Topographic distribution of clear‐sky radiation over the Konza Prairie, Kansas

Abstract

This research analyzes the topographic distribution of clear‐sky incoming solar radiation over the tallgrass Konza Prairie, site of FIFE, the First ISLSCP (International Satellite Land Surface Climatology Program) Field Experiment. Using a two‐stream atmospheric radiation model and digital elevation grids of 25‐, 50‐, and 100‐m grid spacing, clear‐sky radiation is simulated throughout the day for three dates: December 15, March 15, and June 15. Geostatistical analysis is used to characterize the spatial and temporal variability in modeled radiation at each grid spacing. The variance and spatial autocorrelation of simulated incoming radiation depend on Sun angle and elevation grid spacing. The behavior of the variance as a function of Sun angle, optical depth, and mean terrain slope can be explained by considering direct radiation variability on a simplified terrain model of uniform albedo where slopes are equal and azimuths are distributed uniformly in all directions. For this constant‐slope model it can be shown analytically that the solar zenith angle at which variance is maximized is a function of optical depth only and is independent of elevation, slope, and aspect. Results from the two‐stream simulations support this conclusion and suggest its applicability to real terrain.