The interplay of Arctic surface fluxes, stratocumulus clouds, and cloud-driven mixed layers

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Description

In recent years, Arctic stratiform clouds have been shown to form and persist over long periods via a complex web of interactions and feedbacks within the climate system. Doppler measurements from ground-based remote sensors have helped to elucidate the dynamical structure of these clouds, wherein radiative cooling in the cloud layer itself drives turbulent mixing within and below the cloud. This so-called cloud-driven mixed layer can have important implications for the cloud layer related to local-scale energy and moisture feedbacks that help to maintain the cloud in the face of dissipative processes. One key source of energy and moisture, as well as aerosols, for low-level Arctic clouds can be the surface, which seasonally consists of open water, moist or dry tundra, sea-ice, snow, and various combinations of these. The degree to which the cloud-driven mixed layer interacts with the surface and atmospheric boundary layer has implications both for sustaining the cloud itself and for determining the impact of the cloud on the surface energy budget. Moreover, these interactions are likely to vary by season. This study draws linkages between these cloud and surface processes using two groups of derived parameters at the North Slope of Alaska site. One is a product that characterizes the cloud properties including microphysics, turbulence, and the cloud-driven mixed layer. This product is used to assess the coupling state of the cloud system with the surface and the effect that the clouds have on atmospheric radiation. The second product assembles important terms in the surface energy budget, including both radiative and turbulent heat fluxes. The relation of these various quantities under conditions when the cloud system is coupled to, and decoupled from, the surface are contrasted to examine the processes that determine the cloud-surface coupling state and its impact on the surface.