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

Abstract

Abstract. 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 atmospheric and snow radiative transfer simulations were performed 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 interest is the remote sea-ice-covered Arctic Ocean in the vicinity 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 +0.2 W m−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 conditions was embedded in the surface snow layer. The total net surface radiative forcing combining the effects of BC embedded in the atmosphere and in the snow layer strongly depends 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 atmospheric heating rate by water vapor or clouds is 1 to 2 orders of magnitude larger than that by atmospheric BC. Similarly, 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.

Arctic black carbon during PAMARCMiP 2018 and previous aircraft experiments in spring

“…The Polar Airborne Measurements and Arctic Regional Climate Model simulation Project (PAMARCMiP) 2018 aircraft-based field experiment was carried out around the northern Greenland Sea (Fram Strait) from 23 March to 4 April 2018 using Station Nord (81.6 • N, 16.7 • W) as the operation base (Herber et al, 2012(Herber et al, , 2019Donth et al, 2020;Koike et al, 2021), as part of the ArctiC Amplification: Climate Relevant Atmospheric and SurfaCe Processes, and Feedback Mechanisms or (AC) 3 project (Wendisch et al, 2017). In this paper, we report vertical profiles of BC mass concentrations, size distributions, and mixing states measured using a single-particle soot photometer from The University of Tokyo (Yoshida et al, 2020).…”

Assessment of the combined radiative effects of black carbon in the atmosphere and snowpack in the Northern Hemisphere constrained by surface observations

“…8,17,18 For example, Hansen and Nazarenko 8 provided a plausible snow albedo forcing estimate of +0.3 W m −2 (TOA) for the Northern Hemisphere (NH), whereas Flanner et al 17 reported a global mean annual BC/snow-surface RE of 0.007–0.12 W m −2 , which is considerably lower than estimates (5–10 W m −2 ) for Northern China reported by Zhao et al 18 Although the atmospheric BC-DRF and BC snow albedo elements have been investigated separately in these previous studies, to date, little attention has been paid to the total radiative effect of BC in both the atmosphere and snow cover concurrently. 19…”

“…8,17,18 For example, Hansen and Nazarenko 8 provided a plausible snow albedo forcing estimate of +0.3 W m À2 (TOA) for the Northern Hemisphere (NH), whereas Flanner et al 17 reported a global mean annual BC/ snow-surface RE of 0.007-0.12 W m À2 , which is considerably lower than estimates (5-10 W m À2 ) for Northern China reported by Zhao et al 18 Although the atmospheric BC-DRF and BC snow albedo elements have been investigated separately in these previous studies, to date, little attention has been paid to the total radiative effect of BC in both the atmosphere and snow cover concurrently. 19 Existing uncertainties in the BC-RE are relatively large, owing to external factors including the surface albedo, water vapor, and, most notably, the presence of clouds and the vertical distribution of BC. [19][20][21] For instance, Haywood and Shine 22 revealed that the presence of highly reective clouds beneath BC aerosol layers can dramatically enhance the overall RE of the atmospheric BC.…”

“…19 Existing uncertainties in the BC-RE are relatively large, owing to external factors including the surface albedo, water vapor, and, most notably, the presence of clouds and the vertical distribution of BC. [19][20][21] For instance, Haywood and Shine 22 revealed that the presence of highly reective clouds beneath BC aerosol layers can dramatically enhance the overall RE of the atmospheric BC. Similarly, Liao and Seinfeld 23 demonstrated that a cloud layer embedded within a broad BC aerosol layer amplies the magnitude of the RE and that this effect inten-sies with increasing cloud thickness.…”

Measurements and Modeling of Optical-Equivalent Snow Grain Sizes under Arctic Low-Sun Conditions

“…In reality, the parameters determining the albedo of snow-covered surfaces are manifold, such as the solar zenith angle (SZA), cloudiness, snow impurities, surface roughness, snow grain size and shape [10][11][12][13][14][15][16][17][18]. E.g., Donth et al [19] quantified the effect of black carbon (BC) impurities, cloudiness, and snow grain size on the broadband snow surface albedo (α bb ). They identified a minor BC effect (∆α bb = 0.01 for a reasonable range of BC mass concentration in snow), but major effects due to cloudiness (∆α bb up to 0.12 for aged snow) and snow grain size (∆α bb = 0.07 for particles of fresh and aged snow).…”