“碧利斯”引发强降水过程的湿位涡诊断分析

Diagnostic Analysis of Moist Potential Vorticity for Heavy Rain Caused by "BILLIS" Typhoon

利用NCEP 1°×1°再分析资料,计算了2006年第4号强热带风暴"碧利斯"过境引发强降水过程的湿位涡(MPV)和假相当位温(seθ),分析了其湿位涡中尺度时空分布特征,探讨了湿位涡发展、减弱与暴雨增幅、减弱的相关性,并结合假相当位温分布对此次强降水发生发展机制进行了分析。结果表明,700 hPa和850 hPa层湿位涡负值中心与强降水区域均有较好的对应关系,强的降水区域在850 hPa层位于湿位涡负中心的暖湿气流一侧,与负中心相距1个纬距左右,MPV负值中心大小可反映降水强度;在低纬地区,MPV的湿正压项MPV1负值区、MPV的湿斜压项MPV2正值中心北部以及seθ等值面陡然向地面转折处是预报强降水中心落区的一个判据;MPV1负值增长期,MPV2由负值向正值过渡期,对应降水增幅期;MPV1向正值过渡期,降水逐渐减弱;降水区完全由MPV2负值区控制时,该区域降水结束。

Based on the NCEP 1°×1° reanalysis data, the mesoscale spatio-temporal distributed characteristics of moist potential vorticity of the heavy rain triggered by the 4th strong tropical storm ＂Billis＂ in 2006 are analyzed. As a result, the negative MPV center at 850 hPa agrees Well with the severe precipitation region in 850 hPa located the side of warm and moist airflow 110 kilometers away from the negative MPV center whose size can reflect the precipitation intensity. In the low latitude area, negative MPV1 region, north of the positive MPV2 centre and the turning point of θse equivalent surface are the indexes to predicting the strong precipitation center. Negative MPV1 rise period and the transition period from negative MPV2 to positive MPV2 correspond with precipitation rise period. When precipitation area is covered completely by negative MPV2 region, the precipitation in this region will end.