A Modeling Study Of The Effects Of Cloud Microphysical Processes On Typhoon Usagi(2013) By CAMS Cloud Scheme

In this study,numerous numerical experiments of super Typhoon Usagi(1319)are conducted using the Weather Research and Forecasting(WRF)model with the Chinese Academy of Meteorological Science(CAMS)two-moment microphysical scheme.The simulated track,intensity,cloud microphysics and rainfall are compared against the typhoon best track dataset and satellite observations to evaluate the performances of CAMS microphysics and investigate the possible effects of cloud microphysical processes on Typhoon Usagi.Based on the overestimated snow content in the CTRL test,three sensitivity experiments are firstly designed: modifying the coefficients of snow particle mass and falling velocity(test SNOW),using the typical oceanic cloud droplet parameter(test NUMC),and including the changes both in the SNOW and the NUMC(test COMB).It is shown that the snow content is significantly reduced in the SNOW and COMB tests due to the increased rate of accretion of snow by graupel and the slightly reduced snow mass flux,and the content of whole ice-phase hydrometeors are also reduced.The rapid intensification process in the early stage of Typhoon Usagi is captured in the NUMC and COMB tests owing to the better simulated CAPE in eye region,and their intensity and track are also better than those in the CTRL.Although the hourly precipitation rate in each test is generally strong,the spatial distribution in the COMB test is more likely consistent with the observation.Since the phase-change process has a considerable impact on a typhoon development,in order to further survey the role of different phase-change microphysical processes,the cloud droplet condensation process(SVC),the raindrop evaporation process(SVR),the melting and deposition of ice-phase particles are chosen.Ten sensitivity experiments are then conducted to study the impacts of phase-change processes on the typhoon.The results show that the cloud droplet condensation is a very important source of latent heat in the development of typhoon.Enhancing the impact of SVC on temperature feedback will increase the energy in maintaining the typhoon evolution,then the moisture convergence in the lower layer will be enhanced.These result in a significant increase in the typhoon's intensity,moving speed and content of hydrometeors.Directly weakening or enhancing the cloud droplet condensation process(i.e.,simultaneously affects the mass mixing ratio and air temperature),will lead to the simulation results are basically the same as the CTRL test due to the adjustment of the water vapor saturation.The raindrop evaporation is the main endothermic process in the typhoon development.Weakening the impact of SVR on temperature will cause a significant increase in the simulated typhoon's intensity and content of hydrometeors.It reproduces well the rapid intensification process in the early stage,but is slightly stronger in the later stage.Note that the overall impacts of SVR are weaker than these of the SVC process.Directly weakening or enhancing the rainwater evaporation process(i.e.,simultaneously affects the mass mixing ratio and air temperature)will result in the smaller differences from the CTRL test.This is because the impacts of cloud droplet condensation and rainwater content caused by the SVR process generally offset the effects of its own latent heat change.In addition,the simulations with turning off the ice-phase melting process(NMT)and deposition/sublimation process(NISG)are less changed in the typhoon tracks.However,due to the removal of endothermic process,the vertical velocity and the typhoon intensity is significantly enhanced.As the deposition process of ice-phase particles is removed in the NISG test(i.e.,no latent heat release from the upper layer),the water vapor consumption in the high layer is then reduced,which leads to the increased cloud droplet condensation process over there as well as a final enhancement of typhoon.In the NMT test,due to the increase of the updraft,cloud water often appears at higher layers and the rainwater is significantly reduced.As the lack of melting process,too much of graupel is then occurred in the low layer.The liquid water content in the NISG test do not change much,but the process of autoconvertion from small supper-cooled droplets to ice crystals causes an increase in the ice crystal content,and the removal of snow deposition process and the weakening of snow riming process result in a distinct decrease in the snow content.These results can not only advance the people's understanding in the mechanism of cloud microphysical processes on the typhoon evolution,but also can provide ideas for improving the cloud microphysical parameterization schemes in simulating typhoons.