Page History

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• black - no initial MJO.
• red - MJO phases 2–3 (enhanced convection over the Indian Ocean).
• blue - MJO phases 4–5 (enhanced convection over the Maritime Continent).
• green - MJO phases 6–7 (enhanced convection over the western Pacific).
• brown - MJO phases 1 and 8 (suppressed convection over the Maritime Continent).

The MJO influences skill in forecasts concerning NAO– circulation pattern:

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The forecast based on 00UTC 25 Feb 2019 12 Jan 2024 illustrates the tele-connection effect of tropical deep convection over the Indian Ocean upon subsequent downstream developments of NAO+ type over the North Atlantic/Europe. 

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Fig8.2.8-4: MJO WheelerMJO Wheeler-Hendon diagram for the monthly forecast based on DT 00UTC 25 February 201912 January 2024.   The colours represent ENS forecasts at various lead times as given by the key above the diagram.   Initially the MJO lies within Sector1  The ENS forecasts of the MJO show a steady progress westward but with increasing spread.  The forecasts for MJO are: 

• initially in Sector3 (Western Indian Ocean) with a small spread among ENS members.
• by Day5 in Sector4 (Eastern Maritime Continent) with only a limited spread among ENS members maintaining high confidence. 
• by Day15 to Day20 in Sectors 6 and 7 Western Pacific) with an increasingly large spread showing fairly high confidence in location but lower for intensity.  ENS members lying within the internal circle correspond to very weak MJO.

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Fig8.2.8-5: Euro-Atlantic weather regime projection Wheeler-Hendon diagram (NAO/BL phase space diagrams) for the monthly forecast based on DT 00UTC 12 January 2024.  As the MJO progresses westward (Fig8.2.8-4), the downstream teleconnection influences changes in the Euro-Atlantic weather regime.  The Euro-Atlantic weather regime is predominantly NAO- initially on 15-21 Jan but is forecast to evolve into NAO+ by 22-28 Jan. 

There is not strong preferential path leading to NAO+ regime, but the chances of NAO+ Euro-Atlantic weather regime increase 10 days after the MJO is in phase 3.

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Fig8.2.8-6: The Euro-Atlantic weather regime presented in histogram form reflecting the regime projection diagrams (Fig8.2.8-5) above.   The regime is generally NAO-(green) 15-21 Jan but is forecast to evolve into predominantly NAO+ (blue) by 11-17 Jan. 

Additional sources of information

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

Read Euro-Atlantic Weather Regimes and Their Modulation by Tropospheric and Stratospheric Teleconnection Pathways in ECMWF Reforecasts and is forecast to progress into Sector2 (Eastern Indian Ocean) by Day5 with a fairly limited spread among ENS members. The mean position of the ENS forecasts during the subsequent ten days show continuing westward progress although with an increasing spread before weakening (moving into the central circle) by Day20.