“98.7”特大暴雨中尺度系统发展的热量和水汽收支诊断

1998年7月20~23日 (“98.7”) 发生在鄂东和鄂西南地区的特大暴雨过程, 不仅与700 hPa上低涡切变线的生成和持续发展密切相关, 而且与沿低涡切变线相继生成和强烈发展的MαCS与MβCS直接关联。利用非静力模式MM5.V2.12成功模拟提供的高分辨输出资料对这次特大暴雨中尺度系统发展的热量和水汽收支进行了诊断。结果发现:当有强对流发生并伴有强降水时, 就会有强的视热源Q₁和视水汽汇Q₂出现, 而强的Q₁与Q₂和强降水区基本是对应的; Q₁随高度增高而增大, 最大加热位面基本上都在486.1 hPa (σ=0.54) 附近; 在对流层深厚的中空加热层是积云对流活跃和强暴雨持续发生、发展的一种重要热力机制; 在对流层上半部的相对冷层为暴雨区上空积云对流提供了极为有利的热力不稳定条件, 积云对流在中、低空的凝结潜热不仅加热对流层中层大气, 而且向高层输送, 加热高层的环境大气; 在暴雨初期, Q₂的双峰结构与低空层积云及中空积云对流凝结变干有关; Q₂的中空峰值大体与Q₁的峰值相应, Q₂的深厚变干层与Q₁的深厚加热层非常一致。 诊断结果表明, 用非静力中尺度模式成功模拟的高分辨输出资料对Q₁和Q₂进行数值诊断是可行的。通过对强暴雨过程Q₁和Q₂的诊断, 可为改进积云对流参数化中加热和增湿廓线提供可靠的物理依据。

DIAGNOSES OF THE MESOSCALE HEAT AND MOISTURE BUDGETS DURING THE "98.7" EXTRAOR DINARY HEAVY RAINFALL

During the period of 20-23 July 1998 ("98.7"), an extraordinary heavy rainfall event occurred in the eastern and southwest parts of Hubei Province, which was in close relationship with the low vortex with shear line on 700 hPa as well as with the successively generated and intensively developing MαCS and MβCS along the shear line. The numerical simulation for this event is conducted successfully using nonhydrostatic version MM5 (V2.12). The mesoscale heat and moisture budgets are diag nosed using the output data of MM5. The finding sare as follows: strong apparent heat sources Q₁ and apparent moisture sink Q₂ would appear while the strong convection occurs with heavy rainfall; Q₁ and Q₂ are basically correspondent with the regions of heavy rains; Q₁ increases with height while the maximum heating level is located at 486.1 hPa (σ=0.54); the deep and thick heating layer in the middle troposphere is the main thermody namic mechanism for the both cumulus convective activities and the successive generation and development of severe rainstorms; the relatively cool layer in the upper troposphere provides a favorable thermody namic condition for intensive cumulus convection over the heavy rain areas; the condensation latent heating of cumulus convection in the lower and middle troposphere is not only heating the middle troposphere atmosphere, but also heating the upper environment atmosphere through transporting heat upward; the double-peak structure of Q₂ at the early stage of heavy rainfall is relevant to the drying associated with convective condensation of both stratocumulus at the lower levels and cumulus at the middle levels; the peak value of Q₂ in the middle level is basically corresponding with that of Q₁; the deep and thick drying layer is consistent with the deep and thick condensation-heating layer of Q₁. The diagnostic results show that it is reasonable to diagnose Q₁ and Q₂ using successfully stimulated output data with high resolution. The reliable physical proof for improving heating and moisturizing profiles in the cumulus convective parameterization can be obtained through diagnosing Q₁ and Q₂ of the rainstorm event.