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JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 111, D22210, doi:10.1029/2005JD006707, 2006

Evaluation of aerosol distribution and optical depth in the Geophysical Fluid Dynamics Laboratory coupled model CM2.1 for present climate

Paul Ginoux

NOAA Geophysical Fluid Dynamics Laboratory, Princeton, New Jersey, USA


Larry W. Horowitz

NOAA Geophysical Fluid Dynamics Laboratory, Princeton, New Jersey, USA


V. Ramaswamy

NOAA Geophysical Fluid Dynamics Laboratory, Princeton, New Jersey, USA


Igor V. Geogdzhayev

Department of Applied Physics and Applied Mathematics, Columbia University and NASA Goddard Institute for Space Studies, New York, New York, USA


Brent N. Holben

NASA Goddard Space Flight Center, Greenbelt, Maryland, USA


Georgiy Stenchikov

Department of Environmental Sciences, Rutgers–The State University of New Jersey, New Brunswick, New Jersey, USA


Xuexi Tie

National Center for Atmospheric Research, Boulder, Colorado, USA


Abstract

This study evaluates the strengths and weaknesses of aerosol distributions and optical depths that are used to force the GFDL coupled climate model CM2.1. The concentrations of sulfate, organic carbon, black carbon, and dust are simulated using the MOZART model (Horowitz, 2006), while sea-salt concentrations are obtained from a previous study by Haywood et al. (1999). These aerosol distributions and precalculated relative-humidity-dependent specific extinction are utilized in the CM2.1 radiative scheme to calculate the aerosol optical depth. Our evaluation of the mean values (1996–2000) of simulated aerosols is based on comparisons with long-term mean climatological data from ground-based and remote sensing observations as well as previous modeling studies. Overall, the predicted concentrations of aerosol are within a factor 2 of the observed values and have a tendency to be overestimated. Comparison with satellite data shows an agreement within 10% of global mean optical depth. This agreement masks regional differences of opposite signs in the optical depth. Essentially, the excessive optical depth from sulfate aerosols compensates for the underestimated contribution from organic and sea-salt aerosols. The largest discrepancies are over the northeastern United States (predicted optical depths are too high) and over biomass burning regions and southern oceans (predicted optical depths are too low). This analysis indicates that the aerosol properties are very sensitive to humidity, and major improvements could be achieved by properly taking into account their hygroscopic growth together with corresponding modifications of their optical properties.

Received 25 September 2005; accepted 16 June 2006; published 21 November 2006.

Keywords: aerosol; modeling; gcm.

Index Terms: 0305 Atmospheric Composition and Structure: Aerosols and particles (0345, 4801, 4906); 0365 Atmospheric Composition and Structure: Troposphere: composition and chemistry; 0360 Atmospheric Composition and Structure: Radiation: transmission and scattering; 0368 Atmospheric Composition and Structure: Troposphere: constituent transport and chemistry.

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Citation: Ginoux, P., L. W. Horowitz, V. Ramaswamy, I. V. Geogdzhayev, B. N. Holben, G. Stenchikov, and X. Tie (2006), Evaluation of aerosol distribution and optical depth in the Geophysical Fluid Dynamics Laboratory coupled model CM2.1 for present climate, J. Geophys. Res., 111, D22210, doi:10.1029/2005JD006707.