Assessing the Spatial Scales of Surface-Atmosphere Interactions

The coupled large-eddy simulation-remote sensing approach is used to investigate the influence of surface length scales on the atmospheric boundary layer. We focus on the interactions between remotely sensed surface conditions (NDVI and radiometric temperature) and large-eddy simulation derived scalar and flux properties in the lower atmosphere. Data available from the SMEX'02 field campaign is utilized to investigate two contrasting days. The first day, July 1, was representative of relatively high heterogeneity in which the remotely sensed data is characterized by high spatial variance in both the NDVI and temperature fields. The second day, July 8, was following rapid crop growth and a rain event which both acted to decrease the spatial variability. This allows investigation of both the influence that the length scales of surface variability has on the lower atmosphere, as well as the effect of the magnitude of contrast in the surface features. Wavelet co-spectra are used to investigate the influence that the spatial length scales calculated from the remotely sensed data has on the persistence of spatial variance into the lower atmosphere. Implications concerning the role of the atmosphere in 'filtering' the surface variability and the calculation of areal averaged fluxes over heterogeneous terrain will be discussed.