Thermodynamic characteristics associated with localized torrential rainfall events in the southwest region of the Korean peninsula

Abstract

This study uses observational data from radar and radiosonde to investigate the thermodynamic conditions related to localized torrential rainfall (LTR) in the southwest region of the Korean peninsula. Three criteria were defined for selecting LTR events: 1) hourly rainfall exceeding 30 mm h−1 recorded at any of the automated synoptic observing systems (ASOS) around Gwangju, 2) an area of rainfall at > 1 mm h−1 (as estimated from radar rain rate) 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) with a duration lasting less than 24 hours. As a result, 10 cases were selected from the summer season (June-August) over the last decade (2004-2013). Results showed all cases occurred during the afternoon hours and that the duration and maximum rain area of convective cells (> 30 mm h−1) was less than 6 hours and smaller than 700 km2, respectively. The majority of cases showed the following thermodynamic characteristics: 1) strong convective available potential energy (CAPE > 1,500 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 10 m2 s−2. The area of rainfall (700 km2) and the duration (6 h) in this experiment were relatively small and short, respectively, compared to those in a previous study in the middle-west region of Korea (1,000 km2, 9 h), but a higher CAPE (1,500 J kg−1) and lower SRH (10 m2 s−2) were involved in this study than in the former (800 J kg−1, 120 m2 s−2).