塔里木河下游荒漠河岸林带辐射平衡特征

利用新疆塔里木河下游河岸林带观测的太阳辐射数据，结合下垫面和天气变化状况，分析该区太阳辐射变化特征，同时评价FAO56辐射估算方法模拟该区域太阳辐射的效果。结果表明：净辐射和辐射四分量的年均日变化，除大气逆辐射在300 W·m-2左右波动外，均呈现出典型的单峰趋势。其中，总辐射平均极大值为629.96 W·m-2，净辐射平均极大值为520.76 W·m-2，净辐射日积分值在一年内呈现单峰对称型趋势，年平均值为7.81 MJ·m-2·d-1，地表长波辐射的峰值在中午前后滞后于总辐射峰值约2 h。较之晴天而言，阴天和风沙天气太阳辐射波动较大，总辐射和净辐射均明显降低。地表反照率的变化与下垫面植被覆盖度密切相关，生长季节为0.18左右，非生长季节为0.20左右，年均值为0.19。FAO56方法模拟日尺度辐射结果表明：总辐射、净短波辐射和净辐射模拟效率分别为0.94、0.87、0.80，而有效辐射模拟效率仅为0.19；各辐射通量均方根误差均在1.67~1.98，平均偏差值均较小。有效辐射量在总辐射中所占比例较小，虽模拟效率较低，但其对净辐射的贡献较小，使得净辐射模拟误差在合理的范围内，故认为FAO56辐射模拟方法经验系数可用于计算该地区日尺度净辐射值。

Radiation Balance over Riparian Forest Belt in the Lower Reaches of the Tarim River

Solar radiation plays a critical role in the process of energy and material exchange over land surface. It is not only the drive force of land surface physical process, but also the input parameter of Land Surface Model and Remote Sensing Model. Researchers focused on the semiarid and arid regions because of its special geographic environment. Therefore this paper took a typical arid area in the lower reaches of the Tarim River as a case to discuss the radiation balance over riparian forest belt and the measured radiation data, and to evaluate the applicability of FAO56 method used to calculate the net radiation in arid region. FAO56 method is used to calculate shortwave radiation through sunshine duration and long wave radiation through air temperature, humidity and cloud amount. Accuracy was evaluated by Model Efficiency (ME), Root Mean Square Difference (RMSD) and Mean Bias Error (MBE). Statistical results of measured values showed that the daily variation of radiation flux was in a typical normal distribution trend. The maximal values of solar radiation, reflected radiation and net radiation occurred at Beijing time 14:00 o’clock and were 629.96 W·m-2, 106.51 W·m-2 and 520.76 W·m-2 respectively. Maximal value of averaged ground surface long wave radiation occurred at Beijing time 16:00 o’clock and was 460.08 W·m-2. As a result, response of surface temperature to solar radiation lagged for about 2 hours. Seasonal difference was highly related to zenith angle and albedo. Annual variation of net radiation was unimodal with a slight inter annual fluctuation, the net radiation increased gradually from January to June, reached its maximum in June, and decreased gradually from June to December. Daily total value of net radiation fluctuated between 0.5 MJ·m-2·d-1 and 18 MJ·m-2·d-1, and its average in full year was 7.81 MJ·m-2·d-1. Weather conditions, such as windy or cloudy weather, affected significantly the radiation flux. Wind and cloud could reduce solar radiation and correspondingly reflected radiation. Effective radiation was slightly affected, thus net radiation dropped to some extent compared with that on sunny day. The curve of daily albedo was U shaped, it was high at sunrise and sunset but low around midday. Albedo was closely related to the stage of vegetation growth. The averaged albedo was 0.18 at vegetation growth stage and 0.20 at non growth stage. Simulated result showed that ME values of net shortwave radiation and net radiation were 0.87 and 0.80 respectively. The slopes of the correlation analysis for them were 0.95 and 0.89 respectively, for effective radiation, although ME was 0.19, the slope of the correlation analysis was 0.99. It could be concluded that FAO56 radiation simulation could be applied to calculate net radiation over the lower reaches of the Tarim River.