A CLOUD-RESOLVING MODELING STUDY OF SURFACE RAINFALL PROCESSES ASSOCIATED WITH LANDFALLING TYPHOON KAEMI(2006)
CUI Xiao-peng1,XU Feng-wen 2 (1. Laboratory of Cloud-Precipitation Physics and Severe Storms (LACS),Institute of Atmospheric Physics,Chinese Academy of Sciences,Beijing 100029 China; 2. National Meteorological Center,China Meteorological Administration,Beijing 100081,China)
The detailed surface rainfall processes associated with landfalling typhoon Kaemi(2006) are investigated based on hourly data from a two-dimensional cloud-resolving model simulation. The model is integrated for 6 days with imposed large-scale vertical velocity,zonal wind,horizontal temperature and vapor advection from National Center for Environmental Prediction (NCEP) / Global Data Assimilation System (GDAS) data. The simulation data are validated with observations in terms of surface rain rate. The Root-Mean-Squared (RMS) difference in surface rain rate between the simulation and the gauge observations is 0.660 mm h-1,which is smaller than the standard deviations of both the simulated rain rate (0.753 mm h-1) and the observed rain rate (0.833 mm h-1). The simulation data are then used to study the physical causes associated with the detailed surface rainfall processes during the landfall. The results show that time averaged and model domain-mean Ps mainly comes from large-scale convergence ( QW VF) and local vapor loss (positive QW VT). Large underestimation (about 15%) of Ps will occur if QW VT and QC M(cloud source/sink) are not considered as contributors to Ps. QW VF accounts for the variation of Ps during most of the integration time,while it is not always a contributor to Ps. Sometimes surface rainfall could occur when divergence is dominant with local vapor loss to be a contributor to Ps. Surface rainfall is a result of multi-timescale interactions. QW VE possesses the longest time scale and the lowest frequency of variation with time and may exert impact on Ps on longer time scales. QW VF possesses the second longest time scale and lowest frequency and can explain most of the variation of Ps. QW VT and QC M possess shorter time scales and higher frequencies,which can explain more detailed variations in Ps. Partitioning analysis shows that stratiform rainfall is dominant from the morning of 26 July till the late night of 27 July. After that,convective rainfall dominates till about 1000 LST 28 July. Before 28 July,the variations of QW VTin rainfall-free regions contribute less to that of the domain-mean QW VT while after that they contribute much,which is consistent to the corresponding variations in their fractional coverage. The variations of QW VF in rainfall regions are the main contributors to that of the domain-mean QW VF,then the main contributors to the surface rain rate before the afternoon of 28 July.