位涡诊断在云南夏季强降水预报中的应用

通过对云南夏季常见的"滇黔辐合型"强降水的个例分析,探讨位涡诊断在低纬高原的应用前景。发现干、湿位涡能较好地反映天气系统的演变特征,干位涡能反映冷空气活动的路径和暖湿气流的活动。高层干位涡具有向对流层低层延伸和低层干位涡具有向上伸展的特点,当高层干冷空气与低层的暖湿气流汇合,加上低层低涡切变的辐合机制,产生强烈的上升运动,这种形势极有利于对流不稳定能量的储存和释放,造成强降水。当高、低层干位涡减弱,两者相互作用减弱时,降水趋于结束。云南夏季常见的"滇黔辐合型"强降水过程的干位涡场表现在对流层中低层,高低纬呈现南北向或东北西南向高值带,当PV高值带断裂时,云南省强降水过程趋于结束。对流层低层湿位涡MPV1较PV能更好地反映对流层低层西南涡的移动和发展,在云南强降水过程中,700hPa上MPV1<0,MPV2>0。

Application of Potential Vorticity Diagnoses in Yunnan Summer Heavy Rain Forecasting

This is an approach to application of the potential vorticity diagnosis technique to Yunnan heavy rain forecasting through one of most often occurring strong precipitation cases so-called as \!Yunnan-Guizhou convergence pattern\" summer. The main results are as follows: Both the dry and moist potential vorticity(PV) can well present the features of the weather systems. The dry PV reflect both the cold and warm air flow activities. The upper tropospheric dry PV tends downward to the lower-levels and vice versa for the lower-level troposheric dry PV. It is favourable for causing the heavy rainstorm when the dry air in upper levels meets with the warm and wet air in the lower-levels along with the convergence conditions of low and shear line in lower-layers; but once the PV weakens in upper- and lower-levels the precipitation will be ended soon. The \!Yunnan-Guizhou convergent pattern\" rainstorms show usually there are a dry PV high value oriented belt in NE to SW or N to S in the mid-and lower-troposhere, and when the high value belt is broken, the process of heavy rain over Yunnan will end up. The moist potential vorticity(MPV)presents the cyclones on the 700 hPa much better than the dry PV. Commonly, the conditions MPV1<0 and MPV2>0 on 700 hPa occur during the heavy rain process in Yunnan.