台灣北部地區混合層高度的觀測與模擬

Simulation and Observation of Mixing Height over Northern Taiwan

彭啟明(Chi-Ming Peng) ； 林松錦(Song-Chin Lin)

《大氣科學》 23卷3-4期 (1995/12) Pp. 311-336

摘要

混合層高度為估計空氣污染潛勢和擴散濃度的重要參數，配合探空、聲波雷達及RASS的觀測，本文利用Holzworth法及一大氣邊界層模式來計算混合層高度，透過模式模擬來探討影響混合層高度的氣象因子，並藉此經由統計回歸的方式來修正聲波雷達低估混合層高度的現象。分析結果顯示，Holzworth法的準確性並不如預期的好，這可能是台灣為海島型氣候，地形複雜，局部天氣系統相互影響，使得邊界層內發展的變化因素較多，而Holzworth法無法掌握這種變化。模式計算結果與探空曲線估計經比較發現頗為接近。由模式敏感度測試中，找出了影響混合層高度的氣象因子包括地面風速、混合層頂以上的溫度遞減率、地面溫度的變化、太陽仰角、地表粗糙程度、雲量及逸入區的作用等。混合層高度由聲波雷達的觀測發現，白天時在鄰近時間的變動情形很大，對混合層高度的觀測有低估的現象，在夜間大氣較為穩定時，聲波雷達則可較準確的測出地面逆溫層的高度。而與RASS的觀測資料比較，在逆溫層較低且很明顯時，聲波雷達觀測及模式計算與利用RASS的垂直溫度剖面所估計的混合層高度相當接近，而在大氣為中性時則有較大的出入。

關鍵字

混合層高度

並列摘要

Mixing height is an important parameter in the study of air pollution diffusion. In this study, Hoizworth method and an atmospheric boundary layer model were utilized to estimate mixing heights over the Northern Taiwan area. Computed mixing heights were verified by rawinsound and RASS observations and compared with Sodar measurements. Meteorological factors that account for the development of mixed layer were also studied by model simulation and a regression formula was determined to correct the underestimation of mixing heights measured by Sodar.Results show that mixing heights estimated by the Holzworth method are not as accurate as would be expected. However, model computations are rather comparable with rawinsound observations. Sensitivity test of model simulation found that the development of mixed layer is influenced by surface wind speed, temperature lapse rate above mixed layer, surface heating rate, solar elevation angle, surface roughness, cloud cover and entrainment at the top of mixed layer. In the daytime, due to strong thermal effect, mixing heights measured by Sodar are underestimated and have large temporal variations. In the nighttime when the boundary layer is stable, Sodar captures the height of inversion layer pretty well. Comparison with RASS temperature soundings also points out the same indications.

並列關鍵字

Mixing height