Global pattern of potential evaporation calculated from the Penman-Monteith equation using satellite and assimilated data

Potential evaporation has been used to provide a reference level for actual evaporation in many studies of land surface heat and water balance. While Thornthwaiteʹs formula has been used in many regional and global studies, the Penman-Monteith equation has been shown to provide an accurate estimate of this evaporation. Thus, global pattern of potential evaporation has been caleulated from the Penman-Monteith equation using satellite and assimilated data for a 24-month period, January 1987 to December 1988. The albedo and surface resistance have been taken to be, respectively, 0.23 and 70 s m−1, which are considered to be representative values for actively growing well-watered grass covering the ground. Satellite observations have been used to obtain spatially representative monthly values of solar radiation, fractional cloud cover, air temperature, and vapor pressure, while aerodynamic resistance has been calculated using four-dimensional data assimilation results. Meteorologic data derived from satellite observations are compared with the surface (station) measurements. The calculated potential evaporation values are compared with lysimeter observations for evaporation from well-watered grass at 35 widely distributed locations in different climatic regimes to quantify the accuracy of the calculated values. The evaporation values have been archived for distribution. http://hydro4.gsfc.nasa.gov/STAFF/ChoudhuryBj/pmpotevap.html.