The Relationship Between Sea Breeze and Urban Rainfall over Seoul Metropolitan Area

We examined the urban rainfall under sea breeze penetration over Seoul Metropolitan area (SMA). To examine how often sea breeze induced rainfall occurred over SMA, we first analyzed rainfall data from automatic weather stations (AWS) over SMA for 5 years. Afternoon sea breeze induced rainfall occurred 5-10 times a year and mainly occurred in northeastern SMA. The rainfall covered only small area (about 5-10 %) of SMA and most of rainfall amounts were less than 20 mm. On 6 July 2017, large rainfall more than 50 mm occurred under sea breeze penetration over SMA. We evaluated the performance of Weather Research and Forecasting (WRF) model to simulate the sea breeze induced rainfall. The model captured the onset of sea breeze, the development of afternoon rainfall and location of the maximum rainfall over SMA but slightly overestimated rainfall amount. To understand the urban effect on the rainfall event, we performed four sensitivity tests (NA: no anthropogenic heat, LB: low roughness over urban area, NALB: no anthropogenic heat and low roughness over urban area, NOURBAN: cropland replaces urban area). The sensitivity test showed that urban effect changed penetrating speed of sea breeze, low-level convergence and convective available potential energy along sea breeze wind, resulting in difference in location and amount of maximum rainfall.

Acknowledgments: This research was funded by the Korea Environmental Industry & Technology Institute (KEITI) of the Korea Ministry of Environment (MOE) as "Advanced Water Management Research Program". (79615).