I was inspired by David Dilley’s weather forecasting based upon Atlantic water pulsing into the Arctic Ocean (see post: Global Weather Oscillations). So I went looking for that signal in the AMO dataset, our best long-term measure of sea surface temperature variations in the North Atlantic.
ATLANTIC MULTI-DECADAL OSCILLATION (AMO)
For this purpose, I downloaded the AMO Index from Kaplan SST v.2, the unaltered and untrended dataset. By definition, the data are monthly average SSTs interpolated to a 5×5 grid over the North Atlantic basically 0 to 70N.
For an overview the graph below presents a comparison between Annual, March and September averages from 1856 to 2016 inclusive.
We see about 4°C difference between the cold month of March, and warm September. The overall trend is slightly positive at 0.27°C per century, about 10% higher in September and 10% lower in March. It is also clear that monthly patterns resemble closely the annual pattern, so it is reasonable to look more closely into Annual variability.
The details of the Annual fluctuations in AMO reveal the pulse pattern suggested by Dilley.
We note firstly the classic pattern of temperature cycles seen in all datasets featuring quality-controlled unadjusted data. The low in 1913, high in 1944, low in 1975, and high in 1998. Also evident are the matching El Nino years 1998, 2009 and 2016, indicating that what happens in the Pacific does not stay in the Pacific.
Most interesting are the periodic peaking of AMO in the 8 to 10 year time frame. The arrows indicate the peaks, which as Dilley describes produce a greater influx of warm Atlantic water under the Arctic ice. And as we know from historical records and naval ice charts, Arctic ice extents were indeed low in the 1930s, high in the 1970s, low in the 1990s and on a plateau presently.
I am intrigued but do not yet subscribe to the Lunarsolar explanation for these pulses, but the AMO index does provide impressive indication of the North Atlantic role as a climate pacemaker. Oceans make up 71% of the planet surface, so SSTs directly drive global mean temperatures (GMT). But beyond the math, Atlantic pulses set up oscillations in the Arctic that impact the world.
In the background is a large scale actor, the Atlantic Meridional Overturning Circulation (AMOC) which is the Atlantic part of the global “conveyor belt” moving warm water from the equatorial oceans to the poles and back again. For more on this deep circulation pattern see Climate Pacemaker: The AMOC