C02: Interactions of snow on sea ice with atmospheric constituents including black carbon
PIs: Rüdiger Gerdes, André Ehrlich
Providing the existing trend of summer sea ice decline continues, the Arctic Ocean may become more accessible for shipping and the exploration of the Arctic’s potentially vast resources. The potential increase of marine activity in the Arctic would lead consequently to increasing local emissions of aerosols and Black Carbon (BC) with feedback to the atmospheric radiation field (surface cooling) and the sea ice/snow surface albedo (surface warming). Both effects may significantly affect Arctic Amplification by their potential influence on the surface energy budget, sea ice thickness and content. About 40% of the Arctic Amplification was attributed to the surface albedo feedback associated with melting snow and ice. Since sea ice is covered with snow most of the year, snow surface properties are important drivers of the surface energy balance, but can be substantially changed due to particle deposition from the atmosphere, as snow is known as efficient integrator of BC. Atmospheric BC itself is known to warm the aerosol layers and cool the surface. The competition between both effects is still unclear.
However, concurrent observations of atmospheric BC, and BC in snow and surface properties are rare. Hence, this project will combine airborne and ground–based observations of aerosols and BC concentrations and snow optical properties to investigate their feedback mechanisms in Arctic regions. In–situ measurements of atmospheric BC (ground–based and airborne) along with sampling of BC in snow and remote sensing observations of snow properties will be merged.
The first goal of the project is to characterize the temporal variability, horizontal and vertical distributionof BC in the atmosphere and concentrations of BC in snow. Trajectory calculations will be used to relate BC concentrations to either long–range transport of anthropogenic and natural aerosol or local emitted anthropogenic aerosol. Simultaneously, snow optical properties such as spectral albedo and bidirectional reflectance distribution function (BRDF) will be derived from ground–based and airborne observations.
Snow albedo will be analysed in dependence of BC concentrations, snow grain size, surface roughness and the variability of snow and sea ice thickness. The correlation between snow albedo changes and absorptive properties of BC will be evaluated. To fill the gap in the understanding of connections between the observed albedo changes and the distribution of aerosols and BC within the Arctic Atmospheric Boundary Layer (ABL), we aim to quantify deposition rates (wet and dry) of aerosols as well as source regions and physical/chemical state of the observed BC–containing aerosol. Differences of surface optical properties and changes of the surface radiation budget for aerosols originating from long–range transport of anthropogenic and natural aerosol and local emitted anthropogenic aerosol will be analysed.
Hypothesis: Solar energy absorbed by BC–containing aerosol particles leads to a warming of the near–surface air when locally produced/emitted constituents reside at low altitudes and are partly deposited onto the snow surface. Contrarily, long–range transport of BC into the Arctic, remaining in higher atmosphere layers, will lead to a cooling of the surface.
Role within (AC)³
Prof. Dr. Rüdiger Gerdes
Alfred-Wegener-Institute Helmholtz Center for Polar and Marine Research (AWI)
Dr. Cornelia Köberle
Alfred-Wegener-Insitute Helmholtz Center for Polar and Marine Research (AWI)
Ehrlich, A., Bierwirth, E., Istomina, L., and Wendisch, M., 2017: Comined retrieval of Arctic liquid water cloud and surface snow properties using airborne spectral solar remote sensing, Atmos. Meas. Tech., 10, 3215-3230, doi:10.5194/amt-10-3215-2017.