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Redemann, J., Russell, P.B, Bergstrom, R.W., (2004). Aerosol-induced radiative flux changes in the Pacific Basin troposphere. Eos Trans. AGU, 85(47), Fall Meet. Suppl. 2004, Abstract # A11C-0080

In April and May 2001, the Aerosol Characterization Experiment - Asia (ACE-Asia) was conducted to investigate the aerosols of the Pacific Basin troposphere and their potential impact on climate. One of the goals of ACE-Asia was to assess the regional direct aerosol radiative forcing by combining the results from suborbital aerosol measurements with satellite derived aerosol parameters, thereby putting the regional intensive observations into a larger scale context. One methodology to calculate the direct aerosol radiative forcing is to use the suborbital measurements of aerosol properties to devise a parameterization between column aerosol optical depth and direct aerosol radiative forcing, which can then be applied to satellite-derived maps of aerosol optical depth (AOD). The uncertainties in this method stem from the uncertainty in the accuracy and representativeness of the suborbital and spaceborne measurements of aerosol parameters. Using previously published aerosol column closure studies, we have developed a mean model for the vertical structure of aerosol properties in the Asian region during spring of 2001. This model includes the vertical structure of the aerosol single scattering albedo, as well as the wavelength dependence and absolute magnitude of aerosol extinction. The model reflects the predominance of pollution-type particles in the lowest 3 km of the atmosphere and the occurrence of large mineral dust particles at altitudes between 4 and 8 km. At a latitude of 35N, the model yields an instantaneous shortwave aerosol forcing of -30 Wm$^{-2}$ per unit aerosol optical depth at the top of the atmosphere and 65 Wm$^{-2}$ at the surface. In the first part of this paper, we will examine the importance of the various assumption used in this model for the parameterization between aerosol optical depth and aerosol radiative forcing. In the second part of our paper we investigate the consistency between aerosol optical depth fields derived using SeaWiFS, MODIS and MISR. We will review the relevant AOD validation results published to date and we will compare the monthly mean aerosol optical depth derived by these sensors for April 2001 in the latitude region between 25 and 55N and the longitude region between 130W and 130E. A preliminary analysis shows interesting features such as generally lower AOD values in the SeaWiFS retrievals and a stronger longitudinal gradient in MODIS derived AODs across the Pacific Basin when compared to the other two sensors. We will discuss the comparability of these measurements based on the level of coincidence between the three sets of observations, and we will investigate the representativeness of sparse aerosol observation in a generally cloud-dominated environment.

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Updated: 14-Jan-2005