365 Days of Climate Awareness 109 – The Indian Ocean Dipole

 

The Indian Ocean Dipole (IOD) is also known as the Indian Niño, because it features the irregular variation of warm and cold sea surface temperatures on the eastern and western regions of the Indian Ocean basin. There is no obvious mechanism, as it is not, like El Niño, due to a failure of the westward trade winds allowing the eastward flow of warm water.

Indian Ocean Dipole index, 1896-1998.

The Dipole exists in three phases: positive, neutral and negative. In the positive phase, the western surface waters off the coast of East Africa, between the horn (coastal Somalia) and Madagascar are warm, and the eastern waters around Indonesia are cool. In the neutral phase, there is little temperature difference. In the negative phase, Indonesian waters are warm, while east African waters are cool.

IOD, positive phase: warmer, wetter west, and cooler, drier east.

The regional weather effects can be dramatic. Where the ocean surface water is warm, atmospheric updrafts form due to evaporating water, leading to increased rain. Where the surface water is cool, drier air descends to the sea surface, leading to clear, dry weather. A positive IOD phase leads not uncommonly to drought in Australia. For these reasons the IOD is considered to be a joint oceanic and atmospheric variation.

IOD neutral phase: weather patterns closer to average.

The IOD seems to be correlated to ENSO. A positive IOD phase is often accompanied by an El Niño event, the negative by La Niña, but the correlation is not extremely strong, and the mechanism is not yet understood.

IOD negative phase: warmer, wetter east, cooler, drier west.

Tomorrow: the Madden-Julian Oscillation (MJO).

Be brave, and be well.