Indian Ocean Dipole

Explanation :

• The Indian Ocean Dipole (IOD) is the Indian Ocean counterpart of the Pacific El Nino and La Nina.
• It is defined by the difference in sea surface temperature between two areas (or poles, hence a dipole) – a western pole in the Arabian Sea (western Indian Ocean) and an eastern pole in the eastern Indian Ocean south of Indonesia.
• The IOD is one of the key drivers of Australia's climate and can have a significant impact on agriculture. This is because events generally coincide with the winter crop growing season.
• The Indian Monsoon is invariably influenced by the IOD.
• The IOD has three phases: neutral, positive and negative. Events usually start around May or June, peak between August and October and then rapidly decay when the monsoon arrives in the southern hemisphere around the end of spring.

Positive Event:

• warmer sea surface temperatures in the western Indian Ocean relative to the east
• easterly wind anomalies across the Indian Ocean and less cloudiness to Australia's northwest
• less rainfall over southern Australia and the Top End

Negative Event:

• cooler sea surface temperatures in the western Indian Ocean relative to the east
• winds become more westerly, bringing increased cloudiness to Australia's northwest
• more rainfall in the Top End and southern Australia