基于ERA-interim再分析资料的近30年九龙低涡气候特征

Climatic characteristics of the Jiulong low vortex in recent 30 years based on the ERA-interim reanalysis data

利用ERA-interim再分析资料,统计分析了1986年1月1日—2015年12月31日不同生命史九龙涡的时空分布特征和活动规律。结果表明:持续1—2个时次的九龙涡(T_(1-2)JLV)和3—4个时次的九龙涡(T_(3-4)JLV)初生高频中心位于27°—28.5°N,100°—101.5°E,持续5—6个时次的九龙涡(T_(5-6)JLV)初生高频中心位于29°—30.5°N,102°—103.5°E,持续时间大于7个时次的九龙涡(T_(≥7)JLV)初生高频中心位于28°—29.5°N,101.5°—103.5°E,生命史越长越易生成于四川盆地的西南部;九龙涡生成频数30年呈增长趋势,但近几年呈下降趋势;九龙涡生成频数随月份大致呈先增加后减少的变化趋势,1—5月随月份增加,5—12月随月份减少,5月最大,9月最小,3月T_(1-2)JLV生成最多,9月最少,4月T_(3-4)JLV生成最多,12月最少,6月T_(5-6)JLV、T_(≥7)JLV生成最多,1—4月无T_(5-6)JLV生成,12月T_(≥7)JLV生成最少,夏季九龙涡频数虽不是最高,但最易生成长生命史九龙涡,且最易移出源地;生命史低于24 h的九龙涡(T_(1-2)JLV、T_(3-4)JLV)夜发性不突出,生命史超过24 h的九龙涡(T_(5-6)JLV、T_(≥7)JLV)具有显著的夜发性特征;移出源地的九龙涡频数随月份表现出先增加后减少的变化趋势,1—6月随月份增加,6—12月随月份减少,6月移出源地的频数最多。T_(≥7)JLV的移动路径以偏东路径为主,6月后有东南路径和东北路径,T_(5-6)JLV移出路径只有偏东路径和东北路径,生命史小于24 h的九龙涡由于靠近统计区边缘地区也有可能移出源地。

Based on the ERA-interim reanalysis data,the weather processes that are associated with the Jiulong low vortex（JLV）have been counted and analyzed during the period of 1 January 1986 to 31 December 2015.The result suggests that T_（1-2） JLVs with a lifespan of 1-2 hours and T_（3-4） JLVs with a lifespan of 3-4 hours usually occur at 100°-101.5°E,27°-28.5°N;T_（5-6） JLVs with a life span of 5-6 hours usually occur at 102°-103.5°E,29°-30.3°N,T_（≥7） JLVs with a life span of more than 7 hours usually occur at 101.5°-103.5°E,28°-29.5°N,and vortexes with even longer life spans often occur at the southwestern gap of Sichuan Basin.The occurrence frequency of Jiulong low vortex increased during the past 30 years,but decreased in recent years.Annually,the frequency increases first and then gradually decreases with month,i.e.,it increases from January to May and decreases from May to December with the maximum in May and the minimum in September.T_（1-2） JLVs occur most frequently in March and least frequently in September,T_（3-4） JLVs occur most frequently in April and least frequently in December,T_（5-6） JLVs and T_（≥7） JLVs occur most frequently in June,T_（5-6） JLVs never occur from January to April,and T_（≥7） JLVs occur least frequently in December.Summer is not the highest frequency season for Jiulong low vortex occurrence,but it is the easiest time for long life span Jiulong low vortexes to form and move out of the genesis place.The Jiulong low vortexes with life spans more than 24 hours（T_（5-6） JLV、T_（≥7） JLV）occur more frequently in the night than in the daytime,whereas the nighttime occurrence of vortexes with life spans less than 24 hours（T_（1-2） JLV,T_（3-4） JLV）are not obvious.The frequency of Jiulong low vortexes that can move out of their genesis field first increases and then decreases gradually with month,i.e.the frequency increases from January to June and decreases from June to December with the maximum in June.T_（≥7） JLVs mainly move forward following the east path at the first several months,and then follow the southeast path and the northeast path after July.T_（5-6） JLVs move forward only following the east and northeast paths.The Jiulong vortexes with the life span of less than 24 hours may move out of the genesis place because they occur near the edge of the statistical area.