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Here’s what’s been pulling the strings on Australia’s weather recently — and it’s not just El Niño


From a parched, hot September and October — on the brink of extreme drought — to flooding rains in summer, the past few months have thrown up a range of weather extremes across the country.

Much of it comes down to the natural variability of weather in general.

But in the background, several climate drivers have been helping guide the weather in certain directions — and not just El Niño.

So how have they each been behaving recently?

Indian Ocean Dipole likely helps with spring dry

The Indian Ocean Dipole (IOD), sometimes referred to as El Niño’s cousin, forms over waters to Australia’s west.

Exerting its influence during winter and spring, it has two phases: negative, which is the wet phase, and positive, the dry phase.

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You’re probably familiar with El Nino, but there’s another climate driver in town, and researchers say it has an even more powerful impact on Australia.

Since August, the IOD has been in a positive phase — peaking at its second-highest values ever recorded by the Bureau of Meteorology, according to climatologist Catherine Ganter.

Based on its typical influence, Ms Ganter said it was likely to have played a role in the intense dry conditions experienced during winter and spring, which set up an early start to the bushfire season, and saw several regions in serious rainfall deficits.

This is especially true given some of the more unusual characteristics of this year’s El Niño may have dampened its drying influence, according to Ms Ganter.

“So this positive IOD was on the strong end, and it would have likely contributed to the below-average rainfall that we saw, particularly in August to October which was that dry three month period,” she said.

In parts of the country, warmer-than-average temperatures have continued into summer.(Facebook: Weather Obsessed/Helen Browne)

The IOD has lingered for longer than normal this year, but is now breaking down, so is no longer having an influence on Australia’s climate, according to Ms Ganter.

Southern Annular Mode encourages summer rainfall

Though September and October were parched, rainfall kicked up a notch in November for large parts of Queensland, NSW, the NT and northern WA.

Since then, the eastern states have seen repeated bouts of heavy rainfall.

Many parts of Victoria and South Australia have recorded an entire summer’s worth of rainfall already, and others face flooding emergencies.

Waterfalls are pumping in New South Wales after several heavy downpours.(Supplied: Trudy Locke)

One of the likely reasons for this enhanced summer rainfall — particularly over the south-eastern states — is a driver known as the Southern Annular Mode (SAM), according to Monash University climate scientist Kimberley Reid.

The SAM refers to the north-south position of a belt of westerly winds over the southern ocean, and is linked to rainfall patterns across Australia.

This diagram from the Bureau of Meteorology shows the impact of the Southern Annular Mode.(Supplied: Bureau of Meteorology)

Since early December, the SAM has persistently been in a positive phase, meaning the belt of winds is closer to Antarctica, which tends to favour rainfall in summer for the eastern states.

“What that does in summer, for south-eastern Australia, is it sort of draws tropical, warm, moist air further south,” Dr Reid said.

“It also allows for more onshore winds over the east coast, which again helps push moist air over Australia.

“So that’s probably why we are seeing a higher-than-average number of wet weather systems in summer this year.”

Something a bit unusual about the SAM’s behaviour this summer, according to Dr Reid, is that it’s happening during an El Niño event,

Typically, a persistent positive SAM is associated with the El Niño-Southern Oscillation’s opposite, phase — La Niña, which is the wet phase for Australia.

There have been several severe summer storms already this year.(Facebook: Nicole Bates)

Monash University climate science professor Julie Arblaster said it may have been pulled further south this year partly due to conditions in the Antarctic region, including the sea ice extent and the ozone hole.

“We do associate the positive SAM with more sea ice, usually. I think the fact that the sea ice has grown back a bit closer to [normal] since we’ve had that positive SAM is consistent with that,” Dr Arblaster said.

“The other thing in the Antarctic region is that we had an ozone hole [that] lasted a lot longer than it usually does.

“[That] can also have an impact on a positive SAM.”

El Niño driving warmth, but not following usual script

An El Niño climate pattern was declared underway by the Bureau of Meteorology in September, after months of speculation.

It is one of the world’s most consequential climate drivers, and is linked to hotter, drier weather in Australia — particularly during winter and spring — with its warming influence continuing into summer.

Though some characteristics of the event have made it unusual, Dr Reid said the driver likely played a part in the warmer, drier conditions in spring, as well as the later onset to the monsoon in northern Australia.

The climate outlook for summer is drier and hotter than average, according to the Bureau of Metereology.(Facebook: Waz Powter)

The event is still underway, which means it may be contributing to the warmer-than-average temperatures that have continued into summer too, along with climate change, according to Dr Reid.



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