Barotropic Processes And Radiative Processes Of Cloud Hydrometeors Associated With The Development Of Mei-yu Precipitation System

Barotropic processes associated with the development of precipitation systems and their responses to cloud radiative processes are investigated through the analysis of two-dimensional sensitivity cloud-resolving model simulations of Mei-yu torrential rainfall events over eastern China in mid-June 2011. During the model integration period, there were three major heavy rainfall events, respectively, in 9-12,13-16 and 16-20 June.The analysis shows that the perturbation kinetic energy is converted to the mean kinetic energy in the first period, and the mean kinetic energy is converted to the perturbation kinetic energy in the third period, indicating that the precipitation system becomes unstable in the third period. The further examination of barotropic conversion reveals that the barotropic stability of precipitation system is determined by the vertical flux of zonal momentum. As the upward flux of zonal momentum in the first period is changed to the downward flux in the third period, the precipitation system becomes dynamically unstable. Although the vertical wind shear is a necessary condition for barotropic conversion, it cannot control the vertical flux of zonal momentum and thus the barotropic conversion. The tendency equation of vertical flux of zonal momentum is derived from the momentum equations, the analysis shows that zonal flux of cloud hydrometeor and heat is responsible for the variation of vertical flux of zonal momentum.The radiative effects of five cloud hydrometeors on the precipitation system are different in the three periods. The change in the rain rate caused by the exclusion of radiative effects is associated with the change in net condensation while hydrometeor loss/gain barely changes. The radiative processes affect the barotropic stability of the precipitation system directly through the vertical flux of zonal momentum. The barotripic stability of Mei-yu precipitation is insensitive to radiative effects of hydrometeors in the first period. The exclusion of radiative effects of water clouds enhances the barotropic instability of the precipitation system in the second and third periods. The removal of radiative effects of cloud ice and snow can enhance the barotropic stability in the second period and increase the barotropic instability in the third periods. In three periods, the elimination of radiative effects of graupel leads to the stable precipitation system.