Features and Causality Analysis on the Unusual Rainstorm in Guangzhou during October,2011

Causality analysis on an unusual rainstorm in Guangzhou during 13-14 October,2011 is conducted from the perspective of background circulation,radar signatures and physical elements with the data of doppler radar,boudary layer wind profiler,mesoscale automatic weather station and the NCEP reanalysis data(1×1deg).Results show that cold air instrusion,movement of the sutropical high ridge triggered the heavy torrential rain event;vertical motion above Guagnzhou,convergence of perstistent southwest moisture jet ahead of westerly trough and the southeast watervapor transportation to the south of low level shear are favorable for the initialization and the maintenance of the heavy rainfall.The start(end) of clockwize rotation of wind direction and the rapid strengthening(Weakening) of wind speed in mid-low layers agreed well with the start(end) of rainfall event;and the covergence of cold and warm air brought the peak of the rainstorm.