Modeling And Quantitative Analysis Of Torrential Rainfall Over North China During Summer

The rainstorm in flood season in North China often causes huge losses to social economy and life and property.Understanding the rainstorm system characteristics and related physical processes in North China can provide theoretical basis for the improvement of rainstorm numerical prediction.Based on the two-dimensional cloud simulation data of four strong rainfall years(1964,1994,1995 and 2013)during July in North China,the daily variation is analyzed from the aspects of precipitation budget,convective and stratiform precipitation,as well as the rainfall intensity and precipitation coverage in convective and stratiform precipitation areas.Based on the threedimensional WRF model sensitivity simulation data of a rainstorm in the south of Shanxi Province in July 2013,effects of the thermal(radiation and latent heat)and microphysical processes of ice cloud as well as the effects of the depositional growth of ice crystal and the accretion of snow by graupel are studied.The research results mainly include:(1)In 1964,1994 and 1995,the daily variation of convective precipitation and stratiform precipitation is mainly related to the daily variation of water vapor convergence and cloud condensate transport from convective precipitation area to stratiform precipitation area,while in 2013,the daily variation of convective precipitation and stratiform precipitation is majorly connected with the daily variation of water vapor convergence.In 1964,1994 and 1995,the daily variation of convective and stratiform precipitation is mainly related to the daily variation of rainfall intensity,while the daily variation of stratiform precipitation is majorly connected with the daily variation of fractional rainfall coverage in 2013.Meanwhile,the crest values of convective precipitation are basically in accordance with the crest values of rain intensity which is connected with the water vapor convergence.(2)At night,the crest value of precipitation reduction caused by the thermal effects of ice clouds is mainly related to the suppression of instability and upward motions by the latent heat effects of ice clouds.In the early morning,the crest value of precipitation increase caused by the thermal effects of ice clouds is mainly related to the radiative effects of ice clouds.The radiative effects of ice clouds reinforce the radiative cooling in the upper troposphere and suppress the radiative cooling in the lower troposphere,thus increasing the instability and upward motions.The microphysical effects of ice clouds enhance precipitation directly through the inclusion of vapor deposition and indirectly through the increase in condensation.(3)The decrease in range of ice crystal radius leads to the peak of precipitation decrease in the evening and the peak of precipitation increase in the morning.The peak of precipitation decrease in the evening is mainly related to the weakening of deposition,while the peak of precipitation increase in the morning is related to the weakening of cloud ice from divergence to convergence and the decrease of deposition.The increase of the efficiency of the accretion of snow by graupel causes the peak of precipitation increase in the evening and the peak of precipitation decrease in the midnight.The peak of precipitation increase in the evening is mainly related to the increase of graupel convergence.The peak of precipitation decrease at midnight is mainly related to the outflow of raindrops from precipitation area.