Tropical Warming Events in the Indian Ocean

Due to a lack of material on the internet concerning how El Nino and La Nina events manifest themselves in the Indian Ocean, I extracted data from the NOAA site mentioned in my previous post.  I broke up the tropical Indian Ocean into 9 blocks in order to find where the signal from a El Nino or La Nina first appears.

Listed below are the regions used.

  Lat Long
Region 1 4 to 12 52 to 66
Region 2 -4 to 4 52 to 66
Region 3 -12 to -4 52 to 66
Region 4 4 to 12 66 to 80
Region 5 -4 to 4 66 to 80
Region 6 -12 to -4 66 to 80
Region 7 4 to 12 80 to 94
Region 8 -4 to 4 80 to 94
Region 9 -12 to -4 80 to 94

 I extracted data for each of these regions, graphed them, and found that the Western Indian Ocean was the first to react to the 1997/1998 El Nino event, followed by the Central Indian Ocean, and finally the Eastern Indian Ocean.  The region reacted simulataneously, regardless of latitude, although latitude did effect the intensity of the variations in sea surface temperature.

Below is a graph of the Western, Central, and Eastern reaction to the El Nino.

And here’s a graph of the Western Indian Ocean at different Latitudes.

And just to show that this isn’t unique to the 1997/1998 El Nino:

So, after this discovery, I went back to compare my Indian Ocean record in the last post with this new Western Indian Ocean record.  Remember that I wasn’t looking for an accurate description of an El Nino/La Nina event; I was looking for the region that first expressed an event, which turned out to be the Western Indian Ocean.

Because this analysis is so dependent on determining the exact time that the El Nino starts, I decided to forgo the 12-point mean smoothing that the website offered and that I had been using.  Instead, to rid the dataset of the influence of seasons, I calculated each month as anomoly from the average temperature of that same month from 1978 through 2007. 

So, when I went to compare my new Western Indian Ocean dataset to my old, smoothed Indian Ocean dataset, I was surprised to find that my old dataset actually responded to the El Nino first.  Out of curiosity, I applied my new data handing technique to the Pacific temperature box that I used in my previous post, and found that my smoothed Pacific preceded my new Pacific, too.

The new, un-smoothed data shows a much smaller lag-time (perhaps only a month) than the old, smoothed data.  This may mean that the apparent inconsistent lag time between the Atlantic and Pacific Nino is an artifact of smoothing rather than an actual phenomena.  I’ll need to revise my last post to use the un-smoothed data.


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