Underwater Glider Observations of the 2014-15 Northeast Pacific Warm Anomaly

In the spring of 2014, unusual patches of warm water were evident both in the northern and southern California Current system. By the fall of 2014, the two warm patches had joined together into a large region of the northeast Pacific with sea-surface temperatures from 1-5ºC warmer than usual; this has persisted into 2015. Here we focus on the physical oceanography of the warm anomalies as observed by repeated and ongoing autonomous underwater glider transects at two locations: the central Oregon Newport Hydrographic (NH) line (44.7ºN) and the northern California Trinidad Head (TH) line (41.1ºN). Both transects extend from the shelf to the deep ocean and are repeated every week (NH) to month (TH), and they are particularly useful for examining subsurface properties and how the offshore warm anomalies eventually reach coastal waters. At both locations, the seasonal upwelling prevents the warm anomaly from reaching the shelf during spring-summer. But in mid-Sept. 2014, with a cessation of upwelling-favorable winds, rapid warming was observed, with NH-line near-surface temperatures rising from 11ºC to 19ºC in just 31 hours. This anomaly is more than two standard deviations warmer than average. While much of the warm water appears to be advected onto the shelf from the surface layer, we also explore evidence for subsurface warming associated with deeper, continental slope processes.