Guest post by Bob Tisdale
In this post I have also provided comparisons to scaled NINO3.4 SST anomalies. As could be expected, some of the rises and falls are related to ENSO events. The step changes also appear to be direct responses to El Nino events. I am not, however, implying that Sea Level variability is only impacted by ENSO.GLOBAL SEA LEVEL
The monthly Global Sea Level data from December 1992 to March 2009 is illustrated in Figure 1. The late 1995 spike in the sea level data stands out similarly to the way the 1997/98 El Nino stands out in global temperature data.
Figure 2 compares Global Sea Level to scaled NINO3.4 SST anomalies. The peak in late 2005 is not directly related to an El Nino. The impacts of the 1997/98 and the 2002/03 El Nino events, however, can be seen in the Global Sea Level data.
MONTHLY SEA LEVEL FOR THE ATLANTIC, INDIAN, AND PACIFIC OCEANS
As preliminary notes, the annual variability in the Atlantic and Indian Ocean Sea Level data can be clearly seen in the monthly data. The Pacific data is noisier, which masks an annual signal.
Note how the smoothed Atlantic Sea Level data, Figure 3, appears to rise in steps. The first step is in 1995. This should be a rebound from the Mount Pinatubo aerosol effects.
The scaled NINO3.4 SST anomaly data has been added in Figure 4. The smoothed Atlantic Sea Level data rises again in 1997, which should be a response to the 1997/98 El Nino. Are the rises in 2003 and 2005 also responses to the 2003/04 and 2004/05 El Nino events?
The raw and smoothed Indian Ocean Sea Level data, Figure 5, show a major step change in 1998 and a curious increase in trend in 2004.
The 1998 upward step in the smoothed Indian Ocean Sea Level data appears to be a lagged response to the 1997/98 El Nino. Refer to Figure 6. The 2004 change in trend does not appear to be ENSO related. Was there a shift in Indian Ocean cloud cover in 2004?
Following the significant increase from 1998 to 2002, the Pacific Ocean Sea Level, Figure 7, has been relatively flat since 2002. The rise in Pacific Sea Level slowed after 2002, and Pacific Sea Level has declined since 2006.
In the comparison with NINO3.4 SST anomalies, Figure 8, note how the Pacific Ocean Sea Level surged upward in mid-1996, one year before the 1997/98 El Nino. Does this indicate that there was a sudden rise in ocean heat content in the year leading up to that El Nino? Does this confirm the findings in my post “Did A Decrease In Total Cloud Amount Fuel The 1997/98 El Nino?” It does seem to show that the 1997/98 El Nino was fueled by a short-term change (one year) in the ocean heat content of the Pacific.
ATLANTIC, INDIAN, AND PACIFIC OCEAN COMPARISONS
Figure 9 is a comparison of Sea Levels for the Atlantic, Indian, and Pacific Oceans. Note how one dataset always appears to be out of phase with the variations of the other two. Rarely do the sea levels of all three oceans rise or fall in unison.
The SST anomalies for the Atlantic, Indian, and Pacific Oceans are illustrated in Figure 10. There are significant differences between the SST and Sea Level curves. (I can’t see any reason to compare the individual ocean sea level and SST data.)
Sea Level data is available through the University of Colorado at Boulder webpage:http://sealevel.colorado.edu/index.php