青藏高原积雪对气候反馈的初步研究

积雪具有很高的反照率,能反射回绝大部分的太阳短波辐射;同时,积雪是热的不良导体,其热阻隔性会抑制地表的长波辐射。因此,积雪的积累和消融会强烈地改变大气层顶的辐射平衡,进而对气候产生反馈。采用ERA-Interim再分析资料和MODIS去云积雪产品,通过改进的偏辐射扰动思想,对青藏高原地区2001~2010年积雪影响下大气层顶的辐射能量收支状况进行模拟,计算对应的积雪辐射强迫,并在此基础上估算积雪反馈。结果表明:研究区99.5%以上地区的大气层顶辐射平衡为负,即积雪对气候存在正的辐射强迫,年平均辐射强迫为3.97 W·m-2。时空分布特征表明,积雪辐射强迫的年际差异不大,但空间差异很大,其空间分布与积雪覆盖率有很强的正相关关系,在绝大多数情况下,短波反照率辐射强迫对积雪辐射强迫起着决定性作用,且青藏高原的积雪反馈强度约为9.35 W·m-2·℃-1。

Preliminary Study on Snow Feedback to the Climate System in the Tibetan Plateau

Snow cover reflects most of the solar radiation due to its very high reflectivity;at the same time,snow cover depresses longwave radiation due to its low conductivity.As a consequence,the accumulation and depletion processes of seasonal snow cover change the radiation energy balance on top of the atmosphere,then feedback to the climate system.ERA-interim reanalysis data,MODIS cloud-free snow products were used to simulate the energy balance on top of the atmosphere in Tibetan Plateau between 2001~2010 using modified partial radiative perturbation method.Results showed that more than 99.5% of the study area has a negative radiation balance,which indicates a positive radiative forcing to the climate system.The annual snow radiative forcing of the study area is 3.97 W m^-2 on average between 2001~2010.There is little difference in the annual snow radiative forcing while big difference lies inside of the study area;the spatial distribution of radiative forcing has a very high correlation with annual fraction of snow cover.Under most circumstances,shortwave radiative forcing is the determinant factor of snow radiative forcing.At last,snow feedback is estimated to be 9.35 W·m^-2℃^-1.