Analysis of daytime fair-weather aircraft and surface-flux tower data from the May-June 2002 International H2O Project (IHOP_2002) and the April-May 1997 Cooperative Atmosphere Surface Exchange Study (CASES-97) are used to document the role of vegetation, soil moisture, and terrain in determining the horizontal variability of latent heat LE and sensible heat H along a 46-km flight track in SE Kansas. Combining the two experiments clearly reveals the strong influence of vegetation cover, with H maxima over dormant vegetation, and, to a lesser extent, LE maxima over green vegetation. Other effects of vegetation and the impact of soil moisture emerge through examining the slope Delta_xy_LE/Delta_xy_H for the best-fit line to plots of LE as a function of H for a given time interval. Based on the surface energy balance, H+LE = Rnet ­ Gsfc, where Rnet is the net radiation and Gsfc the flux into the soil, Rnet ­ Gsfc ~constant implies an approximately ­1 slope. Right after rainfall, H and LE vary too little horizontally to define a slope. After sufficient drying to produce enough horizontal variation to define a slope, a steep (~-2) slope emerges. The slope becomes shallower and better defined with time, as H and LE horizontal variability increases. This trend is based on land-surface model (LSM) runs and observations collected under nearly-clear skies and ample moisture; the vegetation is unstressed for both experiments. The slope remains fairly constant through the day for CASES-97, but steepens during the afternoon for IHOP_2002 due to LE peaking