Abstract:

Based on conventional observed data from 2009 to 2011 in Tianjin, weather systems of 33 local rainstorm processes were analyzed. Atmospheric physical parameters were analyzed statistically before local rainstorm happened, and key points of forecasting under different weather systems were compared. The results show that local rainstorms often occur under four weather systems, namely, Mongolia cold vertex, northeast cold vertex, before or after upper trough. Plenty of water vapor throughout the atmosphere and deep convergence ascending motion on the southeast quadrant of vortex system are main factors of forecasting under Mongolia cold vertex, while low-level moisture conditions and middle-level strong convergence uplift are emphasis of forecasting under northeast cold vortex systems. Dynamic, water vapor and energy conditions under upper trough system are more balanced. However, all kinds of strong convective characteristics are very significant if the local rainstorm happens after upper trough. Diagnosis of falling areas of typical local rainstorms suggests that precipitable water, convection effective potential energy and vertical wind shear between ground to 3 km height are of indicative to falling area of rainstorm, because these three parameters are calculated based on data in Tianjin radiosonde station where temperature, humidity and wind are considered fully. At the same time, the case analysis shows that a TJ-WRF numerical model has a good ability for predicting local rainstorms, and physical parameters calculated by the model can be used to well forecast the local rainfall area.

Key words: Local rainstorm, Severe convection parameters, Tianjin constructed encryption sounding, Local numerical models