Indian Ocean - A More Detailed Look

INTRODUCTION

Before returning to the series on the tropics, I felt it would be good idea to learn more about the Indian Ocean, more than what I’d reported in a prior post.
http://bobtisdale.blogspot.com/2008/08/indian-ocean-and-south-atlantic-ocean.html

The Indian Ocean is the third largest ocean, representing approximately 20% of global surface waters. It’s obviously impacted by neighboring oceans: the Atlantic, Pacific, and Southern Oceans. It shares the Indo-Pacific Warm Pool (aka Pacific Warm Pool) with the Pacific, and, due to its proximity with the Pacific, it is strongly impacted by ENSO events. The Indian Ocean is unlike the Atlantic and Pacific Oceans in one major detail; the Northern Hemisphere portion of the Indian Ocean is very much limited in size, while the Atlantic and Pacific Oceans extend northward to interact with the Arctic Ocean. There are a good many phenomena taking place in the Indian Ocean: the Indian Ocean Dipole (IOD) for one. In this post, I have no intention of delving deeper than an introductory look at the IOD.

Figure 1 illustrates monthly Indian Ocean SST anomaly data from 1854 to 2008. (The data has been smoothed with a 37-month filter.)
http://i34.tinypic.com/smznt1.jpg
Figure 1

The Indian Ocean SST anomalies exhibit an overall trend that’s slightly different than Global SST anomalies, and the periodic variations due to ENSO events and other perturbations are amplified. Refer to Figure 2. The clearly visible difference is the magnitude of the rise up to and the spike centered around 1940, which coincides with a series of significant El Nino events.
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Figure 2

Subtracting the Global SST anomalies from the Indian Ocean SST anomalies, Figure 3, illustrates the influence of the Southern Ocean as shown in Figure 4.
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Figure 3
http://i34.tinypic.com/dcora.jpg
Figure 4

INDIAN OCEAN CURRENTS AND THE INDIAN OCEAN GRIDS USED IN THIS POST

Figure 5 is the most detailed, easily readable illustration of Indian Ocean sea surface currents I could readily find. (Figure 5 is a large file; it will expand greatly when downloaded.)
http://i35.tinypic.com/b3lqo9.jpg
Figure 5

While the South Equatorial Current appears to be the dominant current in the Indian Ocean, there are a multitude of others: equatorial counter currents, coastal currents, monsoon drifts. The southernmost current identified as the West Wind Drift is better known as the Antarctic Circumpolar Current or ACC. I’ve elected to continue to identify it as the West Wind Drift to maintain a common name between illustrations. I did, however, note it as the Antarctic Circumpolar Current parenthetically in Figure 13.

Using the currents as a guide, but without segmenting the data too far, I first divided the Indian Ocean into latitude bands. Refer to Figure 6. The first division isolated the Arabian Sea and the Bay of Bengal. Then I separated the areas just north and south of the equator. Further south, I divided the Indian Ocean Gyre (for lack of a better identifier) into north and south components. That left the West Wind Drift (ACC). Each of the latitude bands I subdivided into west, central, and east areas, with hope of identifying significant differences, if any existed. That left the area west and southwest of Madagascar, which I have identified as the Mozambique Channel (Plus).
http://i34.tinypic.com/v2tnde.jpg
Figure 6

SEGMENTED INDIAN OCEAN SST ANOMALIES

Initial note: The exaggerated spike in temperatures around 1940 does decrease in amplitude as the data sets proceed farther south. Keep an eye out for it, because it does resurrect itself in the western portion of the South Gyre data set.

Figure 7 shows the SST anomalies for the Arabian Sea and the Bay of Bengal. Keying off the 1940 spike, the Arabian Sea has greater periodic variations. Its overall trends are slightly larger too. Yet, it is larger in area than the Bay of Bengal, indicating the larger variations in signal are not size related. Are the SST anomalies amplified as we travel farther west?
http://i35.tinypic.com/k3rwoj.jpg
Figure 7

It will be tough to determine from the next group, since the westernmost North Equatorial data set is the smallest in area. Refer to Figure 8, which illustrates the SST anomalies for the west, central, and east portions of the North Equatorial section of the Indian Ocean. Note, though, that the perturbations in the east section are significantly less than the central section, implying that some of the exaggeration of the west area may result from its location.
http://i37.tinypic.com/azc3kz.jpg
Figure 8

Let’s drop another tier to the South. The SST anomalies for the west, central, and east sections of the South Equatorial Indian Ocean are shown in Figure 9. Again, the westernmost data set has the greater periodic variations even though its area is not significantly smaller than the others. Also note that the western data set also flattens somewhat, while the central and eastern SSTs continue to rise. Is this an indication of a Southern Ocean influence? Referring again to the currents in Figure 5, it would be possible. Is it likely?
http://i35.tinypic.com/ridmq8.jpg
Figure 9

A BRIEF OVERVIEW OF THE INDIAN OCEAN DIPOLE

Figure 10 is an illustration of the positive mode of the Indian Ocean Dipole (IOD). During a positive IOD, anomalously warm SSTs form in the western equatorial Indian Ocean, while anomalously cool SSTs form in the southeastern equatorial Indian Ocean. The reverse occurs during a negative IOD. As a result, anomalous sea level pressures and convection occur, which alter rainfall patterns in eastern Africa and Indonesia.
http://i38.tinypic.com/25p79j8.jpg
Figure 10

For a further overview of the IOD, refer to the source of Figure 10:
http://www.jamstec.go.jp/frsgc/research/d1/iod/INDIAN-OCEAN-DIPOLE1.html
There are also many studies of the IOD that can be found online.

RETURNING TO SEGMENTED INDIAN OCEAN SST ANOMALIES

Figure 11 shows SST anomalies (west, central, and east) for the northern portion of the Indian Ocean Gyre. The greatest swings at this tier occur in the eastern portion, which is impacted by a number of major currents. The Indonesian Throughflow brings water into the East Indian Ocean from the western Pacific, passing through the Indonesian Archipelago. This is shown but not identified in Figure 5. The West Australian Current carries water north into the area, while the Leeuwin Current off the Australian coast (not illustrated in Figure 5) transports water southward. The western Australian coast is also an upwelling area.

Note in Figure 11 how the west and central SST anomalies in the northern portion of the Indian Ocean Gyre periodically appear out of synch with the east SST anomalies. Is this representative of the IOD?
http://i34.tinypic.com/r21ftk.jpg
Figure 11

In Figure 12, we’ve dropped south another tier to the southern portion of the Indian Ocean Gyre and again illustrate SST anomalies for the west, central, and east portions. What catches the eye in this graph are the significant anomalous drops in SST in the early 1960s in the west and central data sets.
http://i35.tinypic.com/9sx83c.jpg
Figure 12

That drop in the 1960s can also be seen in the central section SST data of the West Wind Drift (Antarctic Circumpolar Current) illustration. Refer to Figure 13. Also, what seems counterintuitive, the SSTs in the West Wind Drift areas upstream and downstream (west and east sections) rise in opposition to the decrease in SSTs in the central section. Most illustrations of the global Thermohaline Circulation circuit show an upwelling in the Indian Ocean. Is the anomalous decrease in SST in the central West Wind Drift (Figure 13) and in the west and central sections of the South Gyre (Figure 12) a component of THC?

Note how the curves of the data no longer bear a resemblance to the curve of the Indian Ocean, that they are taking on more charateristics of South Ocean, Figure 4.
http://i34.tinypic.com/2s9srgy.jpg
Figure 13

The SST anomalies for the area identified as the Mozambique Channel are illustrated in Figure 14. The curve appears very similar to the western data in the South Equatorial section of the Indian Ocean, Figure 9. This is logical since the Mozambique Current transports waters southward along the East African coast.
http://i33.tinypic.com/1z6w8z4.jpg
Figure 14

The final illustration, Figure 15, is my favorite of the entire post. It shows SST anomalies for the area south of South Africa, bordered by the coordinates 30-60S and 20-30E. It brought to mind Igor’s line, “What hump?” in “Young Frankenstein” by Mel Brooks.
http://i34.tinypic.com/2s97p20.jpg
Figure 15

That graph has prompted me to add the Antarctic Circumpolar Current to my list of future posts. Considering the opposing anomalies in the 1960s in areas that are adjacent to one another, a post on the ACC should be interesting.

CLOSING

While this post introduced more questions than it answered, it does give me enough of a background to return to the series on the tropics.

SOURCE

Sea Surface Temperature Data is Smith and Reynolds Extended Reconstructed SST (ERSST.v2) available through the NOAA National Operational Model Archive & Distribution System (NOMADS).
http://nomads.ncdc.noaa.gov/#climatencdc

Figure 5, which shows Indian Ocean currents, is from Wikipedia and is originally titled “Indian Ocean Gyre”. Refer to:
http://commons.wikimedia.org/wiki/Image:Indian_Ocean_Gyre.png

SST Anomalies By Global Quadrants

INTRODUCTION

Normally, I’ve been segmenting data according to ocean and hemisphere or some portion thereof. I needed a break from the series I’ve been doing on the tropics, so I decided to divide the Globe into quadrants, Figure 1, and see what oddities came to light when I plotted the SST anomalies for the four areas.

http://i37.tinypic.com/345izb4.jpg
Figure 1

As you’ll note, the simplistic approach did a reasonable job of isolating ocean data sets. There’s some overlap--Pacific with Atlantic, Atlantic with Indian, etc.--but it’s a starting point to see if there would any reason to carry an investigation further. The quadrants also include their respective portions of the Arctic and Southern Oceans, so they’re not solely those major oceans. The findings do justify that I put time into creating full ocean data sets and present them in a future post.

Note: All graphs in this post are of monthly long-term data sets, 1854 to 2008. The comparison graphs have been smoothed with 37-month filters, while the graphs of single data sets use 12-month filters. The NINO3.4 data in Figure 3 has not been smoothed.

SST ANOMALIES BY GLOBAL QUADRANTS

Figure 2 shows the SST anomalies for four segments of the globe:
- Far West - 90 to 180W (Purple)
- Near West – 0 to 90W (Red)
- Near East – 0 to 90E (Green)
- Far East – 90-180E (Blue)

The big eye catcher is the 6- to 7-year lag of the Far West SST anomalies during the late 1800s/early 1900s drop in SST. The Eastern Pacific makes up the majority of this area.
http://i36.tinypic.com/k3oev4.jpg
Figure 2

There were 4 moderate El Nino events in 1896/97, 1899/1900, 1902/03, and 1904/05, Figure 3, with only 2 mild, slightly counteracting La Ninas in 1898/99 and 1903/04.
http://i37.tinypic.com/nly5pj.jpg
Figure 3

The relative strengths of those El Ninos versus the La Ninas at that time are better illustrated by the NINO3.4 data that’s been smoothed with a 37-month filter. Refer to Figure 4. Could these El Ninos have delivered sufficient heat to the East Pacific to keep its SSTs from dropping at the same time as the other data sets?
http://i34.tinypic.com/2gwwbk3.jpg
Figure 4

Figures 5 through 8 are graphs of the individual data sets for the four quadrants smoothed with 12-month filters. They’re being provided as reference. All four quadrants display the typical drop in SST anomaly from the late 1800s to the early 1900s. SSTs rise to the 1940s in the Near West, Figure 6, and Near East, Figure 7, quadrants, then decrease to the mid-1960s, when then they rise again. The spike around 1940 in the Near East data (Figure 7) is an extreme example of the abnormal rise in SST anomaly in the Indian Ocean and in parts of the Southern Hemisphere. Illustrating good portions of both hemispheres of the Pacific Ocean, the Far West, Figure 5, and Far East, Figure 8, data sets rise more gradually from 1910s to present, with a comparatively minimal rise in the 1940s.
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Figure 5

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Figure 6

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Figure 7

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Figure 8

COMPARATIVE GRAPHS

Figure 9 illustrates the SST anomalies for the Far East and Far West quadrants. The delayed decrease in the Far West SST anomaly around 1900 is very clear in this illustration. The two data sets, while they do share common overall trends, appear at times to be out of synch, as if heat is shifting back and forth across the Pacific. Which it does.

During El Nino events, the Pacific Warm Pool (contained within the Far East data set) delivers heat to the NINO3.4 area (part of the Far West data set), where it is upwelled. Through oceanic Rossby waves, the warm surface water is sent east, where it rebounds off the Central and South American Coasts. The oceanic Rossby waves then travel North and South along the coasts and westerly in multiple directions. In addition, clockwise ocean currents in the North Pacific and counterclockwise ocean currents in the South Pacific return the heat to the West Pacific (Far East data set). Refer to the following video from NASA, especially the 97/98 El Nino that starts in January 1997 with the first of two Kelvin waves travelling west to east. Note: It’s a large video, 17mb.
http://topex-www.jpl.nasa.gov/gallery/tiffs/videos/tpglobal.mpeg
http://i34.tinypic.com/sm850y.jpg
Figure 9

Figure 10 illustrates the SST anomalies for the Near East (primarily the Indian Ocean) and the Near West (primarily the Atlantic). While they follow the same overall trends, there are substantial periodic differences that do not appear to be caused by ENSO.
http://i33.tinypic.com/1jkll4.jpg
Figure 10

Subtracting the Near East (Indian) from the Near West (Atlantic), creates a curve, Figure 11, that bears what appears, at first, to be a function of the Atlantic Multidecadal Oscillation (AMO).
http://i38.tinypic.com/117v1ih.jpg
Figure 11

But when the curve created by subtracting the Near East from the Near West data set is compared to the AMO, the differences become obvious. See Figure 12.
http://i36.tinypic.com/bdp007.jpg
Figure 12

A comparative graph of the North Pacific Residual and “Near West Minus Near East” data shows a better correlation, but it’s not perfect. Also, it would be tough to explain.
http://i36.tinypic.com/240zul5.jpg
Figure 13

What’s that cycle induced by? Maybe that will become obvious when I divide Global SST into ocean data sets, including both hemispheres.

SOURCE

Sea Surface Temperature Data is Smith and Reynolds Extended Reconstructed SST (ERSST.v2) available through the NOAA National Operational Model Archive & Distribution System (NOMADS).
http://nomads.ncdc.noaa.gov/#climatencdc

Tropical SST Anomalies Revisited – East Pacific Ocean

PREVIOUS POSTS IN SERIES

Tropical SST Anomalies Revisited – Introduction
http://bobtisdale.blogspot.com/2008/09/tropical-sst-anomalies-revisited.html

Tropical SST Anomalies Revisited – Atlantic Ocean
http://bobtisdale.blogspot.com/2008/09/tropical-sst-anomalies-revisited_24.html

AREAS INCLUDED

Figure 1 illustrates the geographic areas included in this post and their coordinates. They include the:
-Tropical Northeast Pacific (0-20N, 90-180W)
-Tropical Southeast Pacific (0-20S, 70-180W)
-Northeast Pacific (0-65N, 90-180W)
-Southeast Pacific (0-60S, 70-180W)
-Northeast Pacific Upwelling Area (32-48N, 116-132W)
-Southeast Pacific Upwelling Area (16-48S, 70-78W)
http://i36.tinypic.com/24fn23m.jpg
Figure 1

NORTHERN AND SOUTHERN TROPICAL EAST PACIFIC

The long-term (January 1854 to August 2008) SST Anomalies for the Northern and Southern Tropical East Pacific are shown in Figure 2. The data has been smoothed with an 85-month running average filter. Note how the sign of the difference between the two data sets shifts with time. Before the 1920s and after 1976, the Southern Tropical East Pacific anomalies are higher in temperature than the Northern Tropical East Pacific, and between the 1920s and 1976, the Southern Tropical East Pacific anomalies are lower in temperature than the Northern Tropical East Pacific.
http://i38.tinypic.com/2quutuf.jpg
Figure 2

In Figure 3, I’ve subtracted the Southern Tropical East Pacific anomalies from the Northern Tropical East Pacific anomalies. I’ll have to examine oceanic SST dipoles in a future post.
http://i34.tinypic.com/2vd20rn.jpg
Figure 3

Figure 4 (raw data) shows the short-term (January 1978 to August 2008) SST Anomalies for the Northern and Southern Tropical East Pacific. The Southern Tropical East Pacific shows the greater variation.
http://i37.tinypic.com/25i2gas.jpg
Figure 4

OFF TOPIC – THE GREAT PACIFIC CLIMATE SHIFT OF 1976

Refer back to Figure 2. Note the sharp rise in SST anomalies at 1976 in both Northern and Southern Tropical East Pacific data sets. Is that an indicator of the Great Pacific Climate Shift of 1976? Normally, that shift is discussed in terms of changes in the Pacific Decadal Oscillation and in El Nino frequency. There are a few papers, however, that discuss the actual shift in basin-wide Pacific SST. In Figure 5, I’ve provided a short-term graph of the Northern and Southern Tropical East Pacific SST anomalies from January 1960 to December 1985. Note how the trends before and after 1976 are different.
http://i34.tinypic.com/2iiz9qu.jpg
Figure 5

To help illustrate the change in trend and the jump in SST, I’ve shown only the Southern Tropical East Pacific SST anomalies and added linear trend lines for two periods, from January 1960 to December 1975 and from January 1977 to December 1955, in Figure 6. Based solely on the end and start points of the two trend lines, the Southern Tropical East Pacific SST anomalies stepped up almost 0.5 deg C during 1976. When I’m finished with this series, I will examine the Pacific Ocean on a basin wide basis to determine the total impact of the Great Pacific Climate Shift.
http://i38.tinypic.com/16aa03o.jpg
Figure 6

IS THE SOUTHERN OCEAN INFLUENCIAL?

In Figure 7, I’ve compared Southern Ocean SST anomaly data to Northern and Southern Tropical East Pacific SST anomalies. There appears to be little relationship between the Southern Ocean and the Tropical Pacific.
http://i35.tinypic.com/c262r.jpg
Figure 7

However, Smith and Reynolds provided a much updated representation of the Southern Ocean in their latest version of SST data, ERSST.v3. In Figure 8, I’ve replaced the ERSST.v2 data for the Southern Ocean with the ERSST.v3 data. The Southern Ocean definitely influences the Eastern Tropical Pacific Ocean.
http://i37.tinypic.com/10pygaq.jpg
Figure 8

Subtracting the Southern Ocean SST anomalies from the Northern and Southern Tropical East Pacific SST anomalies creates two curves with an apparent long-term oscillation. Refer to Figure 9. I found the overall shape of the curve in Figure 9 and the points at which the trends changed interesting. (Note that the ERSST.v3 data is only available, in simple format, in specific latitude bands and only from January 1880 to April 2008. They stopped updating it in April. For this reason, the span of the graph has been reduced.) Don’t concern yourself with the spikes at 1994, three years before the 97/98 El Nino. It’s simply a product of the smoothing.
http://i34.tinypic.com/11v07mc.jpg
Figure 9

If the smoothing is changed from 85 months to 12 months, Figure 10, the El Ninos and La Ninas appear at the correct times for the most part.
http://i34.tinypic.com/10fdj0l.jpg
Figure 10

In Figure 11, I’ve returned to a straight comparison of monthly data for the Southern Ocean and the Northern and Southern Tropical East Pacific SST anomalies for the years 1965 to 1985. The data is raw. The Southern Ocean data appears not to be the cause of the 1976 climate shift.
http://i34.tinypic.com/zmczna.jpg
Figure 11


COMPARISON TO NINO3.4

As one would expect, SSTs in the NINO3.4 area are a major influence on the SSTs of the Tropical East Pacific. Refer to Figure 12. But there are differences in the underlying trends. These differences would be caused by the additional influences of the North and South Pacific.
http://i35.tinypic.com/2s1kkjl.jpg
Figure 12

The magnitudes of the variations caused by ENSO make a simple cause and effect evaluation difficult, which will be seen in the following, much more difficult than that of the Tropical Atlantic in the prior post.

NORTHERN TROPICAL EAST PACIFIC

Figure 13 illustrates SST anomalies for the Northeast Pacific and for the Northern Tropical East Pacific. The overall changes in trend agree with one another. There are differences in the overall amplitude of the decadal variations, which may be due to the additional thermohaline circulation/meridional overturning circulation component in the North Pacific, or due to the reductions in the effects of NINO3.4 as the perturbations are spread out over a large area, or a combination of both.
http://i33.tinypic.com/sczvyo.jpg
Figure 13

Figure 14 compares the SST anomalies of the North East Pacific Upwelling area and for the Northern Tropical East Pacific.

Ocean currents do run from North to South along the North American coast, so the Upwelling area waters do feed the tropics. But ENSO events also distribute changes Northward through Rossby waves. These ENSO fed variations should then be returned over time to the tropics, creating a delayed feedback to the tropics. The North East Pacific Upwelling area is also smaller in area than the Northern Tropical East Pacific so it should reflect the variations more.
http://i33.tinypic.com/33mtl3b.jpg
Figure 14

Note: I could but will not attempt to extract the base NINO3.4 component from the other signals. Maybe a future post.

SOUTHERN TROPICAL EAST PACIFIC

The SST anomalies for the Southeast Pacific and for the Southern Tropical East Pacific are compared in Figure 15. Like their Northern counterparts, there are differences between the two. However, the Southern Ocean would also have an influence on these data sets.
http://i33.tinypic.com/2lsk4ma.jpg
Figure 15


The Southern Tropical East Pacific and the coastal upwelling area off the Southwest coast of South America are compared in Figure 16. Again, like the Northern Tropics and Upwelling area, the influences of ENSO on both these data sets, along with the feedbacks due to ocean currents, would make it difficult to isolate the variables using simple tools.
http://i34.tinypic.com/5evg4p.jpg
Figure 16

CLOSING COMMENTS

While I had expected to find a clearer relationship between the North and South American west coast upwelling areas and the Tropical East Pacific, I was not disappointed with this post. The relationship between the Southern Ocean (ERSST.v3) and the Tropical East Pacific (Figure 8) was revealing, especially when the negative trend in the Southern Ocean SST over the last 20+ years is considered. Will the Tropics follow? The other find I was pleased with was the 1976 SST shift that’s easily visible in the North and South Tropical East Pacific data. Refer again to Figures 2, 5, and 6.

SOURCES

Sea Surface Temperature Data is Smith and Reynolds Extended Reconstructed SST (ERSST.v2) available through the NOAA National Operational Model Archive & Distribution System (NOMADS).
http://nomads.ncdc.noaa.gov/#climatencdc

The more recent version of the Smith and Reynolds Extended Reconstructed SST (ERSST.v3), along with land surface temperature and combined (land + ocean) surface temperatures, are available in various latitudinal bands at:
ftp://eclipse.ncdc.noaa.gov/pub/ersst/pdo
Don’t let the PDO in the address confuse you. There’s much more there. The overview for the update is here:
http://www.ncdc.noaa.gov/oa/climate/research/sst/ersstv3.php

Tropical SST Anomalies Revisited – Atlantic Ocean

PREVIOUS POST

Tropical SST Anomalies Revisited – Introduction
http://bobtisdale.blogspot.com/2008/09/tropical-sst-anomalies-revisited.html

AREAS INCLUDED

Figure 1 illustrates the geographic areas included in this post and their coordinates. They include the:
- Tropical North Atlantic (0-20N, 78W-10E)
- Tropical South Atlantic (0-20S, 50W-15E)
- North Atlantic (0-70N, 70W-10E)
- South Atlantic (0-60S, 70W-20E)
- North Atlantic Upwelling Area (12-28N, 14-24W)
- South Atlantic Upwelling Area (12-30S, 4-14E)

http://i33.tinypic.com/28i2mp1.jpg
Figure 1

NORTHERN AND SOUTHERN TROPICAL ATLANTIC

The long-term (January 1854 to August 2008) SST Anomalies for the Northern and Southern Tropical Atlantic are shown in Figure 2. The data has been smoothed with an 85-month running average filter. The Southern Tropical Atlantic has the greater swing in SST over the term of the data, with much of that variation caused by a significant drop in SST from the late 1890s to 1906 and the rebound from 1906 to the mid-1920s.
http://i36.tinypic.com/2akd210.jpg
Figure 2

Figure 3 (raw data) shows the short-term (January 1978 to August 2008) SST Anomalies for the Northern and Southern Tropical Atlantic. Again, the Southern Tropical Atlantic shows the greater variation. I found two differences between the two data sets interesting. In 1984, the Southern Tropical Atlantic almost appears to be reacting to an El Nino when none took place that year; to the contrary, 84/85 included a La Nina. Also, there was a dip in Southern Tropical Atlantic SST early in 1997, before the 97/98 El Nino.
http://i33.tinypic.com/spyt7s.jpg
Figure 3

Smoothing the short-term data with a 12-month filter, Figure 4, helps illustrate two things. That early 1997 dip in temperature appears it might lose its novelty and looks like it might have been part of a possible periodic oscillation. The second noticeable effect revealed by the smoothed data is the shift (rise) in the Southern Tropical Atlantic SST trend after the 97/98 El Nino.
http://i35.tinypic.com/29p83v9.jpg
Figure 4

NORTHERN TROPICAL ATLANTIC

Figure 5 is a comparative graph of SST anomalies for the North Atlantic and for the Northern Tropical Atlantic. While the overall changes in trend agree with one another, it is clear that the one of the two data sets had an additional driver prior to the mid-1960s. They agree remarkably well afterwards. I have no explanation.
http://i36.tinypic.com/x3tuyu.jpg
Figure 5

Figure 6 is the short-term data for the North Atlantic and for the Northern Tropical Atlantic. In recent years the two data sets coincide well. The Tropical data has the greater variation, which is expected for an oceanic data set with a smaller area.
http://i38.tinypic.com/e8ka36.jpg
Figure 6

In Figure 7, the Northern Tropical Atlantic data is compared to the coastal upwelling area off the Northwest coast of Africa. Those two data sets agree over the term of the data, with the upwelling area having exaggerated swings in SST. Since the Canary Current is from North to South along the West coast of Africa, the North Atlantic Upwelling area appears to drive the temperature of the Tropical North Atlantic. It must be recalled however that SSTs of those areas “upstream” of the upwelling area also impact the Tropical North Atlantic, as do the surface waters passing from the South Atlantic to the North Atlantic as part of the overall thermohaline circulation circuit.
http://i34.tinypic.com/15he5hc.jpg
Figure 7

The short-term comparison of SST anomalies for the Northern Tropical Atlantic and the North Atlantic Upwelling area is illustrated in Figure 8. Again, the signals in the smaller geographic region are not dampened by area, so the variations in the Upwelling area are greater. Note that the anomaly (spike) at 2002 is greater than the value at 1998 even though the 2002/2003 El Nino was significantly smaller than the 97/98 El Nino. Interesting.
http://i34.tinypic.com/2rnu78o.jpg
Figure 8

SOUTHERN TROPICAL ATLANTIC

The SST anomalies for the South Atlantic and for the Southern Tropical Atlantic are compared in Figure 9. There are enough differences between the two data sets to suggest that the South Atlantic does not drive the Southern Tropical Atlantic.
http://i34.tinypic.com/245apae.jpg
Figure 9


The Southern Tropical Atlantic and the coastal upwelling area off the Southwest coast of Africa are compared in Figure 10. Those two data sets agree over the term of the data, with the upwelling area having exaggerated swings in SST. The Benguela Current would carry the waters from the upwelling area northward along the Southwest coast of Africa to the Tropical Southern Atlantic. The South Atlantic Upwelling area appears to drive the temperature of the Tropical South Atlantic. Again, it must be remembered that SSTs of those areas “upstream” of the upwelling area also impact the Tropical South Atlantic.
http://i38.tinypic.com/5d76zp.jpg
Figure 10

Figure 11 illustrates the short-term SST anomalies for the Southern Tropical Atlantic and the South Atlantic Upwelling area. Again, the signals in the smaller geographic region have greater variations. But note that the significant drop in SST immediately before the 1997/98 El Nino also appears in the upwelling data. As opposed to being a part of a possible oscillation as noted in the discussion of Figure 4, this time the plunge in SST appears anomalous. I’ll have to keep an eye out for that in other upwelling areas.
http://i38.tinypic.com/r2w07p.jpg
Figure 11

For information purposes only, the last graph, Figure 12, provides a comparison of the SST anomalies for the upwelling areas for the North and South Atlantic.
http://i37.tinypic.com/w0krqd.jpg
Figure 12

SOURCE

Sea Surface Temperature Data is Smith and Reynolds Extended Reconstructed SST (ERSST.v2) available through the NOAA National Operational Model Archive & Distribution System (NOMADS).
http://nomads.ncdc.noaa.gov/#climatencdc