Distinct patterns of lower-level and upper-level atmospheric circulation anomalies accompany the MJO-related pattern of enhanced or decreased tropical rainfall across the tropics. These circulation features extend around the globe and are not confined to only the eastern hemisphere.
The Madden–Julian oscillation moves eastward at between 4 m/s and 8 m/s across the tropics, crossing the Earth’s tropics in 30 to 60 days—with the active phase of the MJO tracked by the degree of outgoing long wave radiation, which is measured by infrared-sensing geostationary weather satellites.
The lower the amount of outgoing long waves radiation, the stronger the thunderstorm complexes, or convection, is within that region.
Enhanced surface (upper level) westerly winds occur near the west (east) side of the active convection. Ocean currents, up to 100 metres (330 ft.) in depth from the ocean surface, follow in phase with the east-wind component of the surface winds. In advance, or to the east, of the MJO enhanced activities, winds aloft are westerly. In its wake, or to the west of the enhanced rainfall area, winds aloft are easterly. These wind changes aloft are due to the divergence present over the active thunderstorms during the enhanced phase.
Its direct influence can be tracked pole ward as far as 30 degrees latitude from the equator in both northern and southern hemispheres, propagating outward from its origin near the equator at around 1 degree latitude, or 111 kms, per day.
PHASES OF MADDEN – JULIAN OSCILLATION
MJO consists of two parts or phases. Strong MJO activity often dissects the planet into halves. One half within the enhanced convective phase and the other half in the suppressed convective phase.
Enhanced rainfall (or convective) phase: winds at the surface converge, and the air is pushed up throughout the atmosphere. At the top of the atmosphere, the winds reverse (i.e., diverge). Such rising air motion in the atmosphere tends to increase condensation and rainfall.
Suppressed rainfall phase: winds converge at the top of the atmosphere, forcing air to sink and, later, to diverge at the surface. As air sinks from high altitudes, it warms and dries, which suppresses rainfall.
Impact of MJO on Indian Monsoon: When it is over the Indian Ocean during the Monsoon season, it brings good rainfall over the Indian subcontinent.On the other hand, when it witnesses a longer cycle and stays over the Pacific Ocean, MJO brings bad news for the Indian Monsoon.
IRREGULARITIES OBSERVED IN MJO
- Effect of Global Warming: Due to global warming: Change in the residence time of MJO clouds has altered the weather across the world.
- Impact over global climate: Madden Julian Oscillation (MJO) clouds are altering the residence time in Indian and Pacific Ocean. This has implications for global climate: Increased the rainfall over Northern Australia & Declining rainfall in Central Pacific and along west coast of Africa.
