Regional Diurnal Albedo Climatology and Diurnal Time Extrapolation of Reflected Solar Flux Observations: Application to the ScaRaB Record

Abstract

A regional (2.5° ? 2.5° resolved) diurnal (hourly) albedo climatology for low and midlatitudes is derived for each month from the 5?-yr narrow-field-of-view data record obtained from the Earth Radiation Budget Satellite (ERBS). It is used in a quasi-operational diurnal interpolation/extrapolation procedure (DIEP) to calculate regional monthly means of the reflected shortwave radiation flux (RSR) from instantaneous albedo observations. This climatological approach (CDIEP) replaces the questionable assumption of diurnally constant cloud conditions made in the conventional DIEP by assuming a diurnal variation of cloudiness corresponding to the mean long-term diurnal variation of the planetary albedo. Validation of CDIEP, using the three-satellite Earth Radiation Budget Experiment (ERBE) data for December of 1986, indicates that on regional scales monthly time sampling errors for single satellite products are generally reduced but not completely removed in comparison with the currently applied diurnal model (EDIEP). On a global scale, rms errors are reduced by 16% and 28% for ERBE NOAA-10 and NOAA-9 monthly mean RSR, respectively. The efficiency of CDIEP is satisfactory by accounting for coherent diurnal variations of cloudiness, if present, and by reproducing the results obtained by EDIEP elsewhere. Applying CDIEP to the full-year record of ScaRaB-Meteor ERB measurements enables the analysis of its impact with regard to the varying local observation time of each month. The standard deviation between regional monthly means of the RSR calculated by CDIEP and EDIEP varies between less than 2 W m?2 and about 4 W m?2 for high-noon and near-terminator time sampling conditions, respectively. On regional scales, time sampling errors with a 3½-month period, induced by the orbit?s precession, can be reduced, in particular for marine areas characterized by persistent stratocumulus, where the amplitude often exceeds 10 W m?2.