The simulations reproduced well the most important features of the mesoscale dynamic and thermodynamic and cloud-rain physical structures during its landfall. It shows that cyclonic inflow circulation on lower levels and outflow on higher levels near the typhoon center and strong upward motion formed by low level convergence existed at the eye-wall and subsidence in the eye. The horizontal wind field was distributed asymmetrically near the typhoon center, stronger at the northeast quadrant, which was associated with the typhoon northwestward moving after landfall at Fujian province. The diagnostic analyses with common synoptic scale sounding data show the typhoon center was "warm", but the model simulations with higher space resolution show that the mid-tropospheric region of eye-wall, where existed strong upward motion and more cloud- and rain-water, was warmer than the eye. The cloud and rain band was spirally distributed around typhoon center, and consisted of meso-beta-scale rain cores. During the period of typhoon HERB staying near and passing over Taiwan, the low level cloud was developed in the eye so that made the previous clear typhoon eye on the satellite pictures becoming fuzzy.
During the period of typhoon passing over Taiwan, the amount of rainfall on Taiwan was affected obviously by the Taiwan Central Mountains, which made the cyclonic airflow converge and lift over the mountain and hence enhance rainfall on Taiwan Island more than six times.
The case simulation shows the non-hydrostatic mesoscale model MM5 is quite helpful not only for studying the mesoscale dynamic and thermodynamic processes and cloud-rain physical structures associated with typhoon, but also providing valuable information for determine the location of eye and hence forecasting the landfall of typhoon, especially on the case when the typhoon eye is not clear shown on satellite cloud pictures.
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