El Nino Update
By Paul Homewood
Today I want to take a slightly different look at current ENSO conditions, and concentrate on subsurface temperature anomalies along the equator:
This is the latest situation:
Despite positive, albeit weakening, anomalies on the surface, below the surface a huge pool of cold water has been building up in the last three months.
How does this compare to previous El Nino events? Unfortunately NOAA have no archived data for the 1998 event, but we can look at 2010, which was a much weaker one, but still the biggest since 1998 until the current El Nino.
In May 2010, the El Nino was already on the verge of petering out. Indeed, by June, La Nina conditions were in full swing. This was what subsurface temperatures looked like then:
Subsurface anomalies had only just started to go negative, but more significantly the cold pool of water below the surface was small and patchy, compared to the current situation.
We can see how this evolved over following months.
Warmer water quickly re-established itself in the western Pacific, as naturally occurs during La Ninas, with easterly winds pushing the warm surface water from east to west. This allows colder water to well up in the east.
The difference is that this time there is already a huge body of cold water below the surface across the whole of the equatorial Pacific. This is likely to mean that strong and long lasting La Nina conditions will follow.
Finally, let’s see how subsurface anomalies have developed over the last year:
A tremendous amount of heat that was built up below the surface of the east Pacific has been released into the atmosphere, causing the spike in temperatures. That will take time to dissipate, but that heat has now gone from the ocean.
There is a layman’s guide to how ENSO works here.