Indian Ocean Dipole Monitoring Indices

Climate Prediction Division
Japan Meteorological Agency

   Regarding Indian Ocean Dipole (IOD) monitoring indices, the elnino/index/ 
directory contains two ASCII document files, Readme_iod.txt (this file) and 
one sub-directory for Sea Surface Temperature Indices (sstindex).


1. Sea Surface Temperature (SST) Indices

   SST indices consist of monthly mean SSTs, monthly mean SST anomalies
(for the 1991 - 2020 base period), monthly mean SST deviations (for the
latest sliding 30-year base period), and related three-month means 
for the IOD monitoring regions listed below since January 1950. 
The latest values are preliminary.

   Monthly mean SSTs are analyzed by JMA's Climate Prediction Division.

   The IOD Monitoring Regions - WIN and EIN - and Dipole Mode Index (DMI) 
are:

       WIN:   10N - 10 S   50 E - 70 E
       EIN:   Eq. - 10 S   90 E - 110 E
       DMI:   Difference between WIN and EIN

   The directory (elnino/index/sstindex) contains two sub-directories
corresponding to the two base periods of 1991 - 2020 and the latest sliding
30-year period (directories: base_period_9120 and sliding_30year_period).

   SST indices are derived from MGDSST datasets (Kurihara et al. 2006) after June 2015 and those of COBE-SST2 (Hirahara et al. 2014) before this.


1-1. base_period_9120 directory 

   This directory (elnino/index/sstindex/base_period_9120/) contains
three sub-directories corresponding to the three IOD Monitoring indices.

   There are three data files under these sub-directories:

       (1) Monthly mean SST (file name: sst)

       (2) Monthly mean SST anomaly (file name: anomaly)
           (The base period for the normal is 1991 - 2020)

       (3) Three-month running mean SST anomaly (file name: 3rmean)
           (The base period for the normal is 1991 - 2020)

   Data files are in text format. The first line in each shows month, 
and subsequent lines contain data from 1949 to the latest year. 
The unit is degrees centigrade, and entries of 99.9 (or 99.90) represent 
undetermined values.


1-2. sliding_30year_period directory

   This directory (elnino/index/sstindex/sliding_30year_period/) contains
three sub-directories corresponding to the DMI, WIN and EIN.

    There are three data files under each of these sub-directories:

       (1) Monthly mean SST climatological reference based on the latest sliding 30-year
           period (file name: sst)
           The SST climatological reference is defined as a linear extrapolation 
           with respect to the latest sliding 30-year period.

       (2) Monthly mean SST deviation (file name: deviation)
           SST deviation is defined as the difference between the monthly
           mean SST and the climatological reference based on the latest sliding 30-year
           period.

       (3) Three-month running mean SST deviation (file name: 3rmean)

    Data files are in text format. The first line in each shows
the month, and subsequent lines indicate data from 1949 to the latest year. 
The unit is degrees centigrade, and entries of 99.9 (or 99.90) represent 
undetermined values.


Directory structure

TOP
 |
 +-- elnino
         |
         +-- index
               |
               +-- Readme_iod.txt
               |
               +-- sstindex
                      |
                      +--- base_period_9120
                      |            |
                      |            +-- WIN  ---- sst, anomaly, 3rmean
                      |            |
                      |            +-- EIN  ---- sst, anomaly, 3rmean
                      |            |
                      |            +-- DMI  ---- sst, anomaly, 3rmean
                      |
                      +--- sliding_30year_period
                                   |
                                   +-- WIN  ---- sst, deviaiton, 3rmean
                                   |
                                   +-- EIN  ---- sst, deviaiton, 3rmean
                                   |
                                   +-- DMI  ---- sst, deviaiton, 3rmean


  For inquiries relating to this data set, see
http://www.data.jma.go.jp/tcc/tcc/contact.html.

References

    Hirahara, S., M. Ishii, and Y. Fukuda, 2014: Centennial-scale sea surface temperature analysis and its uncertainty. J. Climate, 27, 57-75.

    Kurihara, Y., T. Sakurai, and T. Kuragano 2006: Global daily sea surface temperature analysis using data from satellite microwave radiometer, satellite infrared radiometer and in-situ observations. Weather Service Bulletin, 73, Special issue, s1-s18 (in Japanese).