Cloud Feedback Key to Marine Heatwave off Baja California Geophysical Research Letters

Between 2013 and 2015, the northeast Paci fic Ocean experienced the warmest surface temperature anomalies in the modern observational record. This “marine heatwave ”marked a shift of Pacific decadal variability to its warm phase and was linked to signi ficant impacts on marine species as well as exceptionally arid conditions in western North America. Here we show that the subtropical signature of thiswarming, off Baja California, was associated with a record de ficit in the spatial coverage of co-located marine boundary layer clouds. This de ficit coincided with a large increase in downwelling solar radiation that dominated the anomalous energy budget of the upper ocean, resulting in record-breaking warm seasurface temperature anomalies. Our observation-based analysis suggests that a positive cloud-surface temperature feedback was key to the extreme intensity of the heatwave. The results demonstrate the extent Grant no. NA14OAR4310278