藉由莫拉克颱風及西南氣流個案探討雲微物理參數化法模擬雷達回波結果之比較

Influence of microphysics schemes on radar reflectivity: Typhoon Morakot and a case during SoWMEX/TiMREX

陳怡彣(Yu-wen Chen)

指導教授 ： 隋中興

國立中央大學/地球科學學院/水文與海洋科學研究所/碩士(2011年)

摘要

本研究利用雷達觀測資料評估比較一個較具代表性的單變數滴譜分佈（single-moment DSD）總體水物雲微物理參數化法：Lin方案(Lin et al. 1983)。藉由WRF模式（the Weather Research and Forecasting Model）中使用此參數化法，針對選取的莫拉克颱風（2009年8月7日2000UTC）及西南氣流個案（2008年6月14日1700UTC）的雲雨模擬滴譜，利用雷達模擬軟體計算其雷達反射率(Z)，與對應的雷達觀測Z值比較，分析雲微物理參數化法的模擬結果。
頻率分布而言，3公里高度時，莫拉克颱風個案模式結果與七股雷達觀測的分布趨勢較相近，西南氣流個案模式雷達回波結果有60%介於20~25dBz間，SPOL雷達觀測結果60%分布在20~35dBz間；7公里高度時，莫拉克颱風個案與七股雷達觀測資料分佈一致，西南氣流的模式頻率分布則有高值高估的現象。平均雷達回波結果顯示西南氣流及莫拉克颱風個案與雷達觀測資料相比Lin方案整體皆呈現高估，而層狀區底層模式結果與觀測值相近，6公里以上隨高度增加與SPOL雷達觀測值差異愈大，有高估現象，對流區則整體呈現高估。

關鍵字

水象粒子 ； 有效雷達反射率因子 ； 雲微物理參數化法

並列摘要

In order to evaluate the influence of microphysics scheme on radar reflectivity, the single-moment microphysics scheme (Lin scheme; Lin et al., 1983) was used in the Weather Research and Forecasting (WRF) Model to provide the initial condition for QuickBeam radar simulation. Two rainfall cases were chosen in this study: Typhoon Morakot (2000UTC 7 Aug 2009) and an experiment during SoWMEX/TiMREX (1700UTC 14 Jun 2008). The simulated radar reflectivity were compared to the observed radar data (RCCG and SPOL data).
At the altitude of 3 km, the frequency distribution of simulated radar reflectivity in case of the Typhoon Morakot was similar to the observation of RCCG. In case of SoWMEX/TiMREX, 60% of radar reflectivity was distributed in 20-25 dBz, which was more concentrative than the observation of SPOL(20-35 dBz). At the altitude of 7 km, the frequency distribution of radar reflectivity in case of the Typhoon Morakot was still similar to the observation of RCCG. But the frequency distribution of large value in case of SoWMEX/TiMREX was overestimate. The results of vertical mean radar reflectivity show that the simulated radar reflectivity by Lin scheme was overestimate in both cases of the Typhoon Morakot and SoWMEX/TiMREX. In addition, the simulated radar reflectivity was similar to the observation at the bottom of stratiform region. Above the altitude of 6 km, the difference between the simulation and observation of SPOL increased with height. Besides, the results of all region of convection was overestimate.

並列關鍵字

hydrometeor ； effective radar reflectivity factor ； microphysics scheme

參考文獻

[2] Bringi, V. N.,V. Chandrasekar, J. Hubbert, E. Gorgucci, W. L. Randeu, and M. Schoenhuber, 2003: Raindrop size distribution in different climatic regime from disdrometer and dual-polarized radar analysis. J. Atmos. Sic., 60, 354-365.

[3] Brown, P. R. A. and Swann, H.A., “Evaluation of key microphysical parameters in three-dimensional cloud-model simulations using aircraft and multiparameter radar data”, Q. J. R. Meteorol. Soc., Vol.123, pp.2245-2275, October 1997.

[4] Bull.Amer. Meteor. Soc., Vol.88, pp.1723-1727, November 2007. Platt, C. M. R., “A parameterization of the visible extinction coefficient in terms of the ice/water content”, J. Atmos. Sci., Vol.54, pp.2083-2098,August 1997.

[4] Chen, J.‐P., and D. Lamb, 1994: Simulation of Cloud Microphysical and Chemical Processes Using a Multicomponent Framework. Part I: Description of the Microphysical Model. J. Atmos. Sci., 51, 2613‐2630.

[6] Ferrier, B. S., 1994: A double-moment multiple-phase four-class bulk ice scheme. Part _: Description. J. Atmos. Sci., 51, 249-280.