过去的研究结果指出,冬季青藏高原地面净辐射场是一个由地理因子决定的基本场叠加上一个降雪后地面积雪区造成的扰动场组成。为定量研究冬季青藏高原降雪对地面净辐射的扰动幅度,利用作者已经建立的冬季青藏高原雪后地面反射率与降雪量的关系以及地面无(有)积雪时计算地面净辐射的公式,计算了不同强度降雪后地面净辐射日总量及其变化。结果表明:降雪量主要控制雪后地面净辐射负值的持续时间,降雪量为2.0mm,雪后净辐射负值的持续时间约为6d,降雪量为10.0mm,可长达20d。雪后天空状况影响地面净辐射负值的大小,同样强度的降雪后,净辐射为负值的总量在晴天(日照百分率S₁=0.9)条件下约为阴天(S₁=0.2)的2倍。那曲地区冬季地面无积雪时净辐射为正值,12月的月总量估计为2.52-2.88MJ/m²,一次10.0mm降雪后持续约20d的地面净辐射负值的总量可达-2.62MJ/m²,接近当月拉萨地面净辐射(正值)的月总量,成为明显的冷源区。

The results of the previous studies show that the geographic distribution of surface net radiation over the Qinghai-Xizang Plateau in winter consist of a basic pattern determined by the geographic conditions and a perturbation pattern caused by snow.In order to study quantitatively the perturbations of surface net radiation caused by snow,the daily totals of surface net radiation and their variations after snow with different snowfall were calculated by use of the relationship between the albedo after snow and the snowfall,and the empirical formulae for calculating surface net radiation in cases of snowcover.The results show that the duration of negative surface net radiation after snow is determined mainly by the snowfall,6 days of the duration of negative surface net radiation may occur when snowfall is 2.0mm,but 20 days when snowfall is 10.0mm.The sunshine duration affects strongly the magnitude of surface net radiation,the absolute value of the totals of net radiation in case of the clear day(S₁=0.9) is greater than that in cloudy day(S₁=0.2) after snow with the same snowfall.In winter,the surface net radiation is positive in Nagqu if none of snowcover,the monthly totals of surface net radiation in December is about 2.52-2.88MJ/m².But the totals of the negative surface radiation budget after snow with the snowfall 10.0mm is -2.62MJ/m²,the absolute value of which is nearly equal to the monthly totals of the positive surface radiation budget(3.19MJ/m²) in Lhasa.