A Closer Look At Oceanic Oscillation Cycles

In the past, I’ve presented some charts on the different Oceanic Oscillations for PDO, AMO, and ENSO. I’ve started to take a look at these again with an eye towards running a correlation analysis. The initial work I’ve done today is something I considered somewhat interesting, so I thought I’d share it.

The first thing I’ll present is the chart for Arctic Ocean Oscillation Indices since 1950, smoothed at one year, 5 years, and 10 years. These are presented below:

The overall Arctic Oscillation index data since 1950 - 1 year smoothing.

The overall Arctic Oscillation index data since 1950 - 5 year smoothing.

The overall Arctic Oscillation index data since 1950 - 10 year smoothing.

Unlike the AMO, PDO, and ENSO charts, there is no apparent cyclicality showing up in the Arctic Oscillation chart. There does appear to be a trend upward overall, and there are certainly ups and downs within that. The 1-year chart looks much like an ENSO chart would be. Unlike ENSO, though, I’m not picking up a longer cycle.

Well, I wanted to show that chart to start, since the Arctic seems to be the focus of a lot of attention. I guess it bears musing whether or not the Oscillation has a root cause from the Ocean itself, or the sun, or melting ice, or freezing ice, or other factors that override any cyclical nature that would otherwise be apparent.

That’s all I really did on that piece. But I’d like to move on to some work I did with the AMO, PDO, and ENSO (as well as a look at those Arctic Oscillations).

Pacific Decadal Oscillation (PDO) Index – Back into the Negative

The PDO index is a measure of another one of those weird oceanic oscillation patterns.  The ENSO index is a shorter-term varying event, whereas the PDO index is considered a longer-term event.  Interestingly, however, when you collapse the ENSO index into longer average time periods, there does appear to be persistency in the ENSO index, as well. However, the short-term cyclical nature of the ENSO index is much more evident than the PDO index, even if the averages show similar persistency.

The PDO index is predominant in the Northern Pacific and secondarily evident in the tropics, whereas the ENSO index is the other way around. ENSO receives so much attention because of the large short-term cyclical variations, but the PDO has very significant swings as well, just usually over a longer period of time.

The index, however, is measured on a month-to-month basis and the data can be located here.

November has not yet been updated, but the October index value was -1.76. This was the single coolest reading in any month since November 1999, and was the 14th consecutive negative reading in a row. While there have been other stretches of 14 consecutive negative readings – the last being 1999-2000, it is interesting to note that the current streak of seven consecutive readings of less than -1 has not been seen since the period ending February 1976. That particular stretch ended at 7 months. If this month’s reading is below -1, it will mark the first time since the period ending June 1972. And that streak ended at 8. Beyond that point takes us to a streak in the early 1960s. So I’ll keep an eye on that.

As I did with the ENSO index, I collapsed the raw data into different average periods. Since the PDO does seem to vary over a longer period of time, I went up to a 10 year average. The persistency in the index is very clear once you take longer-term averages.

Below are a few charts of the PDO. The first is the raw data. Taking the edges off with 12-month smoothing follows that. I then present 5-year and 10-year averages.

The PDO monthly index has been negative for a bit already, as has the five-year average. But the 10-year average recently went negative, as well. Of course, all the same arguments apply as in the ENSO discussion – the persistence matters. You keep a heater running and the temperature gets warmer than the temperature an hour ago, depending on insulatory effects. Persistence in both ENSO and PDO correspond with the warming we see in the global temperature readings. The 10-year average PDO is slightly negative, and we’ve cooled slightly in the last few years. Coincidence?

The overall PDO index data since 1900.

The overall PDO index data since 1900 with 12-month smoothing.