Arctic cloud interactions with the boundary layer and surface

Description

At Barrow, the most frequently observed clouds are those at low-levels. These typically contain supercooled liquid water, often with accompanying ice crystal precipitation. These clouds are remarkably persistent under conditions that do not, at first glance, appear to be conducive to sustaining liquid water. However, the fact that liquid water is sustained for long periods has significant ramifications for the Arctic climate system. The enhanced radiative effects of this liquid water lead to atmospheric layers of intense radiative flux divergence, which force buoyancy-driven turbulent processes that serve to both mix and stratify certain layers of the atmosphere. Moreover, cloud radiative and dynamical effects interact with the surface in a two-way interplay that influences surface turbulent heat fluxes. Ultimately it is the complexity of these cloud-atmosphere-surface interactions that contributes to the longevity of the clouds and their ultimate impact on the Arctic climate system. Ongoing research using the ground-based remote sensor suite at the North Slope of Alaska facility continues to provide advances in our understanding of the Arctic cloud-atmosphere-surface system. This poster summarizes two particular areas of advancement. The first is the presentation of longer term retrievals of turbulence parameters derived within low-level clouds from the temporal variance of Doppler cloud radar measurements. This dataset is used to statistically examine the evolution of vertical cloud mixing on daily-to-seasonal time scales. Turbulence structure is placed within the context of other cloud properties such as the liquid water path, derived from microwave measurements, and cloud height. The second area of focus is the interaction of cloud-atmosphere processes aloft with surface turbulent heat fluxes that are derived from ground-based, eddy-correlation measurements. Under certain circumstances, such as the advection of cold air over a warm surface, the surface turbulent heat fluxes provide substantial energy to the atmosphere and can influence vertical mixing depths and cloud properties. Under other conditions, typically with weak temperature gradients and snow-covered surfaces, surface fluxes are small and vertical mixing processes are primarily driven by clouds or other processes aloft. Long term observations at Barrow offer a unique perspective on the interplay of these processes as it changes seasonally.