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The Madden-Julian Oscillation affects the North Atlantic Oscillation.   The mid-latitude jet streams in turn can affect the flow over the North Atlantic which has a strong impact on the tracking of depressions (e.g. towards Europe).  The cross-Atlantic flow can be categorised as positive or negative phases or regimes of the North Atlantic Oscillation (NAO).

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An MJO Hovmoeller diagram displays the time evolution of the ensemble mean anomaly.  The longitude within the equatorial band (15S-15N) is shown on the x-axis. Time is shown on the y-axis.  The analyed data at the data time of each extended range forecast run is shown above the horizontal line.  The forecast mean ensemble values are shown below the horizontal line.  Several MJO forecast products are available:

• Time-longitude section of ensemble mean anomalies of outgoing long wave radiation, zonal wind at 850hPa, and velocity potential at 200hPa averaged over a tropical band (15N-15S) in Hovmoeller diagram form.
  Postage Stamp charts of the  time-longitude sections of anomalies of outgoing long wave radiation, zonal wind at 850hPa and velocity potential at 200hPa averaged over a tropical band (15N-15S) for each ensemble member (51 stamps).
  

Fig8.2.2.4: Time-longitude section (Hovmoeller diagram) of ensemble mean anomalies averaged over a tropical band (15N-15S, shown in map section at the bottom).  Analysed values above the horizontal black line, forecast values below it. 

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Wheeler-Hendon MJO diagram

The Wheeler-Hendon MJO index plot displays the time evolution, location and magnitude of the MJO predicted by ensemble and described by a multivariate MJO index (Wheeler and Hendon 2004 Mon. Wea. Rev. vol. 132, 1917-1932).  The magnitude of the MJO is essentially proportional to the distance of the point from the centre of the diagram.

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