The diagnostic method of the mixing layer height
Date Issued
2004
Date
2004
Author(s)
Chen, Shih-Fang
DOI
zh-TW
Abstract
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.
Subjects
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
Type
thesis
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