As the Wind Slowed, the Pacific Began to Change

El Niño is not simply a phenomenon of warming sea water. When the trade winds in the equatorial Pacific weaken, the distribution of warm surface water piled up in the west expands eastward, and the upwelling that normally brings cold, nutrient-rich water along the coast of Peru can also weaken. Below the sea surface, the east-west slope of the thermocline becomes gentler, with the warm layer deepening more in the east.

This change in turn alters the Walker circulation in the atmosphere, shifting cloud formation and rainfall patterns, creating a feedback loop where the wind and sea reinforce each other. This list connects wind, sea surface temperature, thermocline, upwelling, and precipitation zones sequentially without merely looking at one sea temperature map. It focuses on understanding that this is a marine-atmospheric coupling phenomenon that lasts for several months, not just a few days of anomalies in temperatures.

To read the start of El Niño, instead of selecting just one cause, one should look at the sequence of changes. Weakened trade winds help the movement of warm water eastward, and the deepened eastern Pacific thermocline reduces cold water upwelling. The expanded warm ocean can shift convection and precipitation zones, weakening the Walker circulation again. This interaction signifies that the ocean and atmosphere have connected!

However, not every weakening of wind grows into a strong El Niño. The amount and location of heat in the ocean, equatorial waves, and seasonal changes all participate in development and dissipation. This is why data from NOAA and meteorological institutions around the world examine not just sea temperatures but also wind, precipitation, and underwater heat content side by side. Let's look at whether multiple observations persist in the same direction, rather than focusing solely on one indicator from the news.