>Figure 1 illustrates the Global and Mid-Latitude North Pacific SST Anomalies from January 1854 to May 2008. The data have been smoothed with a 37-month running-average filter, comparable to a 3-year filter. In Figure 2, the residual of those two curves (Mid-Latitude North Pacific SST Anomaly MINUS Global SST Anomaly) is shown. I had never seen curves like these illustrated before and I was sure I had made a mistake, in data selection while downloading, in merging East and West Pacific data sets. I repeated the process and came up with the same result.
How else could I verify the North Pacific had those curves? I picked four areas in the North Pacific, illustrated in Figure 3 and graphed the data from them.
The coordinates for the North Pacific data sets are:
Northwest = 40 to 50N, 150 to 160E
Northeast = 40 to 50N, 130 to 140W
East Central = 15 to 25N, 150 to 160W
West Central = 15 to 25N, 160 to 170E
Figure 4 illustrates the SST anomaly data for those four regions, all smoothed with 85-month filters. (With areas that small, a 3-year filter still leaves too much noise.) Based on the general shapes of the four curves, I concluded I had not made a mistake with the earlier data and graphs.
The second thing that stood out in Figure 4 was the significant drop in SST between 1900 and 1930. Next were the lag times between the temperature drops, and the different recoveries. The fourth thing I noted was that the amplitude and frequency of the oscillations in North Pacific temperature varied per region, but they too were decadal to multidecadal in nature. The North Pacific is teaming with decadal and multidecadal temperature oscillations that vary in amplitude and frequency.
The SST temperature anomaly curve for the North Pacific (south of 65N) was added in Figure 5. I elected not to use Mid-Latitude North Pacific data (Figure 1), since the two lower latitude data sets used in the comparison were outside that area. While the influence of the regions is apparent, there are obviously other areas, the equatorial Pacific and the Arctic, that impact the regional and hemispheric North Pacific data.
Did late 19th and early 20th century volcanic aerosols cause the drop in North Pacific SST? Refer to Figure 6. In it I added a very much scaled SATO index of optical thickness for reference. Based on the lack of a similar response in the latter half of the 20th century to volcanic eruptionsof comparable size, and based on the time lags for the central Pacific data sets to react to the drop in temperature, I’d have to say that it wasn’t volcanic aerosols. What else? Thermohaline circulation? The North Pacific, in some reports, is an area of upwelling of subsurface water.
Bloggers constantly proclaim “The PDO has flipped”, or “switched,” and forecast its influence on global temperatures, without understanding that the PDO is statistical function of North Pacific SST. It is not North Pacific SST. The PDO explains regional climate variations. There is also a coincidence between the phase of the PDO and the sign, frequency, and magnitude of ENSO events. As discussed in numerous papers, ENSO events drive the PDO. ENSO events do not, however, drive the oscillations illustrated in this post.
Sea Surface Temperature Data is Smith and Reynolds Extended Reconstructed SST (ERSST.v2) available through the NOAA National Operational Model Archive & Distribution System (NOMADS).