Tiramisu snow and the weakening of snow surface albedo

Abstract:

Since 1850, earth's cryosphere has shown a global shrinking trend. The retreat of snow and ice in cryosphere has strongly impact on the hydrological cycle and the energy balance. Light absorbing impurities deposited on the snow surface are main factor that resulted in melting of snow and ice, which absorbs solar radiation and accelerates snow aging process. Light absorption due to impurity content in snow and ice is involved in complex mechanisms such as the snow albedo positive feedback. Previous studies mostly based on model results to explain the effect of light-absorbing impurities on snow albedo and its climate effects. Due to the lack of observation data, the influence of light-absorbing impurities on snow surface albedo is still uncertain. On December 1, 2018, strong wind, heavy snowfall, and dust-storm events occurred in Urumqi, China. It provides an excellent natural experiment for quantifying the effect of dust of fresh snow on surface albedo. It is found that large-scale strong cold due to the Siberian trough and sustain water vapor transport resulted in heavy snowfall. The influence of the northwesterly wind and the local vertical upward movement lead to dust-storms particles accumulation in Urumqi. The observation data used is snow depth, total cloud cover, and the hourly irradiance over Urumqi from 1993 to 2016. It is found that clouds, snowfall, and dust particles led to a significant reduction of total solar radiation and direct radiation on December 1^st. The total solar radiation was only 60 Wm^-2 and the direct radiation decreased to zero. Compared with old snow, the continuous accumulation of fresh snow will greatly weaken the heating effect of light-absorbing impurities. As a result, the albedo on December 2^nd was significantly higher than that on December 1^st. In addition, the current numerical model seriously underestimates the effect of light-absorbing impurities on snow surface albedo. The reduction of surface albedo caused by dust-polluted fresh snow is mainly due to the reduction of reflected radiation, which reduced by 0.25 (about 38%) compared to pure snow. In addition, the effect of polluted fresh snow on snow surface albedo is more severely affected by meteorological conditions such as large-scale cooling and high cloud cover. Therefore, the radiation variation caused by clouds, snowfall and LAIs in the atmosphere should be considered comprehensively.