Aerosol effect on the light precipitation in association with the urbanization effect

Many observational and numerical studies have indicated that urbanization and aerosol can change or modify local and nearby meteorological phenomenon. Our previous study presented the analysis of long-term (1972-2007) precipitation treads in the mid-Korean peninsula around Seoul for the westerly condition, along with the WRF model simulations with the change of anthropogenic heat and surface roughness length. From 1972 to 2007, the precipitation amount (PA) and frequency (PF) together in the downwind region of Seoul significantly increased for the westerly and light precipitation (PA≤1 mm d-1) cases, while PA and PF for the downwind area vs. urban area remarkably increased, implying the possible urbanization effect on the downwind precipitation. The WRF simulation applied for a golden case also demonstrated enhanced updraft and its associated convergence in the downwind area, leading to an increase in the cloud mixing ratio. Sensitivity simulation with an increase in anthropogenic heat shows that updraft is enhanced in the near-downstream region together with the low-level convergence, but an insignificant change in cloud water mixing ratio. On the other hand, additional simulations with WDM6 (WRF Double-moment Six class) microphysics scheme varying CCN concentrations demonstrate a decrease in cloud water mixing ratio in near-downstream region (up to 60 km from the urban region) and its increase in far-downstream region. In spite of limitations in the observation-based analysis and simulation, the preliminary result could represent combined response such as cancellation and enhancement of urbanization and aerosol effects especially on the light precipitation in mid-Korean peninsula.