Marine Cold-Air Outbreak Snowfall in the North Atlantic: A CloudSat Perspective

Abstract

This study analyzes the influence of marine cold-air outbreaks (MCAO) on snowfall and cloud properties in the North Atlantic Ocean using CloudSat observations. Comparing reanalysis-determined MCAO conditions (low-level instability) against “non-CAO” conditions, we find that MCAO conditions are associated with predominantly light snowfall rates (<2 mm day−1 liquid water equivalent) whereas non-CAO conditions are more frequently associated with higher snowfall rates. Near cold-air sources, such as sea ice or cold continents, MCAO-forced snowfall rates tend to be more frequent and more intense. Additionally, 76% of snowing clouds identified during MCAO conditions are shallow (mean cloud top height <3 km) stratocumulus, whereas 44% (43%) of clouds in non-CAO conditions are deeper nimbostratus (stratocumulus). With greater boundary layer instability (stronger MCAO conditions), CloudSat observes higher cloud-top heights, reflecting a deepening boundary layer and the presence of two distinct cloud modes during MCAO conditions.