Real-time multivariate Madden Julian Oscillation projection coefficients for GEFSv12 Reanalysis and Reforecasts (NCEI Accession 0259491)

The Real-time multivariate Madden Julian Oscillation (RMM) indices for the Global Ensemble Forecast System version 12 (GEFSv12) reanalysis and reforecast datasets are provided. They were computed using the methodology outlined in Wheeler and Hendon (2004).

For the GEFSv12 reanalysis (Reanalysis RMMs), anomalies of outgoing longwave radiation (OLR), 200 hPa zonal winds (U200), and 850 hPa zonal winds (U850) are provided for January 1, 2000 through March 31, 2020. The mean of the most recent 120 days of anomaly data for that field is subtracted to remove the influence of low frequency variability (e.g., ENSO), and the anomalous fields are latitudinally averaged and each of the latitudinally averaged sets of anomalies is projected onto the GEFSv12 reanalysis EOFs.

For the GEFSv12 reforecasts (Reforecast ensemble mean RMMs), each of the 11 ensemble members for a given reforecast initialization are first averaged together. The MJO indices are then calculated using the adaptations of WH04 methodology applied to forecast datasets detailed by Gottschalck et al. (2010).

For Reforecast individual member RMMs, rather than averaging together the 11 ensemble members for a given reforecast initialization as in the ensemble mean calculations, each member is preserved and from it, the corresponding lead time dependent climatology for the relevant field is removed. This allows for the calculation of anomalies for each member of each reforecast and subsequently calculation of RMMs as described above.