EOF representations of the Madden-Julian Oscillation and its connection with ENSO
Kessler, W.S., 2001: J. Climate, 14, 3055-3061
Although recent El Niņo events have seen the occurrence of strong intraseasonal winds apparently associated with the Madden-Julian Oscillation (MJO), the usual indices of interannual variability of the MJO are uncorrelated with measures of the ENSO cycle. An EOF decomposition of intraseasonal OLR and zonal wind identifies two modes of interannual variability of the MJO: a zonally stationary variation of amplitude that is unrelated to ENSO, and a roughly 20° longitude eastward extension of the MJO envelope during El Niņo events. The stationary mode is represented by the first two EOFs, which form the familiar lag-correlated quadrature pair, while the eastward extending mode is represented by the third EOF which is usually ignored although it is statistically significant. However, the third EOF also has a systematic phase relation with the first pair, and all three should be considered as a triplet; rotating the EOFs makes the phase relation clear. The zonal shift represents about 20% of total MJO variance (which itself is about 55% of intraseasonal variance over the tropical strip). While the eastward shift is small compared to the global scale of the MJO, it produces a large proportional shift of MJO activity over the open Pacific where interactions with the ENSO cycle can occur.
Download the paper as it appeared in J. Climate (pdf, 293 Kb)
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Another paper on this topic: Rectification of the Madden-Julian Oscillation into the ENSO cycle (Kessler and Kleeman) (published in J.Climate, Oct 15 2000).
Dr. William S. Kessler
NOAA / PMEL / OCRD
7600 Sand Point Way NE
Seattle WA 98115 USA