This post illustrates differences between ERSST.v3b and HADISST NINO3.4 SST data. I am in no way attempting to indicate if one or the other is correct.
In the December 18, 2008 post NINO3.4 Data Comparison–HADSST and ERSST.v3, I provided a simple comparison of the two datasets in terms of SST anomalies. This post will use SST data, not anomalies, for the NINO3.4 region. This allows illustrations of annual averages, maximums, minimums and the temperature difference between annual maximums and minimums. I’ve also smoothed the above subsets with 11-year running-average filters to help show those differences on decadal bases. There appears to be a multidecadal pseudo-periodic cycle that takes a simple analysis to uncover.
The Panama Canal opened in 1914. Prior to then, sampling of eastern equatorial Pacific SST was very sporadic. Keep that in mind when reviewing any early ENSO SST data.
The earlier post also included a few quotes from the paper “Improvements to NOAA’s Historical Merged Land–Ocean Surface Temperature Analysis (1880–2006)”, Smith and Reynolds (2008), JOURNAL OF CLIMATE, VOLUME 21, provides an explanation for the difference between the ERSST.v3 and HADSST versions. Refer to page 2293, or pdf document page 11 of 14.
I’ll repeat and expand one quote regarding the NINO3.4 data now:
“The all-month anomaly correlation of HadISST with ERSST.v3 in this region for 1880–1997 is 0.90. Both analyses are clearly producing consistent interannual variations. But there are important differences in this region in periods when sampling is sparse. In Niño-3.4 prior to 1950, HadISST is biased about 0.3°C warmer than ERSST.v3. Much of the bias is due to the use of different historical bias adjustments in the two analyses prior to 1942. Another important difference depends on the method used to compute low frequency variations. In HadISST they are computed by fitting data to a global mode, while here simpler averaging and filtering is used, as discussed above.”
Is the HADISST data biased warmer or the ERSST.v3b data biased cooler? That’s the question for you to decide.
ANNUAL AVERAGE SST
Figure 1 compares annual average NINO3.4 SSTs, without smoothing, for the ERSST.v3b and HADISST datasets. The annual variations do agree quite well, as noted in the Smith and Reynolds paper. The underlying differences can also be seen.
Smoothing the two NINO3.4 SST datasets with 11-year running-average filters, Figure 2, emphasizes the differences prior to 1950. From 1900 to 1916, the decrease in the ERSST.v3b data is approximately twice that of the HADISST data.
COMPARISONS TO TROPICAL SST (SMOOTHED)
Figures 3 and 4 are comparisons of Tropical SST and annual average NINO3.4 SST data for the HADISST and ERSST.v3b datasets. The data has been smoothed with 11-year filters. The NINO3.4 region is contained within the tropics. It seemed like a logical comparison.
ANNUAL MAXIMUM SST
The Annual Maximum NINO3.4 SSTs for the ERSST.v3b and HADISST datasets are shown in Figure 5.
The smoothed Annual Maximum data, Figure 6, shows less divergence in the 1880s through 1900 than the annual averages in Figure 2.
ANNUAL MINIMUM SST
Figure 7 illustrates the Annual Minimum NINO3.4 SSTs for the ERSST.v3b and HADISST datasets.
And again the smoothed Annual Minimum data in Figure 8 shows the divergence from the late 1800s to ~1950.
ANNUAL MAXIMUM SST MINUS ANNUAL MINIMUM SST
To create Figure 9, the Annual Minimum Data was subtracted from the Annual Maximum data. This would emphasize those El Nino events that were followed by a significant La Nina.
Smoothing the annual minimum to maximum temperature difference data, Figure 10, reveals a semi-periodic multidecadal variation. The “cycle” disappears before 1910. Is this a result of the limited data availability during early years?
SUPPLIMENTS TO THIS POST
Comparison graphs serve their purpose but can mask characteristics of the individual datasets. For this reason, in supplemental posts, I have included graphs (without commentary) of the Average, Maximum, Minimum, and Max-to-Min delta-T NINO3.4 SST data for the ERSST.v3b and HADISST datasets. Refer to:
The HADISST graphs are included in Supplement 1 to Comparison of Annual ERSST.v3b and HADISST NINO3.4 SST (Not Anomaly) Data
The ERSST.v3b graphs are included in Supplement 2 to Comparison of Annual ERSST.v3b and HADISST NINO3.4 SST (Not Anomaly) Data
The ERSST.v3b and HADISST data are available through the KNMI Climate Explorer website: