A Technique for Global Monitoring of Net Solar Irradiance at the Ocean Surface. Part I: Model

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  • 1 Scripps Institution of Oceanography, University of California, San Diego, La Jolla, California
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Abstract

An algorithm based on radiative transfer theory is presented to generate the first accurate, long-term (84- month) climatology of net surface solar irradiance over the global oceans from Nimbus-7 earth radiation budget (ERB) wide-field-of-view planetary-albedo data. Net surface solar irradiance is computed as the difference between the top-of-atmosphere incident solar in-irradiance (known) and the sum of the solar irradiance reflected back to space by the earth-atmosphere system (observed) and the solar irradiance absorbed by atmospheric constituents (modeled). Apart from planetary albedo and sun zenith angle, the most important parameters governing net surface solar irradiance variability, the model input parameters (water vapor and ozone amounts, cloud absorptance, aerosol type, and surface visibility), are fixed at their climatological values. It is shown that the effects of clouds and clear-atmosphere constituents can be decoupled on a monthly time scale, which makes it possible to directly apply the algorithm with monthly averages of ERB planetary-albedo data. Compared theoretically with the algorithm of Gautier et al., the present algorithm yields higher solar irradiance values in clear and thin cloud conditions and lower values in thick cloud conditions. The agreement, however, remains within 10–20 W m−2.

Abstract

An algorithm based on radiative transfer theory is presented to generate the first accurate, long-term (84- month) climatology of net surface solar irradiance over the global oceans from Nimbus-7 earth radiation budget (ERB) wide-field-of-view planetary-albedo data. Net surface solar irradiance is computed as the difference between the top-of-atmosphere incident solar in-irradiance (known) and the sum of the solar irradiance reflected back to space by the earth-atmosphere system (observed) and the solar irradiance absorbed by atmospheric constituents (modeled). Apart from planetary albedo and sun zenith angle, the most important parameters governing net surface solar irradiance variability, the model input parameters (water vapor and ozone amounts, cloud absorptance, aerosol type, and surface visibility), are fixed at their climatological values. It is shown that the effects of clouds and clear-atmosphere constituents can be decoupled on a monthly time scale, which makes it possible to directly apply the algorithm with monthly averages of ERB planetary-albedo data. Compared theoretically with the algorithm of Gautier et al., the present algorithm yields higher solar irradiance values in clear and thin cloud conditions and lower values in thick cloud conditions. The agreement, however, remains within 10–20 W m−2.

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