EVALUATION OF THE EVAPORATIVE FRACTION FOR PARAMETERIZATION OF THE SURFACE, ENERGY-BALANCE

The evaporative fraction is a ratio of latent heat flux to the sum of latent and sensible heat fluxes. It has been used to characterize the energy partition over land surfaces and has potential for inferring daily energy balance information based on midday remote sensing measurements. The HAPEX-MOBILHY program SAMER system provided surface energy balance data over a range of agricultural crops and soil types. Data from this large-scale field experiment was analyzed to study the behavior and daylight stability of the evaporative fraction in both ideal and general meteorological conditions. Strong linear relations were found to exist between the midday evaporative fraction and the daylight evaporative fraction. Statistical tests, however, rejected the hypothesis that the two quantities were equal. Relations between the evaporative fraction and surface soil moisture as well as soil moisture over the complete root zone were explored, but no correlation was identified.