ESTIMATION OF REGIONAL EVAPORATION FOR A TALLGRASS PRAIRIE FROM MEASUREMENTS OF PROPERTIES OF THE ATMOSPHERIC BOUNDARY-LAYER

Regional scale latent heat flux (LE) was estimated from rawinsonde soundings of the planetary boundary layer (PBL) over the Konza tallgrass prairie in July 1986. Two approaches were used to calculate LE: similarity theory and an algebraic solution of a conservation equation for water vapor in the PBL. Nine of the soundings were complete. However, the latter five soundings only recovered data for every sixth possible level. The results were compared with estimates made by an array of nine Bowen Ratio surface stations. Similarity theory, using vertically averaged values, produced estimates that were reasonably close to the surface values. However, the use of values at the top of the PBL resulted in large overestimation of the evaporation fluxes. When complete soundings were available, the conservation equation yielded estimates which agreed very well with surface values. The agreement was reduced for incomplete soundings. This is likely related to the sensitivity of the equation to uncertainties in the height of the inversion. Overall, the conservation equation produced estimates in closest agreement with the surface stations. The results suggest that adequate vertical resolution of measured profiles is important for proper estimation of regional surface fluxes.