Oceanographers are tracking a deep ocean wave set to arrive in California waters in October.
Unlike the surfable waves that crash along the beach, this so-called Kelvin wave – or “planetary wave” – can travel thousands of miles in the Pacific Ocean and raise the height of the water by up to a foot.
El Niño, the climate phenomenon that is expected to reach historic strength this fall, drives these waves.
“There’s currently a Kelvin wave, which is pretty significant… [that] probably won’t arrive in most of California until October,” Daniel Swain, a climate scientist for the University of California’s Agriculture and Natural Resources group, said during an online briefing. “… This will be an additional half-a-foot elevation on top of what we’ve currently got once that arrives, and we’re anticipating additional large Kelvin waves later this winter.”
During El Niño years, winds that usually blow westward over the Pacific slacken and, in bursts, reverse. Those backward winds trigger Kelvin waves that move east along the equator. After these waves of warm, elevated water slosh into South America, new Kelvin waves slither along the coast to the north and south. Kelvin waves associated with El Niño began entering California waters this spring.
Although Swain described Kelvin waves as “a lot more subtle” than those that break along the shore, they especially impact the coastline during the winter when layered with other influences, such as high tides and storm surges.
“A cresting ocean wave, of course, is ephemeral: It breaks over the course of a few seconds and then it’s gone,” Swain said. But coastally trapped Kelvin waves, he said, are “so slow to arrive and so slow to depart, that it can impart elevated sea level in any given location near its crest for days or even weeks at a time.”
Josh Willis, a senior research scientist for NASA’s Jet Propulsion Laboratory, described a Kelvin wave “like a wave on the inside of the ocean.” From satellite data, he’s been tracking the elevated sea levels in the eastern Pacific as they build up against Peru and then send Kelvin waves up and down the west coast of the Americas.
“I just made a plot today showing them at the start of this El Niño,” Willis told SFGATE on Tuesday. “There was a faint one around February and March. … And then the big ones were like May, June and maybe July, and those really signaled the onset of El Niño. You can really see those zipping across the equator. And then the El Niño really starts in earnest, and you get these huge shifts in the sea level.”
Temperatures in the Pacific Ocean are still rising as this year’s El Niño continues to rapidly strengthen. El Niño is the warm phase of a natural pattern that emerges in the central and eastern tropical Pacific. The September outlook from the National Oceanic and Atmospheric Administration’s Climate Prediction Center gave a 75% chance that El Niño will become “historic” from October to December.
Kelvin waves signal El Niño arriving in California.
Kelvin waves are one part of a larger equation this winter, according to Michael McPhaden, a senior oceanographer for NOAA’s Pacific Marine Environmental Lab. He described a “quintuple whammy” that includes sea level rise from climate change and thermal expansion from a marine heat wave in California waters.
“A Kelvin wave adds another potential 10 inches to that,” he added. “If you’re unlucky enough for those to coincide with high tides and storms kicked up by a hurricane offshore, like with Marie, you have a quintuple whammy in terms of coastal sea level and potential erosion.”
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This article originally published at Planetary waves are creeping into California right now.