The DSD characteristics and precipitation development mechanisms

Presentation Type: 
Hyeon-Joon Kim (Dept. of Environmental Atmospheric Sciences, Pukyong National University)
Dong-In Lee (Department of Environmental Atmospheric Sciences, Pukyong National University)
Keun-Ok Lee (Atmospheric Environmental Research Institute, Pukyong National University)
Sung-A Jung (Department of Environmental Atmospheric Sciences, Pukyong National University, Republic of Korea)

During Changma season from June to July in 2012, intensive field observation was conducted to investigate the orographic rainfall over Mt.Halla in Jeju Island (oriented west east; height 1,950 m, width 78 km, length 35 km). During intensive observation period, two precipitation systems which developed on the mountainous region of the island were obtained; 1) SP: stratiform precipitation on 1 July, and 2) CP: convective precipitation on 4 July. The characteristic of drop size distribution (DSD) and development mechanisms of the selected precipitation systems were investigated using 3-D reflectivity data (dual S-band Doppler radars at the west and east of the island) and surface disdrometer data of 7 PARSIVELs (across the mountain from west to east of the island). Both SP and CP were occurred in a moist environment during Changma season, with surface RH of 82 % and 93 %, respectively. For SP, westerly winds of 10 ms-1 were dominant in low altitudes (surface 800 hPa); for CP, southwesterly winds of 8.5 ms-1 prevailed in the low altitudes. SP moved from the northwestern side to the southeastern side of the island and developed on the western slope. When SP developed on the western slope (windward side) of the island, adjoining area of reflectivity e35 dBZ from 4 km to 2 km height was characterized. During SP passages to the western slope of the mountain, the reflectivity in heights of 4-6 km was intensified from 48 to 51 dBZ. Along the western slope, 4 PARSIVELs (P1, P2, P3 and P4) were installed and the observed data were analyzed for SP. With dominant southwesterly wind (Fr, 0.4), liquid water content (LWC) was increased along the western slope from 0.16 g/m3 (P1, height 58m) to 0.23 g/m3 (P4, height 975m); the number concentration (N(D)) of middle size drop (1 mm d" D < 3 mm) and large size drop (D e"3 mm) were increased, in contrast N(D) of small size drop (D <1 mm) was decreased. CP moved from the southwestern side to the northeastern side of the island, and it developed on both western slope (windward side) and the eastern slope (lee side) of the mountain. On the windward side, the intense reflectivity e"50 dBZ of CP developed mainly in heights of 2 5 km; on the lee side, the development of the intense reflectivity was characterized in the heights with temperature below 0 !. 7 PARSIVELs (P1 P4 windward side, P5 P7 lee side) data were analyzed for CP. High LWC (0.6 g/m3) and high N(D) with large and middle size drop were characterized at P1 (western coastal region). As CP moved from P1 (height 58 m) to P2 (height 332 m) region, the LWC and the N(D) of large and middle size drop were decreased at P2 (LWC 0.47 g/m3), however these values increased passing on P3 (height 571 m, LWC 0.78 g/m3) and P4 (height 975 m, LWC 0.54 g/m3) along the western slope. Subsequently CP moved to the lee side showing the decrease of LWC (0.28 g/m3) and N(D) of small, middle, and large size drop. In summary, two precipitation system (SP and CP) passed on the mountainous region of Jeju Island, showing development on the upslope in moist environment during Changma season. During the SP and CP passages from the western coastal region onto the western slope of the mountain, LWC was increased. With the LWC increase, N(D) of middle and large size drop increased on the western slope in both SP and CP. In CP, even precipitation development was apparent in heights with temperature below 0 ! on the lee side of the mountain, N(D) of all size drop decreased. The detailed characteristics of DSD variables and development mechanism of SP and CP will be introduced in conference.