Prosper in a dynamic world
Search

Indian Ocean Dipole hits highest level since 2019

A positive Indian Ocean Dipole pattern has started to emerge to the northwest of Australia, increasing the likelihood of abnormally warm and dry weather over large parts of the country this spring.

The Indian Ocean Dipole (IOD) refers to an index that measures sea surface temperatures in the tropical Indian Ocean.

A positive IOD occurs when warmer than average water builds up in the western tropical Indian Ocean, near the Horn of Africa, and unusually cold water lies in the eastern Indian Ocean, near Indonesia.

Positive IOD events reduce the amount of atmospheric moisture flowing towards Australia from the northwest, which typically suppresses rainfall and increases daytime temperatures over parts of the continent.

Image: Typical structure and impacts of a positive IOD.

By contrast, negative IOD events occur when abnormally cool water lies near the Horn of Africa and unusually warm water sits near Indonesia. This typically increases rainfall and decreases daytime temperatures over parts of Australia.

Image: Typical structure and impacts of a negative IOD.

The Bureau of Meteorology declared negative IOD events in 2021 and 2022. Unsurprisingly, both years featured above average rain in parts of Australia, particularly in 2022.

The last positive IOD event was in 2019. This was a very strong IOD event and resulted in Australia’s driest year on record.

The maps below show the contrast in rainfall between the positive IOD in 2019 and the 2022 negative IOD. While the IOD wasn’t the only climate driver influencing Australia’s weather in these years, this comparison shows how the IOD can contribute to widespread and extreme rainfall anomalies in Australia.

Image: Rainfall deciles during 2019 (left) and 2022 (right), showing the contrast between positive and negative IOD years.

The IOD index has been in a neutral state (between -0.4 and 0.4) since October last year. However, the latest weekly value rose to 0.79, which is the highest value since December 2019.

If the IOD index continues to exceed 0.4 in the coming weeks, which forecast models suggest will happen, the Bureau of Meteorology will officially declare the onset of a positive IOD.

Image: Weekly IOD index values between January 2019 and August 2023.

These recent IOD observations and the strong agreement between forecast models suggest that a positive IOD will occur this spring. This increases the likelihood that large parts of Australia will see below average rain and above average daytime temperatures in the next few months.

Latest news

Satisfy your weather obsession with these news headlines from around the nation, and the world.

How is DTN APAC equipped to service the offshore wind farm industry?

Wind turbines are usually pictured on rolling hills far from cities and people, but what if they were on rolling swells off the coast of populated areas? Australia’s National Electricity Market (NEM) and WA renewable power network currently harnesses wind power from 115 wind farm facilities and a capacity of 15,617 MW, according to OpenNEM. […]

Quarter million lightning strike and heavy downpours smash southwest WA businesses

The southwestern tip of Western Australia is the latest corner of the country to see exceptionally heavy winter rainfall, with 24-hour totals topping 100mm at some locations, and over 250,000 lightning strikes causing costly shutdown procedures. Storms and heavy downpours pelted much of the South West Land Division on Wednesday as a cold front and […]

East Coast Low brings intense night of wind, rain and surf to NSW businesses

The East Coast Low lashed large parts of the NSW coastline in the 24 hours to Wednesday morning as damaging to destructive winds, intense rainfall and large waves disrupted industries from aviation to ports, and transport to power utilities. The stretch of NSW coastline from the Hunter region to the South Coast has been most […]

East Coast Low deepening near NSW coast disrupting aviation, transport and utility industries

Heavy rain, destructive winds and damaging surf will batter eastern NSW in the coming days following the explosive development of an East Coast Low leading to significant disruptions to transport, aviation and utilities. A coastal trough located off the southeast Queensland and northeast NSW coast rapidly intensified into a low pressure system overnight into Tuesday […]