Analysis of dust and anthropogenic aerosol forcing over the global oceans from Terra

Using 6 years of combined Terra CERES radiance and MODIS aerosol data, we compute the global, ocean-only, shortwave (SW) and longwave (LW) radiative effect (SWRE, LWRE) for dust and anthropogenic aerosols. We will first use MODIS derived aerosol size properties to broadly classify aerosols into either sea salt, dust, or anthropogenic categories. We then use the quasi-linear relationship between SW flux and aerosol optical thickness (AOT) to derive a clear sky, aerosol free SW background. Since this relationship does not exist for LW, only pixels with low AOT are used to derive an aerosol-free LW background. Total aerosol SWRE and LWRE are calculated by subtracting the observed flux values from the clear sky background. SWRE and LWRE from individual aerosol components are then calculated using applying the ratio of the AOT from an individual aerosol species to the total AOT on a pixel-by-pixel basis. The uncertainties in the aerosol classifications will be applied to the individual SWRE and LWRE statistics to determine the overall uncertainty of individual aerosol radiative effect and the significance of differences in this effect from one aerosol species to another. Preliminary results indicate that globally averaged values for individual aerosol SWRE may not be representative of their true importance. Averaged over the entire ocean-only global, SWRE from anthropogenic sources exceeds dust SWRE by a factor of nearly 2. However, dust and anthropogenic SWRE are often maximized in certain regions during certain times of the year, are negligible elsewhere. As a result, we quantify SWRE on smaller regional and temporal scales to better examine the relationship between each. Similarly, LWRE does not appear to be significant on a globally averaged basis, but can offset SWRE up to 20 percent in high AOT, dust regions.