中文摘要：

利用1961-2011年广东省86个测站地面观测逐日降水资料及1979-2011年NCEP-DOE第2套分析资料,提出了广东暴雨日的定义指标,分析了近51a广东前汛期及其各月持续性暴雨的变化特征,进一步诊断了持续性暴雨过程的环流特征和水汽输送来源.结果表明,广东暴雨新指标避免了原指标定义存在的不合理情况和需要人工操作等问题,并且得到的广东暴雨日数及暴雨累积雨量的年际变化更能反映广东的旱涝情况.51a平均前汛期持续性暴雨过程在4、5、6月分别占10%、29%和61%,20世纪60年代后期至80年代持续性暴雨多发生在5月,而60年代前中期、90年代至2011年持续性暴雨则主要在6月出现,这种年代际变化是由东亚地区中低纬度大气环流系统的变化所造成的.除了过去所认识的“三脊两槽”和“两脊一槽”两种类型天气形势外,广东前汛期持续性暴雨过程的500hPa中高纬度环流还有一种“高纬阻塞-中纬平缓型”（称为Ⅲ型）,Ⅲ型主要出现于6月,占6月持续性暴雨过程的22%,因此,这种环流类型的补充提出,将减少6月持续性暴雨过程的漏报现象.由于气候背景场各月有所不同,无论是三脊二槽型还是二脊一槽型,各区域槽（或脊）的相对强弱和形态也随月份有所不同,例如二脊一槽型,东北亚地区高压脊4、5、6月逐月加强向北扩展,贝加尔湖槽区逐月变宽,中低纬度阿拉伯海以东槽逐月向西移动,孟加拉湾槽、西太平洋副热带高压逐月加强.前汛期持续性暴雨过程的主要水汽来源随月份发生变化,4月热带西太平洋地区水汽来源贡献最大,5月孟加拉湾、西太平洋和中国南海的水汽都有贡献,而6月则主要来源于孟加拉湾的水汽输送.所有类型持续性暴雨过程,广东大部分地区都处于水汽通量辐合区,说明动力辐合作用和水汽来源是暴雨的必备条件,持续性暴雨是各类中高纬度环流型的稳定维持与来?

英文摘要：

An index to define the days of torrential rain in Uuangdong was advanced to facilitate automatic judgement by computcr using 51-year （1961-2011）86-station daily precipitation observations of Uuangdong Province.The variation characteristics of sustained torrential rain during the pre-flooding season and its each month in Uuangdong were analyzed.The circulation pattern and the water vapor transport were diagnosed by using daily atmospheric data from NCEP-DOE Rcanalysis 2 during 1979-2011.It was shown that the present index of torrential rain in Guangdong may avoid unreasonable situations of the originali ndex and manual operation.And the interannual variations of both the number of days and the amount of cumulative rain fall of torrential rain derived from the present index can reflect better the drought and flood situation of Uuangdong.The percent of sustained torrential rain is 10%,29% and 61% in April,May and June respectively averaged over the 51-year.Most of sustained torrential rain occurs in May from latter stage of 1960s to 1980x.But most of sustained torrential rain occurs in June during early and middle stage of 1960x, and during 1990-2011.The inter-decadal variation is resulted from the change of atmospheric circulation systems in the middle and low latitudes of East Asia.In addition to the two types of circulation pattern used to be known as ＂3-ridge and 2-trough＂ and ＂2-ridge and 1-trough＂,another type of circulation pattern in the middle and high latitudes at 500 hPa is found,which is ＂blocking in high latitudes-placid in middle latitudes＂ （named as pattern Ⅲ）.Pattern Ⅲ occurs in Junc, account for 22% of the total sustained torrential rain processes in June.So the reveal of the circulation pattern Ⅲ would decrease the forecasting omission of sustained torrential rain process in June.The intensity and form of troughs （or ridges） over each region change with months because of the changing of climate background among the different months,for either the pattern of ＂3-ridge