The Madden-Julian Oscillation and Mean Global Easterly Winds

The Madden-Julian Oscillation (MJO) affects weather and climate on both short, and long time scales. To better predict climate and weather we need to understanding physical mechanisms controlling the initiation and destabilization of the MJO. Observational research recognizes the MJO as the dominant eastward propagating global disturbance of wavenumber 1 to 3. Based on their analytical model, Fuchs and Raymond (2017) suggest that the destabilization of the MJO, and its strength, depends on the wind-induced surface heat exchange (WISHE) mechanism caused by the mean global equatorial easterly winds, for the wavenumber 1 mode.

We test the hypothesis of Fuchs and Raymond by looking at observational and reanalysis data. To identify MJO events, we perform Wheeler-Kiladis space-time filtering on the NOAA outgoing longwave radiation (OLR). The mean equatorial easterly winds are obtained from NCEP FNL and ERA-Interim reanalysis data.

We find that all MJO events occur with mean global easterly winds, irrespective of their strength. Furthermore, we investigate the correlation between the strength of the MJO, defined as the minimum of the Wheeler-Kiladis filtered OLR, and easterly winds prior to the MJO initiation. We also test this theory on a number of models from the recent CLIVAR global circulation model inter-comparison, in order to test the usefulness of this tool for evaluating how well the global climate models model the MJO.