REGIONAL SURFACE FLUXES UNDER NONUNIFORM SOIL-MOISTURE CONDITIONS DURING DRYING

The fifth intensive field campaign of FIFE (First ISLSCP Field Experiment (International Satellite Land Surface Climatology Project)) was conducted in northeastern Kansas during late summer 1989, in order to study the dry down of a surface with prairie vegetation prior to senescence and dormancy. As precipitation became sparse and rare, the surface developed nonuniform features at the scales of the rainfall events. Nevertheless, lower boundary layer measurements used together with remotely sensed surface temperatures on the basis of Monin-Obukhov similarity allowed the estimation of the flux of sensible heat for a region with characteristic dimensions of 10(4) M. In contrast, under these conditions it was difficult to aggregate an array of local flux measurements into a true regional mean. On account of the same problem in the aggregation of local measurements of net radiation and ground heat flux, the reliability of the estimation of regional evaporation by the energy budget method was hard to assess.