>This is the first post of a three-part series that examines NINO3.4 SST (not NINO3.4 anomaly) data. In it, I’ll illustrate the subtle differences between the SST and the SST anomaly data and show unusual aspects of NINO3.4 SST data (other than the magnitude of its variations) that differentiate it from other SST data sets.
COMPARISION OF NINO3.4 SST and SST ANOMALY DATA
Figures 1 and 2 illustrate long- and short-term NINO3.4 SST data. The long-term data spans the period of January 1854 to July 2008, and the short-term data, January 1978 to July 2008. Due to the volume of data in the long-term graph, Figure 1, it’s difficult to visualize any difference between it and NINO3.4 anomaly data. The short-term data, however, shows a slightly greater period of elevated temperatures during the 82/83, the 86/87/88, and the 97/98 El Nino events.
Figures 3 and 4 are comparative graphs of NINO3.4 SST and NINO3.4 SST anomaly data. To bring the SST data down to a similar scale, I shifted it 26.521 deg C, which was the SST value for January 1854. You’ll have to use the Tinypic links because I had to decrease the weight of the anomaly curve to assure it wasn’t obscuring the SST curve. As shown in the long-term graph, Figure 3, the SST data presents the monthly cycles over the course of a year, while the anomaly data is suppressed by its comparison to a monthly mean. In the short-term graph, Figure 4, the SSTs for the April 1992 and May 1993 are shown to be comparable to the SSTs in January 1983 and November 1997, which are the peak SSTs of the significant 82/83 and 97/98 El Nino events. Using the ONI index for reference, May 1993 is not considered an El Nino month, though its SST is similar to that of the “super” El Ninos. In the second part of this series, I’ll determine the temperature differences between NINO3.4 SST and other variables to illustrate the importance, or lack thereof, of elevated NINO3.4 SSTs like that of May 1993.
ANNUAL TRENDS OF MAXIMUM, MINIMUM, AND AVERAGE NINO3.4 SST
Figure 5 illustrates the annual Maximum, Average, and Minimum NINO3.4 SST from 1854 to 2007. The unusual aspect of the NINO3.4 SST data is that the trend in the minimum annual SSTs is negative. Why is that unusual? In all other data sets I’ve investigated so far, such as minimum global and hemispheric SSTs and minimum global Land Surface Temperature (LST), they all have positive trends.
Why would NINO3.4 minimum annual SSTs have dropped when minimum temperatures for all other data sets rose? Sorry, you won’t find the answer here.
ADDITIONAL VIEWS OF NINO3.4 MINUMUM AND MAXIMUM TEMPERATURES
The next two graphs provide additional views of the differences between minimum and maximum annual NINO3.4 SST. I’ll offer no additional input other than to explain the graphs.
To better illustrate the differences in trends between the NINO3.4 annual maximum and minimum SSTs, I zeroed both data sets at their 1854 values in Figure 6.
The last graph, Figure 7, shows the difference between NINO3.4 annual maximum and minimum SST.
PREVIEW OF PART 2
In Part 2 of this series, I’ll examine the temperature differences between NINO3.4 SST and other SST data and between NINO3.4 SST and absolute global combined (land plus sea surface) temperatures.
Sea Surface Temperature Data is Smith and Reynolds Extended Reconstructed SST (ERSST.v2) available through the NOAA National Operational Model Archive & Distribution System (NOMADS).