| Summary: | 碩士 === 國立中央大學 === 大氣物理研究所 === 98 === This study uses Weather Research and Forecasting Model (WRF) version 3.1 to simulate Typhoon Sinlaku (2008). The first part of this study is to examine how Tropical Cyclone (TC) bogus scheme modifies the vortex intensity of the first guess field, and try to understand the impact on simulation for different vmax_ratio values used in the TC bogus scheme. The results show that application of the TC bogus scheme can improve the vortex structure and intensity in the first guess field, and can also improve the simulated intensity, but lead to rapid movement and westward deviation in track. It was also found that the track and intensity of the typhoon is somewhat sensitive to different model domains.
The second part applies the potential vorticity (PV) inversion and quasi-balanced ω equation to analyze the simulated typhoon for understanding of the structure of the vortex core. The results show that most characteristics of typhoon structures can be successfully inverted, but exhibiting larger differences at high-level outflow and low-level inflow with the boundary layer. Differences may result at high-level from the assumption of inversion system and at low-level due to the friction. Transferring the data from the model height to the pseudo-height may also introduce inversion errors, especially, for the intense typhoon with a central sea-level pressure as low as 930 mb.
Using quasi-balanced ω equation to calculate the vertical motion induced by the balanced flow, we find that the ω equation tends to underestimate the magnitude of the vertical motion, but the convergence and divergence associated with the lower-level inflow and upper-level outflow can be reasonably derived. Contributions to the vertical motion in the ω equation indicate that latent heating dominates the updraft in the eyewall and the downdraft in the eye. The vertical motion can reach to 10 km, as induced by the friction in the low-level inflow like Ekman pumping. Dry dynamic process is in response to the interaction between the typhoon vortex and the vertical shear of horizontal wind, and may be attributed to the formation of the asymmetric typhoon vortex.
Results from piecewise PV inversion in dry dynamic process indicate that the PV pieces above and below 10 km height both can induce perturbation pressure down to the lower boundary, and produce a deep clockwise vertical circulation. Pieced latent heating at upper and lower levels produces the dominant vertical motion at upper and lower levels, respectively.
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