Abstract. In the context of September 2006–August 2010 eddy covariance data of the Semi-Arid Climate Change and Environment Observatory, Lanzhou University (SACOL) as a platform of the Key Laboratory of Semi-Arid Climate Change, Ministry of Education, an intensive study is performed of the SACOL data quality and energy balance closure (EBC) characteristics on a seasonal basis, the EBC impacts of the flux contribution from the target source zone, the low-frequency part of the turbulence spectra, turbulent mixing intensity and diverse schemes for surface soil heat fluxes. Evidence suggests that (1) through the steady state test (SST) and integral turbulence characteristics (ITC) tests as well as analysis of flux contribution from target area to the EBC, it is found that most of the eddy covariance data are within a domain of effective quality. The valid data account for 77.5, 75.4, 68.3 and 61.6% of seasonal total for spring, summer, autumn and winter, respectively; (2) the EBC shows its appreciable seasonal variability, with the energy residual making up 19.0, 14.8, 11.6 and 7.7% of net radiation in winter, summer, autumn and spring, respectively; (3) (i) Flux contribution from the target zone has greater EBC impact and as the flux contribution in percentage increases, EBC is correspondingly improved. Even the percentage reaches 100%, the energy balance fails to be closed entirely. (ii) The Ogive function analysis shows that the EBC suffers the effect of relatively small (maximum) low-frequency turbulent flux in spring and summer (winter). (iii) Turbulence intensity exerts noticeable impact on the EBC; when turbulent mixing arrives at certain intensity, the EBC is in an optimal state and stabilized. (iv) Different schemes of surface soil thermal flux have significant effect on the EBC.
On the factors influencing surface-layer energy balance closure and their seasonal variability over semi-arid loess plateau of Northwest China
