The impact of TRMM data on mesoscale numerical simulation of Supertyphoon Paka

Abstract

This paper assesses the impact of TRMM Microwave Imager (TMI) derived surface rainfall data on the numerical simulation of Supertyphoon Paka (1997). A series of mesoscale numerical simulations of Supertyphoon Paka is performed during its mature stage by using the Pennsylvania State University-National Center for Atmospheric Research (Penn State-NCAR) Mesoscale Model (MM5). The model initial and boundary conditions were derived from Goddard Earth Observing System (GEOS) global analyses with and without assimilation of the TMI surface rainfall data. Simulation results clearly demonstrate that the GEOS analysis with TMI rainfall data leads to an improved simulation of Supertyphoon Paka in terms of its intensity and kinematical and precipitation structures, because rainfall assimilation modifies the environment of the storm such that the initial conditions are more favorable for development of the storm. Since a bogus vortex is often necessary for initialization of typhoon (hurricane) simulations, additional numerical experiments are also performed by introducing mesoscale bogus vortices into GEOS analysis at the initial time using a four-dimensional variational technique. Simulation results indicate that a well-designed bogus vortex can play a dominant role in the improvements of forecasts of typhoon intensity and track. However, incorporation of the TMI data with a bogus vortex is still beneficial because it improves the simulation of the asymmetric storm structure.