To study spatial variability of the atmospheric boundary layer in response to soil moisture variation, over 150 passes were flown over the "El Reno" track during the Southern Great Plains Hydrology Experiment by the Canadian NRC Twin Otter aircraft and the NOAA LongEZ. Using ground markers, the data for each pass are aligned and stretched according to the aircraft ground speed, allowing accurate compositing of sequential aircraft passes. The 12 km track consists of active grazing land with large NDVI in the eastern third, senescent winter wheat or harvested fields with low NDVI in the central part
of the track and hilly grazing land in the far west with high NDVI.
The eastern green region leads to larger evapotranspiration and less sensible heat flux on many of the days but not all of the days. The failure of the spatial variation of vegetation to impact the atmosphere on some days appears to be related to strong winds or substantial recent precipitation in which case the direct evaporation from the soil in the central region is almost as large as the
evapotranspiration in the east. In the latter case, the carbon dioxide flux shows greater sensitivity to the spatial variation of vegetation and allows qualitative inference of the fraction of the total evapotranspiration due to direct soil evaporation. The surface heterogeneity exerts the biggest influence with weaker winds and when the top layer of soil has dried. The spatial variation of the moisture and heat flux is greatest during the morning boundary layer transition when the boundary layer development is more advanced over drier areas.