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JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 106, NO. D6, PAGES 5295–5316, 2001

Evaluation of aerosol direct radiative forcing in MIRAGE

Steven Ghan


Nels Laulainen


Richard Easter


Richard Wagener


Seth Nemesure


Elaine Chapman


Yang Zhang


Ruby Leung


Abstract

A variety of measurements have been used to evaluate the treatment of aerosol radiative properties and radiative impacts of aerosols simulated by the Model for Integrated Research on Atmospheric Global Exchange (MIRAGE). The treatment of water uptake in MIRAGE agrees with laboratory measurements, and the growth of aerosol extinction with relative humidity in MIRAGE simulations agrees with field measurements. The simulated frequency of relative humidity near 100% is about twice that of analyzed relative humidity. When the analyzed relative humidity is used to calculate aerosol water uptake in MIRAGE, the simulated aerosol optical depth agrees with most surface measurements after cloudy conditions are filtered out and differences between model and station elevations are accounted for, but simulated optical depths are too low over Brazil and central Canada. Simulated optical depths are mostly within a factor of 2 of satellite estimates, but are too high off the east coasts of the United States and China and too low off the coast of West Africa and in the Arabian Sea. The simulated single-scatter albedo is consistent with surface measurements. MIRAGE correctly simulates a larger Ångström exponent near regions with emissions of submicron particles and aerosol precursor gases, and a smaller exponent near regions with emissions of coarse particles. The simulated sensitivity of radiative forcing to aerosol optical depth is consistent with estimates from measurements. The simulated direct forcing is within the uncertainty of estimates from measurements in the North Atlantic.

Received 28 October 1999; accepted 9 August 2000.

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Citation: Ghan, S., N. Laulainen, R. Easter, R. Wagener, S. Nemesure, E. Chapman, Y. Zhang, and R. Leung (2001), Evaluation of aerosol direct radiative forcing in MIRAGE, J. Geophys. Res., 106(D6), 5295–5316.