利用WRF3DVAR同化GPS折射率資料探討 對於颱風預報的影響

周濤(Tao Chou)

指導教授 ： 黃清勇

國立中央大學/地球科學學院/大氣物理研究所/碩士(2006年)

摘要

本文使用WRF3DVAR，將GPS掩星資料及傳統觀測資料同化於中尺度模式之中，藉由此方法了解同化折射率對於數值模擬預報結果的影響。本文將使用CHAMP 的衛星觀測資料，選取兩個颱風個案分別為海棠（2005）以及敏督利（2004）進行模擬，將每一個颱風作數組模擬，主要分為沒有同化GPS掩星資料，以及在初始場加入GPS掩星觀測資料同化的，另外還有在初始場加入GPS掩星觀測資料同化並且在之後加入GPS掩星觀測資料做cycling來分別模擬。模擬的結果發現對於路徑的影響較小，而對於水氣方面比較有明顯的修正。而在差異增量可以瞭解折射率在水氣方面有較大的回饋，在溫度方面回饋較小。
由於CHAMP衛星的掩星觀測資料只能提供水汽跟溫度的資料，缺乏風場資料，因此由QuikSCAT衛星提供的海面風場可作為一觀測資料同化到模式中，本篇透過同化掩星資料及QuikSCAT風場資料到WRF模式中，模擬2005年的海棠颱風及2004年的敏督利颱風去探討同化掩星資料及同化QuikSCAT風場對預報的影響，發現模式同化掩星資料後，主要在水氣方面有影響，同化QuikSCAT風場可使降雨特徵更加接近觀測值。

關鍵字

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並列摘要

In this study, the Weather Research and Forecasting (WRF) Model with three-dimensional data assimilation (3DVAR) is utilized to investigate influences of GPS occultation refractivity on simulations of typhoons past Taiwan. Two recent cases were simulated, including Typhoon Mindulle in June 2004 and Typhoon Haitang in July 2005. The GPS observation data are taken from CHAMP satellites that provide several retrieved refractivity profiles in the simulated domain near the initialization time and cycling time. As compare to the impacts between the simulated results with and without GPS occultation refractivity assimilation, we choose several experiments to examine the impacts of GPS refractivity. The results of model simulated indicated the GPS data have benefit in terms of the water vapor.
Although GPS data can provide useful information on the thermodynamic variables, they lack the ability to measure wind. Wind information may play a dominant role in an assimilated vortex through geostrophic adjustment of the pressure field to the ingested wind field in low latitudes. So, we ingest observed NASA Quick Scatterometer (QuikSCAT) near-surface wind data into the model. The result displays the further improved in the accumulated rainfall.

並列關鍵字

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參考文獻

黃清勇、朱延祥，2004年：FORMOSAT-3/COSMIC科學研究簡介。『大氣科學』，32, 293-328。

Barker, D., W. Huang, Y.-R. Guo and Al. Bourgeois, 2003: A Three-Dimensional Variational (3DVAR) Data Assimilation System for Use with MM5. NCAR Technical Note (NCAR/TN-453+STR), 68 pp.

Huang, C.-Y., Y.-H. Kuo and W. Huang, 2002: Numerical simulations with MM5 3D-VAR initialization. TAO, 13, 417-448.

Huang, C.-Y., Y.-H. Kuo, and S.-H. Chen, 2005:Improvements on Typhoon Forecast with Assimilated GPS Occultation Refractivity Weather and Forecasting, 20, 6, 931–953.

Kursinki, E. R., G. A. Hajj, K. R. Hardy, L. J. Romans, and J. T. Schofield, 1995: Observing tropospheric water vapor by radio occultation using the global positioning system, Geophs. Res. Letter, 22, No. 17, 2365-2368.