臺灣背風渦旋特性分析及其對空氣污染物傳輸過程影響;Characteristics of a lee-side vortex and its impact on air pollution dispersion in Taiwan

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Title:	臺灣背風渦旋特性分析及其對空氣污染物傳輸過程影響;Characteristics of a lee-side vortex and its impact on air pollution dispersion in Taiwan
Authors:	周彥誠;Chou, Yen-Cheng
Contributors:	大氣科學學系
Keywords:	背風渦旋;細懸浮微粒;空氣污染物傳輸;Lee-side vortex;PM2.5;air pollution dispersion
Date:	2021-08-12
Issue Date:	2021-12-07 11:07:38 (UTC+8)
Publisher:	國立中央大學
Abstract:	臺灣在秋冬季節容易受大陸冷高壓出海影響，導致綜觀風場以偏東風為主，此時位於背風側之臺灣海峽常見背風渦旋生成。此渦旋環流結構與海陸風交互作用直接影響污染物傳輸擴散過程，並常造成嚴重高污染事件。為瞭解背風渦旋環流結構特性及其對臺灣空氣污染物傳輸之影響，本研究使用氣象局、環保署地面測站、局屬自動測站、剖風儀及光達觀測資料，針對2018年12月19日發生之高污染事件日進行分析。結果發現位於背風側之中部地區除了受海陸風局部環流影響之外，上午亦有南風分量出現，顯示背風渦旋對地面風場結構的改變。此外，因背風渦旋受到環境風場、臺灣複雜地形地貌影響，加上缺乏海上觀測資料導致其模擬不確定性相當高，本研究另外使用21組氣象系集成員(WRF-LETKF)進行背風渦旋特性分析。氣象模式結果，底層200-m內靠近陸地之渦旋南風結構易受海風影響而不明顯，這與觀測風場隨時間由南風逐漸轉為西風(海風)結果不謀而合。400-m高度處受地表熱、動力影響較小，渦旋環流結構較近地表清晰。進一步分析渦旋垂直剖面，顯示渦旋厚度約800-m，且隨高度增加逐漸向西傾斜。分析CMAQ空氣品質模式模擬結果，在17至18日白天，處在東北風背風尾流區之南部地區容易累積污染物，直到18日白天邊界層發展增強垂直混合作用，將近地表污染物帶往高空，爾後夜間背風渦旋環流建立，其南風把污染物往北吹輸送至桃園地區，再受到向岸風影響使污染物難已擴散，最終導致19日的高污染事件。 ;During autumn and winter season, with the eastward movement of the Asia continental anticyclone, the synoptic wind in Taiwan changes into easterly direction. The western Taiwan due to situated in lee-side of the mountain, exhibits the stagnant wind conditions. Sometimes the leeside vortex can form when the airflow bypasses the mountain of Taiwan, which in turn influence the transport of air pollutants and cause subsequent high PM2.5 event. In order to understand the structural characteristics of the leeside vortex and its influence on the transport of air pollutants, we using the observation data from Central Weather Bureau (CWB), air quality monitoring station of Environmental Protection Administration (EPA), the wind profiler and the lidar in Taiwan to analyze the day of the high pollution event that occurred on December 19, 2018. It was found that the central area on the leeside was not only affected by the local circulation (ex. the land sea breeze), but also existed the southerly wind in the morning, indicating that the leeside vortex could change the structure of the ground wind field. In addition, because the generation of the leeward vortex is affected by the wind field and Taiwan′s complex topography, coupled with the lack of marine observation data, the simulation uncertainty of the leeward vortex is quite high, this study also uses 21 ensemble members (WRF-LETKF) to analyze the characteristics of the leeside vortex. From the simulation results, it is found that the vortex southerly wind structure close to the land within 200 meters of the bottom layer is easily affected by the sea breeze. The result coincides with the observation that the wind field has gradually changed from southerly to westerly (sea breeze) over time. The vortex circulation structure is clear at the height of 400 meters than on the ground due to the reducing thermal heating effect. Further analysis of the cross section of the vortex shows that the thickness of the vortex is about 800 meters and gradually tilt to the west as the height increases. CMAQ simulation results show that the southern area is easy to accumulate air pollutants under northeast wind weather condition. Until the development of the boundary layer enhances the vertical mixing effect, bringing near-surface pollutants to the upper air in the morning. Then the southerly wind blows the air pollutants north to the Taoyuan area.
Appears in Collections:	[大氣物理研究所 ] 博碩士論文

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