Turbulent fluxes were measured by an eddy covariance system at three levels over an intricate land surface on the southern part of the Loess Plateau, consisting of heterogeneous flat terrain and a large valley 500 maway from the observation site to the southeast. The surface roughness length, the seasonal variation of bulk transfer coefficient for sensible heat (CH),and the seasonal variation of surface moisture availability(β) were also analyzed based on the observation.The flux footprint was carefully considered in this study.A relatively dry period of the experimental areaexistedfrom June to the first week of July 2004 when the land surface offered turbulent energy to the atmospheric surface layer mainly by sensible heat flux with a maximum value of around230Wm-2.A wet durationlasted from the second week of July to the end of September 2004 with very frequentrainfall eventsin conditions whenthe winds were mainly from the southeast;latent heat flux was dominant during the wet seasonand reached a peak value of around 280Wm-2.The surface parameters of CH andβwere calculated when the mean winds coming from the flat terrain, i.e., from the northwest direction. The values of CH ranged between 0.004 and 0.006 during the observational year of June 2004 to June 2005.The surface moisture availabilityβchanged with seasons as anticipated with high values during June and July 2004and lowest values around0.03 inFebruary 2005. Its peak value of 0.91 occurred in July; the mean value ofβduring the wet seasonwas 0.29. Furthermore, the relationship between the surface soil water content andβindicated that changes in soil water content contributed much to variations of surface moisture availabilityβ.
Cite this paper
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