Oceansat-3 Spots Early El Niño Signals in Pacific, ISRO Says

An Indian satellite orbiting 741 kilometres above Earth has picked up some of the clearest early signals yet of a strengthening El Niño in the equatorial Pacific, according to the Indian Space Research Organisation.

Data from EOS-06, also known as Oceansat-3, show a marked drop in surface chlorophyll-a across parts of the tropical Pacific in June 2026 compared with the same period in 2024 and 2025, when conditions were largely neutral. Chlorophyll-a is the pigment found in phytoplankton, the microscopic marine plants that anchor the ocean food chain.

The analysis was carried out by ISRO's National Remote Sensing Centre in Hyderabad. Alongside the biological change, the satellite recorded a reversal of ocean surface winds from easterlies to westerlies — a classic marker of El Niño development.

According to Dr Prakash Chauhan, Director of the NRSC, warming waters in the eastern Pacific weaken the upwelling of colder, nutrient-rich water from deeper layers. As that supply falls, phytoplankton growth declines, a shift captured by the Ocean Colour Monitor on board EOS-06. The same satellite carries a Scatterometer that tracks the associated wind reversals.

"The important inference is that apart from Sea Surface Temperature, phytoplankton depletion also gives clear indication of El Niño status and its impact on ocean response in the Pacific Ocean," Chauhan said.

Scientists note that chlorophyll responds almost immediately to shifts in ocean dynamics, which may make its depletion an earlier indicator than sea surface temperature-based indices. Those traditional measures typically require sustained warming over several weeks before an event is formally declared.

ISRO said the EOS-06 observations complement the outlook issued by the World Meteorological Organization. In its June 2026 update, the WMO estimated roughly an 80% probability of El Niño conditions developing during June–August 2026, with several models pointing to the possibility of a strong event. By late July, the agency reported that conditions were intensifying and were expected to strengthen further during August–October 2026.

The India Meteorological Department says moderate El Niño conditions currently prevail over the equatorial Pacific, with sea surface temperature anomalies above normal across the central and eastern Pacific. It expects these conditions to strengthen through the rest of the southwest monsoon season, a view echoed by forecasts from the Monsoon Mission Coupled Forecast System.

El Niño is the warm phase of the El Niño Southern Oscillation, one of the most influential climate systems on the planet. In normal years, trade winds push warm surface water westward across the Pacific, allowing cooler, nutrient-rich water to rise near South America. During El Niño, those winds weaken or reverse, warm water spreads eastward, upwelling collapses and marine productivity falls. The resulting shifts in atmospheric circulation can alter rainfall, drought, floods and temperatures across multiple continents.

For India, the phenomenon matters because it has historically been linked to weaker southwest monsoon rainfall. Not every El Niño brings drought, but strong events have often coincided with deficient rain, reduced soil moisture and pressure on agriculture and water resources.

The WMO has warned that a very strong El Niño is emerging and could persist into early 2027, raising concerns about extreme weather, higher global temperatures and wider climate disruption. The prospect of a powerful event at a time when global temperatures remain exceptionally high has drawn close attention from climate scientists.

Launched on 22 November 2022 aboard the Polar Satellite Launch Vehicle, EOS-06 carries the Ocean Colour Monitor-3 and a Scatterometer to track marine ecosystems, ocean winds and atmosphere-ocean interactions. Combining chlorophyll and wind measurements allows scientists to follow the ocean's response to El Niño almost in real time.

Researchers caution that while chlorophyll decline and wind reversals are strong indicators, the evolution of the event will continue to be tracked alongside sea surface temperature, thermocline depth, sea level height and ocean circulation patterns. If current forecasts hold, the low-chlorophyll region across the Pacific could become more pronounced in the months ahead.