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 May 24, 2005

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

3. Overview • The Kelvin wave initiated by westerlies near the date line in late January 2005 has reached the South American coast and warming of the ocean waters along the west coast of South America has ended. • During mid March the MJO became active and strong and completed one cycle around the global tropics with a period of approximately 45 days. Westerly anomalies in the western Pacific during mid-April associated with this MJO activity did not extend far enough east to initiate another Kelvin wave. • The MJO continued to gradually weaken during the past week. The enhanced phase of the MJO is currently located in the western hemisphere and continues to result in enhanced convection across sections of South America and Africa. Suppressed convection is evident in the eastern Indian Ocean and Indonesia. There is considerable uncertainty in the evolution of the MJO during the next 1-2 weeks. MJO activity ongoing since mid-late March may be ending. • Impacts in the global tropics, during week 1, include the chance of above average rainfall across northern South America, in proximity to the Atlantic ITCZ, and central Africa with drier than average conditions possible across Indonesia.

4. 850-hPa Vector Wind Anomalies (m s-1) Note that shading denotes the magnitude of the anomalous wind vectors. For the most part, equatorial anomalies are unorganized from the Indian Ocean through the Pacific.

5. Low-level (850-hPa) Zonal (east-west) Wind Anomalies (m s-1) Weaker-than-average easterlies (orange/red shading). Stronger-than-average easterlies (blue shading). Westerly anomalies developed over the western equatorial Pacific in early January and persisted through February. Time Easterly anomalies are evident in the Indian Ocean while weak westerly anomalies have developed in the eastern Pacific. Longitude

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) The eastward propagation of the positive/negative anomaly dipole over the Indian Ocean and Indonesia (late December 2004-early January 2005) was associated with the MJO. Time Enhanced convection became persistent in the region of the anomalously warm water near the date line during February. The MJO was strong from late March through early May. Currently, suppressed convection has entered the Indian Ocean and Indonesia while enhanced convection is evident across northern South America. Longitude

7. Anomalous OLR and 850-hPa Wind: last 30 days Positive OLR anomalies (below-average rainfall) developed over Indonesia during the middle of the period with the suppressed phase of the MJO. Recently, the ITCZ has become enhanced and negative anomalies have developed across Central America. Low-level (850-hPa) easterly wind anomalies (m/s) observed over the western equatorial Pacific have dissipated during the last ten days.

8. 200-hPa Velocity Potential Anomalies (5°S-5°N) Positive anomalies (orange/red shading) indicate unfavorable conditions for precipitation. Negative anomalies (blue shading) indicate favorable conditions for precipitation. A stationary pattern of upper level divergence developed during February as enhanced convection remained near the date line. Beginning in early-mid March, the MJO became quite active and regular. Upper-level divergence propagated from the western Indian Ocean across the Pacific and through the western Hemisphere during a 45 day period from mid March to early May. Currently, equatorial upper-level divergence is focused over northern South America. Time Longitude

9. 200-hPa Vector Winds and Anomalies (m s-1) Note that shading denotes the magnitude of the anomalous wind vectors. Strong upper-level westerly anomalies are evident across south-central Africa and the western Indian Ocean mainly south of the equator.

10. Heat Content Evolutionin the Eq. Pacific • Through 2004 there were several cases of eastward-propagating oceanic Kelvin waves (indicated by dashed black lines in the figure). • Each Kelvin wave was initiated when the easterlies weakened over the equatorial Pacific in association with Madden-Julian Oscillation (MJO) activity. • Between August 2004 and January 2005 Kelvin wave activity weakened and the average heat content (0-300 m) decreased. • During February 2005, a stronger Kelvin wave developed and continued to strengthen during March and reached the South American coast during early April. Heat content has returned to near average in the western and central Pacific with no new Kelvin wave activity. Time Longitude

11. Empirical Forecast Based on the Real-time Multivariate MJO index Suppressed convection in the Indian Ocean and Indonesia is forecast to shift slightly east and weaken during the period.

12. Potential Global Impacts –Week 1 1 2 • (1) Increased chance of above average rainfall from northern South America into central Africa • (2) Increased chance of drier than average conditions stretching from the eastern Indian Ocean across Indonesia into the western Pacific Ocean

13. Potential Global Impacts – Week 2 No global impacts expected for week 2

14. Summary • The Kelvin wave initiated by westerlies near the date line in late January 2005 has reached the South American coast and warming of the ocean waters along the west coast of South America has ended. • During mid March the MJO became active and strong and completed one cycle around the global tropics with a period of approximately 45 days. Westerly anomalies in the western Pacific during mid-April associated with this MJO activity did not extend far enough east to initiate another Kelvin wave. • The MJO continued to gradually weaken during the past week. The enhanced phase of the MJO is currently located in the western hemisphere and continues to result in enhanced convection across sections of South America and Africa. Suppressed convection is evident in the eastern Indian Ocean and Indonesia. There is considerable uncertainty in the evolution of the MJO during the next 1-2 weeks. MJO activity ongoing since mid-late March may be ending. • Impacts in the global tropics, during week 1, include the chance of above average rainfall across northern South America, in proximity to the Atlantic ITCZ, and central Africa with drier than average conditions possible across Indonesia.