2001—2015年4—9月九龙涡时空分布与动力热力特征

Spatio-temporal Distribution and Dynamic-thermodynamic Characteristics of Jiulong Low Vortex from April to September during 2001—2015

本文利用ERA5再分析资料,通过人工识别统计了2001—2015年4—9月四类不同生命史九龙低涡的时空分布,并对其生成前6 h动力热力特征进行了合成分析。结果表明:(1)2001—2015年4—9月四类九龙涡共有221个;维持时间小于4个时次的九龙涡(T_(1~2)JLV、T_(3~4)JLV)生成源地集中在27°~28.5°N、100°~101.5°E;维持时间为5~6个时次的九龙涡(T_(5~6)JLV)生成源地集中在29°~30.3°N、102°~103.5°E;维持时间不低于7个时次的九龙涡(T_(≥7)JLV)生成源地集中于28°~29.5°N、101.5°~103.5°E。(2)生成前6 h,九龙涡生命史越长,其生成源地高频中心周围的低层气旋性环流场更明显,500 hPa副热带高压位置更偏西偏北,200 hPa南亚高压范围更广。(3)生成前6 h,四类九龙涡高频中心周围中低层均为正涡度,低层呈东北-西南向分布,九龙涡生命史越长,其正涡度带越狭长且范围越广。(4)生成前6 h,四类九龙涡高频中心附近低层辐合而中高层辐散,九龙涡生命史越长,其水汽通量散度越强,且越往高层辐散强度越大,但最大辐散强度仍小于低层辐合强度。(5)生成前6 h,九龙涡生命史越长,其生成源地高频中心附近层结越不稳定,更有利于低涡的进一步发展和维持。

Based on the ERA5 reanalysis data,the spatio-temporal distribution of four types of Jiulong Low Vortex(JLV)with different life histories from April to September during 2001—2015 was statistically analyzed by artificial identification and the dynamic,and thermodynamic characteristics of JLV in the 6 hours prior to their formation were analyzed.The results demonstrate the following:(1)There were 221 JLVs in total from April to September during 2001—2015.The source high-frequency center of T_(1~2)JLV and T_(3~4)JLV was located in 27°~28.5°N,100°~101.5°E.The high frequency center of T_(5~6)JLV mainly was concentrated in 29°~30.3°N,102°~103.5°E.The high frequency center of T_(≥7)JLV was located in 28°~29.5°N,101.5°~103.5°E.(2)In the 6 hours prior to formation,the longer the life span of JLV was,the more obvious the low-level cyclonic circulation field around the high-frequency center of its generating source was,the more westerly and northerly position of the subtropical high at 500 hPa was,and the wider range of tthe South Asian high at 200 hPa was.(3)In the 6 hours prior to the formation,the four types of JLV had positive vorticity in the middle and lower layers around the center of HF,and the lower layers were distributed in a northeast-southwest direction,and the longer the life history of JLV was,the narrower and wider the positive vorticity band was.(4)In the 6 hours prior to formation,the four types of JLV had strong convergence at the low level near the high-frequency center and had divergence at the middle and high levels.The longer the life span of JLV was,the stronger the divergence of water vapor flux was,and the higher the level was,the stronger the divergence intensity was,but the maximum divergence intensity was still less than the convergence intensity in the low level.(5)In the 6 hours prior to the formation,the longer the life span was,the more unstable the layer junctions near the center of the HF at the source of JLV generation was,allowing further development and maintenance of JLV.