“98．5”华南前汛期暴雨的湿位涡异常诊断:质量和热力强迫的数值分析

DIAGNOSTIC ANALYSIS OF MOIST POTENTIAL VORTICITY ANOMALY DURING THE MAY 1998 HEAVY RAINFALL OF SOUTH CHINA IN THE FLOOD SEASON

利用MM5输出的高分辨率资料对“98．5”华南暴雨的湿位涡进行了诊断分析,分析了质量强迫和热力强迫引起的湿位涡异常。结果揭示：降水区位于负湿位涡的下方,负湿位涡的趋势走向与降水区的一致。造成本次暴雨的成因中包括湿对称不稳定和对流不稳定两种机制,湿位涡MPV(moist potential vorticity)的分量MPV2对MPV起主要作用,其中主要是MPV2v的贡献。质量强迫和热力强迫共同作用引起湿位涡异常变化,它们的作用大小相当,在研究暴雨时,不可忽略因降水造成的质量强迫。

Moist potential vorticity（MPV） was diagnosed by using the simulated output data from MM5 with high resolution, and the MPV anomaly caused by the mass forcing and heat forcing were calculated. The results are as follows. The precipitation is below the negative MPV, and their shapes were the same; the baroclinic component MPV2 of MPV was most important to MPV, and the south-north wind shear mainly induced the development of MPV; the mass forcing and heat forcing caused the MPV anomaly together and their values were close; when studying the rainfall, the mass forcing would not be ignored; there were both the convective instability and the moist symmetry instability in this rainfall.