While I was investigating North Atlantic Meridional Overturning Circulation, an area of the North Atlantic kept coming up in papers: the North Atlantic Subpolar Gyre. Refer to Figure 1. The red box (the borders for the data used in the following graphs) picks up the center of the “heart-shaped” gyre that’s located south of Greenland. The North Atlantic Subpolar Gyre includes the North Atlantic Drift, and the Irminger, Greenland and Labrador Currents. (The Irminger Current is not identified on the map, but it’s south and west of Iceland.)
There’s an interesting correlation between the cycles of the North Atlantic Gyre SST anomalies and those of another data set. I believe the explanation of this would have to come under the all-encompassing heading of teleconnections. But first let’s take a look at the…
NORTH ATLANTIC SUBPOLAR GYRE SST ANOMALIES
Figure 2 illustrates the North Atlantic Subpolar Gyre [45N-60N, 60W-30W] SST anomaly data from January 1854 to October 2008 that’s been smoothed with a 12-month running-average filter. The cycle is the first thing to catch the eye. The second: If trend lines were to be drawn from peak-to-peak and from trough-to-trough, they would be relatively flat. That is, there does not appear to be a significant, if any, underlying “global warming” trend. The curve almost appears to be a residual like the Atlantic Multidecadal Oscillation (AMO).
Figures 3 and 4 illustrate the North Atlantic Subpolar Gyre SST anomaly data smoothed with 37- and 85-month filters, to help minimize the noise.
In case someone was interested, in Figure 5, I’ve illustrated the short-term data (November 1981 to October 2008) as a comparative graph between ERSST.v2 data (used for the long term graphs) and OI.v2 SST data.
AN INTERESTING CORRELATION IN THE TIMING OF THE CYCLES
Keep in mind that in the following two graphs, SST data is being compared to scaled residual data.
The first thing one would think of when they see a cycle in any North Atlantic SST anomaly data would be the AMO. In looking at a comparative graph of the AMO (scaled) and the North Atlantic Subpolar Gyre SST anomalies, Figure 6, the cycles do compare well after the early 1900s. But they are out of synch before then.
To my eye, and seeming to be counterintuitive, the timing of the cycles in the North Pacific Residual agree with those of the North Atlantic Subpolar Gyre SST anomalies. Refer to Figure 7, which compares the North Pacific Residual (scaled) with the North Atlantic Subpolar Gyre SST anomalies.
Or maybe the North Atlantic Subpolar Gyre SST anomalies have been impacted by both over the term of the data. Could the dominant influence change with time?
Smith and Reynolds Extended Reconstructed SST Sea Surface Temperature Data (ERSST.v2) and the Optimally Interpolated Sea Surface Temperature Data (OISST) are available through the NOAA National Operational Model Archive & Distribution System (NOMADS).