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Saturday, May 17, 2008

Long-Term Monthly NINO 3.4 SST Data

The majority of ENSO SST-based data available online is anomaly data that has been normalized, standardized, smoothed, filtered, or combined with other variables. I went searching for and found what I believe to be unadulterated NINO 3.4 SST data. It’s available from NCDC.

Main Time Series Page:

NINO 3.4 Time Series Page:

NINO 3.4 SST Data from 1871 to Present:

There is nothing in their description to indicate anything other than raw data based on the reconstructions or composites noted.

Figure 1a illustrates the raw monthly NINO3.4 SST data for a little more than 137 years. There’s a minor increase in temperature, using the linear trend line as reference. Replacing the linear with a 6th order polynomial trend, NINO3.4 temperature has a slow underlying oscillation and it peaked in the early 1990s. Refer to Figure 1b. Only a 3rd order polynomial trend shows a minor upswing toward the end of the data series, not illustrated.

Figure 1a: NINO3.4 SST - Monthly - January 1871 to March 2008 – Linear Trend

Figure 1b: NINO3.4 SST - Monthly - January 1871 to March 2008 – Polynomial Trend

What also stands out in the monthly NINO3.4 SST data is the increase in the range of extremes in later years, the higher amplitude. But if NINO3.4 reflects changes in solar irradiance, doesn’t that seem to agree with the increasing amplitude in the solar cycle. Refer to Figure 2.

Figure 2: Solar Irradiance – Lean + ACRIM - 1880 to 2007

For those who don’t know where the NINO 3.4 region is located, I’ve provided a map with it highlighted in Figure 3. I’ve always found it remarkable that a 1 to 2 degree temperature swing in the SST of that relatively small section of the planet, and in the other adjoining NINO areas, can create havoc with global temperature and precipitation.

Figure 3: NINO 3.4 Region

The annual maximums, minimums, and average NINO3.4 data for each year from 1871 to 2007 are shown in Figure 4.

Figure 4: NINO3.4 SST Annual Maximum-Minimum-Average 1871 to 2007

Based on the linear trend in Figure 5, annual average NINO3.4 SST rose less than 0.3 deg C over 136 years. Other than that the average temperature graph appears similar to most representations of NINO3.4 temperature.

Figure 5: NINO3.4 SST Annual Average 1871 to 2007

Again using the trend lines as reference, annual maximum NINO3.4 SST, Figure 6, rose while annual minimum NINO3.4 SST, Figure 7, was flat.

Figure 6: NINO3.4 SST Annual Maximum 1871 to 2007

Figure 7: NINO3.4 SST Annual Minimum 1871 to 2007

This of course creates an increase in the difference between annual temperature extremes, as illustrated in Figure 8.

Figure 8: NINO3.4 SST Maximum minus Minimum 1871 to 2007

I hesitated before posting the next graph, because correlation might be in the eye of the beholder. In other words, I may be reading too much into what appears to be a possible influence of solar irradiance on Minimum NINO3.4 temperature. Figure 9. To scale the TSI, I used the following equation.

Figure 9 TSI Scale = (TSI-1351.8)*1.8

Someone with filtering capabilities may be able to extract a better visual.

Figure 9: NINO3.4 SST Minimum vs TSI Scaled – Lean + ACRIM 1871 to 2007

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