南海季風實驗期間加密探空對MM5模式模擬之影響

An Impact Study of Supplementary Soundings on MM5 Simulations during SCSMEX

簡芳菁(Fang-Ching Chien) ； 羅靜瑜(Jing-Yu Lo)

《大氣科學》 30卷2期 (2002/06) Pp. 117-134

摘要

本文使用國際南海季風觀測實驗計盡(SCSMEX)在1998年6月5日至6月24日期間的加密探空資料(0600UTC及1800UTC)，探討其對中尺度模式MM5在梅雨期間豪／大雨預報的影響。
研究結果發現，透過客觀分析及四維資料同化(FDDA)的方法把加密探空加入MM5模擬中，風場的預報可獲得顯著的改進，溫度、壓力、及溼度的預報也有幫助，不過僅在較低層之大氣及較長的預報時其效益才較明顯。當校驗的範圍縮小至僅包括華南及台灣地區時，加密探空資料有更明顯的效益，原來預報改進較不明顯的溫度場、海平面氣壓、相對溼度，甚至重力位高度，在模式預報36小時可以得到較正面幫助。
當我們把所有個案區分成多雨期（梅雨期間）及少雨期（梅雨結束後）進行分析時，發現加密探空資料對於模式在多雨期的預報，較少雨期的預報更能顯現其對各個氣象場預報的改善。另外，當我們僅針對初始時間為1200UTC的個案進行分析時，加密探空資料對於模式預報結果的貢獻比初始時間為0000UTC的個案之貢獻為明顯。在降水預報方面，全期的三組實驗在12~24小時降水預報以含有加密探空則表現最佳，最差的是有四維資料同化者。但是，當預報時間增長至24~36小時，四維資料同化對於模式的降水預測能力有了實質的幫助，為三者中最好的。

關鍵字

南海季風觀測實驗 ； 中尺度模式MM5 ； 四維資料同化

並列摘要

This paper presents an impact study of supplementary sounding data on MM5 simulations during the second intensive observation period (5-25 June) of South China Sea Monsoon Experiment (SCSMEX) in 1998. The data are soundings at 0600 UTC and 1800 UTC, in addition to the regular ones (0000 UTC and1200 UTC), that were carried out by about 37 rawinsonde stations over southeastern China and Taiwan. The results show that the inclusion of the extra soundings does improve the MM5 simulations, especially on the wind field. Applying the Four-Dimensional Data Assimilation (FDDA) technique further reduces the simulation errors. As for temperature, pressure, and relative humidity, the assistance only shows up at low levels and increases slightly for longer integration. When the verified region is further shrunk into smaller areas (e.g., southeastern China and Taiwan) such that most grid points over ocean are eliminated, the improvement of the model simulations as a result of the supplementary soundings increase significantly.
We also divided the verified samples into two groups: one for a time period with intensive rainfall events (5-10 June), the other with nearly no rainfall (11-25 June). It is found that the supplementary data helped the MM5 simulations more significantly for the rainy period than the droughty one. In other words, if more observations could be obtained, the model is likely being able to do a better job in simulating the rainfall events. In another analysis, we found that the extra soundings have more positive impact on the simulations that are initialized at 1200 UTC than those started at 0000 UTC.
The supplementary soundings, though mostly located in the upstream, increased the model's skill in predicting rainfall over the Taiwan area. Adding the FDDA technique in the model further contributed to increasing the model performance in rainfall predictions as integration getting longer.

並列關鍵字

South China Sea Monsoon Experiment (SCSMEX) ； MM5 ； Four-Dimensional Data Assimilation (FDDA)