Analysis of an extremely heavy rain event caused by a tropical depression in the north of Zhejiang

By using the conventional data of meteorological observations, NCEP 6-hourly reanalysis data with resolution 1°× 1°, and FY-2E satellite cloud and related quantitative products, we analyzed an extremely heavy rain event occurred from August 18 to 19 of 2013 in the north of Zhejiang. The results show that (1) the tropical depression is the system that direct impacted on the event. In addition, the easterly jet stream between the depression and subtropical high over the west Pacific provide moisture and energy for the formation of the event; (2) There is evidently an asymmetric structure with tropical depression, which the centers of depression lean westward with height. Strong convective cloud clusters distributed mainly in the north side of low pressure circulation at 500 hPa lead directly to the event, and the movement of clusters are in accordance with the distribution of the strong precipitation; (3) Analysis of satellite cloud images and related products indicate that changes of blackbody temperature (TBB) and lower value center of outgoing longwave radiation (OLR) are of indicative significance to thedistribution of the strong precipitation, whose magnitudes have a good response for the precipitation intensity; (4) Water vapor required by the event comes mainly from the East China Sea, and the water vapor flux convergence zone is situated in boundary layer. Strong precipitation area is perpendicular to the concentrated pseudo-equivalent potential temperature isoneph zone. Meso- and micro-scale systems at ground level provide favorable lifting conditions for the occurrence of the event, and the trumpet-shaped topography in Hangzhou bay has clear effect on the increase of rainfall.