ENSO Index According to JMA SSTA (1868-present)

 

Some ENSO impact analyses, particularly those in COAPS, categorize application data as belonging to one of three phases of ENSO: El Niño (warm SST anomalies in the Pacific) El Viejo (cool SST anomalies), or neutral based on an index derived from observed SST anomalies. The particular index chosen is that from the Japan Meteorological Agency (JMA) because it selects well the known ENSO events. The index is a 5-month running mean of spatially averaged SST anomalies over the tropical Pacific: 4°S-4°N, 150°W-90°W. If index values are 0.5°C or greater for 6 consecutive months (including OND), the ENSO year of October through the following September is categorized as El Niño, El Viejo (index values equal or exceed -0.5°C), or neutral (all other values). A plot of these data show their relative values since 1970.

For the period 1949 to present, the JMA-Index is based on observed data. However, for the years 1868-1948 the index is based on reconstructed monthly mean SST fields. The reconstructed SST fields were computed using an orthogonal projection technique (Meyers et al., 1997). The JMA index for 1868-1949 was calculated just as for the 1949-present, meaning the JMA climatological values were used to calculate the JMA SST anomalies. A 5-month running mean was then applied resulting in the JMA index.The JMA Index values for each month of the 1868-1949 period are available via ftp. (ftp://www.coaps.fsu.edu/pub/JMA_SST_Index/).

Correction - (17 July 2003): The ENSO years of 1870 and 1974 were reclassified from neutral to cold phases. The original classification of these years was the result of inconsistent application of the -0.5C threshold for cold phases. In these two cases, several 5-month running mean values in the six month period that included OND were equal to -0.5C, but the years were incorrectly classified as neutral. This correction only affects the list in Table 1, not any files available from the ftp site.

Table 1: The years in each category correspond to the first three months of the ENSO year namely October, November, and December. For example, the ENSO year 1970 starts October 1970 and ends September 1971.

Cold PhaseNeutral PhaseWarm Phase
1869
1870
1871
1872
1873
1874
1875
1886
1889
1892
1893
1903
1906
1908
1909
1910
1916
1922
1924
1938
1942
1944
1949
1954
1955
1956
1964
1967
1970
1971
1973
1974
1975
1988
1998
1999
2007
2010
1876
1878
1879
1881-1885
1887
1890
1891
1894
1895
1897
1898
1900
1901
1907
1912
1914
1915
1917
1919
1920
1921
1923
1926
1927
1928
1931-1937
1939
1941
1943
1945-1948
1950
1952
1953
1958-1962
1966
1968
1977-1981
1983
1984
1985
1989
1990
1992-1996
2000
2001
2003-2005
2008
2011
2012
2013
1868
1877
1880
1888
1896
1899
1902
1904
1905
1911
1913
1918
1925
1929
1930
1940
1951
1957
1963
1965
1969
1972
1976
1982
1986
1987
1991
1997
2002
2006
2009
2014
2015

Special thanks to David M. Legler for starting this index.