Large Eddy Simulations of Arctic stratus: ASCOS case studies

The central Arctic boundary layer is dominated by persistent low level clouds, particularly in the summer where they are present near 80% of the time. Several previous studies have shown that Arctic stratus and stratocumulus (ASC's) have an important influence on the Arctic boundary layer and in particular the surface energy balance of the central Arctic sea ice.

Despite the increased interest in Arctic meteorology over the past decade, the central Arctic boundary layer remains poorly understood which most likely contributes to the poor performance of GCM's in this climatically important region. Some of the difficulty in studying Arctic clouds relates to the problem of collecting in situ measurements in such an extreme environment, and for this reason there is still a lack of data available to effectively analyse the macrophysical and microphysical properties of the clouds. A popular and successful modelling tool for understanding such processes, particularity where there is a lack of detailed measurements, has been large eddy simulation. In this study the UK Met Office's Large Eddy Model (LEM) with 2-moment bulk microphysics has been utilised to study dynamical-microphysical-radiative interactions in summertime ASC's.

Idealised simulations constrained by meteorological observations from the Arctic Summer Cloud Ocean Study (ASCOS) field campaign will be presented. In particular we examine the apparent extension of cloud top into the Arctic temperature inversion and test the sensitivity of cloud microphysics to aerosol source. Results are compared against observations from a suite of remote sensing and direct measurement instruments including surface based cloud radars, laser ceilometers, and wind profiler, along with radiosonde profiles. Physical aerosol and cloud properties are compared to flight data collected during the concurrent Arctic Mechanisms of Interaction between the Surface and Atmosphere (AMISA) field project.