mechanism of the unusual track of Morakot in the Taiwan Strait are discussed and examined based on the potential vorticity(PV)inversion.The diagnostic results of NCEP data showed that Morakot's track was mainly steered by the subtropical high.The breaking of a high-pressure zone was the main cause for the northward turn of Morakot.A sensitivity test of initial conditions showed that the existence of upper-level trough was the leading factor for the breaking of the high-pressure zone.When the intensity was strengthened of the upper-level trough at initial time,the high-pressure zone would break ahead of time,leading to the early northward turn of Morakot.Conversely,when the intensity was weakened,the breaking of the high-pressure zone would be delayed.Especially,when the intensity was weakened to a certain extent,the high-pressure zone would not break.The typhoon,steered by the easterly flow to the south of the high-pressure zone,would keep moving westward,with no turn in the test.The diagnostic analysis of the physical fields based on the sensitivity test revealed that positive vorticity advection and cold advection associated with the upper-level trough weakened the intensity of the high-pressure zone.The upper-level trough affected typhoon's track indirectly by influencing the high-pressure zone.
基金supported by the National Natural Science Foundation of China (Grant Nos. 42105004, 41930967, 42192554, and 42105011)the Natural Science Foundation of Zhejiang Province of China (Grant No. LQ20D050001)the Scientific Research Foundation of Hangzhou Normal University (Grant No. 2020QDL015)。
文摘Predecessor rain events(PREs) in the Yangtze River Delta(YRD) region associated with the South China Sea and Northwest Pacific Ocean(SCS-WNPO) tropical cyclones(TCs) are investigated during the period from 2010 to 2019.Results indicate that approximately 10% of TCs making landfall in China produce PREs over the YRD region;however,they are seldom forecasted. PREs often occur over the YRD region when TCs begin to be active in the SCS-WNPO with westward paths, whilst the cold air is still existing or beginning to be present. PREs are more likely to peak in June and September. The distances between the PRE centers and the parent TC range from 900 to 1700 km. The median value of rain amounts and the median lifetime of PREs is approximately 200 mm and 24 h, respectively. Composite results suggest that PREs form in the equatorward jet-entrance region of the upper-level westerly jet(WJ), where a 925-hPa equivalent potential temperature ridge is located east of a 500-hPa trough. Deep moisture is transported from the TC vicinity to the remote PREs region. The ascent of this deep moist air in front of the 500-hPa trough and frontogenesis beneath the equatorward entrance region of the WJ is advantageous for the occurrence of PREs in the YRD region. The upper-level WJ may be affected by the subtropical high and westerly trough in the Northwest Pacific Ocean, and the occurrence of PREs may favor the maintenance of the upper-level WJ. The upper-level outflow of TCs in the SCS plays a secondary role.
文摘针对2007年6-7月的淮河致洪暴雨,采用NCEP资料、卫星TBB（Temperature of Black Body）资料、地面加密资料和1 h的降水资料对此次暴雨过程进行了详细的分析,得到结果如下：1）2007年6-7月主汛期的暴雨带主要位于淮河流域,而不是像通常那样集中在长江中下游。时间长达30余天,超过2003年（持续20余天）。2）整个汛期从6月19日开始至7月26日结束,根据影响系统和雨区分布的不同,可将降水分为3个阶段。其中,第2阶段（6月29日-7月10日）降水最强,影响最大,与梅雨的降水有更多相似。在第2阶段中又有4次降水过程,其中第4次过程（7月7-9日）降水最强,导致10日在王家坝开闸泄洪。3）高纬度的阻塞形势（西阻型）有利于环流的稳定维持和暴雨的持续发生。4）副热带高压稳定在26°N,有利于雨带维持在32°N,另外南海季风涌沿副高西侧将大量水汽输送至淮河流域。5）在阻高和副高之间的西风带上,巴尔喀什湖为低槽区,不断有小股冷空气经我国西北和黄河上游沿偏西路径移至淮河流域,西风槽加深甚至在中国大陆出现切断低压,这在过去淮河暴雨期间不太多见,表明存在明显的中低纬度的相互作用。与此同时,在7月8日高空急流入口区（右侧）与低空急流出口区（左侧）相迭置耦合,非常有利于垂直运动的加强和暴雨的发生。6）在暴雨期间有中尺度低压（扰动）的发生发展,并有与之相关的中尺度云团、雨团甚至更小的中尺度对流系统出现,致使8日寿县24h降水量达262 mm之多。该次强暴雨与淮河流域前期多场强降水形成的高水位“遭遇”,引发了严重的洪水,其影响超过了2003年,成为了1954年以来淮河流域最严重的洪涝。
文摘对2002年8月5日发生在陕西境内一次槽后'湿'对流风暴过程进行了中尺度分析,结果表明:500 hPa槽后冷平流是这次过程的直接影响系统;850 hPa能量锋区和高能区提供了能量和强位势不稳定区;南海'北冕'台风和高原东侧副热带高压为此次过程提供了充沛的水汽,中、低空水汽通量超常;高、低空急流耦合产生的次级环流提供了持续强劲的上升运动;地面中尺度涡旋发展、合并及扩散是次级环流部分上升支演变过程的具体反映;产生强对流风暴的块状回波强度为45～55 dBz,高度为12～14 km.
