El Nino Monitoring Indices Climate Prediction Division Japan Meteorological Agency < Notice of Correction > ----------------------------------------------------------------------- ( Novemver 11th 2013 ) Since some satellite data had been used incorrectly to estimate SSTs in sea ice areas, monthly mean SST data from January 2006 to December 2009 and SST normals were re-calculated and El Nino Monitoring Indices were replaced with new ones. Please download the data again, if you obtained them previously. ----------------------------------------------------------------------- The elnino/index/ directory contains two ASCII document files, Readme.txt (this file) and historical data of the Southern Oscillation Index (file name: soi) and one sub-directory for Sea Surface Temperature Indices (directory name: sstindex). 1. Southern Oscillation Index (SOI, file name: soi) This index represents the strength of trade winds over the equatorial Pacific. When the index is negative, trade winds are weaker than normal and characteristics seen with El Nino events are shown. The data comes from monthly mean sea-level pressure values reported by CLIMAT messages from Tahiti in the South Pacific and Darwin in Australia. The index is defined as SOI = X / SD(X), where X = ANM(Ps(T))/SD(Ps(T)) - ANM(Ps(D))/SD(Ps(D)), and Ps(A) is the sea-level pressure for point A, ANM(B) and SD(B) are the anomaly and standard deviation of element B, and T and D represent Tahiti and Darwin, respectively. The base period for the normal is 1991 - 2020. The latest values are preliminary ones. *) Past SOIs were recalculated to correct a somewhat inappropriate round-off procedure, and the data on this site were replaced on 12 June, 2008. 2. Sea Surface Temperature (SST) Indices The 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 thirty-year base period), and their five-month mean values averaged over the five El Nino Monitoring Regions listed below since January 1949. The latest values are preliminary ones. The monthly mean SSTs are analyzed by JMA's Climate Prediction Division. The five El Nino Monitoring Regions are defined as follows: NINO.1+2: EQ. - 10 S 90 W - 80 W NINO.3: 5 N - 5 S 150 W - 90 W NINO.4: 5 N - 5 S 160 E - 150 W NINO.WEST: 15 N - EQ. 130 E - 150 E IOBW: 20 N - 20 S 40 E - 100 E 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 (directory names: base_period_9120 and sliding_30year_period). 2-1. The base_period_9120 directory This directory (elnino/index/sstindex/base_period_9120/) contains five sub-directories corresponding to the five El Nino Monitoring Regions. There are three data files under those 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) 5-month running mean SST anomaly (file name: 5rmean) (The base period for the normal is 1991 - 2020) The data files are in text format. The first line in each file shows the name of the 12 months. The subsequent lines indicate the data for each year from 1949 to the latest year. The unit is degrees centigrade, and entries of 99.9 (or 99.90) represent undetermined values. 2-2. The sliding_30year_period directory This directory (elnino/index/sstindex/sliding_30year_period/) contains three sub-directories corresponding to the Nino.3, Nino.West, and IOBW regions. 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 the SST averaged over the latest sliding 30-year period for Nino.3, and as linear extrapolations with respect to the latest sliding 30-year period for Nino.West and IOBW.) (2) Monthly mean SST deviation (file name: deviation) (The 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) Five-month running mean SST deviation (file name: 5rmean) The data files are in text format. The first line in each file shows the name of the 12 months. The subsequent lines indicate the data for each year 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.txt | +-- soi | +-- sstindex | +--- base_period_9120 | | | +-- Nino_1+2 ---- sst, anomaly, 5rmean | | | +-- Nino_3 ---- sst, anomaly, 5rmean | | | +-- Nino_4 ---- sst, anomaly, 5rmean | | | +-- Nino_West---- sst, anomaly, 5rmean | +--- sliding_30year_period | +-- Nino_3 ---- sst, deviaiton, 5rmean | +-- Nino_West---- sst, deviaiton, 5rmean | +-- IOBW ---- sst, deviaiton, 5rmean For correspondence relating to this data set, please refer to http://ds.data.jma.go.jp/tcc/tcc/contact.html