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Robert Frouin, Catherine Gautier, Kristina B. Katsaros, and Richard J. Lind

Abstract

Surface insulation data collected during the Mixed Layer Dynamiccs Experiment are used to intercompare the satellite technique of Gautier et al. (1980) and five commonly referenced empirical formulas for estimating daily insulation over the oceans. The results demonstrate the superiority of the satellite technique, which exhibits a 0.97 correlation coefficient, a 12.0 W m M−2 error of estimate, and a −4.9 W m−2 bias error, and which is also able to account for water vapor, ozone, and dust amount variations in the atmosphere and monitor quasi-instantaneously vast extents of ocean. Among the empirical formulas, Mosby's (1936) yields the best predictions with a 0.84 correlation coefficient, a 19.1 W m−2 standard error of estimate, and a 3.4 W m−2 bias. Kimball'(1928) and Reed's (1977) formulas however, perform nearly as well. The largest biases are obtained with Berliand's (1960) and Laevastu' (1960) formulas, which overestimate insolation by 15.2 and 24.5 W m−2, respectively. It is suggested the empirical formulas, even though established from visual cloud cover observations, would provide useful insolation estimates if employed with satellite-derived cloud cover.

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Mamoudou B. Ba, Robert Frouin, Sharon E. Nicholson, and Gérard Dedieu

Abstract

Downward surface solar irradiance and albedo of the African continent are estimated from Meteosat B2 data at 30-km spatial resolution. The algorithm, based on Dedieu et al.’s approach, is verified against other satellite estimates and ground-based measurements. In the computations, the International Satellite Cloud Climatology Project’s (ISCCP) radiometric calibration is adjusted using the Libyan desert as a reference target of constant reflectance properties. Surface albedo is corrected for sun zenith angle effects, allowing for better detection of seasonal changes due to the vegetation cycle. The estimates obtained with Meteosat B2 data agree generally well with other satellite estimates, although biases of 20 W m−2 (downward surface solar irradiance) and 0.15 (surface albedo) are obtained in some cases. There is evidence, from comparisons with surface measurements, that the clear-sky downward surface solar irradiance is overestimated over semiarid regions of Africa because of uncertainties in aerosol characteristics. In the Sahel region, where spatial albedo gradients are high, it is advantageous to use 30-km Meteosat B2 products instead of the current, coarser 280-km-resolution ISCCP products.

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Akiko Higurashi, Teruyuki Nakajima, Brent N. Holben, Alexander Smirnov, Robert Frouin, and Bernadette Chatenet

Abstract

Global distributions of the aerosol optical thickness and Ångström exponent are estimated from National Oceanic and Atmospheric Administration Advanced Very High Resolution Radiometer channel-1 and -2 radiances for four months in 1990. Global distributions of those Ångström parameters are consistent with present knowledge on the distributions of desert-derived, biomass-burning, and anthropogenic pollutant aerosols obtained by ground-based and aircraft measurements. Especially, it is found that thin anthropogenic aerosols can be identified with large Ångström exponent values around the east coast of North America, Europe, and eastern Asia. Satellite-retrieved values of Ångström parameters are further compared with measured spectral optical thickness obtained by the National Aeronautics and Space Administration Aerosol Robotic Network sky radiometer network.

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Arthur J. Miller, Michael A. Alexander, George J. Boer, Fei Chai, Ken Denman, David J. Erickson III, Robert Frouin, Albert J. Gabric, Edward A. Laws, Marlon R. Lewis, Zhengyu Liu, Ragu Murtugudde, Shoichiro Nakamoto, Douglas J. Neilson, Joel R. Norris, J. Carter Ohlmann, R. Ian Perry, Niklas Schneider, Karen M. Shell, and Axel Timmermann
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