Simulation Of Aerosol Radiative Effect And Its Meteorological Field Response Using CAML Lidar And Aethalometer Measurements

Using the Aethalometer^TM observation data, we retrieved the absorption coefficient of aerosol at the Lanzhou's outer suburb -Yuzhong district. Combining the extinction coefficient retrieved by the lidar (CAML^TM CE-370-2) observation data, we got the aerosol optic parameters in Yuzhong; Using the initial field and large background flow fields provided by WRF model, we improved the simulation ability of a 1.5-order closed 3D atmospheric boundary model; In addition, a radiation transfer model, which took LOWTRAN 7 as the key frame, was also improved; Based on these facts, we developed a set of comprehensive model for simulating the aerosol radiative effect and its meteorological field response in atmospheric boundary layer (ABL) with complicated underlying surface.(1) The black carbon aerosol was measured by Aethalometer. Results show that black carbon concentration is affected not only by weather condition change, but also by human activity. It has the typical daily, weekly and seasonal variations. Daily variation characterizes that black carbon has the bimodal pattern and the peak value appeared at 08:00～10:00 and 18:00～21:00, which is related closely to the local weather conditions and human activities. The weekly variation shows that Saturday and Sunday have the lowest black carbon concentration, and it becomes higher from Monday through Thursday. In spring, summer and autumn, black carbon concentration is relatively lower and the mean value is about 1300ng/m³, and in winter, black carbon concentration increases obviously with mean value of 3000ng/m³.By HYSPLIT-4 model, we simulated the air current coming direction, and found the black carbon aerosol sources during the heating period in Yuzhong. Results show that local source is the main source for the black carbon, but it is also affected by the surrounding cities and towns. In heating period in winter, coal burning is the main black carbon source in Yuzhong. With the black carbon concentration, we retrieved the absorption coefficient for the first time and calculated the direct radiative flux in Yuzhong. The results show that black carbon aerosols derived from coal-burning reduce obviously the direct radiation. Generally speaking, during the heating period (November to March), direct radiative flux is reduced by 128W/m² compared with the one on April 2007. At noon especially, it is reduced by 154W/m².We also analyzed the dust storm process on March 2007, and it showed that, during the dust period, black carbon concentration is four times higher than the usual.(2) We analyzed the lidar observation data and retrieved the extinction coefficient in Yuzhong. Results show that the method used in the paper is able to retrieve extinction coefficient well. However, when there is low cloud or high aerosol concentration, the extinction coefficient truncation appears. Two kinds of optic thicknesses retrieved respectively by lidar and sun photometer were compared, and results show that there are 15.54% of relative error and 0.0629 of average absolute error, which demonstrate that the retrieval result from the lidar data can reflect aerosol optic property well.The analysis of dust process on March 2007 demonstrated that the lidar measurement is able to reflect the dust aerosol concentration vertical distribution well.(3) With WRF model, we simulated the meteorological fields in ABL on a typical fine day in Yuzhong. By schemes comparison and selection, we obtained a microphysical parameterization scheme suit for Yuzhong.Simulation of the meteorological fields in ABL during the period of dust storm showed that the WRF simulation ability is decreased in the severe weather situation.(4) We improved the aerosol scheme in the radiative transfer model, in which LOWTRAN 7 is the main frame. By the method of input the local absorption and extinction coefficients, we can obtain aerosol absorption and scattering property objectively in Yuzhong, which make the calculation results much closer to the real situation. (5) We also improved the previous ABL model. The WRF simulation results provide initial field and adjusting fields, which can improve greatly the simulation ability of the ABL model. Combining the LOETRAN 7, we simulate the aerosol radiative effect on 17 April 2007. Results demonstrate that aerosols lower down the temperature at night and increase at daytime. The temperature at lower layer is reduced by 0.23K at 01:00. While at daytime, aerosols increase temperature by 0.3K at 13:00.(6) We simulated the dust radiative effect with the comprehensive model of this paper. Results show that dust aerosol has the cooling effect at night. The lower layer temperature is reduced by 0.4K at 01:00. While at daytime, dust aerosol has the warming effect. The lower layer temperature increases by 0.39K at 13:00. With the temperature change, wind field is adjusted, and the wind speed at lower layer is reduced by 0.56m/s at 01:00, while lower layer temperature increases by 0.57m/s at 13:00.In this paper, we developed a comprehensive model to simulate aerosol radiative effect and its metrological field response. The model has the strong applicability, and it provides not only the platform for simulating and analyzing the aerosol radiative effect, but also the input parameters for the numerical weather forecast. So it has the significant scientific and application values. Combining Aethalometer and CAML lidar, we are able to make the long term atmospheric aerosol observation. In addition, we can also calculate the local aerosol radiative effect. They are helpful to improve the radiative parameterization scheme in the atmospheric model. By capturing every aerosol property in different weathers, we can obtain the real time aerosol radiative effect, which may be used in the model as the important parameter. This kind of effective, flexible simulation method will hopefully provide the technical support to weather forecast model.