探討CALMET模式與變分分析方法對台灣地區風場 與逆軌跡模擬之差異性

Abstract

本研究利用變分分析方法與CALMET模式探討台灣地區風場模擬之相關性及差異性，並與環保署以及中央氣象局測站之風場實測值比較，最後利用逆軌跡推估雲嘉南地區臭氧污染之來源。在水平風場模擬部份，變分分析方法較能反映風場在近地面層受到地形效應之影響以及污染事件日之盛行風向；其模擬之結果也比較接近實際測站的觀測值。在垂直風場模擬部份，變分分析的結果顯示造成朴子與嘉義兩測站發生臭氧超標事件的原因是受到風場的匯聚以及山前的回流將高空中的汙染物又帶回至地面。在靠近山區的部份，CALMET模式的風場模擬，無法顯現出受地形影響產生之變化。最後針對雲嘉南地區進行逆軌跡之模擬，發現變分分析模擬之逆軌跡線對於台灣地形效應及海陸風影響之機制表現較明顯，其結果顯示逆軌跡線大都通過雲林麥寮與彰濱工業區外海。

In this study, variational analysis and CALMET model are applied to simulate the wind field in Taiwan and estimate the ozone pollution sources for the Yunlin-Chiayi-Tainan (Y-C-T) area through the back trajectory, and then the relation and difference of the results, which are compared with the data collected by EPA and CWB stations, are discussed. In the horizontal wind field simulation case, the results show that variational analysis responds better to the wind field affected by terrain effects near the surface layer, and prevailing wind direction of the ozone pollution episodes; the results of variational analysis are similar to the observations of EPA and CWB stations. In the vertical wind field simulation case, variational analysis shows that the downward flow form the higher altitude would bring the pollutant back to the ground and cause the ozone pollution at Puzi and Chiayi station; however, the vertical wind simulation of CALMET model can not reflect the terrain effects near the mountain. Within the Y-C-T area, the terrain effect and sea-land breeze have significant influence on the back trajectory through the variational analysis - most of the back trajectory lines pass through the Mailiao industrial estate and Changhua coastal industrial estate.