利用MM5 4DVAR模式探討同化虛擬渦旋和掩星折射率資料對於珊珊颱風（2006）數值模擬之影響

The Impact of Assimilation with a Bogus Vortex and Radio Occultation Refractivity Data on Simulation of Typhoon Shanshan (2006) Using MM5 4DVAR

黃清勇(Ching-Yuang Huang) ； 吳俊澤(Chun-Tze Wu)

《大氣科學》 40卷2期 (2012/06) Pp. 153-170

摘要

本研究利用MM5 4DVAR模式，探討渦旋的虛擬資料同化（Bogus Data Assimilation, BDA）和GPS掩星觀測資料同化對於初始分析場的改進及颱風預報的影響，模擬個案為珊珊颱風（2006）。本文的BDA包括氣旋的海平面氣壓及三維平衡風場與近地面徑向入流，可以有效地強化模式初始颱風，更能幫助維持颱風垂直結構，模擬結果顯示對颱風預報有明顯的改善。個案實驗結果顯示，加入GPS掩星折射率資料可以修正模式初始場，只是調整的輻度遠不及虛擬渦旋同化大。個案模擬結果亦顯示，虛擬渦旋同化主導颱風的路徑及強度預報，遠較無同化時要好很多，而僅同化GPS掩星折射率在路徑預報亦有一些的影響。同時同化虛擬渦旋及折射率，則較單純BDA在路徑預報上可進一步改善，同時亦改善台灣地區的劇烈降雨預報。

關鍵字

四維變分 ； 虛擬資料同化 ； GPS掩星折射率

並列摘要

This study employs the MM5 4DVAR to investigate influences of assimilation with GPS radio occultation (RO) data and a bogus vortex on initial analysis and prediction of Typhoon Shanshan (2006). In this study, the bogus data assimilation (BDA) includes sea-level pressure, 3-D wind, and surface balanced gradient wind and radial inflow component of a symmetric cyclone. The BDA appears helpful to intensify the initial typhoon and maintain its vertical structure.Results of the experiments show that assimilation with GPS refractivity data improves the initial field in the vicinity of the RO surroundings but with smaller magnitudes as compared to those from the BDA which significantly improves the weak initial typhoon vortex from the control experiment without BDA. Assimilation with GPS refractivity data only has some minor impacts on the track and intensity prediction. However, the combined assimilation with both GPS refractivity data and a bogus vortex further improves the track from BDA only. This in turns improves the skill scores on prediction of severe rainfall over Taiwan.

並列關鍵字

4DVAR ； Bogus Data Assimilation (BDA) ； GPS RO Refractivity