IMAU: cool from pole to pole, hot in the Caribbean and El Nino 2015

/ March 23, 2015/ IMAU, Ocean Circulation and Climate

DeRuijterThis newsletter is filled with winners who have been able to convince the funding bodies that it is worthwhile to support their search for the needle in the haystack. Caroline Katsman was awarded a VIDI project to continue her search for where the cold northern polar waters sink to the deep ocean, Jan Lenaerts received a fellowship and prefers Antarctica to determine the winner between freezing and thawing, an issue that Aarnout van Delden is also often confronted with when he tries to say something useful about our future winter weather. Henk Dijkstra has made a smart move by discovering the warm waters of the Caribbean. He is starting up a national program around the BES islands (Bonaire, St Eustatius, Saba) now that they have become three special Dutch municipalities. I myself also prefer the tropics as we continue our studies on El Niño.

In June 2013 I gave a talk on El Niño for the joint Pacific and Indian Ocean Panels of the World Research Climate Program in Lijang, China. A beautiful, well conserved place that made it to the world Heritage list of UNESCO. I predicted a big El Nino for early 2015.

The surface of the western Indian Ocean had been anomalously cool since spring 2013. This cool surface generated subsidence in the atmosphere above it and enhanced convection over Indonesia. That would in turn stimulate easterlies over the equatorial Pacific, build-up of a warm water volume (WWV) in the West Pacific and, in fact, create a relatively strong La Niña in the equatorial Pacific. This process would continue until being halted after about a year by westerly wind bursts or upwelling Kelvin waves in the Indian Ocean, arriving at Sumatra. That would release the WWV and lead into an El Niño. So I predicted that an El Niño would be in full swing by now (winter 2015).

The TOGA-TAO chain of instruments along the equatorial Pacific indeed revealed an impressive WWV-‘monster’ propagating below the surface to the east. A surge of Niño predictions emerged. I thought I made a win-win bet with Mike McPhaden, who is in charge of the US program, about the size of this upcoming El Niño: I expected a really big one while Mike was more conservative and went for an average one. The winner would get a free dinner to be paid by the loser. It seems we will both be losers on this bet!

El Niño doesn’t behave the way it is supposed to. The atmosphere seems to be non-receptive to the oceanic surface temperature signal and usual feedbacks don’t kick in… Even for the coming two months the model predictions range between full Niño and full Niña. So even with such a dense observation system and the great progress made in coupled atmosphere-ocean modelling, a prediction of this dominant climate mode is still very hard to reliably make.

The predictors should show some humbleness in their battle with the real system.

Will de Ruijter

PS: about a week ago the ENSO Alert System Status was changed from neutral to “El Niño Advisory”. I may turn into a winner after all…