A comparison of eddy-covariance and large aperture scintillometer measurements with respect to the energy balance closure problem

摘要

We analyzed the seasonal variations of energy balance components over threedifferent surfaces: irrigated cropland (Yingke, YK), alpine meadow (A'rou,AR), and spruce forest (Guantan, GT). The energy balance components weremeasured using eddy covariance (EC) systems and a large aperturescintillometer (LAS) in the Heihe River Basin, China, in 2008 and 2009. Wealso determined the source areas of the EC and LAS measurements with afootprint model for each site and discussed the differences between thesensible heat fluxes measured with EC and LAS at AR. The results show thatthe main EC source areas were within a radius of 250 m at all of the sites.The main source area for the LAS (with a path length of 2390 m) stretchedalong a path line approximately 2000 m long and 700 m wide. The surfacecharacteristics in the source areas changed with the season at each site,and there were characteristic seasonal variations in the energy balancecomponents at all of the sites. The sensible heat flux was the main term ofthe energy budget during the dormant season. During the growing season,however, the latent heat flux dominated the energy budget, and an obvious"oasis effect" was observed at YK. The sensible heat fluxes measured byLAS at AR were larger than those measured by EC at the same site. Thisdifference seems to be caused by the so-called energy imbalance phenomenon,the heterogeneity of the underlying surfaces, and the difference between thesource areas of the LAS and EC measurements.