If you live in southern Australia, you may have noticed it’s been a rather wet couple of months. What you might not realise is the role that the tropical Indian Ocean has played in helping to create this weather.

Since late May, the ocean has been in what we call a “negative Indian Ocean Dipole (IOD) phase” – and it seems set to be one of the strongest such events in at least 15 years.

Compared to its Pacific cousins, El Nino and La Nina, the IOD is something of a mystery to many people. So what is it, and what does it mean for our climate, and does it explain why this winter has been such a wet one for many Australians?

The Indian Ocean Dipole is similar to the more famous El Nino-Southern Oscillation (ENSO) in the Pacific. That system seesaws between El Nino conditions – characterised by a “warm blob” of surface waters in the eastern tropical Pacific – and La Nina, where the warm patch is in the western Pacific.