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The intensive observation (ProbeX-2010) with 6-hour launches of radiosonde was performed over Seoul metropolitan area (Dongducheon, Incheon Airport, and Yangpyeong) from 13 Aug. to 3 Sep. 2010. Five typical heavy rainfall patterns occurred consecutively which are squall line, stationary front, remote tropical cyclone (TC), tropical depression, and typhoon patterns. On 15 Aug. 03 KST, when squall line developed over Seoul metropolitan area, dry mid-level air was drawn over warm and moist low-level air, inducing strong convective instability. From 23 to 26 Aug and from 27 to 29 Aug. Rainfall event occurred influenced by stationary front and remote TC, respectively. During the stationary frontal rainy period, thermal instability was dominant in the beginning stage, but dynamic instability became strong in the latter stage. Especially, heavy rainfall occurred on 25 Aug. when southerly low level jet formed over the Yellow Sea. During the rainy period by the remote TC, thermal and dynamic instability sustained together. Especially, heavy rainfall event occurred on 29 Aug. when the tropical air with high equivalent potential temperature (>345 K) occupied the deep low-middle level. On 27 Aug. and 2 Sep. tropical depression and typhoon Kompasu affected Seoul metropolitan area, respectively. During these events, dynamic instability was very strong.

Abstract:The intensive observation (ProbeX-2010) was performed to investigate an urban effect on summer rainfall over the Seoul metropolitan area from 13 August to 3 September 2010. Two kinds of urban effect were detected. First, weak rainfall (≤1 mm hr ) was observed more frequently in the downwind area of Seoul than any other area of the country. The high frequency of weak rainfall in the downwind area was also confirmed from the recent five years of observational data (2006)(2007)(2008)(2009)(2010). Because the high frequency was more apparent in mountainous regions during nighttime, the weak rainfall seems to be caused by a combined effect of urbanization and topography. Second, sporadically, a convective system was developed rapidly in the downwind area of Seoul, causing heavy rainfall (≥10 mm hr −1). It can be most clearly seen in series of radar images around 1300-1500 KST 27 August 2010. We investigated in detail the synoptic and local weather and upper air conditions. As a result, not only urban-induced high sensible heat but also conditionally unstable atmosphere (especially unstable in low level) and low level moisture were pointed out as important factors that contributed to urban-induced heavy rainfall.