Warm events in the California Current: El Niño or not

The El Niño – Southern Oscillation (ENSO) is a dominant mode of interannual climate variability throughout the Pacific. However, warm events occur in the extra-tropical California Current System (CCS) that are neither contemporaneous with an El Niño nor mechanistically linked to ENSO. Likewise, not every tropical El Niño is reflected by a CCS warming. The paradigm that changes in the surface layer of the eastern equatorial Pacific propagate poleward along the coasts of North and South America does not completely account for CCS warmings. Atmospheric variations affecting winds that drive surface heat and momentum fluxes must be considered. These wind fluctuations result from local/regional pressure anomalies, which are only sometimes clearly related to remote forcing by atmospheric teleconnections. We document the history of El Niño and CCS warm events since 1950 and show how the ocean-atmosphere interactions forcing these events, and the relationships between them, vary over time. The 2013-2014 warming of the NE Pacific, known as “the Blob”, is a notable example of a CCS warming that was not a result of ENSO-generated teleconnections. The Blob has persisted as the 2015-2016 El Niño develops. The coincidence of these two events in 2015 is now causing major changes in the California Current Ecosystem.