Clouds, Aerosols and Precipitation (CM-CAP)

Principal Participants:O'Neill, Duck, Hudak; Stakeholders: Servranckx, Freemantle, Garand, Gong, Strawbridge; Canadian Gov't Departments: EC, CSA; International Orgs: AERONET; HQP: 50% RA + PDF + 1 graduate student.

Rationale Understanding clouds and aerosols in the Arctic is a multi-faceted problem that links to both composition and the energetics and dynamics of the atmosphere. Aerosols are a source of Arctic pollution that largely originates from the south: because removal mechanisms are weak in the Arctic, they tend to be a long-lived indicators of background anthropogenic influence. Clouds play a fundamental radiative forcing role that is intrinsically linked to the quantity and properties of aerosols acting as cloud condensation and ice-forming nuclei. The relatively large uncertainty in the radiative forcing effects of clouds and aerosols (IPCC, 2007) is all the more critical in the Arctic where albedo feedback effects magnify climate change. This is particularly true during the polar winter when the emissive properties of clouds dominate the radiative balance.

We are participating in a transformative era in Arctic atmospheric monitoring with the advent of remote sensing innovations such as the suite of active and passive sensors on the A-train and the likely launching of geosynchronous-like Arctic missions such as the Polar Communications and Weather (PCW) satellite: these missions require a strong ground truth capability for validating retrievals and testing hypotheses at the process level. The analysis of cloud and aerosol data will requires expertise in satellite retrievals, ground-based remote sensing and Arctic-domain modeling. We will focus on the understanding of process level measurements at Eureka and other optical “super sites” located at Barrow and Ny Alesund (in collaboration with our research partners at these sites) and to extend our understanding of local dynamics to a pan-Arctic scale using satellite data and modeling. Aerosol and cloud modeling via GEM-based, polar-domain models will play an important role in terms of process - to climatology-level understanding of the ground-based and satellite data, the interpolation / extrapolation of the aerosol and cloud dynamics and the validation of model physics and meteorology. We will carry out model evaluation exercises for both bulk and per particle (extensive and intensive) properties of clouds and aerosols, both during the polar night and polar day. The process of model training is mutually beneficial to the measurement stakeholders since it permits an iterative approach to a physically consistent extrapolation/interpolation over the entire 4D Arctic domain.