The dogs are off the leash! Climate with Kate

Kate Finger
editor
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What happens when working dogs are let of the leash? Well in some instances not much. But sometimes, particularly when more than one is let off, they run absolutely wild. And this is exactly what the climate dogs have been doing in 2022!

ENSO, Indy, Sam and Mojo have all been let off running amok and bringing above average to highest on record rainfall to much of Australia not only for the last three months (image 2) but the whole year (image 3).

Image 1: The climate dogs running amuck across Australia.

Image 2: Rainfall deciles for August to October 2022.

Image 3: Rainfall deciles for January to October 2022.

So, what mischief did each dog get up to?

The El Niño Southern Oscillation, or ENSO describes what is happening in the Pacific Ocean. It can be in the El Niño or La Niña phase or neutral.

In early spring 2022 a La Niña event was declared for the third consecutive year by the Bureau of Meteorology. A La Niña typically transports greater amounts of moist tropical air across northern and eastern Australia during spring and summer and when it tees up with some of the other climate drivers i.e., IOD and SAM significant amounts of rain can fall—just like what we have recently experienced.

Indy, also known as the Indian Ocean Dipole (IOD) describes the conditions in the Indian Ocean and can be positive, negative or neutral.

In 2022 Indy was negative which meant that there was significant warm water to the north-east of the Indian Ocean which can generate moisture and when combined with southern weather systems can deliver significant rainfall across Australia. It’s also worthy to note that this was the first time since reliable records (1960) that a consecutive negative IOD event has occurred. Although the 2021 event was quite weak and shortlived.

SAM’s full name is the Southern Annular Mode and it controls the westerly winds and weather systems in the Southern Ocean.

SAM’s behaviour changes depending on whether it is spring/summer or winter and can be positive, negative or neutral.

During spring/summer if SAM is positive, like it was for most of spring 2022, the westerly winds sit further south which encourages the movement of more moisture and rain over parts of eastern and northern Australia.

Note in this phase SAM typically has a drying influence over western Tasmania and southwest WA which has been observed in 2022 (see figure 2).

Mojo represents the Madden-Julian Oscillation (MJO) which moves a pulse of cloud and rainfall eastwards close to the equator.

There are eight phases of the MJO and during spring 2022 the MJO was locked in phases six and seven. In phase six it is posited over the Coral Sea and in phase seven it is moving on towards phase eight which is in the Tonga Sea.

By moving between phases six and seven it meant that the MJO was constantly ‘pulsing’ cloud and rainfall onto mainland Australia.

 

We can’t solely blame the climate dogs though, as there has been other influences that have contributed to bringing all this rain across much of Australia.

Other Influences

Warmer water off northern Australia

The sea temperatures to the north of Australia have been hot, record breaking hot in fact since July 2022. This has been helping to generate large amounts of tropical moisture which has then moved down across Australia by various weather systems and the activities of the different climate dogs.

Pressure patterns

For much of spring 2022 two high pressure systems sat off to the west and east coast of Australia and a band of low pressure was positioned over Australia. This created a funnel type effect allowing the tropical moisture to move down over much of Australia.

A polar vortex

There is a band of winds in the upper atmosphere that move around Antarctica (like SAM) known as the Stratospheric Polar Vortex. When the polar vortex is strong, westerly winds slip under Australia which can lead to increased rain in the south-eastern parts of the continent.

In Spring 2022 we had a strongly polar vortex which meant the westerly winds contracted and circulated closely around Antarctica and allowed easterly winds to transport moisture from the Pacific Ocean to south-east Australia. This effect was confounded by the predominantly positive SAM which contracted the westerly winds in the lower atmosphere.

For more information about the polar vortex check out this article Strong Antarctic polar vortex adds to south-east Australian rainfall and flood risk, BOM says.

Chaining the dogs up

For now, the wetter conditions are here to linger for a little longer but there are signs our main climate drivers are starting to calm down. For the latest on what the climate drivers are up to visit the Bureau’s Long-range forecasts page.

Learn more about Kate

https://www.bcg.org.au/meet-the-team-podcast-research-and-extension-officer-kate-finger/

https://www.bcg.org.au/about-bcg/our-staff/

 

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