Our weather and climate is governed by many factors and phenomenon, either man-made or natural.
One of those is the Indian Ocean Dipole (IOD), which is currently undergoing in the Indian Ocean, resulting in severe droughts in Australia and an intense ‘Indian Summer’ in Europe.
Australia’s big dry is approaching apocalyptic extremes. Huge swathes of the country’s eastern interior have been ravaged by wildfires; regional towns are having to import literal truckloads of water to keep the community going; and, according to ecologists, kangaroos have resorted to eating the stomachs and intestines of other, dead kangaroos in a desperate attempt to sustain themselves.
And all of this is due to a rare weather phenomenon called an Indian Ocean Dipole or IOD, which is very strong this year.
As the name implies, this weather phenomenon takes place in the Indian Ocean and consists of two poles:
- The east pole is situated near Sumatra, Indonesia.
- The west pole sits in the western Indian Ocean.
Sustained changes in the difference between sea surface temperatures of the tropical western and eastern Indian Ocean are known as the Indian Ocean Dipole (IOD).
Positive Indian Ocean Dipole
During a positive IOD, westerly winds weaken along the equator allowing warm water to shift towards Africa.
Changes in the winds also allow cool water to rise up from the deep ocean in the east.
This sets up a temperature difference across the tropical Indian Ocean with cooler than normal water in the east and warmer than normal water in the west.
Generally this means there is less moisture than normal in the atmosphere to the northwest of Australia. This changes the path of weather systems coming from Australia’s west, often resulting in less rainfall and higher than normal temperatures over parts of Australia during winter and spring. In other words, a drought!
In contrast, the western side of the Indian ocean is hit by higher temperatures than normal as Europe is experiencing right now.
Looking at the ocean temperature data from Mercator, we can clearly see this trend with cool water temperatures in the east and much warmer temperatures in the west.
This year the positive IOD is unusually strong, reaching record values for at least the past 60-80 years.
The ocean phenomenon has started in June and only increased close to its maximum intensity end of September when strong easterly winds started cooling the waters in the eastern pole dramatically.
Looking at the official analysis for the past 3 months, you clearly observe that large parts of Australia have experienced below average to record-low rainfall, a textbook signature of a positive IOD event.
According tho the latest weather forecasts, Australia is going to suffer record-high temperatures and isn’t going to reach average rainfall until December 2019. And that’s is another two long months.
A correlation between the surface pressure and the IOD index from September to October 2019 clearly shows (map below):
- A positive correlation between the IOD and pressure rise over Indonesia and Australia. This is what we observe right now.
- A higher-than average pressure over Europe. This is also happening right now.
Although we can’t say fore sure that the current warm conditions in Europe are directly linked to the strong IOD, it is highly likely that the weather phenomenon is playing a major role in the current “European Indian summer.” It is indeed relatively close to the European sector, and has a major influence on Africa and the subtropical pressure patterns.