Impacts of meteorological surface nudging on air quality simulation in Taiwan
| Autor: | Ting-Chi Wu, 吳婷琦 |
|---|---|
| Rok vydání: | 2009 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 97 Meteorological fields are necessary input for air quality modeling. Wind field is responsible for pollutant transport and turbulent mixing in the troposphere. In this work we studied the impact of analysis nudging of meteorological variables on model performance both for meteorological variables and for air quality variables. Taiwan Environmental Administration has maintained a network of densely distributed monitoring stations for air quality with associated meteorological observations. We applied this network of 72 meteorological observations to nudge hourly wind speed, wind direction and temperature. Then we used the new meteorological data to conduct air quality study. We first noted that the standard analysis nudging technique as in MM5 and WRF models needs to be modified in order to be applicable to simulation domains such as Taiwan where nudging observations are all located near the center of the simulation domain. In such case surface nudging with the MQD method leads to undesirable changes in oceanic areas around Taiwan. With our modified MQD technique we are able to develop physically acceptable nudging meteorological fields. We first studied the impact of variations of the three surface nudging constraints, nudging coefficients, nudging variables and nudging domain on meteorological simulation. We found that surface nudging of wind field every 6 hours can reduce hourly surface wind speed to near observations for most of the simulation period. But temperature nudging can lead to unacceptable results if the nudging coefficient is too large. We found this is mostly due to unreasonably fast and deep planetary boundary layer development in the morning and at the evening. Such nudging will while improves surface temperature simulation does lead to overly strong vertical mixing and highly reduced surface pollutant mixing ratios very different from actual observation. Careful structuring of 3-D nudging domains also can improve meteorological simulations such as for the Typhoon Nockten period in 2004 which happens to be within the early part of our selected study period. For air quality study we found that surface nudging while improved simulation of surface wind field it did not change surface ozone simulation significantly, at least around the land based monitoring stations. But the change in 3-D wind structure did change local circulations that led to differences in off shore flow of pollutants and deposition of acidic materials. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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