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Wednesday, June 25, 2008

Solar Signal in East Equatorial Pacific SST?

In a prior post “Equatorial SST Comparison”, the Eastern Equatorial Pacific (5S to 5N by 80 to 180W) displayed an oscillation that appeared to have an 11-year cycle, a solar signature. Refer to Figure 1, which has been smoothed with an 85-month filter.
Figure 1

Unfortunately, I haven’t found a TSI reconstruction with monthly data, but the SST anomaly data is monthly, so sunspots will have to do in the initial comparison. Figure 2 illustrates raw and smoothed monthly sunspot data. Note that the smoothing gives the sunspot minimums a curve.
Figure 2

In Figure 3, the two data sets, Eastern Equatorial Pacific SST Anomaly and Scaled TSI, are compared. I’ve highlighted peaks in the two curves that indicate there may be a correlation if the TSI data set was shifted. This would infer a 30-year+ lag in Eastern Equatorial Pacific to changes in solar irradiance, which could be possible because the Eastern Equatorial Pacific is considered an upwelling point of thermohaline circulation. So let’s shift the TSI data.
Figure 3

Figure 4 compares the TSI and Eastern Equatorial Pacific SST Anomaly data sets, with the TSI data shifted 33 years. Considering the amount of noise in the raw SST data and the time span between the two data sets, that’s not a bad correlation. If this lag is correct, the small area of the Pacific Ocean is reacting today to changes in TSI that occurred in 1975.
Figure 4

There will be those who believe the smoothing creates the appearance of a correlation, when, if fact, none exists. Figure 5 illustrates the raw TSI and East Equatorial Pacific SST anomaly data. Is the correlation still visible in it?
Figure 5

To compare against TSI, which does have a different basic curve than sunspots, the other alternative is to annualize the SST anomaly data. Refer to Figure 6. The correlation still exists, but the scaling factor used indicates an SST sensitivity much greater than accepted climate sensitivities. Is this a problem? Possibly not, if the surface area of the thermohaline circulation upwelling points is compared to the total oceanic surface area. If these upwelling areas of relatively small area are dissipating the variations in total stored heat of deep water, the signals should be amplified above what would be considered normal for sea surface sensitivity.
Figure 6


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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