Influence of moist processes on track and intensity forecast of cyclones over the north Indian Ocean

Abstract

In this study, we address the problem of incorporating moist processes (parameterizing the subgrid scale and resolving the grid scale) at resolutions of 10 km and 3.3 km (triple nested) in predicting the track and intensity of tropical cyclones over the north Indian Ocean. First, the sensitivity of three convective parameterization (CP) schemes on the cyclone track and intensity are evaluated. Kain-Fritsch (KF) shows a realistic simulation of track and intensity and therefore is considered for all the experiments at 10 km with four bulk microphysical (MP) schemes (hybrid experiments). At 3.3 km resolution the simulation is carried out resolving the grid-scale convection explicitly with the four MP schemes. Hybrid moist convection treatment at 10 km is found to produce a better simulation as compared to only explicit MP experiment at 3.3 km. The main reason is found to be heating within the inner core of the cyclone which is influenced dominantly by production of graupel hydrometeors in the inner core region. The latent heat released in the formation of graupel mixing ratio is responsible for net middle level heating rate in the cyclone core. Higher net heating in the middle level enhances the divergence in the upper level and convergence in the lower level which in turn helps in the intensification of the system. The role of graupel is further established by deactivating its production, where the model cannot simulate the midlevel heating and intensification of the system.