The Arctic Cloud-Atmospheric Boundary Layer-Surface (CAS) System: Process Interactions and Sensitivities in Observations and 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 from a variety of Arctic data sets and sites 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.