中文摘要：

利用青藏高原多年冻土北界西大滩地区2005年度的辐射及气象观测资料,分析探讨了该地区光合有效辐射（PAR）的基本特征.结果显示：PAR日变化与总辐射（Q）日变化趋势一致,表现为中午大,早晚小;晴天的日变化曲线呈单峰型,变化相对比较平滑,阴天的日变化曲线不稳定,晴天的PAR大于阴天日.PAR具有明显的季节变化特征,表现为春夏季大,秋季次之,冬季最小,最大值出现在5月,最小值出现在12月.光合有效辐射系数ηQ值阴天大,晴天小;ηQ的日变化是中午小,早晚大,年变化呈双峰型,在1.75~1.96 mol.MJ-1之间变化,年平均值为1.88 mol.MJ-1.最后,提出了适合本地区PAR的气候学计算方法.

英文摘要：

In this paper,the characteristics of Photosynethically active Radiation（PAR） and the ratio of the PAR to global radiation（ηQ） are analyzed and studied by using the observation solar spectral radiation and meteorological data in Xidatan at the northern boundary of Tibetan Plateau permafrost regions in 2005.The results show that diurnal variation of PAR is larger at noon than that in morning and evening,similar to the daily variation trend of Q.The PAR shows a single peak and changes smoothly on clear days.Oppositely,it is instability and less in value in the cloudy days than that on clear days.The PAR is larger in spring and summer than that in autumn and winter.The maximum of PAR occurs in May and the minimum occurs in December.The ηQ is larger on cloudy day than that on clear day.The daily variation of ηQ is smaller at noon than that in morning and evening.The annual variation of ηQ shows a bimodal type and varies between 1.75 mol·MJ-1 and 1.96 mol·MJ-1.The annual average of ηQ is 1.88 mol·MJ-1.At last,the climatological calculation means of the photosynthetically active radiation for this region are put forward.