Kelvin Waves, Explained

You may be hearing a lot about Kelvin waves in the news. What are Kelvin waves, and how are they related to El Niño? We asked oceanographer Michael Jacox, from the Southwest Fisheries Science Center and NOAA Physical Sciences Laboratory, to explain the phenomenon.

What is a Kelvin wave and is there currently one moving across the Pacific?

Unlike the waves we're used to seeing at the beach, Kelvin waves travel underwater, are very long, and only change sea level slightly. They often form in the western equatorial Pacific, then travel along the equator from west to east. After reaching South America, they continue as coastal trapped waves away from the equator-both north along the Central and North American coasts and south along the South American coast.

As of early October, there is one making its way up the North American West Coast, and behind it there are one or two more that are still in the tropics.

What is the role of Kelvin waves in El Niño?

Kelvin waves are a key part of El Niño's development, shifting warm ocean temperatures from the west towards the east along the equator. Coastal Kelvin waves are also one of the main ways El Niño impacts the U.S. West Coast; as they pass they can raise sea level and increase ocean temperatures.

How fast does a Kelvin wave typically travel?

They travel about 6 miles per hour, or 150 miles per day.

How could a Kelvin wave influence coastal impacts along the West Coast?

Kelvin waves by themselves are not a threat to coastal communities. In terms of sea level rise, Kelvin waves can add up to 6-12 inches, which on a temporary basis does not pose much danger. But when there are very high tides or storm surges, their effects can be amplified because the sea level is already a bit higher.

Kelvin waves also change ocean temperatures, pushing cold water deeper and raising temperatures near the surface. Kelvin waves also can suppress the upwelling of cold, nutrient-dense water. These changes can then reduce growth of phytoplankton that form the base of the marine food web.

In addition to Kelvin waves, what other factors are impacting West Coast waters?

Kelvin waves are coming on top of several factors that are increasing sea level and ocean temperatures off the U.S. West Coast. Sea levels have already been abnormally high for months as the West Coast has been feeling the effects of marine heatwaves. El Niño is predicted to bring weaker coastal upwelling and warmer-than-normal water temperatures along the U.S. West Coast from fall through winter, and likely into spring.

Why do you think Kelvin waves are getting extra attention this year?

Kelvin waves are nothing new, and are a key part of El Niño events. This year, we are using ocean models and observations to track the progression of coastal Kelvin waves in real time. That new view into what's happening-along with general interest in an El Niño that is expected to be extremely strong-is bringing more attention to Kelvin waves.

Why are they called Kelvin waves?

Kelvin waves are named after the prominent scientist, Lord Kelvin, who first described these unique wave phenomena in 1879.