Wednesday, 13 January 2016
It has been known that the turbulence-induced collision enhancement (TICE) affects cloud development and precipitation and regulates the aerosol effects on cloud development. To examine the effects of TICE on the heavy precipitation, a heavy precipitation event that occurred on September 21, 2010 over the middle Korean Peninsula is numerically simulated. For this purpose, an updated bin microphysics scheme incorporating TICE for drop-drop and drop-graupel collisions is implemented into the Weather Research and Forecasting (WRF) model. The numerical simulation captures well the important features of observed surface precipitation and radar reflectivity, as well as synoptic conditions. The mean surface precipitation averaged over the middle Korean Peninsula increases due to the TICE effects. In particular, the maximum surface precipitation rate near Seoul increases by up to 35% due to TICE, which is closer to the observation compared to the maximum surface precipitation rate in the case without TICE. The frequency of high radar reflectivity near the surface also becomes higher due to TICE. TICE accelerates the coalescence between small cloud droplets, which induces a decrease in condensation and an increase in water vapor transported upward following the front. This causes an increase in relative humidity with respect to ice at high altitudes, hence increasing the depositional growth of ice crystals and snow particles. Therefore, the snow mass increases due to TICE, and this increase induces the increase in surface precipitation. Although riming is reduced by TICE because of the decreased small droplets aloft, the increase in depositional growth is predominant over the decrease in riming. Peak radius in the snow size distribution is little changed, whereas the snow number concentration increases over the entire snow radius range.
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