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 8, 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 weakened in the middle to latter half of January 2005. Currently suppressed convection is located over Indonesia with an area of enhanced convection extending eastward from 120oE to just east of the date line. The enhanced convective activity over the Indian Ocean has weakened over the last week. • Statistical model forecasts of the MJO are inconclusive as MJO activity is currently weak. Close monitoring of the enhanced convection extending from 120oE to just east of the date line is warranted over the upcoming period. Observations suggest that this area of convection has been stationary over the last 10-14 days exhibiting little propagation.

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 are concentrated to the west of the date line. To the east of the date line weaker-than-average easterlies have strengthened in the last week. Longitude

5. 850-hPa Vector Wind Anomalies (m s-1) Note that shading denotes the magnitude of the anomalous wind vectors. Westerly anomalies have strengthened and expanded eastward toward the central Pacific.

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. Over the last week the enhanced convection over the Indian Ocean weakened, while enhanced (reduced) convection remains centered near 160oE (90oE). 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 convergence (divergence) centers are centered near 150oE in the tropical Pacific. Longitude

8. 200-hPa Vector Winds and Anomalies (m s-1) Note that shading denotes the magnitude of the anomalous wind vectors.

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 far eastern Pacific. Longitude

10. Niño Indices: Recent Evolution At the beginning of February, SST anomalies greater than or equal to +0.5C were restricted to the Niño 4 region. Recently, departures have decreased east of the date line (Niño 3.4, Niño 3 and Niño 1+2 regions).

11. Empirical Forecast Based on the Real-time Multivariate MJO index MJO activity is forecasted to remain weak over the next 6-10 day period.

12. Potential Global Impacts Impacts in the global tropics attributable to the MJO are not clear over 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 weakened in the middle to latter half of January 2005. Currently suppressed convection is located over Indonesia with an area of enhanced convection extending eastward from 120oE to just east of the date line. The enhanced convective activity over the Indian Ocean has weakened over the last week. • Statistical model forecasts of the MJO are inconclusive as MJO activity is currently weak. Close monitoring of the enhanced convection extending from 120oE to just east of the date line is warranted over the upcoming period. Observations suggest that this area of convection has been stationary over the last 10-14 days exhibiting little propagation.