Experimental Study On Land Surface Radiation Over The Northwest Arid And Semiarid Areas

In this study, the variation of surface radiation and albedo over Semi-Arid area are analyzed by using the land-surface radiation data observed over Semi-Arid Climate and Environment Observatory of Lanzhou University (SACOL) during April 2006 to April 2010. The variation of surface radiation over Arid area in spring were also analyzed and compared with the surface radiation over the SACOL by using the land-surface radiation data observed over Zhangye National Climatological Observatory during April 2008 to June 2008. The contribution of dust to land-surface radiation were estimated and the characteristic of radiation (scattering and absorption coefficient) of the dust aerosol were discussed on dust day and no-dust day in spring over Zhangye site. The main results are as follows:1)The monthly maximum of surface solar radiation at SACOL, is 451.1 Wm-2 in May, the minimum is 275.8 Wm-2 in December.2)The monthly maximum of reflected solar radiation is 104.9 Wm"2 in June, the minimum is 3.2 Wm-2 in December.3)The monthly maximum of land-surface albedo is 0.31 in February, the minimum is 0.17 in September; The value of land-surface albedo is higher in winter than that in other seasons in general.4)Because the concentration of aerosol over SACOL is higher than that over Zhangye site, the daily extremums of solar radiation are higher than that at Zhangye site in both the sunny days and cloud days.5)Dust in the air can reduce the solar radiation reached to the surface, the estimation of reduction is about 10.45 Wm-2 while 0.1 atmospheric turbidity is added. If the atmospheric turbidity is unchanged, the smaller the dust particles are, the higher the efficiency of reduction of dust will be. When atmospheric turbidity is less than 0.3, there is a trend that atmospheric inverse radiation increases with the atmospheric turbidity. When atmospheric turbidity is more than 0.3, the atmospheric inverse radiation decreases with the atmospheric turbidity.6)The daily variation of total scattering coefficients and absorption coefficients over Zhangye site present a bi-peaks type in no dust weather period, and the peaks occurred around almost the same time. During dust weather period, total scattering coefficients present a bi-peaks type, while absorption coefficients present three peaks. Proportion of the fine aerosol particles changes obviously in no-dust weather period, daily range of it was more large than in dust weather period. The total scattering coefficient had a sharp break when dust-storm occurred.