Redistribution of Cloud Weather States Across the Marine Cold-Air Outbreak Intensity Range in the Midlatitude North Atlantic
Abstract
Marine cold-air outbreaks (MCAOs) enhance air–sea exchange and are accompanied by substantial cloud-population reorganization over the North Atlantic. Previous satellite studies have documented MCAO-related cloud properties and International Satellite Cloud Climatology Project (ISCCP) weather-state distributions, but the continuous redistribution of the complete cloud population and its dependence on sampling scale remain less well quantified. We combine the merged H-series ISCCP (ISCCP-H) weather-state product with the ERA5 reanalysis over the North Atlantic sector of 35–50°N, 55–20°W during January–March and November–December of 2000–2009. Three complementary analytical strategies are used to examine scale-dependent cloud associations: intensity-binned analysis of positive-MCAO native ERA5 grid-point-days, domain-daily regressions, and ISCCP-H cell fixed-effect models. Across 1459 MCAO dates and 256,518 strict-ocean ISCCP-H cell-days, the combined frequency of shallow-cumulus-like and stratocumulus-like low-cloud weather states decreases systematically with MCAO intensity, with a domain-daily slope of −0.0562 K−1. Compensating regional increases occur mainly in the midlatitude-storm and middle-to-high-cloud weather states, while the deep convective and anvil state shows no robust increase. After cell and calendar-month climatological differences are removed, the low-cloud reduction persists, together with positive associations for the midlatitude-storm and optically thick middle-top weather states. Cirrus is positively associated with MCAO intensity at the regional scale but negatively associated within fixed cells, consistent with geographical composition contributing to its regional response. MCAO intensity is therefore more consistently associated with total low-cloud weather-state occupancy than with the internal composition of the low-cloud subset. The closed weather-state framework provides an observational benchmark for satellite and climate model evaluation.