A First-Order Assessment of Direct Aerosol Radiative Effect in the Southeastern U.S. Using over a Decade Long Multisatellite Data Record

Abstract

Aerosols comprise a critical portion of the Earth's climate due to their radiative properties. More emphasis is now being placed upon understanding radiative effects of aerosols on a regional scale. The primary goal of this research is to estimate the aerosol direct radiative effect (DRE) and examine its dynamical nature in the Southeastern U.S. based on satellite data obtained from the moderate-resolution imaging spectroradiometer (MODIS) and multi-angle imaging spectroradiometer (MISR) instruments onboard the Terra satellite from 2000 to 2011. This 12-year analysis utilizes satellite measurements of aerosol optical depth (AOD), surface albedo, cloud fraction, and single-scattering albedo over the Southeastern U.S. as inputs to a first-order approximation of regional top of the atmosphere DRE. Results indicate that AOD is the primary driver of DRE estimates, with surface albedo and single-scattering albedo having some appreciable effects as well. During the cooler months, the minima (less negative) of DRE vary between -6 and -3 W/m2, and during the warmer months, there is more variation with DRE maxima varying between -24 and -12.6 W/m2 for MODIS and -22.5 and -11 W/m2 for MISR. Yet if we take an average of the monthly DRE over time (12 years), we estimate Δ F = -7.57 W/m2 for MODIS and Δ F = -5.72 W/m2 for MISR. Regional assessments of the DRE show that background levels of DRE are similar to the 12-year average of satellite-based DRE, with urbanized areas having increased levels of DRE compared to background conditions. Over the study period, DRE has a positive trend (becoming less negative), which implies that the region could lose this protective top of the atmosphere cooling with the advancement of climate change impacting the biogenic emissions of aerosols.