The role of Equatorial Heat Content for Stand-Alone Pacific Coastal Niño Events

Abstract:

Anomalously high sea surface temperatures (SSTs) at the Peruvian coast in the tropical Pacific can have large impacts on the marine ecosystem and cause heavy rainfalls and flooding over land. These Coastal Warm events are often linked to El Niño conditions in the central equatorial Pacific, but there are also events such as in early 2017 that are not accompanied by basin-scale anomalies.

On the basis of several SST products spanning the time period 1900 to 2010 we show here that there are only very few “stand‐alone” coastal warming events. Most of the events that start with a coastal warming spread into the eastern-to-central equatorial Pacific, in agreement with the mechanisms described for westward propagating SST anomalies during canonical El Niños before the climate shift in the 1970s. Notably, the few events that are restricted to the coast occur in the aftermath of large El Niño events with a lag of about one year and are characterized by comparatively low equatorial heat content. Our results suggest that - consistent with recharge-discharge oscillator theory - the depleted heat content in the equatorial Pacific in the wake of strong El Niños prevents the coastal warming to spread westward.