International Sea Level Satellite Spots Early Signs of El Nino

International Sea Level Satellite Spots Early Signs of El Nino
by Staff Writers
Paris (ESA) May 15, 2023

Kelvin waves, a potential precursor of El Nino conditions in the ocean, are rolling across the equatorial Pacific toward the coast of South America. The most recent sea level data from the U.S.-European satellite Sentinel-6 Michael Freilich indicates early signs of a developing El Nino across the equatorial Pacific Ocean.

The data shows Kelvin waves - which are roughly 2 to 4 inches (5 to 10 centimeters) high at the ocean surface and hundreds of miles wide - moving from west to east along the equator toward the west coast of South America.

When they form at the equator, Kelvin waves bring warm water, which is associated with higher sea levels, from the western Pacific to the eastern Pacific. A series of Kelvin waves starting in spring is a well-known precursor to an El Nino, a periodic climate phenomenon that can affect weather patterns around the world. It is characterized by higher sea levels and warmer-than-average ocean temperatures along the western coasts of the Americas.

Water expands as it warms, so sea levels tend to be higher in places with warmer water. El Nino is also associated with a weakening of the trade winds. The condition can bring cooler, wetter conditions to the U.S. Southwest and drought to countries in the western Pacific, such as Indonesia and Australia.

The Sentinel-6 Michael Freilich satellite data shown here covers the period between the beginning of March and the end of April 2023. By April 24, Kelvin waves had piled up warmer water and higher sea levels (shown in red and white) off the coasts of Peru, Ecuador, and Colombia. Satellites like Sentinel-6 Michael Freilich can detect Kelvin waves with a radar altimeter, which uses microwave signals to measure the height of the ocean's surface. When an altimeter passes over areas that are warmer than others, the data will show higher sea levels.

"We'll be watching this El Nino like a hawk," said Josh Willis, Sentinel-6 Michael Freilich project scientist at NASA's Jet Propulsion Laboratory in Southern California. "If it's a big one, the globe will see record warming, but here in the Southwest U.S. we could be looking at another wet winter, right on the heels of the soaking we got last winter."

Both the U.S. National Oceanic and Atmospheric Administration (NOAA) and the World Meteorological Organization have recently reported increased chances that El Nino will develop by the end of the summer. Continued monitoring of ocean conditions in the Pacific by instruments and satellites such as Sentinel-6 Michael Freilich should help to clarify in the coming months how strong it could become.

"When we measure sea level from space using satellite altimeters, we know not only the shape and height of water, but also its movement, like Kelvin and other waves," said Nadya Vinogradova Shiffer, NASA program scientist and manager for Sentinel-6 Michael Freilich in Washington. "Ocean waves slosh heat around the planet, bringing heat and moisture to our coasts and changing our weather."