一次连续性暴雨中双雨带的成因分析

利用NCEP/ NCAR 1 ?×1 ?再分析资料，对2005年6月17—22日发生在长江以南的一次连续性暴雨过程分析发现，在连续性暴雨过程中，长江以南有两支雨带存在，北雨带与冷锋降水以及副热带西风急流右后方的非地转场引起的质量调整有关。南雨带的形成与东、西风急流和南亚高压的共同作用有关：东风急流中心右后部的非地转场可形成反环流，有利于南雨带形成；南亚高压脊线附近以及东风急流的右后方的du/dt<0，可导致雨区附近及南部强的v-vg<0场出现；当西风急流南压，在雨区的北部即西风中心的后部可形成强的v-vg>0，三者共同作用的质量调整使雨区上空出现强辐散场导致暖区强降水出现。分析发现南雨带中层有θe锋区存在，该锋区有利于不稳定能量的释放，使暴雨加强，当南北锋区接近时雨带合并。

RESEARCH ON THE CAUSES OF DOUBLE RAIN BELTS DURING A SUSTAINED RAINSTORM

The NCEP/NCAR reanalysis data, is used to conduct a diagnostic analysis on a sustained rainstorm that happened to the south of Yangtze River during June 17-22 in 2005. It is indicated that there were two rain belts there, one being northern and the other southern. The northern rain belt was mainly related with the adjustment of mass caused by cold-front-induced rainfall and an ageostrophic field to the right of the rear portion of a subtropical westerly jet stream. The formation of the southern rain belt resulted from the interaction between the easterly jet stream and South Asia High; the ageostrophic field, which was to the right of the rear part of the easterly jet stream, may produce anti-circulation, was beneficial for the formation of the southern rain belt. To the right of the rear portion of the easterly jet stream and near the South Asia High ridge line, du/dt<0 may lead to the establishment of a high v-v_g<0 field around and in the south of the rainfall area. When the westerly jet stream moved southwards, a high v-v_g>0 filed may form in the north of the rainfall area, i.e. behind the core of the westerly wind. The mass adjustment resulting from the interaction between the three systems led to the appearance of heavy divergence above the rainfall area and the establishment of heavy warm-sector precipitation. Analysis indicated that there was a θ_e frontal zone at the middle level of the southern rain belt, which was beneficial for the release of unstable energy to strengthen the rainstorm; when they approached towards each other, the southern and northern rain belts merged into one.