The influence of the low-frequency diabatic heating on the low-frequency circulation during the persistent severe rainfall period over South China

This study investigates the distribution and evolution of the low-frequency anomalous diabatic heating and its effects on the low-frequency anomalous circulation on 10-30 d timescales, accompanied with the persistent severe rainfall (PSR) events over South China during May-August. The evolution of the anomalous diabatic heating during the May-June (MJ) PSR and July-August (JA) PSR is different. The low-frequency diabatic heating anomaly propagates southward from north of 30°N to South China over 107°-115°E before the MJ PSR events, while the anomalous diabatic heating propagates northwestward to South China from the South China Sea (SCS) and Philippine Sea before the JA PSR events. The anomalous circulation pattern could control the position and intensity of the rainfall and condensational heating, and the condensational heating could however give a feedback to the anomalous circulation by affecting the vertical vorticity tendency. For two groups of events (MJ and JA) over South China, the significant positive vorticity tendency anomaly on 10-30 d timescals is over South China under the influence of both the anomalous diabatic heating and the advection of vorticity during the rainfall developing period. The vertical nonuniform of the diabatic heating has an important influence on the vorticity tendency, and the vorticity advection is closely related with the mean state of the wind fields. The anomalous vorticity advection is located east of the anomalous diabatic heating during the MJ PSR events, while the anomalous vorticity advection is located north of the anomalous diabatic heating during the JA PSR events. The anomalous diabatic heating and vorticity advection turn to negative ones during the rainfall ending period, the negative vorticity tendency anomaly is over South China which is favorable for the decaying and ending of the anomalous cyclone.