内蒙古半干旱草原下垫面地表辐射特征

中纬度半干旱草原是全球陆地生态系统的重要类型之一，也是我国北方主要的地表类型，为深入了解我国半干旱草原区陆面对大气的辐射强迫，选取锡林浩特国家气候观象台2010年的辐射观测资料，分析了内蒙古半干旱草原下垫面地表辐射平衡各分量、地表吸收辐射和有效辐射以及地表反照率的日变化和季节变化规律，并与西北典型干旱区作了对比分析。结果表明：半干旱草原区太阳总辐射季节变化特征非常明显，季节平均日积分值由大到小依次为夏季、春季、秋季、冬季，年总量为6 036.64 MJ/m²，与黑河地区绿洲接近，明显小于戈壁和沙漠下垫面的值；半干旱草原地表反射辐射年变化趋势较为复杂，在4～10月由于下垫面植被和土壤类型、湿度等的差异，半干旱草原地表反射辐射月平均值低于黑河地区草地和荒漠的值，但高于农田的值；地表吸收辐射季节变化规律与总辐射保持一致；大气长波辐射年总量为8 155.23 MJ/m²，低于黑河地区草地、荒漠和农田下垫面的值，主要是由于半干旱草原区地理纬度较高，全年平均气温较低造成的；在植被覆盖较好的6～9月，半干旱草原区地表长波辐射月总量为4 532.14 MJ/m²，低于黑河流域的荒漠区，而高于草地和农田的值；半干旱草原区地表有效辐射年总量为2 398.75 MJ/m²，小于黑河地区沙漠和戈壁下垫面而大于绿洲；半干旱草原区地表反照率年均值为0.35，均大于西北干旱区不同下垫面，主要由于半干旱草原区冬春季地表积雪覆盖时间明显长于干旱区，可见，地表积雪对反照率的影响非常大。

Surface radiation characteristics on semi-arid grassland in Inner Mongolia

Based on radiation data observed at Xilinhot National Climatological Observatory of Inner Mongolia in 2010, the diurnal and seasonal dynamics of surface radiation balance and albedo over typical semi-arid grassland in Inner Mongolia was analyzed and compared with those in arid area of northwest China in this paper. The radiation data was measured by CNR-1（Kipp & Zonen），a four components radiation sensor of the benchmark radiation observation system. Output data was processed to the mean value of 30 minutes in analysis. In order to control the quality of data, the probable value, the extreme value and the relationship between different radiation components were checked carefully in accordance with the standard proposed by the Basic Surface Radiation Network（BSRN）. The results of this paper indicated that: the seasonal variation of global radiation over semi-arid grassland was quite evident. The annual total of global radiation reached about 6 036.64 MJ/m2，which was lower than that observed from gobi and desert and close to that in oasis. The monthly variation tendency of surface reflected radiation was relatively complicated. The monthly mean values of surface reflected radiation in semi-arid grassland from April to October were smaller than those in grassland and desert of Heihe Basin and larger than those in cropland due to diversity of surface vegetation and soil humidity. The seasonal variation of surface absorptive radiation accorded with that of global radiation. The annual total of atmospheric long-wave radiation was lower than that over different surface of Heihe Basin on account of the lower annual mean temperature and higher latitude in semi-arid grassland. The total value of surface long-wave radiation in semi-arid grassland form June to September was about 4 532.14MJ/m2，which was larger than that in grassland and cropland and smaller than that over desert. The annual total value of surface effective radiation was up to 2 398.75 MJ/m2，which was higher than that in oasis and lower than that in desert and oasis. Since the durations of surface snow cover over semi-arid grassland in Winter and Spring were longer than those in arid area, the annual mean value of surface albedo in semi-arid area reached about 0.35, which was all higher than that on different surface in arid area. This shows that the surface snow cover has a significant effect on surface albedo.