Numerous studies have shown that the structure and intensity of tropical cyclones have been restricted by themselves,as well as the interaction between the airflow and boundary layer,the thermal variations of the sea,and so on.With the numerical model widely used in the weather forecast,there has been increasingly great attention paid to the parameterization scheme of the atmospheric model.Numerous findings have shown that the various physical parameterization processes have obvious effects on simulating tropical cyclones.The impacts of the cloud-radiative forcing(CRF) on tropical cyclones is a complicated process,depending on the cloud microphysics parameterization model.Different aerosol distributions hold different CRF.Some studies have shown that solar radiation affects the structure and tracks of tropical cyclones,in which case the CRF will remain a key overhang.Therefore,this work carries out the study of the sensitivity of cloud radiation on the effects of tropical cyclones,and discusses the possible influences of cloud radiation on the development and structure of typhoons.
In order to highlight the influences of CRF on TC,as well as to avoid the disturbance of uncertainty random circumstance factors such as underlying surface and the interaction between TC and environment,two sets of sensitivity simulations were conducted using the high-resolution Weather Research and Forecasting(WRF) model(WRF-ARW)(version 3.3.1).The simulations were solved using bidirectional double nesting,in which every domain had a 241×241 grid point,the horizontal resolution ratio was 9 km and 3 km,and the vertical direction was divided into 28 layers.The cloud microphysical scheme adopted WSM6.The initial conditions originate from an ideal cyclonic vortex which was symmetric.The initial wind speed was 8 ms^-1,and the maximum wind radius was 125 km.The tangential wind speed of the initial vortex decreased with height.For the sake of simplicity,this paper uses the f plane.The latitude of the center was 15°N.The underlying surface was a uniform ocean,the sea surface temperature was set to 29℃,and the influence of large-scale atmosphere was neglected.According to the setting wind field,the quality field and thermodynamics field elements were obtained by solving the nonlinear equilibrium equation.The cloud-radiative forcing(CRF) in the WRF was controlled by the namelist parameter “iCloud”.When iCloud=1,the CRF effect was considered in the simulation.Conversely,when iCloud=0,the CRF effects were excluded.Through the comparison of the above two simulations,we can obtain the influence of the CRF effect on the development of TC.
The results show that,mainly by changing the tropical cyclone radiation distribution,the CRF had an effect on the convective activity,as well as the tropical cyclone structure and size.In the development process,the strong cooling along the anvil top and weak warming in the cloudy regions under the forcing of cloud and radiation could reduce the static stability at the middle-upper levels,while the change of the middle-lower levels was relatively less significant.The convective activity of the tropical cyclone was enhanced by the CRF.The tropical cyclone developed faster and had a larger size in the case with the CRF than without it.In view of the considerable impacts of the CRF on the size and strength of tropical cyclone,it is necessary to pay more attention to the CRF in the numerical prediction of tropical cyclones.