安徽省寿县农田能量平衡评价

Evaluation on Energy Balance of Farmland in Shouxian County of Anhui Province

为了评估安徽省寿县国家气候观象台新增的近地层通量观测系统业务运行状况,利用2007年9月—2008年8月寿县近地层通量系统观测资料,分析了农田下垫面能量平衡情况。结果表明:全年能量平衡比率平均为0.89,但不同条件下存在差异:白天明显大于夜间,春、夏、秋季明显大于冬季,裸地和麦、稻田明显大于雪地,晴、昙、阴、雨天气情况下差异不大。总体来说,能量不平衡是通量观测中较为普遍的现象,一般认为不平衡程度在10%～30%为合理范围,寿县国家气候观象台全年的能量不平衡程度(11%)恰好属于这个范围,并接近不平衡程度的下限,说明涡度相关法在淮河流域农田生态系统通量观测中可靠性较高。

Energy balance means the balance between the sum of latent heat,sensible heat flux observed by Eddy Covariance（EC）technique and the variance of net radiation flux,soil heat,canopy heat.According to the first law of thermodynamics and basic assumption of EC observation,the ratio of energy balance can be used as an effective evidence to evaluate data quality and system performance of an observation system theoretically. Energy balance ratio of the field has been investigated based on the data of flux observation system on near surface layer observed at the representative station of Huaihe River Basin,Shouxian National Climate Observatory from September 2007 to August 2008 in order to assess operation status of this new system.The results show that the annual average energy balance ratio is 0.89 during the period,and it is higher in the day than that in the night,higher in spring,summer,autumn than that in winter,higher over the bare surface than that over the cropland surface,while different weather conditions make little differences.The largest energy balance ratio is 0.92 over the bare surface,and smaller ratio is 0.9 over wheat field and paddy field,while it＇s only 0.50 over snow surface.It also shows that energy balance is influenced by the negligence of heat reserve during exuberant growing period to some extent and absorption tern,such as thaw,freeze and sublimation.During the observation period,the observed turbulent fluxes are always less than available energy,indicating that turbulent fluxes might be underestimated.The energy balance during daytime seems better than that at night because of stronger turbulence.It can be concluded that the applicability of EC method is best in flat,bare field,better in the day than that in the night, better on the underlying surface with low vegetation than that covered with snow.All in all,the phenomenon of energy imbalance is fairly common in flux observation and it often reaches 10%to 30%.The annual energy balance ratio（0.89）of Shouxian National Climate Observatory is close to the lower limit of ranges, so the EC method of flux observation over farmland ecosystem in Huaihe River Basin is reliable.