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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).

Fig8.2.56-1: Schematic representation of the global teleconnection patterns associated with the Madden-Julian Oscillation (MJO).

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Fig8.2.6-2: Meteosat (IODC) IR (Channel 4) image DT 00UTC 25 Feb 19.  A large area of convection lies over an equatorial region of the Indian Ocean typical of Madden-Julian Oscillations (MJO

Fig8.2.56-23: Schematic diagram of the effects of positive NAO and negative NAO phases in the European and Mediterranean areas.  Positive NAO phase tends to steer depressions towards Northern Europe bringing wetter conditions while the Mediterranean region tends to be drier.  Negative NAO phase tends to steer depressions towards Southern Europe bringing wetter conditions while Northern Europe tends to be drier. 

The MJO Hovmoeller diagrams

Fig8.2.56-34: To view Hovmoeller diagrams:

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• 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.
  

Fig8.2.5-46: 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. 

• Fig8.2.6-5-4(Left): Anomalies of velocity potential at 200hPa. Note the observed and predicted progression eastwards (diagonally towards bottom right of the diagram) of the maxima (red, yellow) and minima (blue, green) of the 200hPa velocity potential.
• Fig8.2.6-5-4(Centre): Anomalies of zonal wind at 850hPa. Note the forecast of a dipole of positive anomaly (red: stronger westerly flow than ER-M-climate) and negative anomaly (blue, green: weaker westerly flow than ER-M-climate) suggesting an area of anomalous convergence in between. The diagonal pattern suggests it has progressed and will continue to progress slowly eastwards.
• Fig8.2.6-5-4(Right): Anomalies of outgoing long wave radiation.  Note the area of negative anomaly (blue, green: weaker outgoing radiation) indicative of enhanced cloud cover with cold radiating cloud-tops and inhibition of transmission of warmer terrestial radiation.
  

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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.  (Current MJO Index Plot)

Fig8.2.56-56: Wheeler-Hendon MJO diagram.  Time evolution of the MJO as predicted by the ensemble using zonal winds at 850hPa, 200hPa velocity potential and simulated OLR, all averaged between 15S and 15N.  Individual ensemble member values at day 1, 5, 10, 15 and 20 are represented respectively by red, pink, orange blue and green circles. The ensemble mean values (black triangles) are joined by a solid black line, and the analysis values of the preceding 30 days are joined by a grey line (with grey dots added every 5 days).  Points representing sequential values trace anti-clockwise trajectories around the origin,indicating systematic eastward propagation of the MJO.  Large amplitudes (outside of the circle) signify strong cycles of the MJO, while weak activity appears as rather random motion near the origin. The phases (broadly geographical regions) are numbered 1 to 8.  See Wheeler and Hendon 2004 Mon. Wea. Rev. vol. 132, 1917-1932 for details.

In the example in Fig8.2.56-5 6 there is initially a strong indication of a large amplitude MJO (red, Day1; pink, Day5) progressing eastwards but this is forecast to probably weaken and become less identifiable (Day15, blue) over the western Pacific, but the ensemble spread becomes large by then implying large uncertainty with some members maintaining a strong signal (plots far from the centre of the diagram), others weak (plots towards the centre and inside the circle).  Compare with the Hovmoeller diagrams (Fig8.2.6-5-4) where:

• at Day1 and Day5 at approximately 170E, the 200hPa velocity potential (divergence) is coincident with 850hPa zonal dipole of zonal winds (convergence) and with reduced outgoing radiation (increased cloud).  Thus a strong signal is shown on the Wheeler-Hendon MJO diagram.
• by Day10 the 200hPa velocity potential (divergence) has progressed to about 140W.  The 850hPa zonal dipole of zonal winds (convergence) has also progressed similarly, if a little more slowly, with continuing dipole of zonal winds (weakened easterly but strengthened westerly zonal flow).  But greater outgoing radiation (because less cloud has been forecast) is evident over the Pacific.    Thus the plots on the Wheeler-Hendon MJO diagram give a gradually less strong signal of the intensity of the MJO.

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