Estimating Turbulent Heat Fluxes With a Weak-Constraint Data Assimilation Scheme: A Case Study (HiWATER-MUSOEXE)

A weak-constraint variational data assimilation (WC-VDA) scheme was developed to estimate turbulent heat fluxes by assimilating sequences of land surface temperature measurements. In contrast to the commonly used strong-constraint VDA system, the WC-VDA approach accounts for the effects of structural and model errors and generates better results. This is achieved by adding a model error term (ω) to the surface energy balance equation. The WC-VDA model was tested at two sites with very distinct hydrological and vegetated conditions: the Daman site (a wet site located in an oasis area and covered by seeded corn) and the Huazhaizi site (a dry site located in a desert area and covered by sparse grass). The two sites represent typical desert-oasis landscapes in the middle reaches of the Heihe River Basin, northwestern China. The results proved that the WC-VDA method performed well over very dry and wet conditions, and the estimated sensible and latent heat fluxes agree well with eddy covariance measurements.