The effects of ice nucleation on the microphysical processes and precipitation for a heavy rainfall event in Beijing

In order to better understand the effects of ice nucleation on deep convective clouds, two parameterizations that represent the high active fraction (H-AF case) and low active fraction (L-AF case) of ice nuclei (IN) are implemented into the Weather Research and Forecasting (WRF) model to investigate an extreme real precipitation case. The results indicate that the maximum value of 24-h surface precipitation for the H-AF case is closer to the observation measurement than that for the L-AF case. In early stage of precipitation, increasing IN leads to stronger competition for water vapor in homogeneous regime (above the-40 degrees C level) and a delay in the growth of ice particles for the H-AF case. With the development of convective system, a large number of ice particles are generated and there are more supercooled droplets occurring above the-20 degrees C level in H-AF case, resulting in significantly increased mass of snow and graupel and heavier precipitation than that in L-AF case mainly through the processes of R_RCW and R_SML