The Last El Niño ?NASA Visualization ? (2015/2016)

As an El Niño pattern develops and trade winds weaken, gravity causes the warm water to move east.

This mass, referred to as the "western Pacific warm pool," extends down to about 200 meters in depth, a phenomenon that can be observed by moored or floating instruments in the ocean: satellite-tracked drifting buoys, moorings, gliders, and Argo floats that cycle from the ocean surface to great depths.

These in situ instruments (more than 3,000 of them) record temperatures and other traits in the top 300 meters of the global ocean.

The visualization above shows a cross-section of the Pacific Ocean from January 2015 through December 2016.

It shows temperature anomalies; that is, how much the temperatures at the surface and in the depths ranged above or below the long-term averages.

Note the warm water in the depths starting to move from west to east after March 2015 and peaking near the end of 2015. (The western Pacific grows cooler than normal.)

By March 2016, cooler water begins moving east, sparking a mild La Niña in the eastern Pacific late in 2016, while the western Pacific begins to warm again.

References

Release "The Birth and Death of an El Niño" via https://www.youtube.com/watch?v=69N494UIlS8

Further reading http://earthobservatory.nasa.gov/Features/ElNino/