江淮流域持续性强降水期间西太副高位置变异与非绝热加热的关系

RELATIONSHIP BETWEEN THE POSITION VARIATION OF THE WEST PACIFIC SUBTROPICAL HIGH AND THE DIABATIC HEATING DURING PERSISTENT HEAVY RAIN EVENTS IN YANGTZE-HUAIHE RIVERS BASIN

采用NCEP/NCAR逐日再分析资料及全国740站逐日降水资料,讨论了江淮流域持续性强降水期间西太平洋副高位置变动特征及其与非绝热加热的关系。通过个例合成研究发现:副高位置变异与强降水持续期间大气非绝热加热关系密切。强降水持续期间,副高北侧的江淮流域和西侧的孟加拉湾北部地区均存在强烈的视热源和视水汽汇。强降水发生前3 d,江淮流域Q1z开始增大,到降水发生后2 d的Q1z达到最大,尔后逐渐减小,降水结束后变化趋于平缓,此期间不利于副高北抬;此外,强降水发生前2 d,孟加拉湾北部地区Q1z开始增大,降水发生后1 d达最大,副高逐渐西伸,此后,Q1z减小,副高相应有所东退。根据全型垂直涡度倾向方程,对流层中层,江淮流域非绝热加热的垂直变化有利于副高北侧气旋性涡度增长,阻碍副高北进,有利于雨带在江淮流域维持,形成持续性降水;孟加拉湾北部地区非绝热加热的垂直变化有利于副高西侧反气旋涡度增加,可能是诱导副高西伸的原因之一。

By using NCEP/NCAR daily reanalysis data and daily precipitation data of 740 stations in China,relationship between the position variation of the west Pacific subtropical high（WPSH） and the diabatic heating during persistent heavy rains in the Yangtze-Huaihe Rivers basin are studied.The results show that the position variation of WPSH is closely associated with the diabatic heating.There are strong apparent heating sources and moisture sinks in both the basin（to the north of WPSH） and the north of Bay of Bengal（to the west of WPSH） during persistent heavy rain events.In the basin,Q1z begins to increase 3 days ahead of intense rainfall,maximizes 2 days later and then reduces gradually,but it changes little after precipitation,thus preventing the WPSH from moving northward.In the north of the Bay of Bengal,2 days ahead of strong rainfall over the basin,Q1z starts to increase and peaks 1 day after the rainfall occurrence,leading to the westward extension of WPSH.Afterwards,Q1z begins declining and the WPSH makes its eastward retreat accordingly.Based on the complete vertical vorticity equation,in mid-troposphere,the vertical variation of heating in the basin is favorable to the increase of cyclonic vorticity on the north of WPSH,which counteracts the northward movement of WPSH and favors the persistence of rain belts over the basin.The vertical variation of heating in the north of Bay of Bengal is in favor of the increase of anti-cyclonic vorticity to the west of WPSH,which induces the westward extension of WPSH.