Radiative signature of absorbing aerosol - acpd-14-2403-2014.pdf

Abstract

The e ff ects of absorbing aerosols on the atmospheric radiation budget and dynam- ics over the Eastern Mediterranean region are studied using satellites and ground- based observations, and model calculations, under summer conditions. Climatology of aerosol optical depth (AOD), single scattering albedo (SSA) and size parameters 5 were analyzed using multi-year (1999–2012) observations from MODIS, MISR and AERONET. CALIOP-derived aerosol vertical distributions and their classifications are used to calculate the AOD of 4 dominant aerosol types: dust, polluted dust, polluted continental and marine aerosol over the region. The seasonal mean (June–August 2010) AODs are 0.22 ± 0.02, 0.11 ± 0.04, 0.10 ± 0.04 and 0.06 ± 0.01 for polluted dust, 10 polluted continental, dust and marine aerosol, respectively. Changes in the atmo- spheric temperature profile as a function of absorbing aerosol loading were derived for the same period using observations from the AIRS satellite. We inferred heating rates in the aerosol layer of ∼ 1.7 ± 0.8Kday − 1 between 925 and 850hPa, which is attributed to aerosol absorption of incoming solar radiation. Radiative transfer model (RTM) cal- 15 culations show significant atmospheric warming for dominant absorbing aerosol over the region. A maximum atmospheric forcing of + 16.5 ± 7.5Wm − 2 is calculated in the case of polluted dust, followed by polluted continental ( + 7.6 ± 4.4Wm − 2 ) and dust ( + 7.1 ± 4.3Wm − 2 ). RTM-derived heating rate profiles for dominant absorbing aerosol show warming of 0.1–0.9Kday − 1 in the aerosol layer ( < 3.0km altitudes), which primar- 20 ily depend on AODs of the di ff erent aerosol types. Diabatic heating due to absorbing aerosol stabilizes the lower atmosphere, which could significantly reduce the atmo- spheric ventilation. These conditions can enhance the “pollution pool” over the Eastern Mediterranean.