Publications

Korras-Carraca, MB; Pappas, V; Hatzianastassiou, N; Vardavas, I; Matsoukas, C (2019). Global vertically resolved aerosol direct radiation effect from three years of CALIOP data using the FORTH radiation transfer model. ATMOSPHERIC RESEARCH, 224, 138-156.

Abstract
We use global aerosol optical depth data from CALIOP with a radiation transfer model to investigate the aerosol direct radiative effect (DRE) and its sensitivity to the aerosol vertical resolution. Our study spans three years (2007-2009) and uses cloud data from ISCCP D2 to take into account cloud-aerosol radiative interactions on a monthly 2.5 degrees x 2.5 degrees resolution. The three-year global average all-sky aerosol DRE at the surface, in the atmosphere, and at the top of atmosphere (TOA) was calculated to be -4.23, 2.40, and - 1.83 Wm(-2), respectively. As expected, local DREs and atmospheric heating rates are shown to vary significantly. The largest magnitudes of the DREs are observed in regions with heavy aerosol load consisting of both natural and anthropogenic particles, such as desert dust, biomass burning and urban/industrial pollution. At TOA the aerosol effect is generally of negative sign, though a planetary heating effect is found in regions characterized by both absorbing aerosol and large surface albedo, such as deserts. Clouds scatter and absorb solar radiation, which generally decreases the aerosol cooling at the surface and the aerosol warming in the atmosphere. However, the latter effect is attenuated due to the enhancement of radiation absorption by the above-cloud aerosols. As a result, clouds decrease the aerosol TOA (planetary) cooling, and sometimes even cause aerosol warming (e.g. over the tropical South Atlantic). The cloud effect on the aerosol DRE depends strongly on the aerosol optical properties and the aerosol load fraction above low clouds. Comparing the effect of the observed aerosol vertical profile against an exponentially decreasing profile, we find a small sensitivity for the surface DRE, but larger for the atmospheric column and the top of the atmosphere. Under all-sky conditions, when continental aerosols are lifted higher in the atmosphere, the outgoing shortwave radiation at TOA decreases, due to the increase of UV and visible radiation absorption by particles while higher oceanic aerosols generally increase the outgoing shortwave radiation through more efficient backscatter and decrease of the NIR radiation absorption by atmospheric gases below aerosol particles.

DOI:
10.1016/j.atmosres.2019.03.024

ISSN:
0169-8095