https://scholars.lib.ntu.edu.tw/handle/123456789/76224
標題: | 混合層高度診斷方法之研究 The diagnostic method of the mixing layer height |
作者: | 陳世芳 Chen, Shih-Fang |
關鍵字: | 乾絕熱遞減方法;海水表面溫度圖;混合層;光化學軌跡模式;Mixing layer;TPAQM;The adiabatic lapse rate meth | 公開日期: | 2004 | 摘要: | 大氣的狀態對於空氣污染物質有著相當重要的影響。因此當空氣污染物質被排放後,其是否對環境產生重大的空氣污染事件,多半取決於大氣的擴散以及傳輸能力。其中混合層的發展更是常常扮演著關鍵性的角色。所謂“混合層”(mixing layer)在氣象學上係指近地面1000m附近,氣流受地表擾動及熱對流效應影響,具有充份的上下混合效應之一大氣邊界層。造成混合層高度發展主要的決定機制為熱浮力紊流與機械紊流兩者,而且此二者之特性在日間與夜間有所不同。在熱力紊流效應上可由大氣溫度的垂直變化剖面來判斷,其日夜變化非常地顯著,與地表受熱有密切關係。 在光化學軌跡模式(TPAQM,Trajectory Photochemical Air Quality Model)中,原先就有計算混合層的步驟,不過計算程序是先計算出全台各氣象測站及環保署測站的混合層高度後再進行內插或外延至整個模擬範圍之網格點中。這種計算程序對於模擬範圍中海上的網格點之混合層高有不合理存在。因此在本研究之中,將採用分別讀入陸上測站及海水表面溫度圖上虛擬測站之溫度值後,再以乾絕熱遞減方法來計算海上及陸上的混合層高度。由於目前在台灣地區並沒有一個單位能提供針對混合層所做即時的觀測或計算,因此沒有一個較具公信力的普遍觀測數據提供給我們作為互相比對之依據。所以權宜之下,我採用環保署在2003年中,於台灣北中南三地利用MTP-5儀器所觀測到的即時探空數據,ㄧ樣進行乾絕熱遞減法來決定混合層高,作為我混合層診斷方式計算結果的比對。 研究的結果顯示,利用地面溫度進行乾絕熱遞減法配合海水溫度及溫度剖面所決定出來的混合層網格氣象場,比起原先TPAQM所模擬出來的更具有海陸性質不同的分野,與我們先前預期出現的現象相吻合;但是再進行混合層比對之後,發現以乾絕熱遞減方法所決定出來的混合層在台中及高雄地區有一定程度的高估,尤以春、冬兩個季節較為嚴重。雖然台北地區在春、冬季節亦有高估現象,但是相較之下高估程度較小。從探空測站的選擇以及混合層計算的結果看來,地域性探空資料對於當地的混合層計算有著相當之影響;如台中及高雄地區多半採用台北地區的探空資料來計算當地混合層,高估情況就明顯比台北就地引用其探空資料所計算之混合層來的嚴重。所以採用乾絕熱遞減方法在局部地區的混合層模擬上,仍然容易受到如探空資料及地面溫度的影響而產生誤差。因此儘管在有限的例行氣象探空觀測下,採用乾絕熱遞減法配合時間權重內插計算是現有條件下的一權宜方法,但是須注意的是,此方法的準確性並不如我們所預期,混合層比對的相關性也不甚理想,因此建議後續研究,如有繼續採用乾絕熱遞減法來決定混合層高度之時,應多加留意探空資料對混合層所產生的高估影響。 After the air pollutant has been discharged, it has to been finally diluted by the atmosphere. Therefore an air pollution episode will happen or not may be determined by the ability of atmospheric diffusion and atmospheric transmission. Above all, the meteorological parameter –mixing layer height, MH– often plays the key role. The mixing layer meteorologically is one kind of the atmospheric boundary layer. In the mixing layer, the air pollutant can be mixed adequately by the convective turbulence and the mechanical turbulence. The mixing layer computed by convective turbulence effect can be observed by the atmosphere temperature profile. We had calculated the MH by the meteorological module of the TPAQM (Trajectory Photochemical Air Quality Model), previously. In this module, it first calculated the hourly MH at every surface station, and then it interpolated the value to the every grid point in the studied domain. But this kind of calculated procedures may lead to the unreasonable result, when we compute the mixing height at the grid point in the sea region. So in my study, I will import the surface sea temperature data from the East Asian surface sea temperature picture, and use the adiabatic lapse rate method to calculate the sea and the land MH respectively. Because presently there is no observational MH data, so I use the continuous temperature profile data observed by the instrument MTP-5 to compute the hourly contrastive mixing layer heights in Taipei、 Taichung, and Kaohsiung. The data was obtained by the EPA program at 2003. The result of my study showed that the grid MH field computed by the adiabatic lapse rate method represented the difference between the sea and land region more clearly than by the TPAQM method. But after the comparison of MH, the mixing layer heights computed in Taichung and Kaohsiung by the adiabatic lapse rate method were over estimated in spring and winter. This phenomenon also appeared in Taipei, but the degree of over estimation was not the same as in Taichung and Kaohsiung. From the selection of regional sounding station and the result of MH calculation, regional sounding data affect the estimation of local MH seriously. For instance, the Taichung and Kaohsiung station used the greater part of sounding data of Taipei to compute the local MH. Therefore the over estimations in this two places was more serious than in Taipei. Consequently adopt the adiabatic lapse rate method to simulate the local MH may occur the inaccuracy by air sounding data and local surface temperature. In spite of the limited air sounding data, we would use the adiabatic lapse rate method and the time interpolation to get the hourly mixing height. It should be noticed that the degree of accuracy was not so good enough that we can completely believe it. As a result, the follow research worker should notice this over estimation by the method. |
URI: | http://ntur.lib.ntu.edu.tw//handle/246246/62678 | 其他識別: | zh-TW |
顯示於: | 環境工程學研究所 |
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ntu-93-R91541126-1.pdf | 23.53 kB | Adobe PDF | 檢視/開啟 |
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