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Madden-Julian oscillation Output
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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The introduction of SPP has had a positive impact in MJO at week 3-4 in monthly forecasts.
Fig8.2.6-1: Schematic representation of the global teleconnection patterns associated with the Madden-Julian Oscillation (MJO).
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
Fig8.2.6-3: 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
Fig8.2.6-4: 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.
Fig8.2.6-5: 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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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. (Current MJO Index Plot)
Fig8.2.6-6: 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.
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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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