Spectral and Diurnal Variations in Clear Sky Planetary Albedo

Bruce Briegleb National Center for Atmospheric Research, Boulder, CO 80307

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V. Ramanathan National Center for Atmospheric Research, Boulder, CO 80307

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Abstract

This study examines the spectral and diurnal variations in the planetary (i.e., top-of-atmosphere) clear sky albedo of the earth. The clear sky planetary albedo is calculated by a radiative transfer model which uses observed mean January and July earth properties on a global 5° × 5° grid. Our model calculations account for the regional, zonal and seasonal variations in humidity, temperature, sea ice and snow cover. In addition, seasonal and zonal variations in ozone are included. We calculate the diurnal cycle of clear sky planetary albedo in the following spectral intervals: 0.2–0.5, 0.5–0.7 and 0.7–4 μm. Model results reveal the strong wavelength dependence of planetary albedo. For all surfaces in our model, the planetary albedo decreases from morning to local noon, with the diurnal variations being particularly strong over water surfaces. We describe in detail the spectral and diurnal variations in planetary albedo over many natural surfaces, such as vegetation, snow, sea ice and ocean. The comprehensive model results presented in our study should find application in studies concerned with the estimation of potential spectral and diurnal sampling errors in satellite radiation budget measurements.

Abstract

This study examines the spectral and diurnal variations in the planetary (i.e., top-of-atmosphere) clear sky albedo of the earth. The clear sky planetary albedo is calculated by a radiative transfer model which uses observed mean January and July earth properties on a global 5° × 5° grid. Our model calculations account for the regional, zonal and seasonal variations in humidity, temperature, sea ice and snow cover. In addition, seasonal and zonal variations in ozone are included. We calculate the diurnal cycle of clear sky planetary albedo in the following spectral intervals: 0.2–0.5, 0.5–0.7 and 0.7–4 μm. Model results reveal the strong wavelength dependence of planetary albedo. For all surfaces in our model, the planetary albedo decreases from morning to local noon, with the diurnal variations being particularly strong over water surfaces. We describe in detail the spectral and diurnal variations in planetary albedo over many natural surfaces, such as vegetation, snow, sea ice and ocean. The comprehensive model results presented in our study should find application in studies concerned with the estimation of potential spectral and diurnal sampling errors in satellite radiation budget measurements.

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