| Summary: | 碩士 === 國立中央大學 === 大氣物理研究所 === 99 === Typhoon Morakot struck Taiwan on 7 Aug 2009. Although the center made landfall in Hualien county along the central east coast of Taiwan and passed over the central northern part of the island, it was southern Taiwan that received the storm where locally as much as 3000mm of rain were reported resulting in the worst flooding there in 50 years.
The Weather Research and Forecasting model (WRF) is used to conduct a 72 hours model integration for high resolution simulation of this high-impact weather event. The horizontal grid resolution of nested domains is 18, 6 and 2 km. The result indicated that the model is able to capture the observed surface rainfall both the total amount and the location. The simulate typhoon intensity was close to the observation between 24 - 72 hours. Three sensitivity experiments were designed for Taiwan terrain height, southwest water vapor transmission and model grid resolution. The results were shown that the 72 hours maximum accumulated rainfall of simulation decreased to 50% and 80% as terrain height was reduced to 50% and 1%. The average vertical velocity on southwest region of Taiwan indicated that the vertical velocity of CTRL is 5 times the magnitude of ter01 in the low level. It confirmed that terrain height is an important factor for rainfall distribution and dynamic process. As relative humidity of southwest flow was reduced 50%, the rainfall intensity was decreased and the 72 hours maximum accumulated rainfall was declined about 20%. It demonstrated that the water vapor transmission from southwest flow is also an important factor of heavy rainfall causing from Typhoon Morakot. When model grid resolution was reduced to 1/2 and 1/4 times from CTRL, the coarse-resolution simulations was difficult to resolve small-scale convection and precipitation. On the other hand, the simulation of coarse-resolution has weak vertical motion caused by terrain-resolution and led the 72 hours accumulated rainfall of simulation was less than CTRL.
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