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El Nino in a Cold PDO – Are they Different?

By Joe D'Aleo
Monday, June 22, 2009

Warming is taking place again this year in the eastern tropical Pacific.

Recently the SOI spiked 5 STD negative indicative of that trend towards El Nino.

Last year the warming peaked below threshold El Nino levels in July and returned to La Nina by winter.

This year there appears to be enough subsurface warmth to take it further.

But the PDO remains cold with some slight rebound. El Ninos tend to be briefer and weaker during cold (negative) PDO eras, which is where we have been it appears most of the time since 1998.

Note the positive PDO is a basin wide El Nino like pattern with more emphasis on cold northwest, the negative a basin wide La Nina like pattern with more northwest basin warmth.

You can see the multidecadal behavior of the PDO with warmth from 1922 to mid 1940s, cold until the late 1970s, warmth 1979 to 1998 and cold again in recent years.

You see how the Multivariate ENSO Index shown here long term follows that pattern.

The ENSO and PDO seem to reinforce each other and track well together. We should expect PDO to bounce some but if the Pacific is really in the cold mode, the El Nino should be brief and at most moderate like they were from the 1950s through the 1970s and again in the middle 2000s. La Nina should return if not by/during winter during 2010.

See in the following cross-sections how the current ocean warmth is in the upper ocean and is a bit stronger than the warmth last year and very similar to June 2002.

It is much weaker than the very warm plume and suppression of the thermocline in 1997/98/

Most of the climate ENSO models range from neutral to strong El Nino (NASA GMAO). We believe a briefly moderate El Nino is likely like we saw in 1965/66 and 1976/77, both El Ninos during cold PDO and with an east QBO, the phase next winter.

The June through January 1977 anomalies were as shown above. CFS model from CPC seems to agree.

Meanwhile global temperatures continue to slide.