Submitted to: American Geophysical Union
Publication Type: Abstract Only
Publication Acceptance Date: October 5, 2007
Publication Date: December 10, 2008
Citation: Bertoldi, G., Kustas, W.P., Albertson, J.D. 2007. Using large eddy simulation to evaluate source area contributions from aircraft flux measurements over heterogeneous land cover [abstract]. EOS Transactions, American Geophysical Union, Fall Meeting Suppliments. 88(52):H24B-03.
The estimation of spatial patterns in surface fluxes from aircraft observations poses several challenges in presence of heterogeneous land cover, related to the effects of turbulence on scalar transport, the different behavior of passive (moisture) versus active (temperature) scalars. This in turn has significant implications associated with uncertainties in the source area/flux footprint estimation and comparison with spatial flux fields produced by land surface models. This may contribute to increased. errors in both modeled and measured sensible (H) and latent (LE) heat fluxes In fact, current footprint models do not adequately consider the role of atmospheric boundary layer (ABL) dynamics affecting source area contributions from aircraft-based flux measurements. This study provides some insight into the ABL processes that are likely to affect footprint/source-area contribution dynamics of H and LE to surface layer turbulent flux measurements from airborne sensors via Large Eddy Simulation (LES) of the land-atmosphere dynamics. We focus on 30 m-level aircraft flux observations collected over a study site in central Oklahoma during the SGP97 experiment. Aircraft-model comparisons provide observational evidence of a difference in source area for turbulent H and LE fluxes. The LES correctly simulates the observed stationary eddies from updrafts originated from local surface discontinuities, and hence provides physical evidence of the observed anomalies in footprint estimation required for matching modeled and measured H and LE. A conceptual model for the interpretation of the aircraft observation will be described. The dependency of the LE/H partitioning and of their spatial correlation with respect to the filtering scale, the scale of the surface heterogeneity, and the distance from the ground will also be discussed. The results provide useful information for developing footprint models that consider differing source area/footprint contributions between active (H) and passive (LE) scalars by considering land surface heterogeneity and ABL dynamics.