Cloud morphology evolution in Arctic cold-air outbreak: A COMBLE case study

Description

Cloud feedbacks play an important role in Arctic warming and sea ice loss. Cloud morphology, e.g., cloud areas and their spatial distributions, is among factors that directly impact their radiative effects. Cold-air outbreak (CAO) in the Arctic features strong heat fluxes from comparatively warmer ocean surface into the advected colder air and induce rapid cloud formation, which is difficult to simulate in numerical models. In this work, we study the area distributions of cloud populations and their organizations along the fetch of cold-air advected from the Arctic through selected cases observed during the Cold-air Outbreaks in the Marine Boundary Layer Experiment (COMBLE) campaign. Cloud structures are identified from Moderate Resolution Imaging Spectroradiometer (MODIS) reflectance images through an object segmentation procedure. Convective cells are found to have larger sizes in environment further away from the ice edge with less stable boundary layer and lower wind speed. Regardless of distance from the ice edge, smaller clouds dominate the population numbers but not areas. We further classify clouds into four exponentially increasing area categories (<1, 1-10, 10-100, and >100 km²) and, for each cloud, identify five nearest neighbors from the same category. The mean nearest neighbor distances normalized by equivalent cloud size (l, square root of cloud area) are found to converge to ~2, suggesting that clouds with comparable sizes tend to separate at a distance of 2l. The statistical results in this study pave the way to examine cloud-environment and cloud-cloud interactions, as well as to evaluate model simulated cloud organizations during CAO events.

Supported by ICLASS SFA, Jerome Fast PI