The utilization of the anomaly method in investigating the location of regional heavy rainfall induced by vortex

The forecast of torrential precipitation caused by vortex is a crucial and challenging aspect of rainstorm forecasting in North China. This paper analyzes the characteristics of atmospheric anomalies during the occurrence and development of two rainstorm events caused by vortex, “Case-20120721” and “Case-20160720”. The results show that if the temperature anomaly front was steep, the falling area of rainstorm was well corresponding with the intersection of temperature anomaly front and ground, and also with the bottom position of gradient zone of anomalous specific humidity. In cases with relatively gentle temperature anomaly front areas, the falling area of the rainstorm corresponded to the intersection of the negative axis of anomalous geopotential height with the ground and the center of specific humidity anomaly. Both cases were accompanied by strong vertical shear of horizontal anomalous wind, and the location where the negative central axis of the anomalous V wind field intersected the ground indicates that the cold air brought by the anomalous northerly wind corresponded well with the heavy rainstorm area at the top of the vortex. Additionally, the areas where the anomaly axes of moist vorticity and moist divergence column connect to the ground always corresponded to heavy precipitation areas. It is worth noting that initially, these axes of anomaly were vertical, but they began to tilt after the precipitation developed strongly.