The sensitivity of Arctic stratocumulus to moisture sources in the subcloud and cloud-top inversion layers
Authors
Amy Solomon — University of Colorado/NOAA- Earth System Research Laboratory
Matthew Shupe — University of Colorado
Ola Persson — CIRES, University of Colorado and NOAA PSL
Category
Cloud Properties
Description
Arctic mixed-phase stratocumulus (AMPS) are observed to occur approximately 45% of the time on the North Slope of Alaska, with a significant increase in occurrence during spring and fall transition seasons (Shupe 2011). Due to the presence of liquid water in these clouds, they play an important role in determining the structure of the Arctic atmospheric boundary layer and magnitudes of surface energy budget terms.Observations indicate that the processes that maintain subtropical and Arctic stratocumulus differ due to the different environments in which they occur. For example, specific humidity inversions (specific humidity increasing with height) are frequently observed to occur coincident with temperature inversions in the Arctic . For example, a recent survey found that specific humidity inversions occurred 75–80% of the time when low-level clouds were present, and that there was a significant relationship between the existence of specific humidity inversions and AMPS that extended into the temperature inversion (Sedlar et al. 2011), highlighting the difference between AMPS and subtropical stratocumulus where the entrainment of dry air aloft prevents cloud liquid water from forming in the temperature inversion.
In this study we examine many details of springtime AMPS using results from large-eddy simulations (LES) of the DOE Atmospheric Radiation Measurement Climate Research Facility's Indirect and Semi-Direct Aerosol Campaign (ISDAC, McFarquhar et al. 2011) using the Weather Research and Forecasting Model (WRF). Results from a series of studies that focus on the sensitivity to moisture sources in the subcloud layer and in the cloud top inversion layer will be presented. The impact of these moisture sources on the dynamical-radiative-microphysical interactions that maintain the AMPS cloud will be discussed. Comparisons to a previous study of the same case with nested WRF simulations will also be presented.