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 15, 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 (enhanced) convection is located over Indonesia (date line). The convection centered over the date line represents the most eastward extent of tropical Pacific convection over the last 5 month period. • Statistical model forecasts of the MJO suggest further eastward propagation of the area of suppressed convection over Indonesia toward the western Pacific. The area of enhanced convection over the date line is expected to remain quasi-stationary and appears to be coupled to the underlying warm SSTs.

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. The westerly anomalies concentrated near the date line have strengthened over 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 centered near the date line have strengthened.

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 area of enhanced convection has propagated eastward beyond the date line. The area of suppressed convection to the east has also propagated eastward toward 120oE. 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) centered near 150oE in the tropical Pacific has remained somewhat stationary over the last week. 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 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 propagate slowly eastward over the next 6-10 day period.

12. Potential Global Impacts Impacts in the global tropics during the next 1-2 weeks; (i) elevated risk of tropical cyclone activity; (ii) above average rainfall in the Southwest United States and Northwest Mexico.

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 (enhanced) convection is located over Indonesia (date line). The convection centered over the date line represents the most eastward extent of tropical Pacific convection over the last 5 month period. • Statistical model forecasts of the MJO suggest further eastward propagation of the area of suppressed convection over Indonesia toward the western Pacific. The area of enhanced convection over the date line is expected to remain quasi-stationary and appears to be coupled to the underlying warm SSTs.