Impacts of cloud microphysics and surface characteristics on the Arctic cloud-atmospheric boundary layer-surface (CAS) system in observations and WRF simulations

The processes governing the interactions between the Arctic free troposphere and the surface are modulated by the clouds within and at the top of the atmospheric boundary layer, the atmospheric boundary layer, and the surface conditions (CAS), and are closely linked. Some linkages within the CAS system can be illustrated by considering the various terms of the surface energy budget and examining the effects of forcing changes in one term on the other terms. Process-oriented diagnostics of observations and model output then give insight to the individual process and the preferred states of the CAS system. Other linkages can be illustrated based on a variety of cloud-boundary layer diagnostics or cloud-surface diagnostics, such as cloud forcing. Example diagnostics will be shown to illustrate 1) the close connection between the structures, properties, and processes associated with the three components of the CAS system, 2) key responses and preferred states of the CAS system, and 3) the use of CAS-system process diagnostics for validating model output. Examples include the impacts of a) microphysical parameterization on the surface turbulent and radiative fluxes and the boundary-layer structure b) surface albedo on multiple reflections and net surface energy flux, and c) sea-ice surface heterogeneity on turbulent fluxes and boundary-layer structure. Observations and simulations from the 2004 Mixed-Phase Arctic Cloud Experiment (MPACE), the 1998 Surface Heat Budget of the Arctic Ocean (SHEBA), the 2008 Indirect and Semi-Direct Aerosol Campaign (ISDAC), and the 2008 Arctic Summer Cloud-Ocean Study (ASCOS) field programs are being examined and will be used as examples.