>PREVIOUS POSTS IN SERIES
Tropical SST Anomalies Revisited – Introduction
Tropical SST Anomalies Revisited – Atlantic Ocean
Tropical SST Anomalies Revisited – East Pacific Ocean
Tropical SST Anomalies Revisited – West Pacific Ocean
While this post deals primarily with Tropical Indian Ocean SST anomalies, it also presents Tropical West Pacific and ENSO data and their relationship with the Tropical Indian Ocean.
I apologize for using light green to represent Southern Tropical Indian Ocean SST anomalies. I now realize it’s hard to see. I’ll refrain from using it in the future, but when I drew up the maps originally in part one of this series, it seemed acceptable. The graphics become clearer, though, if you use the tinypic links to see the full-size graphs.
Figure 1 illustrates all but one of the geographic areas included in this post. They include the:
-Tropical North Indian Ocean (0-20N, 40-100E)
-Tropical South Indian Ocean (0-20S, 35-130E)
-Tropical Northwest Pacific (0-20N, 100-180E)
-Tropical Southwest Pacific (0-20S, 130-180E)
-Eastern Portion of Indian Ocean Gyre (20-35S, 90-120E)
The area not illustrated is:
-NINO3.4 (5S-5N, 120-170W)
NORTHERN AND SOUTHERN TROPICAL INDIAN OCEAN
The long-term (January 1854 to August 2008) SST anomalies for the Northern and Southern Tropical Indian Ocean are shown in Figure 2. The data has been smoothed with an 85-month running average filter. From 1940 to present, the two data sets parallel one another for the most part, with minor variations, but they diverge prior to then.
In Figure 3, I’ve change to a 12-month filter to highlight the differences in the SST anomaly responses to the major El Nino events. In 1888 and 1940, the reactions of the Northern Tropical Indian Ocean to the 1888/89 and 1940/41/42 El Ninos far exceeded the Southern Tropical Indian Ocean. But in later years, the amplification in the North doesn’t appear as great. Refer also to Figure 4, which is the short-term data for the Northern and Southern Tropical Indian Ocean.
COMPARISONS TO NINO3.4 DATA
Figure 5 provides a comparison of the Northern Tropical Indian Ocean and NINO3.4 SST anomaly data from 1854 to 2008, where the data has been smoothed with a 12-month filter. This provides a clearer view of the 1888/89 and 1940/41/42 ENSO events and how they have a much larger impact on the Northern Indian Ocean than more recent large El Ninos.
Figure 6 illustrates SST anomalies for the Southern Tropical Indian Ocean and for the NINO3.4 region. Note that the magnitudes of the responses of the Southern Tropical Indian Ocean to El Nino events are less than the Northern Tropical Indian Ocean. The responses are also more consistent.
COMPARISONS OF TROPICAL INDIAN OCEAN AND TROPICAL PACIFIC OCEAN
Northern Tropical Indian Ocean and Northwestern Tropical Pacific Ocean SST anomalies are compared in Figure 7. The two data sets bear little to no visible relationship to one another. This isn’t surprising since the two areas are separated by Indonesia.
Figure 8 provides a comparison of Southern Tropical Indian Ocean and Southwestern Tropical Pacific Ocean SST anomalies. There appears to be a stronger relationship between the two data sets, though there are significant differences prior to the 1960s.
COMPARISON OF SOUTHERN TROPICAL INDIAN OCEAN AND EASTERN PORTION OF INDIAN OCEAN GYRE
The final graph illustrates the SST anomalies for the Southern Tropical Indian Ocean and the Eastern portion of the Indian Ocean Gyre. Currents in this area of the Indian Ocean Gyre carry waters in a northward direction, feeding the Southern Tropical Indian Ocean. That is very clean in the similarities between the two data sets.
The Northern Tropical Indian Ocean has no direct interaction with another oceanic body of water other than its Southern counterpart. The Northern Tropical Indian Ocean anomalies are amplified in earlier years by a source that has not been identified in this post. As discussed in an earlier post about the Indian Ocean (Link Follows), the variations in the Arabian Sea are greater than in the Bay of Bengal, and since the Arabian Sea is larger in area than the Bay of Bengal, this indicates the amplification is not a function of the size of the body of water.
Sea Surface Temperature Data is Smith and Reynolds Extended Reconstructed SST (ERSST.v2) available through the NOAA National Operational Model Archive & Distribution System (NOMADS).