首先对2008 -2019年4 -9月湖南弱天气尺度背景下暖区暴雨依据500 hPa环流形势分为强西南急流型和副高型， 然后对2018年4月30日（简称“4·30”过程）和2016年7月17日（简称“7·17”过程）两次不同类型暖区暴雨过程进行对比分析。结果表明： （1）两类暖区暴雨具有明显季节差异， 强西南急流型和副高型分别发生在春季和夏季。强西南急流型一天任何时刻均会出现， 夜间降水频次增多。副高型的日变化明显， 降水峰值出现在上午。强西南急流型降水范围广， 多出现在湘南地区， 西南急流北推到长江中下游地区时， 湘北也会出现暴雨。副高型降水分散， 在湘西北、 湘北及湘东南地区均出现强降水， 局地性强， 对流性明显。（2）“4·30”过程暴雨区处于上下一致西南风中， 在切变线南侧辐合上升、 西南急流和地面辐合线共同影响下湘东北出现暴雨， 属于强西南急流型暖区暴雨； 而“7·17”过程， 副高脊线控制湖南， 受中低层弱切变和地面中尺度气旋影响， 湘西北出现暴雨， 属于副高型暖区暴雨。（3）“4·30”过程暴雨区上空垂直螺旋度均为负值， 700 hPa存在负值中心， 意味着700 hPa切变线造成暴雨区强辐合上升， 导致强降水发生； “7·17”过程， 垂直螺旋度呈“上正下负”结构， 900 hPa高度强气旋性旋转辐合最强， 表征近地层中小尺度系统影响造成暴雨。“4·30”过程水汽输送和辐合比“7·17”过程更强。“7·17”过程比“4·30”过程低层热力不稳定能量更大且热力不稳定层结更强。β中尺度辐合线和γ小尺度气旋分别为 “4·30”过程和“7·17”过程的触发机制。

Warm-sector heavy rainfalls under weak synoptic scale background in Hunan during April-September in 2008 -2019 are divided into strong southwest jet type and subtropical high type according to 500 hPa circulation situation， and then two different types of warm-sector heavy rainfall cases under weak synoptic scale background on April 30， 2018 （"4·30" case） and July 17， 2016 （"7·17" case） are analyzed.Results are as follows： （1）There are obvious seasonal differences between the two types of Warm-sector heavy rainfalls.Strong southwest jet and subtropical high occur in spring and summer， respectively.The strong southwestern jet type appears at any time of the day， and the frequency of precipitation at night increases.Diurnal variation of the subtropical high type is obvious， and the peak appears in the morning.The precipitation of strong southwestern jet type is distributed widely， and mostly occurs in the southern Hunan.When the southwestern jet moves northward to the middle-lower reaches of Yangtze River， heavy rainfalls also occur in northern Hunan.Precipitation of Subtropical type distributes dispersedly， and occurs in northwestern， northern， and southeastern of Hunan， with strong locality and obvious convection.（2）Rainstorm area of the "4·30" case is in lower-to-upper southwest wind， and occurs in Northeast Hunan under influences of convergence and updraft on south side of shear line， southwest jet and surface convergence line， belonging to the strong southwest jet type of warm -sector heavy rainfall.The "7·17" case is affected by weak shear in the middle and lower levels and surface mesoscale cyclone， under the control of subtropical high.Heavy rain occurs in the northwest of Hunan， belonging to subtropical high type of warm sector heavy rainfall.（3）The values of vertical helicity over the rainstorm area during "4·30" case are all negative， and there is a negative center in 700 hPa， which means that the shear line in 700 hPa causes strong upward convergence in rainstorm area， leading to this heavy precipitation.During "7·17" case， vertical helicity shows a structure of positive in upper level and negative in lower level， strong cyclonic rotatory convergence is the strongest in 900 hPa level， indicating that the heavy rainfall is caused by the mesoscale and small scale systems in the near surface level.Water vapor transport and convergence in "4·30" case are stronger than that in "7·17" case.Thermal instability energy in the lower level of the "7·17" case is larger， and thermal instability stratification is stronger than that in the "4·30" case.β-mesoscale convergence lines and γ-cyclones are the triggering mechanisms of "4·30 "and "7·17" cases， respectively.