Analysis of Broadband Solar Radiation and Albedo over the Ocean Surface at COVE

Zhonghai Jin Analytical Services & Materials, Inc., Hampton, Virginia

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Thomas P. Charlock Atmospheric Sciences Division, NASA Langley Research Center, Hampton, Virginia

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Ken Rutledge Analytical Services & Materials, Inc., Hampton, Virginia

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Abstract

A coupled atmosphere–ocean radiative transfer model has been applied to analyze a full year of broadband solar irradiances (up and down) measured over an ocean site 25 km east of the coast of Virginia in the Atlantic. The coupled model treats absorption and scattering by layers for both the atmosphere and the ocean explicitly and consistently. Key input parameters for the model (aerosol optical depth, wind speed, and total precipitable water) are also from in situ measurements. Having more observations to specify properties of the atmosphere than of the ocean, better model–observation agreement is obtained for the downwelling irradiance, which depends primarily on the atmospheric optical properties, than for the upwelling irradiance, which depends heavily on the ocean optical properties. The mean model–observation differences for the ocean surface albedo are generally less than 0.01. However, the modeled upwelling irradiances and albedo over the ocean surface are mostly less than the observations for all seasons, implying that more scattering in the ocean needs to be included in the model calculations. Sensitivity tests indicate that the uncertainties in aerosol optical properties, chlorophyll concentration, wind speed, or foams are not the primary factors for the model–observation differences in the ocean surface albedo, whereas the scattering by air bubbles and/or by suspended materials have the potential to significantly reduce or eliminate the model–observation differences in the ocean surface reflection.

Corresponding author address: Dr. Zhonghai Jin, Analytical Services and Materials, Inc., 1 Enterprise Parkway, Suite 300, Hampton, VA 23666. Email: z.jin@larc.nasa.gov

Abstract

A coupled atmosphere–ocean radiative transfer model has been applied to analyze a full year of broadband solar irradiances (up and down) measured over an ocean site 25 km east of the coast of Virginia in the Atlantic. The coupled model treats absorption and scattering by layers for both the atmosphere and the ocean explicitly and consistently. Key input parameters for the model (aerosol optical depth, wind speed, and total precipitable water) are also from in situ measurements. Having more observations to specify properties of the atmosphere than of the ocean, better model–observation agreement is obtained for the downwelling irradiance, which depends primarily on the atmospheric optical properties, than for the upwelling irradiance, which depends heavily on the ocean optical properties. The mean model–observation differences for the ocean surface albedo are generally less than 0.01. However, the modeled upwelling irradiances and albedo over the ocean surface are mostly less than the observations for all seasons, implying that more scattering in the ocean needs to be included in the model calculations. Sensitivity tests indicate that the uncertainties in aerosol optical properties, chlorophyll concentration, wind speed, or foams are not the primary factors for the model–observation differences in the ocean surface albedo, whereas the scattering by air bubbles and/or by suspended materials have the potential to significantly reduce or eliminate the model–observation differences in the ocean surface reflection.

Corresponding author address: Dr. Zhonghai Jin, Analytical Services and Materials, Inc., 1 Enterprise Parkway, Suite 300, Hampton, VA 23666. Email: z.jin@larc.nasa.gov

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