Abstract
In March 2017, sea surface temperatures off Peru rose above 28 °C, causing torrential rains that affected the lives of millions of people. This coastal warming is highly unusual in that it took place with a weak La Niña state. Observations and ocean model experiments show that the downwelling Kelvin waves caused by strong westerly wind events over the equatorial Pacific, together with anomalous northerly coastal winds, are important. Atmospheric model experiments further show the anomalous coastal winds are forced by the coastal warming. Taken together, these results indicate a positive feedback off Peru between the coastal warming, atmospheric deep convection, and the coastal winds. These coupled processes provide predictability. Indeed, initialized on as early as 1 February 2017, seasonal prediction models captured the extreme rainfall event. Climate model projections indicate that the frequency of extreme coastal El Niño will increase under global warming.
Highlights
In March 2017, sea surface temperatures off Peru rose above 28 °C, causing torrential rains that affected the lives of millions of people
In late 2016, a La Niña with moderate amplitude occurred over the tropical Pacific Ocean with near neutral SSTAs off Peru and persistent weak sea surface temperature (SST) warming along the west coast of subtropical South America
SSTAs over the coastal region of tropical South America (CTSA; 85 °W–80 °W, 10 °S–0°) started to increase in mid-January 2017 and reached +3 °C in March while weak negative SSTAs were observed over Niño 3 and Niño 4 regions (Figs. 2 and 3a)
Summary
In March 2017, sea surface temperatures off Peru rose above 28 °C, causing torrential rains that affected the lives of millions of people This coastal warming is highly unusual in that it took place with a weak La Niña state. During January–March 2017, torrential rains (~6 mm day−1; Fig. 1a) devastated northern Peru, causing extreme flooding and widespread landslides that resulted in at least 200 deaths and a huge loss of properties[2] This is one of the worst floods of Peru on record in terms of both the rainfall amount and the number of people affected. It is widely recognized that the strong eastern-Pacific warming is mainly caused by westerly wind anomalies in the central Pacific through equatorial wave adjustments In this classic view, strong coastal warming is associated with a basin-scale El Niño (or eastern-Pacific El Niño).
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