An All-season Real-time Multivariate MJO Index

Using an objectively-defined index to monitor and predict the climate and weather variations related to the tropical Madden-Julian Oscillation (MJO)

Background on the MJO

The Index: RMM1 and RMM2

Based on the first two Empirical Orthogonal Functions (EOFs) of the combined fields of near-equatorially-averaged 850 hPa zonal wind, 200 hPa zonal wind, and satellite-observed outgoing longwave radiation (OLR) data. Projection of the daily observed data onto such multiple-variable EOFs, with the annual cycle and components of interannual variability removed, yields principal component (PC) time series that vary mostly on the intraseasonal time scale of the MJO only. This projection thus serves as an effective filter for the MJO without the need for time filtering, making the PC time series an effective index for real time use. We call the two PC time series that form the index the Real-time Multivariate MJO series 1 (RMM1), and RMM2. For the observations, the OLR data is that measured by the NOAA polar-orbitting satellites, while for the winds we use the NCEP/NCAR Reanalyses and the NCEP Operational analyses. The index is usually available in near real time about 12 hours after the end of each Greenwich day (i.e. at about 1200 UTC). For more details, see Wheeler and Hendon (2004).

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Created and maintained by Matthew Wheeler