Thermodynamic Characteristics associated with Localized Torrential Rainfall Events in the Korean Peninsula

Abstract:

This study uses observational data from radar and radiosonde to investigate the thermodynamic conditions associated with Localized Torrential Rainfall (LTR) events in the Korean peninsula. LTR events in this study are defined by three criteria: 1) hourly rainfall exceeding 30 mm h-1 recorded at any of the automated synoptic observing system (ASOS) around Osan(Middle West) or Gwangju(South West), 2) an area of rainfall at > 1 mm h-1 (as estimated from radar reflectivity) of less than 20,000 km2, and 3) clearly defined stages of genesis and dissipation in a group of rain cells (>10 mm h-1) and these duration is shorter than 24 hours. As a result, 15 cases were selected from the summer season (June-August) over the last decade (2004-2013). It is found that all cases occurred inland during the afternoon hours and that the duration and maximum rain area of convective cells (>30 mm h-1) was less than 9 hours and smaller than 2,000 km2, respectively. The majority of cases showed the following thermodynamic characteristics: 1) strong convective available potential energy (CAPE > 1,000 J kg-1 related to surface heating, 2) weak or no convective inhibition (CIN < 50 J kg-1), 3) adequate moisture and total precipitable water (TPW ~ 55 mm), and 4) values of storm relative helicity (SRH) of less than 120 m2 s-2. These thermodynamic conditions indicated that these cases were caused by strong atmospheric instability, lifting to overcome CIN, and sufficient moisture. Our conclusion is that LTR events in the Korean peninsula occurred by deep moisture convective system. Furthermore, those systems vary according to region such as convective band(Middle west) or scattered small cells(South West).