Covariance Between Atmospheric State Regimes, Arctic Low Clouds, and Sea Ice in Observations and Climate Models

How do clouds respond to variations in sea ice? The answer to this question depends significantly on the characteristics of the Arctic circulation. Sea ice-cloud interactions are important for modeling the Arctic climate. Specifically, understanding the cloud response to sea ice change is necessary for understanding the Arctic surface radiation budget. Previous work has primarily addressed this problem from the interannual variability perspective. A novel perspective of sea ice-cloud interactions in the Arctic is provided here through a satellite footprint-level quantification of the covariance between sea ice and Arctic low cloud properties from NASA A-Train active remote sensing satellite data. The influence of atmospheric state on the cloud field must be considered. The covariance between Arctic low cloud properties and sea ice concentration is quantified by first partitioning each footprint into one of four atmospheric regimes defined by thresholds of lower tropospheric stability and mid-tropospheric vertical velocity. A statistically significant covariance between cloud fraction, cloud liquid water, cloud ice water, cloud total water and their vertical distributions is found with sea ice concentration in each atmospheric regime and season. Results indicate, however, that magnitude of any cloud response to changes in sea ice concentration is at least an order of magnitude smaller than the response of clouds to a change in the atmospheric dynamic and thermodynamic state. The results indicate that the atmospheric dynamic and thermodynamic environment is the most important factor determining the cloud influence on the surface radiation budget and therefore sea ice variability. Lastly, the cloud-sea ice interaction is evaluated in CMIP5 Historical simulations. The results suggest that climate models simulate a cloud response to a change in sea ice that is stronger than observations and that the offset of the surface albedo feedback by an increase in Arctic cloudiness is likely too strong.