>I’ve prepared this post for those who want to compare El Nino Modoki Index data to NINO3.4 SST anomalies. I did not standardize the El Nino Modoki Index data. Note also that I scaled the NINO3.4 SST anomaly data by a factor of 0.5 to bring it into line with the El Nino Modoki Index data.
Last, keep in mind that the El Nino Modoki Index is a calculated value. Ashok et al describe the calculation as follows:
“EMI= [SSTA]A-0.5*[SSTA]B-0.5*[SSTA]C (1)
“The square bracket in Equation (1) represents the area-averaged SSTA over each of the
regions A (165E-140W, 10S-10N), B (110W-70W, 15S-5N), and C (125E-145E, 10S-20N), respectively.”
Link to the Ashok et al (2007) paper “El Nino Modoki and its Possible Teleconnection.”
https://www.jamstec.go.jp/frcgc/research/d1/iod/publications/modoki-ashok.pdf
Figure 1 illustrates those regions used in the El Nino Modoki Index. Keep in mind that the declines in the SST anomalies in Regions B and C help raise the El Nino Modoki Index, and vice versa.
http://i31.tinypic.com/33xeziu.png
Figure 1
Figure 2 is a long-term comparison of El Nino Modoki Index data and NINO3.4 SST anomalies. In Figures 3 through 6, I’ve shortened the time spans. I have not attempted to provide the threshold for the El Nino Modoki events on the graphs. You’ll have to scale that value on your own. You can use Figures 2 and 3 and the accompanying dialogue in my post There Is Nothing New About The El Nino Modoki for reference, but remember that the threshold was established for the standardized data.
Here are the graphs without further commentary.
http://i25.tinypic.com/ilgml5.png
Figure 2
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http://i32.tinypic.com/2gvj8y8.png
Figure 3
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http://i32.tinypic.com/m7yf6w.png
Figure 4
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http://i30.tinypic.com/m833on.png
Figure 5
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http://i27.tinypic.com/2ezn2q9.png
Figure 6
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SOURCE
HADISST SST and SST anomaly data are available through the KNMI Climate Explorer.
http://climexp.knmi.nl/selectfield_obs.cgi?someone@somewhere
Bob Tisdale - Climate Observations 
>if there is nothing new in the modoki index, can we use this index rather than the conventional one?
>OceanOne: How would you like to use the El Nino Modoki Index? Global temperatures also respond to central Pacific El Nino events.
>Hi Bob,I'd like to use this index to see its relation with precipitation in the maritime continent, since many previous studies used NINO3.4 index
>OceanOne: There are papers on central Pacific El Ninos that reference Ashok et al. Those papers have different methods of calculating central Pacific El Nino events, but I don't believe one method is favored yet.
>thanks a lot Bob. I am just wondering, what are the primary large scale climate drivers that affected the tropical area?
>OceanOne: You asked, "…what are the primary large scale climate drivers that affected the tropical area?"If by "climate drivers" you are referring to natural cycles, I would have to think ENSO and the IOD.
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how to calculate SSTA??
gaurav: Select a reference period. NOAA uses 1971 to 2000 for its Reynolds OI.v2 sea surface temperature data. Then calculate the averages of the sea surface temperatures for each month of your reference period. That is, determine the average SST for the Januarys, the average SST for the Februarys…through to the average SST for the Decembers. Then subtract the monthly averages from the corresponding months for all of the data to determine the anomalies. Let’s say your SST data started in January 1950. You’d subtract the average January SST from the January 1950 SST to determine the January 1950 SSTa. Then you subtract the average February SST from the February 1950 SST to determine the February 1950 SSTa. Repeating the process for each month of data.
It’s easy to do in a spreadsheet if your data is laid out in table form with the years in rows and the months in columns.
Regards