Observations and cloud-resolving simulations of Arctic stratus

Improvement of cloud parameterizations in large-scale climate models has long been a focus of the modeling community. Currently, the ARM Cloud Parameterization and Modeling work group is working to improve parameterizations for mixed-phase clouds, particularly those found at high latitudes. Current model capabilities in these situations are unproven at all scales. It is hypothesized that specific environmental conditions lead to development and presence of mixed-phase Arctic stratus layers. Specifically, the distribution of ice-forming nuclei in the atmosphere is thought to be important to persistence of these clouds in a steady state. In support of the ARM effort, we are utilizing the University of Wisconsin Non-Hydrostatic Modeling System (UW-NMS) to simulate steady state, mixed-phase stratus clouds using environmental conditions known to be conducive to their presence. The UW-NMS utilizes a unique microphysics package that allows for inclusion of aerosol effects, and will be run at high resolution. From these cloud-resolving simulations, we will better understand the conditions and cloud dynamics that lead to formation and maintenance of mixed-phase stratus decks.

Ongoing and completed observational campaigns, such as the Mixed-Phase Arctic Clouds Experiment (MPACE) have provided us with a wealth of information about mixed-phase Arctic clouds, and environments in which they are found. Included in this information are measurements taken with the University of Wisconsin Arctic High Spectral Resolution Lidar (UW-AHSRL) and NOAA ETL Millimeter Cloud Radar (MMCR). Data from these two instruments has been combined to provide a robust array of microphysical retrievals such as particle size, number density and liquid and ice water contents at high temporal and spatial resolutions. Information gathered during this campaign can be utilized both as a source of validation as well as a source of initial conditions and constraints for the simulations.

We will present an analysis of our current ability to correctly reproduce mixed-phase stratus scenarios with a high resolution, cloud-resolving model. Findings from these simulations and potential implications that these results have upon successful parameterization of similar situations in coarse-resolution climate models will be conveyed. This analysis will be presented through review of model results, as well as comparison with and evaluation of information from the ground-based remote sensors listed above.