The Madden-Julian Oscillation (MJO) is a fluctuation in
tropical weather, from the upper atmosphere down to surface ocean currents, on
the scale of weeks to months which moves east through the Indian and Pacific
Oceans. It was discovered in 1971 by meterologists Roland Madden and Paul
Julian, and consists of eastward-moving convection cells of alternating rain
and dry weather.
The weather cells move eastward across the basin at between 4 and 8 m/s. Because of the length of time it takes for one phase (stormy or dry) to pass by, the MJO is also known as the 30-60 day wave (oscillation). The upper-atmosphere fluctuations continue around the globe, but the surface weather patterns are confined largely to the Indian and Pacific.
MJO (30-60 day wave) schematic.
The oscillations can affect weather as far as 30°
to north and south. The wind and storm activity associated with these
oscillations drive surface currents to a depth of 100 m. In Northern Hemisphere
summer and fall (Jun-Nov), the cells can at times stall, leading to persistent
rainy weather on the western side of the Indian Ocean basin.
The eastward migration of the stormy and clear cells are consistent with a large-scale type of fluctuation known as a Rossby (planetary) wave, a north-to south wave which appears in wind patterns and ocean currents, and can travel either west or east. No obvious mechanism for these oscillations has been found.
MJO phases.
Tomorrow: Rossby waves.
Be brave, and be well.
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