Where is La Niña? And why did global models err in their predictions?

Sub : Geo

Sec :Climatology

Context:

This year, predictions for La Niña have been off. Initially, weather models predicted its emergence between August and December, but instead, ENSO-neutral conditions prevailed, with sea temperatures near normal.
A weak, brief La Niña may still develop from December to February, but its impact is expected to be minimal.
La Niña last occurred in 2020-2023, and El Niño in 2023-24.

What is La Niña?

La Niña is a phase of the El Niño Southern Oscillation (ENSO), a climate phenomenon that involves variations in sea surface temperatures and atmospheric pressure in the tropical Pacific Ocean.
It can influence weather patterns globally, affecting rainfall, temperatures, and storm systems.
The ENSO has three phases, which occur in irregular cycles of two to seven years.:
- El Niño (warm phase),
- La Niña (cool phase),
- Neutral phase.

What happens during La Nina:

In La Niña, the trade winds (winds blowing from east to west across the Pacific) are stronger than usual, pushing warm surface waters to the western Pacific.
This allows cooler waters from below the surface to upwell along the eastern Pacific, leading to lower-than-normal sea surface temperatures in this region.
In India, El Niño is associated with decreased rainfall and higher temperatures, while La Niña is associated with increased rainfall and hence lower temperatures.

El Niño:

In the El Niño phase, the trade winds weaken, leading to lesser displacement of warmer waters off the South American coast.
Consequently, the eastern Pacific becomes warmer than usual.

Neutral phase:

In the neutral phase, the eastern side of the Pacific Ocean (near the northwestern coast of South America) is cooler than the western side (near the Philippines and Indonesia).
This is due to the prevailing wind systems that move from east to west, sweeping the warmer surface waters towards the Indonesian coast.
The relatively cooler waters from below come up to replace the displaced water.

Why Did La Niña predictions fail this year?

Ocean-atmosphere coupling: The expected interactions between ocean temperatures and atmospheric conditions didn’t occur as expected, likely influenced by lingering El Niño effects.
Westerly wind anomalies: Winds that typically hinder La Niña development dominated, delaying its onset.
Monsoons: There was above normal rainfall over India this year. Monsoon and ENSO interact with each other. A good monsoon can influence the westerly wind anomalies, which in turn can delay the onset of La Niña.