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Saturday, September 12, 2009

Supplement To ENSO Is A Major Component Of Sea Level Rise

I’ve moved to WordPress.  This post can now be found at Supplement To ENSO Is A Major Component Of Sea Level Rise
In my post ENSO Is A Major Component Of Sea Level Rise, I illustrated that ENSO is the cause of the pattern of Sea Level Trends illustrated in Figure 1. The IPCC confirms this in their discussion of regional variations in the rate of Sea Level Change.
Figure 1

The following is that IPCC discussion on the rate of sea level change. The illustrations referenced by the IPCC follow the quote. Refer to page 416 of the IPCC AR4, or page 32 of 48 of AR4, Chapter 5.


“5.5.4 Interpretation of Regional Variations in the Rate of Sea Level Change

“Sea level observations show that whatever the time span considered, rates of sea level change display considerable regional variability (see Sections and A number of processes can cause regional sea level variations.

“ Steric Sea Level Changes

“Like the sea level trends observed by satellite altimetry (see Section, the global distribution of thermosteric sea level trends is not spatially uniform. This is illustrated by Figure 5.15b and Figure 5.16b, which show the geographical distribution of thermosteric sea level trends over two different periods, 1993 to 2003 and 1955 to 2003 respectively (updated from Lombard et al., 2005). Some regions experienced sea level rise while others experienced a fall, often with rates that are several times the global mean. However, the patterns of thermosteric sea level rise over the approximately 50-year period are different from those seen in the 1990s. This occurs because the spatial patterns, like the global average, are also subject to decadal variability. In other words, variability on different time scales may have different characteristic patterns.

“An EOF analysis of gridded thermosteric sea level time series since 1955 (updated from Lombard et al., 2005) displays a spatial pattern that is similar to the spatial distribution of thermosteric sea level trends over the same time span (compare Figure 5.20 with Figure 5.16b). In addition, the first principal component is negatively correlated with the Southern Oscillation Index. Thus, it appears that ENSO-related ocean variability accounts for the largest fraction of variance in spatial patterns of thermosteric sea level. Similarly, decadal thermosteric sea level in the North Pacific and North Atlantic appears strongly influenced by the PDO and NAO respectively.

“For the recent years (1993–2003), the geographic distribution of observed sea level trends (Figure 5.15a) shows correlation with the spatial patterns of thermosteric sea level change (Figure 5.15b). This suggests that at least part of the nonuniform pattern of sea level rise observed in the altimeter data over the past decade can be attributed to changes in the ocean’s thermal structure, which is itself driven by surface heating effects and ocean circulation. Note that the steric changes due to salinity changes have not been included in these figures due to insufficient salinity data in parts of the World Ocean.”

Figure 5.15
Figure 5.16
Figure 5.20


Note that the negative correlation between the Southern Oscillation Index (SOI) and the first principal component of thermosteric sea level time series means that the first principal component would correlate directly (not negatively) with NINO3.4 and Cold Tongue Index SST anomalies.

Also, by using the trend maps, the IPCC fails to present the magnitude of the ENSO component in those sea level trends. I plotted the data in ENSO Is A Major Component Of Sea Level Rise. Figures 2 and 3 illustrate the Sea Level variations (total, not just thermosteric) for the Cold Tongue Index area of the eastern tropical Pacific (6S-6N, 180W-90W) and of the Pacific Warm Pool in the western tropical Pacific (10S-20N, 110E-175E).
Figure 2
Figure 3


John said...

Hi Bob -

I know you are an ocean guy, but do you have any comments on why the UAH september anomalies to date are so high? They are exceptionally above recent years and well over 1 degree F above the 30 year trend. Seems to be the brewing of record breaking month, perhaps.

Is this the El Nino being reflected in the atmospheric temperature? It seems the the El Nino is a bit weak to creat such a large jump ...

Bob Tisdale said...

Sorry, John, I don't keep track of it. Lucia over at the Blackboard does keep an eye on it, though.

John said...

Thanks Bob.

I just found the rises in Sept a bit odd given ocean temps have been declining the past two weeks. I guess it's all about various lags and when they hit.

We had a huge jump in OST in what, June-ish? I wonder if that is now being reflected in the atmosphere.

No need to respond, just ruminating. :)

Anonymous said...

I notice over at Lucia's that there was a comment by Bob Illis in the recent El Nino thread about the effect on Nino on global temperature, at least in the short term. Does this jive with your understanding? It seems rather small.


Let’s compare the Nino region anomalies for the same time of year between this El Nino and the 1997-98 Super El Nino.

Week Nino1+2 Nino3 Nino34 Nino4

10SEP1997 4.0 3.0 2.3 0.8
09SEP2009 0.5 0.8 0.9 0.8

They are not really close. This El Nino is only about 1/4 the strength of the 1997-98 one at the same time of year. There is a definitive seasonal signal to the ENSO with about 80% of El Ninos/La Ninas peaking in the November to January period.

A regression of the Nino 3.4 region on global temperatures results in = 0.07 * Nino 3.4 anomaly of 3 months previous.

So, global early-December temperatures will only be about 0.056C higher than they would have been with neutral Nino conditions. ie, hard to measure and very hard to notice.

The Tropics regression is about = 0.2 * Nino 3.4 anomaly of 2.5 months previous.

So, the Tropics will have slightly higher late-November temperatures but it will also be very hard for anyone to notice.

Bob Tisdale said...

Anonymous: I had to read the following sentence that Bill Illis wrote a few times to realize what he'd said. He wrote, "A regression of the Nino 3.4 region on global temperatures results in = 0.07 * Nino 3.4 anomaly of 3 months previous."

In other words, if there is a rise in NINO3.4 SST anomalies of 1 deg C, global temperatures will rise 0.07 deg C three months later.

The global response varies with the study, I've seen responses as high as 0.092 deg C in global temp per 1 deg C in NINO3.4 SST anomaly, and the lag can vary from 3 to 6 months.

The other thing to consider in Bill's comment is that ENSO neutral conditions run from -0.5 to +0.5 deg C, so he must be subtracting 0.5 deg C from the forecasted NINO3.4 SST anomalies and multiplying the remainder by the 0.07 deg C global response to NINO3.4 SST anomaly coefficient.

John said...

Hi Bob -

Another ramdom question - do you have any good articles on the AMO? A search turns up a lot of data, and I'm curious what you'd recommend as a good primer.

I read the post you made about the Atlantic Ocean being by far the largest component of the temperature trend the past 30 years and found it quite interesting. I'd love to learn more.

Is the basic concept the Atlantic will warm for another 10-ish years or so, then begin to switch back? Has anyone really taken the AMO into account in models?

I'm a fountain of questions. Apologies if it is a bother.


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