ENSO Update

CORRECTION - November 7, 2008

Following Figure 2 this post, I make the following statement: “The Southern Oscillation Index (SOI) is the surface pressure component of ENSO. It usually precedes the NINO3.4 SST changes by a few months.”

The NINO3.4 SST anomaly does NOT always follow the SOI, though it has been doing so for the past few months. They do correlate remarkably well, but there are times when the changes in NINO3.4 will precede the SOI and times when they can become slightly out of synch. Therefore, I’ll retract the sentence “It usually precedes the NINO3.4 SST changes by a few months”.

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The NCEP Reynolds Optimally Interpolated (OI.v2) Sea Surface Temperature data on NOMADS is available on a weekly updated basis from January 1990 and monthly from November 1981. The monthly data appears to include the average of the weekly values for the month in progress, which would allow for early reporting of values. The weekly NINO3.4 data is shown in Figure 1, and the monthly in Figure 2.
http://i37.tinypic.com/2jeqnix.jpg
Figure 1
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http://i33.tinypic.com/5xsn84.jpg
Figure 2

The Southern Oscillation Index (SOI) is the surface pressure component of ENSO. It usually precedes the NINO3.4 SST changes by a few months. The SOI has stalled this month after rising for the 4 consecutive months. Regardless, the SOI for October is significantly higher than this time last year. The SOI for October 2007 was 5.4. This October it is 13.4. Refer to Figure 3. To counter that, the NINO3.4 SST anomaly for October 2007 was -1.38 deg C, while the October 2008 reading is -0.28 deg C. Will the NINO3.4 SST anomaly follow the SOI’s lead? Time will tell.
http://i36.tinypic.com/2w4fcph.jpg
Figure 3

For those who can’t see the relationship between the SOI and NINO3.4, I’ve inverted the SOI in Figure 4.
http://i34.tinypic.com/wahpah.jpg
Figure 4

SOURCE

Reynolds Optimally Interpolated (OI.v2) Sea Surface Temperature data is available through the NOAA National Operational Model Archive & Distribution System (NOMADS).
http://nomads.ncdc.noaa.gov/#climatencdc

SOI data available from the Australian Government Bureau of Meteorology
http://www.bom.gov.au/climate/current/soi2.shtml
Specifically:
ftp://ftp.bom.gov.au/anon/home/ncc/www/sco/soi/soiplaintext.html