An index for the Madden Julian Oscillation (MJO) based on the tropical zonal wind at 200 and 850 hPa is presented. The index is a modified version of the one published by Wheeler and Hendon in 2004 in that it does not include information on the outgoing long wave radiation (OLR). The modified index thus makes it possible to compute time series of the MJO amplitude and phase from reanalysis data before 1974, when OLR analyses are not available. The original and modified indices are compared over a common period of data and are found to be in quite reasonable agreement. Some systematic differences are seen when the modified index is computed with the NCEP/NCAR and ERA-40/Interim reanalyses. The index time series is used to reveal some differences in the preferred phases of the MJO during El Nino and La Nina episodes. The presentation will also include some discussion of the impact of the MJO on the mid-latitudes and the potential benefits that extended range forecasts could draw from a better representation of the MJO dynamics in forecast models. 9-30-2011-->