Marine stratocumulus climatologies

Conditions favourable to the formation and maintenance of marine stratocumulus cloud decks commonly occur in the subtropical latitudes off the west coasts of the major continents. The cloud decks over the eastern North and South Pacific and the eastern South Atlantic are well‐established examples of the phenomenon; the eastern North Atlantic exhibits rather different behaviour. Large‐scale climatological averages based on data extracted from the Comprehensive Ocean‐Atmosphere Data Set are remarkably similar in the three of these regions that exhibit well‐established marine stratocumulus cloud decks. Off the coast of northwest Africa, however, the sea‐surface temperatures are higher and the cloud cover is less overcast than for the other regions. The correlation between interannual changes in clouds and SST is negative in all four areas: years with lower than normal SST tend to be more cloudy. The implication of this for climate system feedbacks is that these clouds have the potential to exert positive feedback in the climate system. A zero‐order estimate of the strength of this positive feedback suggests that it could be comparable to that due to water vapour in the atmosphere.