COMPARISON OF THE EVAPORATIVE FRACTION AND THE PRIESTLEY-TAYLOR-ALPHAFOR PARAMETERIZING DAYTIME EVAPORATION

This is a comparison between the evaporative fraction EF, which is the surface latent heat flux divided by the available energy, and the Pri estley-Taylor parameter alpha. It is shown for the First International Satellite Land Surface Climatology Project (ISLSCP) Field Experiment (FIFE) that the hypothesis that the midday values of EF and a: are the same as their daytime average values must be rejected at the 0.05 lev el of significance. However, correlations are high between the midday and daytime average values for both variables. Daytime average latent heat fluxes were estimated based on midday values of EF and alpha alon g with daytime average available energy and equilibrium evaporation. I n addition, the relationships between soil moisture and the midday and daytime average values of EF and alpha were considered, along with th e utility of these relationships in determining daytime total evaporat ion. The conclusion is that at FIFE formulations based on EF are essen tially interchangeable with corresponding formulations based on alpha.