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Wednesday, February 4, 2009

There Are Also El Nino-Induced Step Changes In The North Atlantic

I’ve moved to WordPress.  This post can now be found at There Are Also El Nino-Induced Step Changes In The North Atlantic
While preparing the January 2009 SST Anomaly Update post, the step changes in the North Atlantic SST anomaly dataset stood out clearly. Refer to Figure 1.
Figure 1

The bases for and processes that contributed to the step changes in the East Indian and West Pacific SST are discussed in:
Can El Nino Events Explain All of the Global Warming Since 1976? – Part 1
Can El Nino Events Explain All of the Global Warming Since 1976? – Part 2
Supplement To “Can El Nino Events Explain All Of The Warming Since 1976?”
Supplement 2 To “Can El Nino Events Explain All Of The Warming Since 1976?”
The processes would be different in the North Atlantic, but the effects are similar. Refer to Figure 2, which compares North Atlantic SST anomalies to scaled NINO3.4 SST anomalies. The NINO3.4 data has not been scaled to illustrate cause and effect. It is provided for timing purposes only.
Figure 2

Using the Sato Index of Stratospheric Aerosols as a reference for timing also, Figure 3, it’s clear that the El Chichon (1982) and Mount Pinatubo (1991) eruptions disrupted the normal heat distribution of the 1982/83 and 1991/92 El Nino events and prevented the step changes at those times.
Figure 3


Figure 4 is the short-term (OI.v2 SST-based) comparison of North Atlantic and East Indian-West Pacific SST anomalies from November 1981 to December 2008. The magnitudes of the two major steps are similar in scale, but there are differences in the reactions to the two volcanic eruptions. Also, the two datasets diverge after the 2002/03 El Nino, when the North Atlantic SST anomalies continue to rise. The North Atlantic SST anomalies do appear to be decreasing with time, though.
Figure 4

I am not implying that the El Nino-induced step changes are the only contributors to North Atlantic SST variability, but they do impact it significantly. If we compare the North Atlantic and the East Indian-West Pacific SST anomalies from 1880 to present (ERSST.v2 data smoothed with 12-month filter), Figure 5, the additional impacts of Thermohaline Circulation/Meridional Overturning Circulation on the North Atlantic are also visible.
Figure 5

Note: Recallthat the Atlantic Meridional Overturning Circulation appears to be impacted by ENSO events as well. Refer to the post titled Atlantic Meridional Overturning Circulation Data.


With a coordinate-based system, to eliminate overlap and minimize the areas missed, the SST anomalies of the remainder of the oceans between 60S and 65 N (not included in the North Atlantic or the East Indian-West Pacific SST anomalies) had to be subdivided into three subsets:
-Northeast Pacific [0-65N, 180W-90W], Figure 6,
-Southeast Pacific-South Atlantic [60S-0, 180W-20E], Figure 7, and
-West Indian Ocean, [60S-30N, 20E-80E], Figure 8.

While there are short-term divergences, the other global ocean SST anomaly subsets follow NINO3.4 SST anomalies well.
Figure 6
Figure 7
Figure 8


In addition to the EL Nino-induced step changes witnessed in the East Indian and West Pacific oceans, the step changes in the North Atlantic also contradict the commonly held belief that ENSO events only have short-term impacts on global temperature.


The NOAA Optimal Interpolated SST Analysis (OI.v2) Data is also available online through the NOAA National Operational Model Archive & Distribution System (NOMADS).

THE ERSST.v2 data had to be accessed through the KNMI Climate Explorer website while NOMADS is being updated.

The Sato Index Data is available from GISS at:

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