The Climatedogs — The six drivers that influence Victoria's climate
Victoria is well known for its variable climate. From year to year, four global climate processes vary their behaviour, potentially resulting in wetter or dryer seasons.
Roundup of Climatedog animations video
This is Enso, Indy, Ridgy and Sam.
They represent four climate processes that affect our rainfall variability across Victoria.
These four sheepdogs love rounding up our rainfall.
From a farmer's perspective when they're are behaving they bring moisture from the oceans and allow it to fall over Victoria as rain. Hopefully delivering the right amount at the right time.
But they don't always work the way we'd like them to and can sometimes scatter the mob, effectively chasing rainfall away from Victoria.
Over recent decades some of these dogs have changed their behaviour contributing to our extended dry spell and the changing weather patterns that many farmers have noticed.
While we can't control what these dogs are up to the Bureau of Meteorology and the Victorian Department of Primary Industries have new and valuable tools that can assist farmers in keeping track of these climate dogs helping to predict the likelihood of rain over the coming season and manage climate risk.
The El Niño Southern Oscillation or ENSO has a big influence on Victorian climate over winter and spring. The Pacific Ocean trade winds blow from an easterly direction, pushing moist air towards Australia. This moist tropical air is a big source of rain across eastern Australia, including Victoria. But Enso's behaviour can vary from year to year.
During La Niña Enso chases greater amounts of moist tropical air across Australia. Many La Niña years have seen higher rainfall in Victoria during winter and spring. During El Niño Enso changes his mind and drives warm moist air towards South America instead. El Niño years have often resulted in drier winter and spring periods for Victoria.
Each year climatologists follow Enso's behaviour providing us with a potential rainfall outlook for Victoria. So Enso is definitely an important dog to keep an eye on.
This is the Indian Ocean Dipole, also known as Indy.
He influences Victoria's rainfall in winter and spring. Indy brings rain to Victoria when the north-eastern Indian Ocean increases the amount of moisture it provides to the atmosphere. This moist air is herded across Australia and can deliver significant rainfall into Victoria. When the north-eastern Indian Ocean produces less atmospheric moisture Indy doesn't drive as much rain towards Victoria, and we can end up with a drier winter and spring.
Historically Indy has been a significant source of rain.However in recent years Indy has not been chasing moisture down south as often as farmers would like reducing the average rainfall for Victoria. Indy is closely watched by scientists who make limited predictions on his behaviour before winter and spring arrive.Keeping an eye on Indy's behaviour can provide an indication on the expected rainfall coming from the north-west to Victoria.
Meet Sam. Sam herds cold fronts up from the Southern Ocean, a significant source of rain for southern Victoria. If we take a look at the southern ocean we can see westerly winds circling around Antarctica throwing out cold fronts of stormy wet weather. The strength and position of these winds is known as the Southern Annular Mode or Sam.
Sam is an unreliable climate dog often changing his behaviour in a matter of weeks which can affect Victoria's rainfall. When Sam is tied up strong winds are pulled in towards Antarctica and there is a reduction in the number and strength of cold fronts that reach southern Australia. When Sam is let of the leash, the westerly winds move further north increasing the chance of frontal activity and potential rainfall.
Over recent decades Sam has found himself tied up more often resulting in less cold fronts and rainfall for some parts Victoria. Sam's behaviour is complicated so scientists are in full swing to try to understand how this climate dog may impact on Victoria's weather down the track.
This is Ridgy, or as scientists like to call him, the Sub-tropical Ridge. Ridgy's one of the four major drivers that shapes Victoria's seasonal weather. So let's look at how he does it.
As warm air in the tropics continually rises, moves south, then cools and falls, large areas of high pressure are created. These high pressures, in this case Ridgy, are great at blocking rain bearing fronts. From November till April Ridgy chases away cold fronts around southern Australia for days or even weeks at a time. Occasionally cold fronts sneak through and if they connect with moist air from the tropics Victoria gets some summer rain.
As winter sets in Ridgy heads north and the cold fronts find it much easier to reach Victoria and deliver their rain, until Ridgy returns next November. Ridgy does this every year but in recent decades he's been getting more effective at chasing away cold fronts from Victoria explaining a lot of our drier weather. The Bureau of Meteorology has observed that Ridgy's increasing strength is related to the rising global average temperature but the scientists are continuing to investigate how this climate dog might change his behaviour in the future.
This is Eastie. Better known as the East Coast Low.
Eastie represents the deep low pressure systems that are an important climate feature along the south east coast of Australia. These deep low pressure systems can be caused by upper atmosphere disturbances, decaying cyclones, existing low pressure conditions or in the wake of passing fronts. Scientists have found that Eastie tends to have a mind of his own and can be quite hard to predict.
This energetic little dog can be triggered into action overnight causing strong winds, big surf, heavy rains and lots of rough weather. Eastie can appear all year round but typically prefers the seasons of autumn and winter. Even one off events can dominate a regions annual rainfall tally, explaining a lot of the seasonal variability east of the Great Dividing Range.
Eastie usually cares little about what the larger climate dogs are up to, however scientists have noticed that Eastie can be a bit timid when Ridgy, with his high, pressure is around. Scientists continue to look into Eastie's behaviour.
In the meantime we'll need to keep a close eye on this powerful little dog, especially when he is sparked into action.
Select a Climatedog to view animation
- View Eastie — East Coast Low
- View Enso— El Niño Southern Oscillation
- View Indy — Indian Ocean Dipole
- View Sam — Southern Annular Mode
- View Ridgy — Sub-tropical Ridge
One other Climatedog explaining other climate features that can affect rainfall in Victoria is Mojo.
The department has more information about climate variability, climate change and emissions in the Break newsletters.
The Bureau of Meteorology has several sections on their website to help explain the drivers of Victoria's climate:
For more information on the Climatedogs series, or to obtain copies of the animations, please contact Graeme Anderson on (03) 5226 4821 or email@example.com