An Analysis of the Effect of Local Heat Advection on Evaporation over Wet and Dry Surface Strips

Abstract

The effect of local advection on evaporation and Bowen ratio over alternating crosswind infinite dry-warm and wet-cool surface strips (patches), by redistribution of surface heat, is analysed. The analysis shows that evaporation over the region is enhanced by local advection, as observed experimentally by other researchers. Results suggest that evaporation can be enhanced more than 10% or 20% by local advection on the area covered by patches smaller than 10tu ?d m or 5tu?d m, respectively, where tu is a unit time and ?d the mean wind velocity in the internal boundary layer. This means that the traditional first-order approximation of surface energy balance, without considering local advection, might lead to significant error for such small-scale inhomogeneity. It may, however, be applicable to large patches (?)10tu ?d m, where energy partition may then be directly approximated from area-weighted averages of properties derived from extended wet and dry surfaces, according to the patchy area fractions involved.