沙尘气溶胶辐射强迫全球分布的模拟研究

A modeling study of global radiative forcing due to dust aerosol

中文关键词:  沙尘气溶胶， 直接辐射强迫， 辐射传输模式， 地表反照率， 太阳天顶角， 云

英文关键词:Dust aerosol, Radiative forcing, Radiative transfer model, Surface albedo, Zenith angle, Cloud

中文摘要:

      为了定量了解沙尘气溶胶对气候的影响，文中利用一个改进的辐射传输模式，结合全球气溶胶数据集（GADS），计算了晴空条件下，冬夏两季沙尘气溶胶的直接辐射强迫在对流层顶和地面的全球分布，并讨论了云对沙尘气溶胶辐射强迫的影响。计算结果表明，对北半球冬季和夏季而言，在对流层顶沙尘气溶胶的全球短波辐射强迫的平均值分别为-0.477和-0.501 W/m 2 ；长波辐射强迫分别为0.11和0.085 W/m 2；全球平均短波地面辐射强迫冬夏两季分别为-1.362和-1.559 W/m 2 ；长波辐射强迫分别为0.274和0.23 W/m 2。沙尘气溶胶在对流层顶和地面的负辐射强迫的绝对值都随太阳天顶角的余弦和地表反照率的增加而增大；地表反照率对沙尘气溶胶辐射强迫的强度和分布都有重要影响。研究指出：云对沙尘气溶胶的直接辐射强迫的影响不仅取决于云量，而且取决于云的高度和云水路径，以及地面反照率和太阳高度角等综合因素。中云和低云对沙尘气溶胶在对流层顶的短波辐射强迫的影响比高云明显。云的存在都使对流层顶长波辐射强迫减少，其中低云的影响最为明显。因此，在估算沙尘气溶胶总的直接辐射强迫时，云的贡献不可忽视。

英文摘要:

      To understand the dust aerosol effects on climate quantitatively, we have calculated the global distribution of direct radiative forcing due to dust aerosol under clear and cloud sky for winter and summer, by using an improved radiative transfer model and the global distribution of dust mass concentration given by GADS (Global Aerosol Data Set). The results in this paper show that the global means of the solar forcing at tropopause for winter and summer are -0.477 and -0.501 W/m2, respectively; the corresponding values for the longwave forcing are 0.11 and 0.085 W/m2, respectively. At the surface, the global means of the solar forcing are -1.362 W/m2 for winter and -1.559 W/m2 for summer, whereas the corresponding values for the longwave forcing are 0.274 and 0.23 W/m2, respectively. It points out by this work that the absolute values of the solar forcing both at tropopause and the surface increase linearly with the cosine of solar zenith angle and surface albedo. Solar zenith angle influences both of the strength and distribution of the forcing greatly. This study shows that cloud takes great effects on the direct radiative forcing of dust, which depends on many factors including cloud cover, cloud height, cloud water path, surface albedo, and solar zenith angle etc. Of all, the effects of low clouds and middle clouds are larger than those of high clouds. The existence of clouds reduces the longwave radiative forcing at tropopause, in which the influences of low clouds are the most obvious. Therefore, the impacts of cloud should not be ignored when estimating the direct radiative forcing due to dust aerosol.