青藏高原唐古拉山多年冻土区夏、秋季节总辐射和地表反照率特征分析

Analysis of Global Radiation and Surface Albedo Features in Summer and Autumn in a Permafrost Region of Tanggula Range,Tibetan Plateau

根据青藏高原唐古拉山多年冻土区2005年6月24日～10月16日的总辐射、分光辐射和分光反照率观测资料，利用总辐射和大气层顶太阳辐射的比值——日有效透射率Teff用聚类分析法将资料划分为晴天、多云和阴天三类天气，分析了该地区夏、秋季节总辐射、分光辐射比例和分光反照率的日变化和季节变化规律．结果表明，夏季总辐射与大气层顶的差值和日际变化幅度最大，秋季以后这种差值和日际变化幅度减小．天空状况对分光辐射比例和地表反照率均有影响，表现为近红外辐射比例晴天比阴天大，可见光比例晴天比阴天小，各波段反照率晴天均比阴天大．反照率在夏季最低，秋季较高，反照率的日变化有依存分光辐射比例的关系，这大致可以解释地表反照率依存太阳高度角而变化的现象．无积雪地面反照率近红外波段大于可见光波段，地表有积雪时，反照率明显不同，其可见光波段反照率大于近红外波段反照率．功率谱分析表明，日有效透射率Teff存在着2～3d的周期，它是该地区天气系统活动影响太阳辐射收入的一个反映，指示出唐古拉山地区天气系统亦有2～3d的周期性．

Based on the global radiation data as well as the data of spectral solar radiation and spectral albedo observed over a permafrost region of the Tanggula Range from 24 June to 16 October, 2005, using the ratio of daily amount of global radiation to daily amount of extraterrestrial radiation, i. e. the daily effective transmissivity, to classify the sky conditions into three kinds （clear, cloudy and overcast） by K--Means Cluster Meth- od. The diurnal and seasonal variation characteristics of global radiation, spectroradio ratio and spectral albedo are analyzed in this paper. The result shows that the difference between global radiation and extraterrestrial radiation, and the intensity of interdiurnal variation of global radiation are maximal in summer season. Both spectroradio ratio and surface albedo are affected by the sky conditions, in clear days, the proportion of incoming inrared radiation is higher and the proportion of incoming visible light is lower than those in overcast days, and the surface albedo of each wave bands in clear days is higher than that in overcast days. The surface albedo is lower in summer and higher in autumn, and their diurnal variation depends on the diurnal variation of spectroradio ratio. This may explain why the albedo varies depending on the solar elevation. The albedo without snow cover is higher in infrared wave band and lower in visible wave band. However, over snow surface, the albedo is quite different： in infrared band the albedo is lower than that in visible band. Power spectral analysis shows that there is a period of 2-3 days in daily effective transmissivity, which reflects that the weather system in the Tanggula Range has a period of 2-3 days too.