Overview of orographic precipitation observation in Jeju island, Korea

Presentation Type: 
Dong-In Lee (Department of Environmental Atmospheric Sciences, Pukyong National University)
Hiroshi Uyeda (Hydrospheric Atmospheric Research Center, Nagaoya University)

In summer monsoon season, Korean Peninsula is influenced by several weather phenomena such as the Changma-front, typhoon, strong low pressure, and local heavy precipitation. Especially, the orography plays an important role in controlling the cloud formation, amount and precipitation distribution in the mountainous regions. To find out the precipitation development mechanism by orographic effect, we performed the intensive field observation around Mt. Halla in Jeju island (33.21∞N and 126.32∞E) which is located at the southern part of Korea. We installed and arranged the observational instruments such as AWSs, 4 radiosondes (including mobile sonde and ship sonde), 7 Parsivels, 3 2DVDs, 3 ultrasonic anemometers, and 15 raingauges along the altitudes in Jeju island. Each of disdrometer site was located in straight line considering topography between two S-band Doppler radars. We analyzed synoptic condition by NCEP/NCAR reanalysis data and kinematic characteristics of precipitation by dual Doppler radar analysis using S-band radars in KMA.

In 2012 case, the Changma-front was located in the northern part of the Jeju island and the precipitation system passed from the southwest to the northeast. The accumulated precipitation of 31.7 mm was recorded at the site D4 which was placed in the highest (H: 975 m). During the passage of precipitation, the south westerly wind (> 12 m s-1) with warm and humid air and the cold (lower layer) and warm advection (upper layer) were observed. The wind field analysis shows that convergence and upward wind were dominated in ahead side of the convective systems. From the microphysical analyses, small size rain drops (less than 0.3 mm) were increased in D2 (windward side, H: 571 m), while increase in middle and large size rain drops (larger than 3 mm) were observed in D6 (leeward side, H: 324 m) site.

In 2013 case, the Changma-front located in the center of Jeju island and precipitation system passed from the southwest to northeast. The warm advection in lower layer and cold advection in upper layer were observed by radiosonde analyses, relatively. Strong southwesterly winds were blown with moist environment in surface layer. By the wind field analysis, convergence in west and divergence in east were existed with updraft in Jeju island and downdraft in ocean area, relatively. During the passage of precipitation, convergence over 0.001 s-1 and upward wind over 1.5 m s-1 observed above the mountain, continuously. High number concentration at D4, D5 and D8 were shown with small size raindrops (less than 2 mm), however large size raindrops (lager than 6 mm) were distributed at D7 (northeast in island) and D9 (southwest in island).

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