A NUMERICAL STUDY ON SUSTAINING OF LANDFALLING TYPHOON MATSA

Numerical simulation has been carried out to investigate the evolution characteristics of typhoon Matsa of 2005 after its landfalling by using the new generation of meso-scale weather research and forecasting (WRF) model. Meanwhile, a preliminary study has been also made on the mechanism of the sustaining of Matsa's intensity in parallel with diagnostic analyses of eddy kinetic energy (EKE) budget. The results show that the sustaining of typhoon Matsa after landfalling is closely associated with the following factors: (1) Existence of two moisture channels，through which warm and moist air was continuously transported to typhoon Matsa with the maximum water vapor flux being about 20×104 g/(s·hPa·cm). (2) Enhanced divergent wind fields in the upper troposphere, whose “pumping" played an important role in the sustaining of the circulation and intensity of Matsa.(3) Sustained vigorous ascending motion, which transported the warm and moist air in the lower troposphere upwards to release latent heat and thus to provide kinetic energy for Matsa's sustaining. (4) Active meso-scale cyclonic vortices embedded in the spiral cloud bands of Matsa, which induced some strong meso-scale ascending motion and low level cyclonic convergence, playing a role of positive feedback to the sustaining of Matsa's intensity. (5) Gaining EKE from the environmental flow fields in the middle and upper troposphere. Diagnostic analyses on the EKE budget indicate that the EKE in lower levels was dissipated by the frictional effect of terrain and horizontal advection, enhanced by the divergence of the vertical flux of EKE. After Matsa’s landfall, the generation term of EKE was positive at almost all levels with the maximum at about 200 hPa, and provided a lot of EKE for Matsa's sustaining. The conversion between mean kinetic energy and EKE was a quantity of lower order in the EKE budget. Furthermore, the frictional dissipation of EKE gradually decreased with time while Matsa increasingly gained EKE from the environmental flow fields in the middle and upper troposphere, and the increased EKE propagated gradually downwards to the middle and lower layers.