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Madden-Julian Oscilation Output

Telecommunicated influence of the MJO on the European region

The Madden-Julian Oscillation (MJO) is a broad-scale wave-like convective phenomena centred on the equator and also the main source of tropical predictability on the monthly time scale.  It is important as it identifies where tropical deep convection interacts with the general atmospheric circulation, and it is observed mainly in a sector spanning the Indian and Pacific oceans.  The feature is typically initiated over the Indian Ocean, and usually advances steadily eastwards, as areas of relatively organised convection, bringing a significant enhancement of rainfall, followed in their wake by much less active convection.  The MJO may be monitored using a combination of lower and upper tropospheric zonal flow patterns and out-going long wave radiation (OLR) or simulations thereof.

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Fig8.2.2.2: 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

Fig8.2.2.3: To view Hovmoeller diagrams:

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Commonly, negative velocity potential at 200hPa and/or indication of 850hPa convergence (and hence upward motion in the atmosphere) coincide with a reduction in outgoing long wave radiation (due to existence of deeper cloud with colder tops).  Broadly, this can be seen on the plots above (e.g. at 150E at T+0 (i.e. 00UTC 25 Jan 2018) marked by the horizontal line.  The greater is the magnitude of each of these components, and the more coincident they are, the greater will be, in general, the magnitude of the MJO.  

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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Individual values of these parameters for the different ensemble members give varying intensities of MJO on the diagram and the spread becomes large.  Note also that by construction, the amplitude of the forecast ensemble mean MJO on this diagram (as shown by black triangles) will tend to reduce, on average, at longer lead-times.

Additional Sources of Information

(Note: In older material there may be references to issues that have subsequently been addressed)

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