广东龙门地区草地下垫面地表辐射和能量平衡观测和分析

Observation and Analysis of Surface Radiation and Energy Balance in the Longmen Area

利用2009年9月-2010年1月在广东省龙门县收集的涡动相关观测资料,比较了广东龙门地区草地下垫面秋、冬季不同天气条件下的地表通量特征。发现地表辐射平衡分量和能量平衡分量都存在明显的月际变化。典型晴天下辐射通量除长波辐射外均表现为标准的单峰日循环形态。在阴、雨天,辐射通量日变化曲线波动大,出现双峰甚至是多峰的形态。地面长波辐射略大于大气长波辐射,两者的差值在雨天、阴天、晴天依次增大。在辐射平衡中,地面长波辐射贡献最大,大气长波辐射次之,再依次为太阳短波辐射、净辐射和反射辐射。与晴天相比,阴天潜热、感热均减少。与秋季相比,冬季潜热减少,感热增加。在晚上存在负水汽输送现象。降水天里地热流量全天为负值,土壤从深层向地表释放热量。无论晴天还是阴天,地表和浅层土壤温度都表现为准正弦曲线。土壤温度的活动层基本在10 cm土壤层内,各层土壤温度峰(谷)值出现的时间随着土层厚度增加而延迟,10 cm以下土壤温度几乎无日变化特征,雨天时地面和浅层土壤温度呈下降趋势。各层土壤温度不仅跟天气状况有关,晴天高于阴天,还存在秋季地温度高于冬季的季节变化。

The characteristics of grass surface heat flux under different weather conditions in autumn and in winter have been analyzed based on data measured with Eddy Covariance method at Longmen long-term observation station during the period of September 2009 to January 2010.The results indicate that there is a large monthly variation in the energy balance under different weather conditions.The daily variation shows a typical single-peak circle on clear days（except long-wave radiation） and a double-peak or more-peak curve on cloudy and rainy days.The value of upward long-wave radiance is slightly larger than that of downward long-wave radiance.The difference of values between these two kinds of radiance is the smallest on rainy days and increases on cloudy and clear days.The upward long-wave radiation,the downward long-wave radiation,the solar radiation,the net radiation and the upward shortwave radiation show the descending contribution to the radiation balance.Each component of surface energy flux shows obvious synoptic conditions and seasonal and monthly variations.The latent heat flux is larger in autumn than in winter,whereas the sensible heat flux is opposite.The latent heat flux and the sensible heat flux are both reduced on cloudy and rainy days.A negative water-vapor transfer exists at night.The soil heat flux is negative on rainy days and the daily average value of rainy days is higher than that of clear and cloudy days.The soil temperature of surface and shallow-layer（5cm） presents accurate sine curve changes regardless of clear days and cloudy days.The soil temperature active layer is in the 10cm scope.The time when the soil temperature reaches the maximum（minimum） is delayed with increasing soil depth.There is no diurnal variation below 10cm depth.The soil temperature of surface and shallow-layer decreases with time on rainy days.The soil temperature of each layer is higher on clear days than that on cloudy days and higher in autumn than in winter.