Warm water creeps into otherwise-calm Central Pacific

June 7, 2018, Jet Propulsion Laboratory
Left, in April, the Jason-3 satellite shows most of the Pacific Ocean at neutral heights (green). In May, a Kelvin wave (red) appears on the equator. Credit: NASA/JPL-Caltech

After a mild La Niña late last year, temperatures, convection and rainfall rates in the equatorial Pacific Ocean returned to normal by early April of this year. An April 9 image of sea level height from the U.S./European Jason-3 satellite mission showed most of the ocean at neutral heights. But by the beginning of May, high sea levels began to build up in the Central Pacific. In the tropics, high sea levels are usually caused by a layer of warm water at or below the surface.

This patch of high sea level is slowly traveling eastward through the tropical Pacific Ocean along the . Known as a downwelling Kelvin wave, this type of signal is often a precursor to an El Niño event.

The Kelvin wave formed after a few short periods when winds changed from the prevailing easterlies to westerly—known as westerly wind bursts—in the far western Pacific in early 2018. In addition, there has been a general weakening of the easterly winds along the equator since January. Both of these wind conditions combine to create the Kelvin wave, which moves east along the equator and results in the spreading of layers that are normally confined to the western Pacific Ocean eastward into the central Pacific. The red pattern visible at the equator on May 9 is the result of this downwelling Kelvin wave.

During a large El Niño, like the 2015-16 event, a huge area where sea levels are more than a foot (30 centimeters) higher than normal is visible in Jason-3 images. The high sea level is caused by a thick layer of warm in the upper several hundred feet of the . Such large El Niño events affect weather and climate across the globe, particularly in the western United States. In California, El Niños usually mean above-average winter rainfall, while Oregon and Washington typically see drier-than-normal winters.

El Niños happen when a series of Kelvin waves like this one spread warm water from west to east along the equator, causing high sea levels in the Central Pacific and sometimes as far east as the coastlines of Central and South America. The warm water is currently confined to the subsurface, with no warming at the ocean surface—a first indicator of an upcoming El Niño event. But forecasters at agencies like NOAA (the National Oceanic and Atmospheric Administration) and ECMWF (European Centre for Medium-Range Weather Forecasts) will be watching closely for more Kelvin waves like this one as summer approaches.

Explore further: A 3-D look at the 2015 El Nino

Related Stories

A 3-D look at the 2015 El Nino

May 26, 2017

El Niño is a recurring climate pattern characterized by warmer than usual ocean temperatures in the equatorial Pacific. Two back-to-back 3-D visualizations track the changes in ocean temperatures and currents, respectively, ...

Will the 2014 El Nino be like 1997?

May 20, 2014

Every ten days, the NASA/French Space Agency Jason-2 satellite maps all the world's oceans, monitoring changes in sea surface height, a measure of heat in the upper layers of the water. Because our planet is more than 70% ...

Could leftover heat from last El Nino fuel a new one?

March 15, 2017

Some climate models are suggesting that El Niño may return later this year, but for now, the Pacific Ocean lingers in a neutral "La Nada" state, according to climatologist Bill Patzert of NASA's Jet Propulsion Laboratory, ...

The Fickle El Nino of 2014

September 24, 2014

Prospects have been fading for an El Niño event in 2014, but now there's a glimmer of hope for a very modest comeback. Scientists warn that unless these developing weak-to-modest El Niño conditions strengthen, the drought-stricken ...

Recommended for you

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.