A case stdy of horizontal variability in Arctic cloud microphysical properties

One of the interesting characteristics of Arctic clouds is the prevalence of mixed phase cloud layers. In these mixed phase clouds the water content tends to dominate the radiative effects, causing them to act as all liquid clouds. Measurements have shown these clouds to be highly inhomogeneous in terms of ice and liquid water content. The horizontal variability is important to proper interpretation of remotely sensed data where properties are averaged over space and/or time. It is also of interest to the modeling community for the parameterization of sub-grid scale features.

Data from the Mixed-Phase Arctic Cloud Experiment (M-PACE) collected by the University of North Dakota Citation aircraft have been analyzed for horizontal variations in microphysical properties. These data were gathered during level legs and ramp climbs and descents between Oliktok Point and Barrow, Alaska, a distance of 267 km. Preliminary analysis is focused on extensive single layer stratus cloud decks sampled on five missions. Results illustrate the spatial distribution of ice and water, including characteristic spacing of liquid water and ice content maxima and the covariance between liquid and ice content. Probability distribution functions of liquid water content are derived at normalized cloud altitudes. Cloud microphysical properties are also related to vertical motion and turbulence fields measured by the Citation. The results are used to infer the scales of cloud forcing for relevance to GCM models.