Eric C. J. Oliver
Historical Reconstruction of the MJO Index

The MJO index of Wheeler and Hendon (2004) has been reconstructed over the period 1/1/1905 to 31/12/2008. This reconstruction was generated by multiple linear regression of surface pressure time series, from the Twentieth Century Reanalysis (20CR), at 12 locations onto the Wheeler and Hendon (2004) index (Oliver and Thompson, Journal of Climate, 2012, pdf).

  • Daily values of the reconstructed index are available for download:
  • The locations from which Twentieth Century Reanalysis pressure series were taken are shown by white circles:



    Exact locations, along with regression coefficients, are given in the table below. The regression coefficients were calculated by least-squares linear regression of the Wheeler and Hendon (2004) index onto the bandpassed pressure series over the 1979 to 2008 period.

    LocationLongitude (oE)Latitude (oN)β1β1,Hβ2β2,H
    1106-61.97-2.372.131.53
    28600.511-1.092.520.442
    3326-141.21-0.1170.4520.713
    411414-0.6550.723-1.090.713
    5336140.55-0.509-0.108-0.424
    65600.4510.1070.9241.12
    79014-1.290.0302-0.427-0.945
    8140-14-0.7290.153-1.72-0.48
    931800.5060.359-0.1880.92
    102746-1.542.08-2.34-1.82
    11801.21.34-1.820.225
    121300-2.87-0.7772.09-2.74

    The reconstructed index, IHR, is generated by linear combination of bandpassed pressure series, p, and their Hilbert transforms, pH:



    where t is a time index and the β are 1 x 12 row vectors with values given in the table above.
  • Through the development of this index it was found that great care must be taken when using reanalysed surfaced pressures from 20CR. By arbitrarily choosing predictor locations one can control the long-term trend in MJO amplitude between approximately zero and an increase of 30%.
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