A Mechanism Study On Typhoon Torrential Rainfall Responses Of Radiative And Microphysical Processes

It is necessary to further study the rainfall responses of typhoon to radiative and microphysical processes of clouds.Base on Typhoon Soudelor(2015),a series of sensitivity experiments are conducted to examine radiative effects of cloud species and effects of cloud microphysical processes on rainfall.The conclusions are listed as follows:(1)The radiative effects of cloud water,raindrops and graupel on rainfall are negligible,while the radiative effects of cloud ice and snow play an important role in rainfall.However,the different vertical distributions of cloud ice and snow lead to opposite radiative effects on rainfall.Since the peak of cloud ice is around 11 km,the inclusion of radiative effects of cloud ice weakens radiative cooling in the upper troposphere and makes little difference in the middle and lower troposphere.Thus the decreased instability suppresses the convection,which reduces the rainfall.The peak of snow appears around 9 km.The inclusion of radiative effects of snow enhances radiative cooling in the upper troposphere and suppresses it in the middle and lower troposphere.The increased rainfall corresponds to the strengthened convection associated with increased instability.(2)The experiments of latent heat indicate that:The release of latent heat of condensation plays a vital role in maintaining typhoon intensity;The evaporation of raindrops decreases the warm-core intensity by absorbing the heat,which is unfavourable to the development of convection as well as typhoon.At last,it substantially reduces the rainfall;Although the release of latent heat of deposition is weaker than that of condensation,it promotes the convection and formation of rainfall.In contrast,the radiative effects of cloud species on rainfall are smaller.(3)The rainfall responses to different parameterization schemes of Bergeron-Findeisen process(Hsie,Krueger and Zeng)with parameters K and T(revised on the basis of K)are studied.The rainfall is not sensitive to the K and T applied in the Hsie or Krueger,but made a huge difference from Zeng with K to Zeng with T.In the Zeng,the T substantially weakens the Bergeron-Findeisen process which releases the latent heat.It directly reduces the production of cloud ice and snow and ascent.The decreased convection reduces the production of cloud ice and snow indirectly.As a result,the Zeng with T produces less rainfall for the weaker melting of graupel to form raindrops.