| Summary: | 碩士 === 國立中央大學 === 大氣科學學系 === 107 === Global model FV3GFS, which has been chosen as the Next Generation Global Prediction System, provides a “grid stretching” technique which could not only increase resolution in the specific area but also keep its computational efficiency at the same time. In this study, we ap-plied this technique to simulate typhoon Maria (2018) with 7 km resolution. The results revealed that FV3GFS had capability of better typhoon track forecast. Compared to other agencies, translation speed and typhoon track deflection could be captured by the model well.
Based on the previous results, we took advantages of FV3GFS to investigate the dynam-ical processes between Taiwan terrain and typhoon Maria. After removing terrain in Taiwan, we found that the northern deflection and the change of wind speed vanished. The results suggested that the terrain might lead to change in the path of typhoon and increase in wind speed around the radius of maximum wind (RMW).
In this study, momentum and angular momentum (AM) tendency budget was preformed to verify the wind speed change, and we found that the strong inflow occurred below the planetary boundary layer, which transported the larger AM into the center and then enhanced the tangen-tial wind near eyewall. Meanwhile, outer part of the typhoon produced negative radial eddy advection, which slowed down the wind speed. Furthermore, vorticity tendency budget was performed to verify the track deflection. During the northern deflection of the typhoon track, we found that the northern deflection of the typhoon track was mainly caused by the horizontal ad-vection, and the sum of other terms decelerated the translation speed of the typhoon. Through these serial analyses, it turned out that the northern deflection of the typhoon track was primarily caused by terrain blocking, which produced a split flow to change the steering flow when ty-phoon was passing through the northwest of Taiwan ocean. The intensification near the eyewall was resulted from the larger AM advection, which was also caused by the split flow from outer part of the typhoon.
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