中国天山西部森林积雪短波辐射收支特征

Characteristics of Shortwave Radiation to Snow Beneath Forest Canopies of the Western Tianshan Mountains,China

基于中国科学院天山积雪与雪崩研究站不同开阔度森林下积雪表面短波辐射的观测资料,分析了森林积雪短波辐射收支、短波辐射透射率特征。结果表明:阴坡林下积雪表面短波辐射小于阳坡,且随森林开阔度的减小而减小;林下雪面短波辐射和净短波辐射随太阳高度角增加而逐渐增加,不同开阔度林下雪面短波辐射和净短波辐射的差异也随太阳高度角的增加而增大;阳坡、阴坡林冠上方和80%开阔度林下雪面短波辐射在晴天日变化呈单峰型,峰值出现时间由林冠上方直接辐射和散射辐射的相对关系决定;多云天气,短波辐射的日变化特征取决于云量的变化;日平均短波辐射透射率随林冠开阔度和太阳高度角的增加而增加,且开阔度越大,其增加速率越快,短波辐射透射率日变化呈"U"型,早晚大于中午。

Downward and upward shortwave radiation beneath different canopy openness forest was measured in Tianshan Research Station for Snow-cover and Avalanche of Chinese Academy of Sciences.The variation of shortwave radiation beneath forest canopy,shortwave transmissivity and the influence of intercept snow above forest crown on shortwave were analyzed.The results showed the downward shortwave radiation beneath forest canopy were less than that on the sunny slope,it decreased with canopy openness decreased.The downward and net shortwave radiation beneath forest canopy increased with solar elevation angle increased,and the difference of downward and net shortwave radiation beneath forest canopy between different canopy openness forests also increased with solar elevation angle.In clear day,the daily variation of downward shortwave radiation in sunny slope,above forest canopy and beneath 80%canopy openness forest presented single peak type,and the peak time was determined by relative proportion of direct shortwave radiation and diffuse shortwave radiation.In cloudy day,the variation of downward shortwave radiation was mainly influenced by cloud cover.The sparser the forest was,the bigger the shortwave transmissivity was.The daily average of shortwave radiation increased with solar elevation angle increased.The sparser the forest was,the more the shortwave transmissivity increase.The daily variation of shortwave transmissivity presented"U"type,the value of shortwave transmissivity in the morning and evening were bigger than that in the period of 12:00—17:00.