Madden/Julian Oscillation: Recent Evolution, Current Status and Forecasts

1. Madden/Julian Oscillation: Recent Evolution, Current Status and Forecasts Update prepared by Climate Prediction Center / NCEP February 1, 2005

2. Outline • Overview • Recent Evolution and Current Conditions • Madden Julian Oscillation Forecast • Summary

3. Overview • Through most of 2004 MJO activity has contributed to month-to-month fluctuations in the patterns of equatorial winds and tropical convection. • This activity has been associated with periods of westerlies in the western Pacific and weaker than average easterlies in the central Pacific which have initiated eastward-propagating oceanic Kelvin waves, contributing to a deeper-than-average oceanic thermocline and an increase in the surface and subsurface temperature anomalies in the central and eastern equatorial Pacific. • Beginning in early November and extending through mid December the MJO was weak. • The MJO strengthened somewhat in late December but again appears to have weakened. Currently suppressed convection is located in Indonesia with areas of enhanced convection evident just west of the date line and in the far western Indian Ocean. • Statistical model forecasts of the MJO are inconclusive. Based on the recent evolution of the MJO, it is likely that suppressed convection will remain in Indonesia and weaken during the next 1-2 weeks. Close monitoring of enhanced convection both west of the date line and in the Indian Ocean is warranted during the upcoming period.

4. Low-level (850-hPa) Zonal (east-west) Wind Anomalies Westerlies (western Pacific) and weaker-than-average easterlies (central/eastern Pacific) (orange/red shading) Stronger-than-average easterlies (blue shading) Time Over the last several months, westerlies have developed on several occasions across the western equatorial Pacific. Most recently, this occurred in mid January. Westerly anomalies remain in the far western Pacific Ocean while winds are near average across the remainder of the Pacific. Longitude

5. 850-hPa Vector Wind Anomalies (m s-1) Note that shading denotes the magnitude of the anomalous wind vectors. Westerly anomalies are evident in far western Pacific. Stronger than average easterlies are located near the date line.

6. Outgoing Longwave Radiation (OLR) Anomalies (7.5°S-7.5°N) Drier-than-average conditions (orange/red shading) Wetter-than-average conditions (blue shading) During October the MJO was active in the Indian Ocean and western Indonesia regions. Time The MJO, however, became very weak in early November and remained so through mid December. The MJO strengthened in late December and currently suppressed convection is located in Indonesia. Areas of enhanced convection are evident just west of the date line and in the western Indian Ocean Longitude

7. 200-hPa Velocity Potential Anomalies 5oN-5oS Upper-level convergence (brown), upper-level divergence (green). The MJO became very weak in early November with little propagation of upper-level convergence and divergence. Time As the MJO strengthened in mid December, upper-level divergence / convergence propagated from the Indian Ocean into the Pacific. Upper level divergence is evident across Africa / far western Indian Ocean and also just west of the date line Longitude

8. 200-hPa Vector Winds and Anomalies (m s-1) Note that shading denotes the magnitude of the anomalous wind vectors. Anomalous upper-level westerlies are evident in the Indian Ocean.

9. Anomalous Depth of the 20°C Isotherm (m) (2°S-2°N) Shallower-than-average thermocline (blue shading); Deeper-than-average thermocline (orange shading). MJO-related weakening of the equatorial easterly winds initiated eastward-propagating oceanic Kelvin waves in early January, in early April, late June, late August and October and has contributed to a deeper-than-average oceanic thermocline in the central and eastern equatorial Pacific. Time The latest Kelvin wave initiated by westerly anomalies in early December has propagated into the equatorial central Pacific. Longitude

10. Niño Indices : Recent Evolution SST anomalies greater than or equal to +0.5 ºC are observed in the Niño 4, and Niño 3.4 regions. Since late December, the Nino 3.4 and Nino 3 anomalies have generally decreased while the Nino 1+2 anomaly remains near normal. The warmth in the Niño 4, 3.4, and 3 regions and lack of significant warmth in the Niño 1+2 region indicates that a mid-Pacific warm (El Niño) episode is continuing.

11. Empirical Forecast Based on the Real-time Multivariate MJO index MJO associated OLR anomalies are forecast to be weak for the next 6-10 days.

12. Potential Global Impacts Impacts in the global tropics attributable to the MJO are not expected during the next 1-2 weeks as the MJO signal is weak

13. Summary • Through most of 2004 MJO activity has contributed to month-to-month fluctuations in the patterns of equatorial winds and tropical convection. • This activity has been associated with periods of westerlies in the western Pacific and weaker than average easterlies in the central Pacific which have initiated eastward-propagating oceanic Kelvin waves, contributing to a deeper-than-average oceanic thermocline and an increase in the surface and subsurface temperature anomalies in the central and eastern equatorial Pacific. • Beginning in early November and extending through mid December the MJO was weak. • The MJO strengthened somewhat in late December but again appears to have weakened. Currently suppressed convection is located in Indonesia with areas of enhanced convection evident just west of the date line and in the far western Indian Ocean. • Statistical model forecasts of the MJO are inconclusive. Based on the recent evolution of the MJO, it is likely that suppressed convection will remain in Indonesia and weaken during the next 1-2 weeks. Close monitoring of enhanced convection both west of the date line and in the Indian Ocean is warranted during the upcoming period.