Analysis Of Structure And Intensity Change For Landfalling Typhoon Meranti (2010)

Using mesoscale numerical model WRF and three-dimensional variational assimilation system3DVAR, we analyze the characteristics of the structure and intensity change for Typhoon Meranti (2010), and investigate the influence of topography on landfalling typhoon through a series of sensitivity experiments. The angular momentum equation, equivalent potential temperature equation, potential vorticity equation are employed to study the interaction between different scales of airflow and Typhoon Meranti.Results show that the structure and intensity asymmetry of Meranti, the offshore intense precipitation and re-strengthen rain after it went into Zhejiang, are caused by the interaction among environmental wind horizontal shear, the subtropical high and typhoon vortex. In the sensitivity experiments, the radial and vertical velocity on the left side of typhoon moving direction is larger than right side. While the left side has strong asymmetric upward eddy with cyclonic circulation, the other side shows strong asymmetric vortices of downward motion. This asymmetric circulations are the reasons of the structure asymmetry along typhoon moving direction. They are due to the horizontal wind shear on the left side which is conducive to the formation and development of cyclonic vortex, and the sinking anti-cyclonic airflow of the subtropical high on the right side. In addition, the asymmetric eddy in CTRL (Control) and FLAT (Land surface) experiments show obvious characteristics of the gravity waves on the left side. especially in CTRL. Because the left sides prone to be convective instability and would trigger gravity during the landfall. The convection gravity wave troughs and ridges dominate the asymmetric eddy.