Simulation of Arctic Lead Generated Cloud Fluxes and Evaluation of Assumed PDF Boundary Layer Cloud Models

Arctic leads are cracks in the ice caused by the plastic deformation of the polar ice sheet leading to gaps being formed exposing open ocean to the atmosphere. These leads allow for both sensible and latent heat flux to permeate into the lowest layers of the atmosphere and have been observed to generate clouds that have observable radiative effects on the lower boundary layer. As leads are widespread phenomena that encompass wide geographic areas of the arctic region, it is important to better understand the effects that they impose. Furthermore, these clouds contain concurrent ice and liquid phase water, complicating the estimation of radiative forcings caused by such cloud masses. Hence, An LES configuration of SAM is used to evaluate the validity of using an assumed PDF based cloud parameterization is appropriate for diagnosing the clouds generated by these leads. This study evaluates three assumed pdf cloud models based on thermodynamic and microphysical accuracy. In order to do so, multiple different cases of varying simulated thermodynamic and dynamic environments over an idealized Arctic lead are employed to identify the successes and failures of such models based on their pdf shape and saturation criteria. Lastly, the models that most accurately estimate the characteristics of this unique environment are identified and improved such that they not only provide more accurate cloud fraction, but also provide more accurate distributions of the assumed pdf with respect to the LES pdf. Evaluating these different cloud models in a unique environment illustrates both the need and feasibility of GCMs to estimate this widespread and significant phenomenon.