Combining atmospheric and snow radiative transfer models to assess the solar radiative effects of black carbon in the Arctic

• Published in: Atmospheric Chemistry and Physics
• Main Authors: Donth, Tobias, Ehrlich, André, Jäkel, Evelyn, Heinold, Bernd, Schacht, Jacob, Herber, Andreas, Zanatta, Marco, Wendisch, Manfred
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: Copernicus Publications on behalf of the European Geosciences Union. 2020
• Subjects: Arctic; Arctic Ocean; Greenland; black carbon; Sea ice; Alaska; Spitsbergen
• Online Access: https://epic.awi.de/id/eprint/52916/; https://epic.awi.de/id/eprint/52916/1/Donth-etal-ACP-2020.pdf; http://www.atmospheric-chemistry-and-physics.net; https://hdl.handle.net/10013/epic.1a628fb1-10ba-4f54-b711-0515f764e903; https://hdl.handle.net/

The magnitude of solar radiative effects (cooling or warming) of black carbon (BC) particles embedded in the Arctic atmosphere and surface snow layer was explored on the basis of case studies. For this purpose, combined at- mospheric and snow radiative transfer simulations were per- formed for cloudless and cloudy conditions on the basis of BC mass concentrations measured in pristine early summer and more polluted early spring conditions. The area of inter- est is the remote sea-ice-covered Arctic Ocean in the vicin- ity of Spitsbergen, northern Greenland, and northern Alaska typically not affected by local pollution. To account for the radiative interactions between the black-carbon-containing snow surface layer and the atmosphere, an atmospheric and snow radiative transfer model were coupled iteratively. For pristine summer conditions (no atmospheric BC, minimum solar zenith angles of 55◦) and a representative BC particle mass concentration of 5 ng g−1 in the surface snow layer, a positive daily mean solar radiative forcing of +0.2Wm−2 was calculated for the surface radiative budget. A higher load of atmospheric BC representing early springtime conditions results in a slightly negative mean radiative forcing at the surface of about −0.05 W m−2, even when the low BC mass concentration measured in the pristine early summer condi- tions was embedded in the surface snow layer. The total net surface radiative forcing combining the effects of BC em- bedded in the atmosphere and in the snow layer strongly de- pends on the snow optical properties (snow specific surface area and snow density). For the conditions over the Arctic Ocean analyzed in the simulations, it was found that the at- mospheric heating rate by water vapor or clouds is 1 to 2 or-ders of magnitude larger than that by atmospheric BC. Sim- ilarly, the daily mean total heating rate (6 K d−1) within a snowpack due to absorption by the ice was more than 1 order of magnitude larger than that of atmospheric BC (0.2 K d−1). Also, it was shown that the cooling by atmospheric BC of the near-surface air and the warming effect by BC embedded in snow are reduced in the presence of clouds.