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Saturday, July 26, 2008

SSTs at the Centers of Ocean Gyres and A Predictor (?) of North Atlantic SST


Figure 1 is a simplistic illustration of ocean gyres. In the following, I’ve illustrated SST anomalies at the “centers” of all five. It appears that SSTs at the center of the North Atlantic gyre lead SSTs for the majority of the North Atlantic by almost three years. Could SSTs at the center of the North Atlantic gyre be used to predict the temperature of the North Atlantic and its impacts on European and North American climate?

Figure 1


Figure 2 depicts the locations of the data sets used in the following. I did NOT perform a detailed analysis of ocean currents to pick the spots; I eyeballed centers based on the representations of the gyres in Figure 1. I’m a blogger, not a climatologist; that’s my excuse. The following are the coordinates used:
North Pacific Gyre = 15 to 25N, 150 to 160W
South Pacific Gyre = 45 to 55S, 135 to 145W
North Atlantic Gyre = 30 to 40N, 35 to 45W
South Atlantic Gyre = 35 to 45S, 15 to 25W
Indian Ocean Gyre = 32 to 42S, 80 to 90E
Figure 2

All five data sets are shown in Figure 3, which clearly illustrates that there are no obvious relationships between the SST anomalies of the group as a whole.
Figure 3

The SST anomalies of the North and South Pacific gyres are illustrated in Figure 4. The mutual influences are obvious, as are the greater variations in the North Pacific signal. Note that both filtered signals are decreasing before, during, and after the 97/98 El Nino.
Figure 4

In Figure 5, the SST anomalies for the North and South Atlantic gyres are presented. At first glance, it almost appears as if the South Atlantic, with additional underlying oscillations, lags the North by around 40 years. However, a closer inspection reveals that the South Atlantic has an SST anomaly rise from the 1960s to the early 1980s, then a drop from 1990 to present, reminiscent of the Southern Ocean SST anomaly curve. This is later compared in Figure 8.
Figure 5

The SST anomalies at the centers Northern Hemisphere gyres are shown in Figure 6. Recall that these data sets may not be representative of the oceans or their climatic effects. They are not from scientifically selected areas and may or may not be at the centers of the gyres based on ocean currents. Regardless, the Atlantic signal has a higher amplitude than the Pacific, with less noise.
Figure 6

Figure 7 shows the SST anomalies at the centers of the three Southern Hemisphere gyres. The South Pacific curve is much flatter than the two others, while the shapes of the South Atlantic and South Indian Ocean data sets agree with the overall shape of the Southern Ocean SST anomaly curve, Figure 8.
Figure 7

Figure 8


Of the SST anomaly data sets illustrated, the North Atlantic gyre signal has the strongest oscillation, with the least noise. In an effort to determine how widespread that THC/MOC signal is, I used the original coordinates of the center of the North Atlantic gyre as a starting point, then expanded the area in 10 degree steps of latitude and longitude. Refer to Figure 9.
Figure 9

As could be expected, the smaller area had the greatest variation. Refer to Figure 10. What was unexpected was how little the variance was between the smallest and largest areas. The final point that stood out was the time lag between the smallest and the largest areas. Could this lag be present in a comparison of the center of the North Atlantic gyre and the North Atlantic SST anomalies?
Figure 10

Figure 11 illustrates the two areas bordered by the Black and the Bronze rectangles used in the following comparison. Disregard the other intermediate areas depicted; their curves simply cluttered the graph.
Figure 11

Figure 12 shows the SST anomalies for the center of the North Atlantic gyre (30 to 40N and 35 to 45W) and the North Atlantic (0 to 65N and 0 to 80W) from 1854 to 2008, smoothed with an 85-month filter. Note how the major changes in trend of the curve for the Center of the North Atlantic gyre occur about 3 years before the curve for the majority of the North Atlantic.
Figure 12

Amazingly, when the time span is shortened to the last 30 years, and when one data set is shifted 35 months, the two curves correlate very well. Refer to Figure 13, in which the data has not been smoothed. This seems to indicate that the SST anomaly at the center of the North Atlantic gyre could be used to predict trends in North Atlantic SST.
Figure 13

Documenting the THC/MOC curve in the North Pacific and this discovery have made all the work that went into creating this series on the Smith and Reynolds SST data worthwhile.


Sea Surface Temperature Data is Smith and Reynolds Extended Reconstructed SST (ERSST.v2) available through the NOAA National Operational Model Archive & Distribution System (NOMADS).

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