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.

鄭芳怡、楊舒芝、王聖翔等人，2019：107 空污防制科技研合作計畫期末成果報告(審查版)。利用資料同化方法改善大氣邊界層內水平傳輸與垂直擴散過程並評估其對空品模式模擬之影響 (第三年)
Appel, K. W., Napelenok, S., Hogrefe, C., Pouliot, G., Foley, K. M., Roselle, S. J., ... & Mathur, R., 2016, December: Overview and evaluation of the Community Multiscale Air Quality (CMAQ) modeling system version 5.2. In International Technical Meeting on Air Pollution Modelling and its Application (pp. 69-73). Springer, Cham.
Burr, M. J. and Y. Zhang, 2011: Source apportionment of fine particulate matter over the Eastern U.S. Part I: source sensitivity simulations using CMAQ with the Brute Force method. Atmospheric Research, 2(3), 300‐317.
Byun, D., & Schere, K. L. (2006). Review of the governing equations, computational algorithms, and other components of the Models-3 Community Multiscale Air Quality (CMAQ) modeling system. Appl. Mech. Rev. 59, 51-77.
Campbell, J. R., Hlavka, D. L., Welton, E. J., Flynn, C. J., Turner, D. D., Spinhirne, J. D., ... & Hwang, I. H. (2002). Full-time, eye-safe cloud and aerosol lidar observation at atmospheric radiation measurement program sites: Instruments and data processing. Journal of Atmospheric and Oceanic Technology, 19(4), 431-442.
Chien, F. C., & Kuo, Y. H., 2006: Topographic effects on a wintertime cold front in Taiwan. Monthly weather review, 134(11), 3297-3316.
Ek, M. B., Mitchell, K. E., Lin, Y., Rogers, E., Grunmann, P., Koren, V., ... & Tarpley, J. D., 2003: Implementation of Noah land surface model advances in the National Centers for Environmental Prediction operational mesoscale Eta model. Journal of Geophysical Research: Atmospheres, 108(D22).
Fang, G.-C. and S.-C. Chang, 2010: Atmospheric particulate (PM10 and PM2.5) mass concentration and seasonal variation study in the Taiwan area during 2000-2008. Atmospheric Research, 98(2), 368-377.
Flynna, C. J., Mendozaa, A., Zhengb, Y., & Mathurb, S. (2007). Novel polarization-sensitive micropulse lidar measurement technique. Optics express, 15(6), 2785-2790.
Hong, J.-S., 2001: Numerical simulation of leeside vortex: Case study.
Hong, S.-Y., Y. Noh & J. Dudhia, 2006: A new vertical diffusion package with an explicit treatment of entrainment processes. Monthly weather review, 134(9), 2318-2341.
Hsu, C. H., & Cheng, F. Y., 2016: Classification of weather patterns to study the influence of meteorological characteristics on PM2.5 concentrations in Yunlin County, Taiwan. Atmospheric Environment, 144, 397-408.
──, & ──, 2019: Synoptic weather patterns and associated air pollution in Taiwan. Aerosol and Air Quality Research, 19(5), 1139-1151.
Jiménez, P. A., Dudhia, J., González-Rouco, J. F., Navarro, J., Montávez, J. P., & García-Bustamante, E., 2012: A revised scheme for the WRF surface layer formulation. Monthly Weather Review, 140(3), 898-918.
Kain, J. S., 2004: The Kain–Fritsch convective parameterization: an update. Journal of Applied Meteorology, 43(1), 170-181.
Krewski, D., et al., 2009: Extended follow-up and spatial analysis of the American Cancer Society study linking particulate air pollution and mortality,140, 5-114. Boston, MA: Health Effects Institute.
Kuo, P. H., Tsuang, B. J., Chen, C. J., Hu, S. W., Chiang, C. J., Tsai, J. L., ... & Ku, K. C., 2014: Risk assessment of mortality for all-cause, ischemic heart disease, cardiopulmonary disease, and lung cancer due to the operation of the world's largest coal-fired power plant. Atmospheric Environment, 96, 117-124.
Lai, H.-C., Lin, M.-C., 2020: Characteristics of the upstream flow patterns during PM2.5 pollution events over a complex island topography. Atmospheric Environment, 117418.
Li, J., & Chen, Y. L., 1998: Barrier jets during TAMEX. Monthly weather review, 126(4), 959-971.
Lin, P. L., Chen, Y. L., Chen, C. S., Liu, C. L., & Chen, C. Y., 2011: Numerical experiments investigating the orographic effects on a heavy rainfall event over the northwestern coast of Taiwan during TAMEX IOP 13. Meteorology and Atmospheric Physics, 114(1-2), 35.
Loomis, D., Grosse, Y., Lauby-Secretan, B., El Ghissassi, F., Bouvard, V., Benbrahim-Tallaa, L., ... & Straif, K., 2013: The carcinogenicity of outdoor air pollution. Lancet Oncology, 14(13), 1262.
Monin, A. S., & Obukhov, A. M., 1954: Basic laws of turbulent mixing in the surface layer of the atmosphere. Contrib. Geophys. Inst. Acad. Sci. USSR, 151(163), e187.
Pueschel, R. F., Valin, C. V., Castillo, R. C., Kadlecek, J. A., Ganor, E., 1986: Aerosols in polluted versus nonpolluted air masses: Long-range transport and effects on clouds. Journal of Climate and Applied Meteorology, 25(12), 1908-1917.
Raaschou-Nielsen, O., Andersen, Z. J., Beelen, R., Samoli, E., Stafoggia, M., Weinmayr, G., ... & Hoek, G., 2013: Air pollution and lung cancer incidence in 17 European cohorts: prospective analyses from the European Study of Cohorts for Air Pollution Effects (ESCAPE). The lancet oncology, 14(9), 813-822.
Skamarock, W. C., J. Klemp, J. Dudhia, D. O. Gill, D. Barker, W. Wang, J. G. Powers, 2008: A Description of the Advanced Research WRF Version 3. 3-27pp.
Smolarkiewicz, P. K., & Rotunno, R, 1989: Low Froude number flow past three-dimensional obstacles. Part I: Baroclinically generated lee vortices. Journal of Atmospheric Sciences, 46(8), 1154-1164.
Spinhirne, J. D., 1993: Micro pulse lidar. IEEE transactions on geoscience and remote sensing, 31(1), 48-55.
Sun, W. Y., & Chern, J. D., 1993: Diurnal variation of lee vortices in Taiwan and the surrounding area. Journal of Atmospheric Sciences, 50(20), 3404-3430.
──, & ──, 1994: Numerical experiments of vortices in the wakes of large idealized mountains. Journal of Atmospheric Sciences, 51(2), 191-209.
Tsimpidi, A. P., M. Trail, Y. Hu, A. Nenes, A. G. Russell., 2012 : Modeling an air pollution episode in northwestern United States: Identifying the effect of nitrogen oxide and volatile organic compound emission changes on air pollutants35 formation using direct sensitivity analysis. Journal of the Air & Waste Management Association, 62(10), 1150-1165.
Turner, M. C., Krewski, D., Pope III, C. A., Chen, Y., Gapstur, S. M., & Thun, M. J., 2011: Long-term ambient fine particulate matter air pollution and lung cancer in a large cohort of never-smokers. American journal of respiratory and critical care medicine, 184(12), 1374-1381.
Wang, S. H., Lin, N. H., Chou, M. D., Tsay, S. C., Welton, E. J., Hsu, N. C., ... & Holben, B. N. ,2010: Profiling transboundary aerosols over Taiwan and assessing their radiative effects. Journal of Geophysical Research: Atmospheres, 115(D7).
Wang, Y.C., Wang, S.H., Lewis, J.R., Chang, S.C., Griffith, S.M., 2021: Determining Planetary Boundary Layer Height by Micro-pulse Lidar with Validation by UAV Measurements. Aerosol Air Qual. Res. https://doi.org/10.4209/aaqr.200336
Welton, E. J., & Campbell, J. R., 2002: Micropulse lidar signals: Uncertainty analysis. Journal of Atmospheric and Oceanic Technology, 19(12), 2089-2094.
Yang, Y., & Chen, Y. L., 2003: Circulations and rainfall on the lee side of the island of Hawaii during HaRP. Monthly weather review, 131(10), 2525-2542.
Yang, Y., Chen, Y. L., & Fujioka, F. M., 2008: Effects of trade-wind strength and direction on the leeside circulations and rainfall of the island of Hawaii. Monthly Weather Review, 136(12), 4799-4818.
Yeh, H. C., & Chen, Y. L., 2003: Numerical simulations of the barrier jet over northwestern Taiwan during the mei-yu season. Monthly weather review, 131(7), 1396-1407.