To understand the causes and characteristics of a torrential rainfall event on 25 August 2014 in the southern part of the Korean Peninsula, synoptic conditions and observational data from radiometer, wind profiler, satellite, radar, AWS, and Parsivel disdrometer were analyzed.
Convective cells that occurred near Shanghai at 0540 LST on 25 August 2014 moved eastward and developed into a MCS. The huge and strong MCS, organized by deep clouds, has passed over Changwon from 1200 LST to 1445 LST. For six and half hour before the start of rainfall, southwesterly winds gradually get stronger as well as an inflow of high temperature and high humidity air in the lower atmosphere by the radiometer and wind profiler observation. It is expected that convection has occurred by cold and arid air that has been descending from the upper level. A vertical upward flow was also observed between 2-5 km levels during this time. Favorable conditions for the development of the convective cell was formed by warm advection in the lower atmosphere below about 3 km and cold advection above that, producing large vertical wind shear. Stability indices calculated from the radiometric retrieval indicated the high possibility of a MCS occurrence.
Rainfall was classified into three types based on vertical properties identified from the three moments observed by the wind profiler from 0600 to 1430 LST. Mixed, stratiform, and deep convective rain types occurred in order during this analysis period. As the rainfall intensity becomes stronger, the drop size distribution analysis showed that the number of large particles has increased. During the deep convective rain (1130-1430 LST), hourly maximum rainfall was greater than 80 mm/hr. A very large and distinct wind veering was found in the hodograph analysis, showing increased wind speeds with height. An upper jet stream of 30 m/s observed at an altitude of 11km helped the outflow of air from cloud top, enhancing the vertical upward flow. Analysis of satellite images indicated that a large and deep developed cloud with a cloud top temperature below -70℃ and cloud top height greater than 15 km was observed.
Therefore, what happened the torrential rainfall on 25 August 2014 is considered that has been caused by the coupling of upper level jet appeared in the synoptic analysis and low level jet observed by multiple sensor instruments.