Climate Change

Satellite data signals early hints of a looming El Nino

During El Nino years, the Indian monsoon appears to be weaker and less consistent

By Arya Rohini
Published: Tuesday 16 May 2023

A  sea level-monitoring satellite has spotted early signs of a looming El Nino across the equatorial Pacific Ocean, according to a statement by the United States National Aeronautics and Space Administration.

The US-European satellite Sentinel-6 Michael Freilich detected Kelvin waves — a potential precursor of El Nino conditions — cruising from west to east along the equator toward the west coast of South America.

A string of Kelvin waves forming in spring is a prominent forerunner to an El Nino, a periodic climate phenomenon that can alter weather patterns across the world.

Also read: India should brace for dry and hot spring-summer, El Nino, say experts

These enormous waves — roughly 5-10 centimetres high at the ocean surface — originate at the equator. They bring warmer water and are linked to increased sea levels. Since water expands as it warms, parts with warmer waters usually see higher sea levels.

The climate dynamics of countries like India are dramatically impacted when these waves move from the warmer western Pacific to the eastern Pacific. As a result of changes in atmospheric patterns, the monsoon circulation across the Indian subcontinent weakens. During El Nino years, the Indian monsoon appears weaker and less consistent.

Even though India occasionally receives normal or above-normal rainfall during El Nino years, the link between El Nino and Indian monsoon rainfall is significant. India saw normal or above-average rainfall in six of the 15 occurrences of the El Niño weather pattern over the last 70 years.

However, the previous four El Nino years have seen a divergent trend, with India continuously experiencing drought and rainfall below 90 per cent of the long-term normal.

El Nino is also connected with a weakening of the trade winds. The condition can bring cooler, wetter conditions to the US.

There are now more possibilities that El Nino may form before the end of the summer, according to recent reports from the World Meteorological Organization and the US National Oceanic and Atmospheric Administration. The upcoming months will show how powerful El Nino can become thanks to the continuous observation of ocean conditions in the Pacific by tools and satellites like Sentinel-6 Michael Freilich.

“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 programme scientist and manager for Sentinel-6 Michael Freilich in Washington.

El Nino may also reduce the upwelling of cold, nutrient-rich water off the coast of South America, which might have a detrimental effect on marine life and the fishing sector.

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.

Read more: 

Subscribe to Daily Newsletter :

Comments are moderated and will be published only after the site moderator’s approval. Please use a genuine email ID and provide your name. Selected comments may also be used in the ‘Letters’ section of the Down To Earth print edition.