The model was then used to calculate H at 44 sites in Oklahoma during the daytime hours of July 1997. In general, H was much larger across western Oklahoma throughout the month. On 12 July, a strong meridional gradient in H was noted across western Oklahoma. The location of the gradient corresponded to an area of enhanced southerly winds, which would be expected due to density differences between the warmer air to the north and the cooler air to the south. The relationship between the flux gradient and the altered surface wind field implies that this technique may be able to be used to improve short-term forecasting of convection initiation. (Abstract shortened by UMI.)

In recent years, there has been a growing appreciation of the importance of land-atmosphere interactions in determining the state of the boundary layer. Recent studies have shown that small horizontal variations in surface fluxes can dictate local alterations in the wind field and in the associated convergence maxima.

Once Rn and G are calculated, their sum is partitioned into LE and H. Since there were no observations of LE at the Mesonet sites, it was decided to use the existing H observations to effectively verify both H and LE. Due to problems with the soil moisture observations at a few of the sites, data from only two Mesonet sites were available to be used as verification from July 1997. The estimates of H were unbiased and within 60 W m -2 (RMSE) at the site in western Oklahoma, while they were either too high or too low at the eastern site.

In order to begin to examine this phenomenon in more detail, a new technique has been developed to calculate the terms in the surface energy budget from meteorological observations at one level only. Using only 5-, 15-, and 30-minute Oklahoma Mesonet data as input, the model output consists of net radiation (Rn), ground heat flux (G), and latent heat flux (LE). The sensible heat flux (H) is calculated as a residual. The Rn term is calculated using observed values of downwelling shortwave radiation, original methods of estimating upwelling shortwave and downwelling longwave radiation, and a simple parameterization of upwelling longwave radiation. Values of r s at the western site were independent of time of year. It was found that rs was strongly related to vapor pressure deficit, with a weaker dependence on temperature and solar radiation. The surface resistance was independent of soil moisture except for very dry soil.