利用2005年1月—2010年12月中国生态研究网络拉萨农田站的观测数据， 分析了拉萨地区光合有效辐射Qp的变化特征\.结果表明， 拉萨地区的Qp与太阳总辐射Rs具有相同的月变化和日变化特征， Rs与Qp的平均日累计值分别为20.2 MJ·m-2和37.2 mol·m-2， Qp呈逐年递减趋势。Rs与Qp的月变化表现为6月最大、 1月最小， 其最大、 最小值分别为25.4 MJ·m-2、 14.0 MJ·m-2和48.7 mol·m-2、 25.2 mol·m-2。日变化表现为正午大、 早晚小。光合有效辐射系数（Qp/Rs）的变化范围在1\^3~3.2 mol·MJ-1之间， 年平均值为1.89 mol·MJ-1， 呈逐年递减趋势， 2010年比2005年降低了6\^7%。Qp/Rs的日变化表现为早晚大、 正午小， 季节变化表现为夏季最大、 春秋季次之、 冬季最小， 而且夏、 冬两季的季节变化较为明显， 冬季比夏季低10.6%。通过分析Qp与晴空指数和太阳天顶角之间的关系建立了拉萨地区Qp的估算方程， 相对误差在4.49%左右。
The characteristics of photo-synthetically active radiation (Qp) at Lhasa station in the Qinghai-Xizang Plateau were analyzed based on long-term insitu measurements of surface radiation data from Chinese Ecosystem Research Network. The observation data from 2005-2010 are used to investigate the temporal variability of Qp. The results indicate that Qp shows the similar seasonal and diurnal features as those observed for broadband global radiation（Rs）. The annual mean of the daily values of Rs and Qp are 20.2 MJ·m-2 and 37.2 mol·m-2. The high values of Rs and Qp both appeared in June and the low values appeared in January. Their maximum and minimum values are 25.4 MJ·m-2 and 14.0 MJ·m-2， 48.7 mol·m-2 and 25.2 mol·m-2, respectively. The analysis of the hourly values also revealed a diurnal pattern, with higher values around noon and lower values around sunrise and sunset. The Qp fraction （Qp/Rs） ranged from 1.3 mol·MJ-1(in winter)~3.2 mol·MJ-1(in summer) with an annual mean value of 1\^89 mol·MJ-1. The seasonal variation between summer and winter is more obvious. The seasonal Qp/Rs value in winter is 10\^6% lower than that in summer. The hourly values also revealed a diurnal variation with high value around sunrise and sunset, low value around noon. Both Rs and Qp present the trend of diminishing. Then, an all-weather estimation equation was established based on analyzing the temporal variability of Qp and its dependence on the clearness index and solar zenith angle. The relative deviation is about 4\^49%.
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