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Tuesday, May 5, 2009

Opposing North Pacific and Indian Ocean SST Residuals

I’ve moved to WordPress.  This post can now be found at Opposing North Pacific and Indian Ocean SST Residuals
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INTRODUCTION

I posted an interesting comparative graph of SST anomaly residuals of the North Pacific and Indian Oceans in Individual Ocean SST Anomalies In Perspective. Refer to Figure 1. The two curves opposed one another.
http://i39.tinypic.com/wbyt5z.jpg
Figure 1

WHAT THE RESIDUALS REPRESENT

Figure 2 compares Global SST anomalies (red curve) with the SST anomalies of the North Pacific (blue curve) and Indian Ocean (green curve). The North Pacific and Indian Oceans SST anomalies follow the global dataset with minor deviations. The residuals represent these minor differences, calculated as Global SST anomalies subtracted from the respective SST anomaly dataset.
http://i42.tinypic.com/2w5twzq.jpg
Figure 2

The comparison of the North Pacific and Indian Ocean residuals from 1978 to present, Figure 3, also shows that the two datasets oppose one another in the short term. (The data in Figure 3 has been smoothed with a 12-month running-average filter.) I’ve highlighted 1998, about the time of the peak of the 1997/98 El Nino, and the periods that would have been impacted by the El Chichon and Mount Pinatubo eruptions. Note the responses of the North Pacific and Indian Ocean residuals after the 1997/98 El Nino. The North Pacific residual exhibits a multiyear dip and rebound associated with the 1998/99/00 La Nina, while the Indian Ocean shows a rise and multiyear decay in the anomalously high residuals over the same period. In terms of NINO3.4 SST anomalies (not illustrated), the 1982/83 El Nino was nearly the same magnitude at the 1997/98, but the responses of the North Pacific and Indian Ocean residuals were not nearly as great. The eruption of Mount Pinatubo appears to have suppressed the responses to the 1982/83 El Nino. And the Mount Pinatubo eruption overpowered the reactions to the 1991/92 El Nino.

But what causes the North Pacific residual to drop after an El Nino event? And what causes the Indian Ocean residual to rise?
http://i43.tinypic.com/301lftf.jpg
Figure 3

To answer those questions, we’ll refer to a short-term graph of Global, North Pacific, and Indian Ocean SST anomalies (not residuals), Figure 4. Starting early in 1997, all three datasets rose in response to the 1997/98 El Nino. Note how the North Pacific SST anomalies dip well below those of the global SST anomalies during the 1998/99/00 La Nina. The North Pacific SST anomaly response is exaggerated at that time because it fully follows the variations in equatorial SST anomalies. This, in turn, causes the North Pacific residual to drop. On the other hand, while temperatures are increasing in 1997, the Indian Ocean response to the 1997/98 is also slightly more than the global dataset, but as SST anomalies drop in response to the resulting La Nina, the SST anomalies of the Indian Ocean do not fall as far as the global SST anomalies. This causes the rise in the Indian Ocean residual.
http://i43.tinypic.com/2zi0ns7.jpg
Figure 4

LOOSE LONG-TERM CORRELATIONS WITH OTHER DATASETS

There is a very loose correlation between the North Pacific and North Atlantic Residuals, Figure 5. Do the SST anomaly variations caused by Thermohaline Circulation/Meridional Overturning Circulation in the North Atlantic impact SST anomalies in the North Pacific? Or does the North Pacific influence the North Atlantic? Most likely, they both have an influence on the other.
http://i39.tinypic.com/33nxe8l.jpg
Figure 5

And it appears that the Indian Ocean Residual may be impacted by the Southern Ocean SST anomalies (not residuals) for the area south of the Indian Ocean. Refer to Figure 6. Note, however, that there is a long-term decline in the Southern Ocean subset from the 1880s to the 1930s and more sudden rise during the 1940s that is not present in the Indian Ocean Residual data.
http://i39.tinypic.com/1zdar9l.jpg
Figure 6

SOURCE

ERSST.v3b data is available through the KNMI Climate Explorer website:
http://climexp.knmi.nl/selectfield_obs.cgi?someone@somewhere

2 comments:

Jeanette said...

Bob, I am curious about your ideas as to why the North Pacific and the Indian Ocean Residuals are opposing. Is it because, first, in a negative PDO, the east and central Pacific are "hot" (your i39.tinypic.com/20v1934.jpg) while west Pacific and tropic SSTs are cooler? And, second, the Indian Ocean would also be cooler because of cooler tropic SSTs?

When I look at the Southern Ocean and the Indian Ocean, in most cases the Indian Ocean appears to lead the Southern Ocean in temperature changes? Is this accurate?

I wonder if you are developing a thesis about ocean circulation and SSTs (and trade winds, and TSI, and pressure, and clouds, and topography, etc)? I remember the one you put forward about the influence of El Nino in the area of tropical Pacific 3.4 (if I have the labeling right). To show its influence all the way across Central America into the Atlantic was remarkable. I look forward to where you are taking all your data. I am a neophyte in ocean (and climate) science, but always very interestred.

Bob Tisdale said...

Jeanette: You asked, “Bob, I am curious about your ideas as to why the North Pacific and the Indian Ocean Residuals are opposing. Is it because, first, in a negative PDO, the east and central Pacific are "hot" (your i39.tinypic.com/20v1934.jpg) while west Pacific and tropic SSTs are cooler? And, second, the Indian Ocean would also be cooler because of cooler tropic SSTs?”

The two residuals oppose one another due to the difference in responses to ENSO events, not necessarily the phase of the PDO. The North Pacific SSTs (not residuals) follow the equatorial Pacific SST anomalies, (Figure 4 above) while the response of the Indian Ocean has a multiyear decay. Also, keep in mind that the North Pacific residual is North Pacific SST anomalies MINUS Global SST anomalies, and the Indian Ocean residual is Indian Ocean SST anomalies MINUS Global SST anomalies. For these reasons, it’s pretty difficult to illustrate the reason for the opposing nature of the two residuals while using a map of SST anomalies.

Let’s look again at Figure 4 above, immediately after the 1997/98 El Nino. If you were to subtract the Global SST anomalies from the Indian Ocean SST anomalies, the Indian Ocean residual would rise as shown in Figure 3. And (referring again to Figure 4), if you were to subtract the Global SST anomalies from the North Pacific SST anomalies, the North Pacific residual would drop, as shown in Figure 3.

You wrote, “When I look at the Southern Ocean and the Indian Ocean, in most cases the Indian Ocean appears to lead the Southern Ocean in temperature changes? Is this accurate?”

Figure 6, above, compares an SST anomaly (Southern Ocean) with a residual (Indian Ocean). I was really trying to illustrate influence, not necessarily cause and effect or lead and lag. Sorry, the way I wrote that did imply cause and effect. They influence one another.

Follow the currents for the Indian Ocean in the lower right-hand corner of the map in the following link. The Southern Ocean feeds the eastern Indian Ocean, while the western Indian Ocean feeds the Southern Ocean. So they influence one another. The Southern Ocean, South of the Indian Ocean, is also influenced by the waters coming from upstream in the Antarctic Circumpolar Current (identified as the West Wind Drift on the current map). And of course the western equatorial Pacific would also influence the Northeastern Indian Ocean, and vice versa.
http://upload.wikimedia.org/wikipedia/commons/6/67/Ocean_currents_1943_%28borderless%293.png

You wrote, “I wonder if you are developing a thesis about ocean circulation and SSTs…”

I’m just a blogger (former engineer, sales engineer, etc.), occupying time with something that interests me.

Thanks for the interest.

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