JISAO data
Walker and Bliss Southern Oscillation (SO) index, 1875-1933

Analyses | Data: original, re-standardized
Described in caption
PostScript | JPEG
December-January-February values of the Southern Oscillation Index and the SST anomalies in the cold tongue region of the equatorial Pacific (CTI). Both series are standardized, and the SOI is inverted from the definition of Walker and Bliss. The two time series are based on independent observations and are correlated at 0.83 for 1882-1930.
Described in caption
PostScript | JPEG
Seasonal values of the index. The processing of the time series for this figure is described below. This index captures ENSO variability.
Walker and Bliss (1932, 1937) produced indices of the Southern Oscillation, the atmospheric part of the El Niño / Southern Oscillation (ENSO), from seasonal mean values of rainfall, surface temperature, and sea-level pressure. They performed what is essentially EOF analysis separately for each of the standard meteorological seasons, December-January-February (DJF), March-April-May (MAM), June-July-August (JJA), and September-October-November (SON). On the basis of extensive experimentation, Walker and Bliss chose the stations and variables that best explained the variability in each season. The stations and variables are different for each season. As practical issues, the period of record is different for the different seasons, and the index values for each season are standardized with respect to the period of record for that season's analysis. The digital values of the index, transcribed from the two referenced papers, are presented as a table. Negative (positive) values of their index are associated with above (below) normal values of sea surface temperature in the equatorial central and eastern Pacific Ocean.

The mean and standard deviation for each seasonal time series are approximately 0 and 4.5, respectively.
The table as an ASCII file. NaNs for missing values. 

       DJF  MAM  JJA  SON
 1875         6    2   -1
 1876         1   -2    0
 1877       -12  -16   -9
 1878       -10    5    6
 1879         7    6    3
 1880         3   -4    0
 1881         0   -2    2
 1882   -2    4    0    4
 1883    2   -1    0    2
 1884   -4   -2   -2   -1
 1885   -3   -7   -2   -5
 1886   -2    2    4    5
 1887    6    6    1    0
 1888    0   -1   -5   -7
 1889   -8   -3    4    6
 1890    7    6    5    3
 1891    0   -5   -5   -3
 1892   -2    7    7    7
 1893    4    5    6    4
 1894    5    6    4    3
 1895    3    5    1   -3
 1896    0    2   -2    5
 1897   -4   -3    0    0
 1898    2    1    0    5
 1899    2   -1   -7   -5
 1900   -4   -9   -2   -1
 1901   -4   -2   -2   -2
 1902   -4   -4   -5  -10
 1903   -8   -4    2    4
 1904    5    1   -6   -1
 1905   -5   -9   -6   -4
 1906   -4   -3    3    4
 1907    6   -4   -4    1
 1908    0    1    2    3
 1909    2    4    6    5
 1910    5    5    5    6
 1911    5    0   -4   -4
 1912   -7   -3    0    1
 1913    0    3   -5   -5
 1914   -6   -5   -4   -9
 1915   -6   -5   -1    6
 1916    4    6    9    7
 1917    9    7    9    7
 1918    9    0   -6   -6
 1919   -7   -6   -4   -3
 1920   -3   -3   -1    4
 1921    4    4    3   -2
 1922    2    2    1    1
 1923    2   -1   -1   -2
 1924   -2    1    4    2
 1925    4    0   -1   -8
 1926   -8   -4   -1   -1
 1927    2    3    1   -3
 1928   -1    2    1    2
 1929    1    1   -1   -2
 1930   -1   -1   -4   -8
 1931         1        -1
 1932        -2         1
 1933         0         2
References:
  • Walker, G. T., and E. W. Bliss, 1932: World Weather V. Mem. Roy. Meteor. Soc., 4, No. 36, 53-84. [Documents DJF and JJA variability.]
  • _____, and _____, 1937: World Weather VI. Mem. Roy. Meteor. Soc., 4, No. 39, 119-139. [Documents MAM and SON variability.]
    A monthly index
    It is useful to have a version of the series in which the various seasonal series are merged into a "monthly" index. The merging is accomplished in three steps.
  • Each seasonal series is standardized with respect to the common period of record, 1882-1929.
  • The seasonal values are ascribed to the months which make up the season.
  • The "monthly" series are then interleaved, and the merged series normalized for all months combined with respect to 1882-1929.
    This is the processing for the (effectively) seasonal resolution (DJF, MAM, SON, ...) plot at the top of this WWW page.

    The data is offered in 3 formats:

  • 3 columns: year, calendar month, index value
  • 1 column (just the index value)
  • table.
    March 2001
    Todd Mitchell (mitchell@atmos.washington.edu)
    JISAO data