Extreme heat and rain: thousands of weather stations show there’s now more of both, for longer



ChameleonsEye/Shutterstock

Jim Salinger, University of Tasmania and Lisa Alexander, UNSW

A major global update based on data from more than 36,000 weather stations around the world confirms that, as the planet continues to warm, extreme weather events such as heatwaves and heavy rainfall are now more frequent, more intense, and longer.

The research is based on a dataset known as HadEX and analyses 29 indices of weather extremes, including the number of days above 25℃ or below 0℃, and consecutive dry days with less than 1mm of rain. This latest update compares the three decades between 1981 and 2010 to the 30 years prior, between 1951 and 1980.

Globally, the clearest index shows an increase in the number of above-average warm days.


Author provided

For Australia, the team found a country-wide increase in warm temperature extremes and heatwaves and a decrease in cold temperature extremes such as the coldest nights. Broadly speaking, rainfall extremes have increased in the west and decreased in the east, but trends vary by season.

In New Zealand, temperate regions experience significantly more summer days and northern parts of the country are now frost-free.




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Extreme temperatures

Unusually warm days are becoming more common throughout Australia. When we compare 1981-2010 with 1951-80, the increase is substantial: more than 20 days per year in the far north of Australia, and at least 10 days per year in most areas apart from the south coast. The increase occurs in all seasons but is largest in spring.

This increase in temperature extremes can have devastating impacts for human health, particularly for older people and those with pre-existing medical conditions. Excessive heat is not only an issue for people living in cities but also for rural communities that have already been exposed to days with temperatures above 50℃.

New Zealanders are also experiencing more days with temperatures of 25℃ or more. The climate stations show the frequency of unusually warm days has increased from 8% to 12% from 1950 to 2018, with an average of 19 to 24 days a year above 25℃ across the country. Unusually warm days, defined as days in the top 10% of historic records for the time of year, are also becoming more common in both countries.

During the summers of 2017-18 and 2018-19, marine heatwaves delivered 32 and 26 (respectively) days above 25℃ nationwide in New Zealand, well above the average of 20 days. This led to accelerated glacial melting in the Southern Alps and major disruption to marine ecosystems, with die-offs of bull kelp around the South Island coast and salmon in aquaculture farms in the Marlborough Sounds.




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More heat, more rain, less frost

In many parts of New Zealand, cold extremes are changing faster than warm extremes.

Between 1950 and 2018, frost days (days below 0℃) have declined across New Zealand, particularly in northern parts of the country which has now become frost-free, enabling farmers to grow subtropical pasture grasses. At the same time, crops that require winter frosts to set fruit are no longer successful, or can only be grown with chemical treatments (currently under review) that simulate winter chilling.

Across New Zealand, the heat available for crop growth during the growing season is increasing, which means wine growers have to shift varieties further south.

In Australia, the situation is more complicated. In many parts of northern and eastern Australia, there has also been a large decrease in the number of cold nights. But in parts of southeast and southwest Australia, frost frequency has stabilised, or even increased in places, since the 1980s.

These areas have seen a large decrease in winter rainfall in recent decades. The higher number of dry, clear nights in winter, favourable for frost formation, has cancelled out the broader warming trend.




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In Australia, extreme rainfall has become more frequent in many parts of northern and western Australia, especially the northwest, which has become wetter since the 1960s. In eastern and southern Australia the picture is more mixed, with little change in the number of days with 10mm or more of rain, even in those regions where total rainfall has declined.

In New Zealand, more extremely wet days contribute towards the annual rainfall total in the east of the North Island, with a smaller increase in the west and south of the South Island. For Australia, there are significant drying trends in parts of the southwest and northeast, but little change elsewhere.

Extremes of temperature and precipitation can have dramatic effects, as seen during two marine heatwaves in New Zealand and the hottest, driest year in Australia during 2019.The Conversation

Jim Salinger, Honorary Associate, Tasmanian Institute for Agriculture, University of Tasmania and Lisa Alexander, Chief Investigator ARC Centre of Excellence for Climate System Science and Associate Professor Climate Change Research Centre, UNSW

This article is republished from The Conversation under a Creative Commons license. Read the original article.

How drought-breaking rains transformed these critically endangered woodlands into a flower-filled vista



Wildflowers blooming in box gum grassy woodland
Jacqui Stol, Author provided

Jacqui Stol, CSIRO; Annie Kelly, and Suzanne Prober, CSIRO

In box gum grassy woodlands, widely spaced eucalypts tower over carpets of wildflowers, lush native grasses and groves of flowering wattles. It’s no wonder some early landscape paintings depicting Australian farm life are inspired by this ecosystem.

But box gum grassy woodlands are critically endangered. These woodlands grow on highly productive agricultural country, from southern Queensland, along inland slopes and tablelands, into Victoria.

Many are degraded or cleared for farming. As a result, less than 5% of the woodlands remain in good condition. What remains often grows on private land such as farms, and public lands such as cemeteries or travelling stock routes.




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Very little is protected in public conservation reserves. And the recent drought and record breaking heat caused these woodlands to stop growing and flowering.

But after Queensland’s recent drought-breaking rain earlier this year, we surveyed private farmland and found many dried-out woodlands in the northernmost areas transformed into flower-filled, park-like landscapes.

And landholders even came across rarely seen marsupials, such as the southern spotted-tail quoll.

Native yellow wildflowers called ‘scaly buttons’ bloom on a stewardship site.
Jacqui Stol, Author provided

Huge increase in plant diversity

These surveys were part of the Australian government’s Environmental Stewardship Program, a long-term cooperative conservation model with private landholders. It started in 2007 and will run for 19 years.

We found huge increases in previously declining native wildflowers and grasses on the private farmland. Many trees assumed to be dying began resprouting, such as McKie’s stringybark (Eucalyptus mckieana), which is listed as a vulnerable species.

This newfound plant diversity is the result of seeds and tubers (underground storage organs providing energy and nutrients for regrowth) lying dormant in the soil after wildflowers bloomed in earlier seasons. The dormant seeds and tubers were ready to spring into life with the right seasonal conditions.

For example, Queensland Herbarium surveys early last year, during the drought, looked at a 20 metre by 20 metre plot and found only six native grass and wildflower species on one property. After this year’s rain, we found 59 species in the same plot, including many species of perennial grass (three species jumped to 20 species post rain), native bluebells and many species of native daisies.




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On another property with only 11 recorded species, more than 60 species sprouted after the extensive rains.

In areas where grazing and farming continued as normal (the paired “control” sites), the plots had only around half the number of plant species as areas managed for conservation.

Spotting rare marsupials

Landowners also reported several unusual sightings of animals on their farms after the rains. Stewardship program surveyors later identified them as two species of rare and endangered native carnivorous marsupials: the southern spotted-tailed quoll (mainland Australia’s largest carnivorous marsupial) and the brush-tailed phascogale.

The population status of both these species in southern Queensland is unknown. The brush-tailed phascogale is elusive and rarely detected, while the southern spotted-tailed quolls are listed as endangered under federal legislation.

Until those sightings, there were no recent records of southern spotted-tailed quolls in the local area.

A spotted tailed quoll caught in a camera trap.
Sean Fitzgibbon, Author provided

These unusual wildlife sightings are valuable for monitoring and evaluation. They tell us what’s thriving, declining or surviving, compared to the first surveys for the stewardship program ten years ago.

Sightings are also a promising signal for the improving condition of the property and its surrounding landscape.

Changing farm habits

More than 200 farmers signed up to the stewardship program for the conservation and management of nationally threatened ecological communities on private lands. Most have said they’re keen to continue the partnership.

The landholders are funded to manage their farms as part of the stewardship program in ways that will help the woodlands recover, and help reverse declines in biodiversity.

For example, by changing the number of livestock grazing at any one time, and shortening their grazing time, many of the grazing-sensitive wildflowers have a better chance to germinate, grow, flower and produce seeds in the right seasonal conditions.




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They can also manage weeds, and not remove fallen timber or loose rocks (bushrock). Fallen timber and rocks protect grazing-sensitive plants and provide habitat for birds, reptiles and invertebrates foraging on the ground.

Cautious optimism

So can we be optimistic for the future of wildlife and wildflowers of the box gum grassy woodlands? Yes, cautiously so.

Landholders are learning more about how best to manage biodiversity on their farms, but ecological recovery can take time. In any case, we’ve discovered how resilient our flora and fauna can be in the face of severe drought when given the opportunity to grow and flourish.

The rare hooded robin has also been recorded on stewardship sites during surveys.
Micah Davies, Author provided

Climate change is bringing more extreme weather events. Last year was the warmest on record and the nation has been gripped by severe, protracted drought. There’s only so much pressure our iconic wildlife and wildflowers can take before they cross ecological thresholds that are difficult to bounce back from.

More government programs like this, and greater understanding and collaboration between scientists and farmers, create a tremendous opportunity to keep changing that trajectory for the better.The Conversation

Jacqui Stol, Senior Experimental Scientist, Ecologist, CSIRO Land and Water, CSIRO; Annie Kelly, Senior Ecologist, and Suzanne Prober, Senior Principal Research Scientist, CSIRO

This article is republished from The Conversation under a Creative Commons license. Read the original article.

We dug up Australian weather records back to 1838 and found snow is falling less often



State Library of South Australia

Joelle Gergis, Australian National University and Linden Ashcroft, University of Melbourne

As we slowly emerge from lockdown, local adventures are high on people’s wish lists. You may be planning a trip to the ski fields, or even the nearby hills to revel in the white stuff that occasionally falls around our southern cities after an icy winter blast.

Our new research explores these low-elevation snowfall events. We pieced together weather records back to 1838 to create Australia’s longest analysis of daily temperature extremes and their impacts on society.

These historical records can tell us a lot about Australia’s pre-industrial climate, before the large-scale burning of fossil fuels tainted global temperature records.

They also help provide a longer context to evaluate more recent temperature extremes.

We found snow was once a regular feature of the southern Australian climate. But as Australia continues to warm under climate change, cold extremes are becoming less frequent and heatwaves more common.

Heatwaves in Adelaide are becoming more common.
David Mariuz/AAP

Extending Australia’s climate record

Data used by the Bureau of Meteorology to study long-term weather and climate dates back to the early 1900s. This is when good coverage of weather stations across the country began, and observations were taken in a standard way.

But many older weather records exist in national and state archives and libraries, as well as local historical societies around the country.




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We analysed daily weather records from the coastal city of Adelaide and surrounding areas, including the Adelaide Hills, back to 1838. Adelaide is the Australian city worst affected by heatwaves, and the capital of our nation’s driest state, South Australia.

To crosscheck the heatwaves and cold extremes identified in our historical temperature observations, we also looked at newspaper accounts, model simulations of past weather patterns, and palaeoclimate records.

The agreement was remarkable. It demonstrates the value of historical records for improving our estimation of future climate change risk.

Weather journal of Adelaide’s historical climate held by the National Archives of Australia.
National Archives of Australia

‘Limpness to all mankind’

While most other historical climate studies have looked at annual or monthly values, the new record enabled us to look at daily extremes.

This is important, because global temperature increases are most clearly detected in changes to extreme events such as heatwaves. Although these events may only last a few days, they have very real impacts on human health, agriculture and infrastructure.

Our analysis focused on the previously undescribed period before 1910, to extend the Bureau of Meteorology’s official record as far as possible.

Using temperature observations, we identified 34 historical heatwaves and 81 cold events in Adelaide from 1838–1910. We found more than twice as many of these “snow days” by conducting an independent analysis of snowfall accounts in historical documents.

Almost all the events in the temperature observations were supported by newspaper reports. This demonstrated our method can accurately identify historical temperature extremes.

For example, an outbreak of cold air on June 22, 1908, delivered widespread snow across the hills surrounding Adelaide. The Express and Telegraph newspaper reported:

Many people made a special journey from Adelaide by train, carriage, or motor to revel in the unwonted delight of gazing on such a wide expanse of real snow, and all who did so felt that their trouble was amply rewarded by the panorama of loveliness spread out before their enraptured eyes.

Snowballing at Mount Lofty 29 August 1905.
Source: State Library of South Australia

From December 26-30, 1897, Adelaide was gripped by a heatwave that produced five days above 40℃. Newspapers reported heat-related deaths, agricultural damage, animals dying in the zoo, bushfires and even “burning hot pavements scorching the soles of people’s shoes”. As The Advertiser reported:

When the mercury reaches its “century” (100℉ or 37.6℃) there must be a really uncomfortable experience for everyone. One such day can be struggled with; but six of them in a fortnight, three in succession — that is a thing to bring limpness to all mankind.

On December 31, 1897, the South Australian Register wrote prophetically of future Australian summers:

May Heaven preserve us from being here when the “scorchers” try and add a few degrees to the total.

Newspaper account of a deadly heatwave published in the South Australian Register on Friday 31 December 1897.
National Library of Australia

A longer view

While Australia has a long history of hot and cold extremes, our extended analysis shows that their frequency and intensity is changing.

The quality of the very early part of the record is still uncertain, so the information from the 1830s and 1840s must be treated with caution. That said, there is excellent agreement with newspaper and other historical records.

Our research suggests low-elevation snow events around Adelaide have become less common over the past 180 years. This can be seen in both temperature observations and independent newspaper accounts. For example, snowfall was exceptionally high in the 1900s and 1910s — more than four times more frequent than other decades.




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We also found heatwaves are becoming more frequent in Adelaide. The decade 2010–19 has the highest count of heatwaves of any decade in the record. Although recent heatwaves are not significantly longer than those of the past, our analysis showed heatwaves of up to ten days are possible.

Previous Australian studies have identified an increase in extreme heat and a corresponding decrease in cold events. However, this is the longest analysis in Australia, and the first to systematically combine instrumental and documentary information.

Number of heatwaves identified in Adelaide from January 1838 to August 2019. No digitised temperature observations are available from 1 January 1848 – 1 November 1856, so these decades are shown in lighter shades.
Author supplied
Number of extreme cold days identified in Adelaide from January 1838 to August 2019. No digitised temperature observations are currently available from 1 January 1848 – 1 November 1856, so these decades are shaded grey.
Author supplied

Learning from the past

This study shows we can use historical weather records to get a better picture of Australia’s long-term weather and climate history. By using different sources of information, we can piece together the significant events in our climate history with greater certainty.

Historical records tell us about more than just exciting day trips of the past. They also hold the key to understanding impacts of extreme events, such as heat-related deaths or agricultural damage, in the future.

A better understanding of these pre-industrial extremes will help emergency management services better adapt to increased climate risk, as Australia continues to warm.




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The Conversation


Joelle Gergis, Senior Lecturer in Climate Science, Australian National University and Linden Ashcroft, Lecturer in climate science and science communication, University of Melbourne

This article is republished from The Conversation under a Creative Commons license. Read the original article.

After a storm, microplastics in Sydney’s Cooks River increased 40 fold



A litter trap in Cook’s River.
James HItchcock, Author provided

James Hitchcock, University of Canberra

Each year the ocean is inundated with 4.8 to 12.7 million tonnes of plastic washed in from land. A big proportion of this plastic is between 0.001 to 5 millimetres, and called “microplastic”.

But what happens during a storm, when lashings of rain funnel even more water from urban land into waterways? To date, no one has studied just how important storm events may be in polluting waterways with microplastics.




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So to find out, I studied my local waterway in Sydney, the Cooks River estuary. I headed out daily to measure how many microplastics were in the water, before, during, and after a major storm event in October, 2018.

The results, published on Wednesday, were startling. Microplastic particles in the river had increased more than 40 fold from the storm.

Particles of plastic found in rivers. They may be tiny, but they’re devastating to wildlife in waterways.
Author provided

To inner west Sydneysiders, the Cooks River is known to be particularly polluted. But it’s largely similar to many urban catchments around the world.

If the relationship between storm events and microplastic I found in the Cooks River holds for other urban rivers, then the concentrations of microplastics we’re exposing aquatic animals to is far higher than previously thought.

14 million plastic particles

They may be tiny, but microplastics are a major concern for aquatic life and food webs. Animals such as small fish and zooplankton directly consume the particles, and ingesting microplastics has the potential to slow growth, interfere with reproduction, and cause death.

Determining exactly how much microplastic enters rivers during storms required the rather unglamorous task of standing in the rain to collect water samples, while watching streams of unwanted debris float by (highlights included a fire extinguisher, a two-piece suit, and a litany of tennis balls).

Back in the laboratory, a multi-stage process is used to separate microplastics. This includes floating, filtering, and using strong chemical solutions to dissolve non-plastic items, before identification and counting with specialised microscopes.

Litter caught in a trap in Cooks River. These traps aren’t effective at catching microplastic.
Author provided

In the days before the October 2018 storm, there were 0.4 particles of microplastic per litre of water in the Cooks River. That jumped to 17.4 microplastics per litre after the storm.

Overall, that number averages to a total of 13.8 million microplastic particles floating around in the Cooks River estuary in the days after the storm.




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In other urban waterways around the world scientists have found similarly high numbers of microplastic.

For example in China’s Pearl River, microplastic averages 19.9 particles per litre. In the Mississippi River in the US, microplastic ranges from 28 to 60 particles per litre.

Where do microplastics come from?

We know runoff during storms is one of the main ways pollutants such as sediments and heavy metals end up in waterways. But not much is known about how microplastic gets there.

However think about your street. Wherever you see litter, there are also probably microplastics you cannot see that will eventually work their way into waterways when it rains.




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Many other sources of microplastics are less obvious. Car tyres, for example, which typically contain more plastic than rubber, are a major source of microplastics in our waterways. When your tyres lose tread over time, microscopic tyre fragments are left on roads.

Did you know your car tyres can be a major source of microplastic pollution?
Shutterstock

Microplastics may even build up on roads and rooftops from atmospheric deposition. Everyday, lightweight microplastics such as microfibres from synthetic clothing are carried in the wind, settling and accumulating before they’re washed into rivers and streams.

What’s more, during storms wastewater systems may overflow, contaminating waterways. Along with sewage, this can include high concentrations of synthetic microfibers from household washing machines.

And in regional areas, microplastics may be washing in from agricultural soils. Sewage sludge is often applied to soils as it is rich in nutrients, but the same sludge is also rich in microplastics.

What can be done?

There are many ways to mitigate the negative effects of stormwater on waterways.

Screens, traps, and booms can be fitted to outlets and rivers and catch large pieces of litter such as bottles and packaging. But how useful these approaches are for microplastics is unknown.

Raingardens and retention ponds are used to catch and slow stormwater down, allowing pollutants to drop to bottom rather than being transported into rivers. Artificial wetlands work in similar ways, diverting stormwater to allow natural processes to remove toxins from the water.

Almost 14 million plastic particles were floating in Cooks River after a storm two years ago.
Shutterstock

But while mitigating the effects of stormwater carrying microplastics is important, the only way we’ll truly stop this pollution is to reduce our reliance on plastic. We must develop policies to reduce and regulate how much plastic material is produced and sold.

Plastic is ubiquitous, and its production around the world hasn’t slowed, reaching 359 million tonnes each year. Many countries now have or plan to introduce laws regulating the sale or production of some items such as plastic bags, single-use plastics and microbeads in cleaning products.




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In Australia, most state governments have committed to banning plastic bags, but there are still no laws banning the use of microplastics in cleaning or cosmetic products, or single-use plastics.

We’ve made a good start, but we’ll need deeper changes to what we produce and consume to stem the tide of microplastics in our waterways.The Conversation

James Hitchcock, Post-Doctoral Research Fellow, University of Canberra

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Why drought-busting rain depends on the tropical oceans


Andrew King, University of Melbourne; Andy Pitman, UNSW; Anna Ukkola, Australian National University; Ben Henley, University of Melbourne, and Josephine Brown, University of Melbourne

Recent helpful rains dampened fire grounds and gave many farmers a reason to cheer. But much of southeast Australia remains in severe drought.

Australia is no stranger to drought, but the current one stands out when looking at rainfall records over the past 120 years. This drought has been marked by three consecutive extremely dry winters in the Murray-Darling basin, which rank in the driest 10% of winters since 1900.

Despite recent rainfall the southeast of Australia remains in the grip of a multi-year drought.
Bureau of Meteorology

So what’s going on?

There has been much discussion on whether human-caused climate change is to blame. Our new study explores Australian droughts through a different lens.




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Rather than focusing on what’s causing the dry conditions, we investigated why it’s been such a long time since we had widespread drought-breaking rain. And it’s got a lot to do with how the temperature varies in the Pacific and Indian Ocean.

Our findings suggest that while climate change does contribute to drought, blame can predominately be pointed at the absence of the Pacific Ocean’s La Niña and the negative Indian Ocean Dipole – climate drivers responsible for bringing wetter weather.

Understanding the Indian Ocean Dipole.

What’s the Indian Ocean Dipole?

As you may already know, the Pacific Ocean influences eastern Australia’s climate through El Niño conditions (associated with drier weather) and La Niña conditions (associated with wetter weather).

The lesser known cousin of El Niño and La Niña across the Indian Ocean is called the Indian Ocean Dipole. This refers to the difference in ocean temperature between the eastern and western sides of the Indian Ocean. It modulates winter and springtime rainfall in southeastern Australia.




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When the Indian Ocean Dipole is “negative”, there are warmer ocean temperatures in the east Indian Ocean, and we see more rain over much of Australia. The opposite is true for “positive” Indian Ocean Dipole events, which bring less rain.

The Murray-Darling Basin experiences high rainfall variability, with decade-long droughts common since observations began. The graph shows seasonal rainfall anomalies from a 1961-1990 average with major droughts marked.
Author provided

What does it mean for the drought?

When the drought started to take hold in 2017 and 2018, we didn’t experience an El Niño or strongly positive Indian Ocean Dipole event. These are two dry-weather conditions we might expect to see at the start of a drought.

Rather, conditions in the Pacific and Indian Oceans were near neutral, with little to suggest a drought would develop.

So why are we in severe, prolonged drought?

The problem is we haven’t had either a La Niña or a negative Indian Ocean Dipole event since winter 2016. Our study shows the lack of these events helps explain why eastern Australia is in drought.

For the southeast of Australia in particular, La Niña or negative Indian Ocean Dipole events provide the atmosphere with suitable conditions for persistent and widespread rainfall to occur. So while neither La Niña or a negative Indian Ocean Dipole guarantee heavy rainfall, they do increase the chances.

What about climate change?

While climate drivers are predominately causing this drought, climate change also contributes, though more work is needed to understand what role it specifically plays.

Drought is more complicated and multidimensional than simply “not much rain for a long time”. It can be measured with a raft of metrics beyond rainfall patterns, including metrics that look at humidity levels and evaporation rates.

What we do know is that climate change can exacerbate some of these metrics, which, in turn, can affect drought.




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Climate change might also influence climate drivers, though right now it’s hard to tell how. A 2015 study suggests that under climate change, La Niña events will become more extreme. Another study from earlier this month suggests climate change is driving more positive Indian Ocean Dipole events, bringing even more drought.

Unfortunately, regional-scale projections from climate models aren’t perfect and we can’t be sure how the ocean patterns that increase the chances of drought-breaking rains will change under global warming. What is clear is there’s a risk they will change, and strongly affect our rainfall.

Putting the drought in context

Long periods when a La Niña or a negative Indian Ocean Dipole event were absent characterised Australia’s past droughts. This includes two periods of more than three years that brought us the Second World War drought and the Millennium drought.

The longer the time without a La Niña or negative Indian Ocean Dipole event, the more likely the Murray-Darling Basin is in drought.

In the above graph, the longer each line continues before stopping, the longer the time since a La Niña or negative Indian Ocean Dipole event occurred. The lower the lines travel, the less rainfall was received in the Murray Darling basin during this period. This lets us compare the current drought to previous droughts.

During the current drought (black line) we see how the rainfall deficit continues for several years, almost identically to how the Millennium drought played out.

But then the deficit increases strongly in late 2019, when we had a strongly positive Indian Ocean Dipole.

So when will this drought break?

This is a hard question to answer. While recent rains have been helpful, we’ve developed a long-term rainfall deficit in the Murray-Darling Basin and elsewhere that will be hard to recover from without either a La Niña or negative Indian Ocean Dipole event.




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The most recent seasonal forecasts don’t predict either a negative Indian Ocean Dipole or La Niña event forming in the next three months. However, accurate forecasts are difficult at this time of year as we approach the “autumn predictability barrier”.

This means, for the coming months, the drought probably won’t break. After that, it’s anyone’s guess. We can only hope conditions improve.The Conversation

Andrew King, ARC DECRA fellow, University of Melbourne; Andy Pitman, Director of the ARC Centre of Excellence for Climate System Science, UNSW; Anna Ukkola, Research Fellow, Australian National University; Ben Henley, Research Fellow in Climate and Water Resources, University of Melbourne, and Josephine Brown, Lecturer, University of Melbourne

This article is republished from The Conversation under a Creative Commons license. Read the original article.

How weather radar can keep tabs on the elusive magpie goose


Magpie Geese taking off from a mango orchard in the Northern Territory.
Rebecca Rogers, Author provided

Rebecca Rogers, Charles Darwin University

You’re probably familiar with weather radar that shows bands of rain blowing in to ruin your plans for the day, or the ominous swirling pattern of a cyclone.

But rain isn’t the only thing that shows up on the radar screen. Anything moving through the sky will – like a large group of birds in flight.

Ecologists have begun to realise that weather radar data have huge potential to reveal the movements of flying animals all over the country.

At the forefront of this research is the magpie goose, an occasionally controversial waterbird prized by some and detested by others.

It’s a lovely day in northern Australia, and you are a magpie goose. These waterbirds are an ideal test case for weather-radar tracking.
Shutterstock

Chasing angels

To understand how we got to this point, first we need to go back 80 years. Prior to World War II, engineers were racing to improve radar systems to detect enemy aircraft when they noticed strange unexplained rings on their screens that they called angels.

Some of these angels, they realised later, were caused by groups of birds and bats taking off and flying through the radar beam. Since this discovery, there has been a steady increase in researchers using weather radar to understand how and why animals move through the air.

How weather radar works

Radar works by sending out a sweeping beam of radio waves and listening for echoes. It processes these echoes to map the positions of objects around it.

With weather radar, the radar beam won’t only bounce off raindrops – it will also reflect back from birds. Some weather radars send out these pulses at a precise frequency, which allows them to use the Doppler effect to determine how fast objects are moving towards or away from the radar.

Meteorologists have ways to filter out clutter caused by flying animals, so they can see where it is raining. Ecologists are doing the reverse, filtering out rain from the raw data collected by weather radars in order to track the movements of birds, bats and even insect swarms.

Weather radars cover a good part of the Australian continent, which makes them very useful for tracking birds.
Rogers et al. (2019) – Austral Ecology

Most weather radars can give us a three-dimensional picture of what is happening in the air every 5–10 minutes. In Australia the data is archived for years and even decades in some places, and it is all available free of charge for researchers. This means we can not only understand how animals are using the airspace now, but also how these movement patterns may have changed over time.

Is it a bird? Is it a plane?

So how do we actually tell whether those pixels on the screen are caused by rain, birds or something less common like bushfire smoke?

This is where things can get a bit more tricky. For some cases, like tracking bats coming out of a cave or roost tree, the job for the ecologist is fairly simple. For roosting species like these, we often observed very characteristic rings on the radar similar to the angels described by those early radar engineers. Examples of the rings can be found all over Australia caused by flying foxes.

Flying animals leave traces in weather radar images. The image at left shows an ‘angel echo’ caused by flying foxes coming out of a roost in NSW, while the one on the right reveals ‘blooms’ of activity on the Darwin radar, likely to be caused by magpie geese and other waterbirds taking off for their morning feeding flights.
Rogers et al. (2019) – Austral Ecology

For broadly distributed species, like the magpie geese found all across northern Australia, the picture is not so easy to interpret. These animals tend to produce patterns best described as blooms of activity: they appear across the radar image, spreading out and then blending together like a bunch of flowers blooming all at once.

These patterns can look similar to rain clouds to the untrained eye. However, with some understanding of how the radar works and the behaviour of the birds – like when they are active or how high they fly – we can quickly begin to narrow down what might be causing different patterns on radar images.

Why track magpie geese?

Magpie geese cross paths with humans in many different ways.

They are hunted by Indigenous people for food, they are considered a pest for mango farmers and a strike risk for planes, and they could be vectors for disease.

Tracking magpie geese can help us better understand this native species and ensure it thrives long into the future.




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Like many waterbirds, magpie geese have distinct daily patterns of movement, which makes them ideal candidates for trialling the use of weather radar to track Australian birds.

In Darwin, blooms of activity occur all over the radar in the morning and evening when magpie geese are taking off from wetlands and mango orchards for their daily feeding flights.

By using GPS tracking collars and annual survey data, we are starting to see how these patterns in the radar data correspond to real behaviour. These results are showing how weather radar could be repurposed to track the movement of magpie geese – and after that, many other kinds of birds in Australia.The Conversation

Rebecca Rogers, PhD Candidate, Charles Darwin University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Firestorms and flaming tornadoes: how bushfires create their own ferocious weather systems



A firestorm on Mirror Plateaun Yellowstone Park, 1988.
Jim Peaco/US National Park Service

Rachel Badlan, UNSW

As the east coast bushfire crisis unfolds, New South Wales Premier Gladys Berejiklian and Rural Fire Service operational officer Brett Taylor have each warned residents bushfires can create their own weather systems.

This is not just a figure of speech or a general warning about the unpredictability of intense fires. Bushfires genuinely can create their own weather systems: a phenomenon known variously as firestorms, pyroclouds or, in meteorology-speak, pyrocumulonimbus.




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Firestorms: the bushfire/thunderstorm hybrids we urgently need to understand


The occurrence of firestorms is increasing in Australia; there have been more than 50 in the period 2001-18. During a six-week period earlier this year, 18 confirmed pyrocumulonimbus formed, mainly over the Victorian High Country.

A pyrocumulonimbus cloud generated by a bushfire in Licola,Victoria, on March 2, 2019.
Elliot Leventhal, Author provided

Its not clear whether the current bushfires will spawn any firestorms. But with the frequency of extreme fires set to increase due to hotter and drier conditions, it’s worth taking a closer look at how firestorms happen, and what effects they produce.

What is a firestorm?

The term “firestorm” is a contraction of “fire thunderstorm”. In simple terms, they are thunderstorms generated by the heat from a bushfire.

In stark contrast to typical bushfires, which are relatively easy to predict and are driven by the prevailing wind, firestorms tend to form above unusually large and intense fires.

If a fire encompasses a large enough area (called “deep flaming”), the upward movement of hot air can cause the fire to interact with the atmosphere above it, potentially forming a pyrocloud. This consists of smoke and ash in the smoke plume, and water vapour in the cloud above.

If the conditions are not too severe, the fire may produce a cloud called a pyrocumulus, which is simply a cloud that forms over the fire. These are typically benign and do not affect conditions on the ground.

But if the fire is particularly large or intense, or if the atmosphere above it is unstable, this process can give birth to a pyrocumulonimbus – and that is an entirely more malevolent beast.

What effects do firestorms produce?

A pyrocumulonibus cloud is much like a normal thunderstorm that forms on a hot summer’s day. The crucial difference here is that this upward movement is caused by the heat from the fire, rather than simply heat radiating from the ground.

Conventional thunderclouds and pyrocumulonimbus share similar characteristics. Both form an anvil-shaped cloud that extends high into the troposphere (the lower 10-15km of the atmosphere) and may even reach into the stratosphere beyond.

NASA image of pyrocumulonimbus formation in Argentina, January 2018.
NASA

The weather underneath these clouds can be fierce. As the cloud forms, the circulating air creates strong winds with dangerous, erratic “downbursts” – vertical blasts of air that hit the ground and scatter in all directions.

In the case of a pyrocumulonimbus, these downbursts have the added effect of bringing dry air down to the surface beneath the fire. The swirling winds can also carry embers over huge distances. Ember attack has been identified as the main cause of property loss in bushfires, and the unpredictable downbursts make it impossible to determine which direction the wind will blow across the ground. The wind direction may suddenly change, catching people off guard.

Firestorms also produce dry lightning, potentially sparking new fires, which may then merge or coalesce into a larger flaming zone.

In rare cases, a firestorm can even morph into a “fire tornado”. This is formed from the rotating winds in the convective column of a pyrocumulonimbus. They are attached to the firestorm and can therefore lift off the ground.




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This happened during the infamous January 2003 Canberra bushfires, when a pyrotornado tore a path near Mount Arawang in the suburb of Kambah.

A fire tornado in Kambah, Canberra, 2003 (contains strong language).

Understandably, firestorms are the most dangerous and unpredictable manifestations of a bushfire, and are impossible to suppress or control. As such, it is vital to evacuate these areas early, to avoid sending fire personnel into extremely dangerous areas.

The challenge is to identify the triggers that cause fires to develop into firestorms. Our research at UNSW, in collaboration with fire agencies, has made considerable progress in identifying these factors. They include “eruptive fire behaviour”, where instead of a steady rate of fire spread, once a fire interacts with a slope, the plume may attach to the ground and rapidly accelerate up the hill.

Another process, called “vorticity-driven lateral spread”, has also been recognised as a good indicator of potential fire blow-up. This occurs when a fire spreads laterally along a ridge line instead of following the direction of the wind.

Although further refinement is still needed, this kind of knowledge could greatly improve decision-making processes on when and where to deploy on-ground fire crews, and when to evacuate before the situation turns deadly.The Conversation

Rachel Badlan, Postdoctoral Researcher, Atmospheric Dynamics, UNSW

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Australia could see fewer cyclones, but more heat and fire risk in coming months


Jonathan Pollock, Australian Bureau of Meteorology; Andrew B. Watkins, Australian Bureau of Meteorology; Catherine Ganter, Australian Bureau of Meteorology, and Paul Gregory, Australian Bureau of Meteorology

Northern Australia is likely to see fewer cyclones than usual this season, but hot, dry weather will increase the risk of fire and heatwaves across eastern and southern Australia.

The Bureau of Meteorology today released its forecast for the tropical cyclone season, which officially runs from November 1 to April 30.




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Also published today is the October to April Severe Weather Outlook, which examines the risk of other weather extremes like flooding, heatwaves and bushfires.

Warmer oceans means more cyclones

On average, 11 tropical cyclones form each season in the Australian region. Around four of those cross the coast. The total number each season is roughly related to how much cooler or warmer than average the tropical oceans near Australia are during the cyclone season.

Map showing the average number of tropical cyclones through the Australian region and surrounding waters in ENSO-neutral years, using all years of data from the 1969-70 to 2017-18 tropical cyclone season.

One of the biggest drivers of change in ocean temperatures is the El Niño–Southern Oscillation, or ENSO. During La Niña phases of ENSO, the warmest waters in the equatorial Pacific build up in the western Pacific and to the north of Australia. That region then becomes the focus for more cloud, rainfall and tropical cyclones.

But during El Niño, the warmest water shifts towards the central Pacific and away from northern Australia. This decreases the likelihood of cyclones in our region.




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And when ENSO is neutral, there is little push towards above or below average numbers of cyclones.

Temperatures in the tropical Pacific Ocean have been ENSO-neutral since April and are likely to stay neutral until at least February 2020. However, some tropical patterns are El Niño-like, including higher-than-average air pressure at Darwin. This may be related to the current record-strong positive Indian Ocean Dipole – another of Australia’s major climate drivers – and the cooler waters surrounding northern Australia.

The neutral ENSO phase alongside higher-than-average air pressure over northern Australia means we expect fewer-than-average tropical cyclones in the Australian region this season. The bureau’s Tropical Cyclone Season Outlook model predicts a 65% chance of fewer-than-average cyclones.

At least one tropical cyclone has crossed the Australian coast every season since reliable records began in the 1970s, so people across northern Australia need to be prepared every year. In ENSO-neutral cyclone seasons, this first cyclone crossing typically occurs in late December.




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Other severe weather

While cyclones are one of the key concerns during the coming months, the summer months also bring the threat of several other forms of severe weather, including bushfires, heatwaves and flooding rain.

With dry soils inland, and hence little moisture available to cool the air, and a forecast for clear skies and warmer days, there is an increased chance that heat will build up over central Australia during the spring and summer months. This increases the chance of heatwaves across eastern and southern Australia when that hot air is drawn towards the coast by passing weather systems.

Australian seasonal bushfire outlook, as of August 2019. Vast areas of Australia, particularly the east coast, have an above-normal fire potential this season.
Bushfire and Natural Hazards CRC/Australasian Fire and Emergency Service Authorities Council

Likewise, the dry landscape and the chance of extreme heat also raise the risk of more bushfires throughout similar parts of Australia, especially on windy days. And with fewer natural firebreaks such as full rivers and streams, even greater care is needed in some areas.

Widespread floods are less likely this season. This is because of forecast below-average rainfall and also because dry soils mean the first rains will soak into the ground rather than run across the landscape.

However, as we saw in northern Queensland in January and February this year, when up to 2 metres of rainfall fell in less than 10 days, localised flooding can occur in any wet season if a tropical low parks itself in one location for any length of time.




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Most of all, it’s always important to follow advice from emergency services on what to do before, during and after severe weather. Know your weather, know your risk and be prepared. You can stay up to date with the latest forecast and warnings on the bureau’s website and subscribe to receive climate information emails.The Conversation

Jonathan Pollock, Climatologist, Australian Bureau of Meteorology; Andrew B. Watkins, Head of Long-range Forecasts, Australian Bureau of Meteorology; Catherine Ganter, Senior Climatologist, Australian Bureau of Meteorology, and Paul Gregory, BOM, Australian Bureau of Meteorology

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Winter storms are speeding up the loss of Arctic sea ice



A scientist checks cracks in the Arctic sea ice after a storm (April 2015, N-ICE2015 expedition).
Amelie Meyer/NPI, Author provided

Amelie Meyer, University of Tasmania

Arctic sea ice is already disappearing rapidly but our research shows winter storms are now further accelerating sea ice loss.




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The research is based on data we gathered during an expedition on a small Norwegian research vessel, the Lance, that was left to drift in the Arctic sea ice for five months in 2015.

Time series of air temperature anomalies in the Arctic for the period 1981-2010: Temperatures in the Arctic in May and June 2019 period were the warmest in the satellite records.
Zack Labe (@ZLabe)

The expedition was intense and felt more like going to the Moon than going on a typical research cruise. What took us by surprise were the many winter storms that battered the ice (and our ship and ice camp).

It has taken us years to collate these data but now we know the winter storms play a key role in the fate of Arctic sea ice, particularly in the Atlantic sector of the Arctic.

Norwegian research vessel ‘Lance’ frozen in the Arctic sea ice in February 2015 during the N-ICE2015 expedition.
Paul Dodd (NPI)

How winter storms amplify climate change

On average, about 10 extreme storms will reach all the way to the North Pole each winter. While these winter storms are short (they last on average 6-48 hours), they can be incredibly intense.

During a storm in winter 2015 we saw the air temperature rise from -40℃ (-40℉) to 0℃ (32℉) in just a day, and then fall back to -30℃ (-22℉) the next day, when cold Arctic air returned after the storm.

These storms bring heat, moisture and strong winds into the Arctic, and next we look at how they impact sea ice and its surroundings.

Warming and weakening the ice

The heat from the storms warms up the air, snow and ice, slowing down the growth of the ice. Moisture from the storms falls as snow on the ice. After the storm, the blanket of snow insulates the ice from the cold air, further slowing the growth of the ice for the remainder of winter.

The strong winds during the storms push the ice around and break it into pieces, making it more fragile and deforming it, more like a boulder field.

The strong winds also stir the ocean below the ice, mixing up warmer water from deeper waters to the surface where it melts the ice from below. This melting of the ice in the middle of winter can happen for several days after the storms when the air is already back to well below freezing.

Processes related to Arctic winter storms. In the first storm phase, strong southerly winds compress the ice cover and transport warm air, moisture, and bring strong winds. In the second phase, northerly winds transport ice southwards. After the storm has passed, cold and calm conditions return, allowing new ice to grow in leads. When the next winter storm arrives, it further drives the ice cover into a relatively thin-ice, snow-covered mosaic of strongly deformed ice floes. These new conditions impact surrounding ecosystems by shaping habitats and light conditions.
Graham et al., 2019 (Scientific Reports)

Thinner ice, shelter for life and accelerated melting

The breakup of the ice opens big passages of open water between ice floes, called leads. In winter these passages end up refreezing rapidly, generating new super-thin ice.

These thinner refrozen patches of ice let more light through in the following spring, allowing ocean plants (phytoplankton) to bloom earlier.

The rougher sea ice landscape becomes a shelter for many ice-associated Arctic organisms, including ice algae, becoming biological hot spots in the following spring.

The broken up and deformed ice drifts faster, reaching warmer waters where it melts sooner and faster.

So really, winter storms precondition the ice to a faster melt in the following spring with an impact that continues well into the following season.

Why is Arctic sea ice declining?

Winter sea ice cover in the Atlantic sector of the Arctic has been retreating at a record breaking pace, especially in the Barents Sea off Norway and Russia.

Average September Arctic sea ice extent from 1979 to 2018. Black line shows monthly average for each year; blue line shows the trend.
National Snow and Ice Data Center

The Arctic is particularly sensitive to human driven climate change. We know the decrease in sea ice is due to both the warming of the Arctic (air and ocean) and changing wind patterns that break up the ice cover.

But there are also amplifying mechanisms or “feedback” mechanisms, in which one natural process reinforces another. Their role in the decrease of sea ice is hard to predict. We now know winter storms in the Arctic contribute to these feedback mechanisms.

More storms ahead

Arctic winter storms are increasing in frequency and this is likely due to climate change.

With the thinner Arctic sea ice cover and shallower warmer water in the Arctic Ocean, the mechanisms we observed during the winter storms will likely strengthen and the overall impact of winter storms on Arctic ice is likely to increase in the future.

Two weeks ago, the Arctic sea ice reached its minimum extent for 2019, after another winter of intense winter storms. The minimum ice extent was effectively tied for second lowest since modern record-keeping began in the late 1970s, along with 2007 and 2016, reinforcing the long-term downward trend in Arctic ice extent. Arctic sea ice has been declining for at least 40 years, and amplifying mechanisms such as the winter storms are accelerating this retreat.

Arctic sea ice extent just reached its annual minimum extent for 2019 on September 18. This season was a tie for the 2nd lowest on record, along with 2007 and 2016 and behind 2012, which holds the overall record minimum.
Zack Labe (@ZLabe)

As highlighted in the recent IPCC Ocean and Cryopshere report, these changes in September sea ice are likely unprecedented for at least 1,000 years.

Remember also that changes in the Arctic don’t just affect the immediate region: Arctic warming has been linked to the polar vortex, and weather extremes across central Europe and north America.




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As we start taking into account feedback mechanisms like the winter storms, our predictions for the first Arctic sea ice free summer are indicating it will likely happen before 2050.The Conversation

Amelie Meyer, Research fellow, University of Tasmania

This article is republished from The Conversation under a Creative Commons license. Read the original article.

The air above Antarctica is suddenly getting warmer – here’s what it means for Australia



Antarctic winds have a huge effect on weather in other places.
NASA Goddard Space Flight Center/Flickr, CC BY-SA

Harry Hendon, Australian Bureau of Meteorology; Andrew B. Watkins, Australian Bureau of Meteorology; Eun-Pa Lim, Australian Bureau of Meteorology, and Griffith Young, Australian Bureau of Meteorology

Record warm temperatures above Antarctica over the coming weeks are likely to bring above-average spring temperatures and below-average rainfall across large parts of New South Wales and southern Queensland.

The warming began in the last week of August, when temperatures in the stratosphere high above the South Pole began rapidly heating in a phenomenon called “sudden stratospheric warming”.




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In the coming weeks the warming is forecast to intensify, and its effects will extend downward to Earth’s surface, affecting much of eastern Australia over the coming months.

The Bureau of Meteorology is predicting the strongest Antarctic warming on record, likely to exceed the previous record of September 2002.

(Left) Observation of September 2002 stratospheric warming compared to (right) 2019 forecast for September.
The forecast for 2019 was provided by the Australian Bureau of Meteorology and was initialised on August 30, 2019.

What’s going on?

Every winter, westerly winds – often up to 200km per hour – develop in the stratosphere high above the South Pole and circle the polar region. The winds develop as a result of the difference in temperature over the pole (where there is no sunlight) and the Southern Ocean (where the sun still shines).

As the sun shifts southward during spring, the polar region starts to warm. This warming causes the stratospheric vortex and associated westerly winds to gradually weaken over the period of a few months.

However, in some years this breakdown can happen faster than usual. Waves of air from the lower atmosphere (from large weather systems or flow over mountains) warm the stratosphere above the South Pole, and weaken or “mix” the high-speed westerly winds.

Very rarely, if the waves are strong enough they can rapidly break down the polar vortex, actually reversing the direction of the winds so they become easterly. This is the technical definition of “sudden stratospheric warming.”

Although we have seen plenty of weak or moderate variations in the polar vortex over the past 60 years, the only other true sudden stratospheric warming event in the Southern Hemisphere was in September 2002.

In contrast, their northern counterpart occurs every other year or so during late winter of the Northern Hemisphere because of stronger and more variable tropospheric wave activity.

What can Australia expect?

Impacts from this stratospheric warming are likely to reach Earth’s surface in the next month and possibly extend through to January.

Apart from warming the Antarctic region, the most notable effect will be a shift of the Southern Ocean westerly winds towards the Equator.

For regions directly in the path of the strongest westerlies, which includes western Tasmania, New Zealand’s South Island, and Patagonia in South America, this generally results in more storminess and rainfall, and colder temperatures.

But for subtropical Australia, which largely sits north of the main belt of westerlies, the shift results in reduced rainfall, clearer skies, and warmer temperatures.

Past stratospheric warming events and associated wind changes have had their strongest effects in NSW and southern Queensland, where springtime temperatures increased, rainfall decreased and heatwaves and fire risk rose.

The influence of the stratospheric warming has been captured by the Bureau’s climate outlooks, along with the influence of other major climate drivers such as the current positive Indian Ocean Dipole, leading to a hot and dry outlook for spring.

Anomalous Australian climate conditions during the nine most significant polar vortex weakening years (1979, 1988, 2000, 2002, 2004, 2005, 2012, 2013, 2016) on both maximum and minimum temperatures, and rainfall for October-November, as compared to all other years between 1979-2016.
Bureau of Meteorology

Effects on the ozone hole and Antarctic sea ice

One positive note of sudden stratospheric warming is the reduction – or even absence altogether – of the spring Antarctic ozone hole. This is for two reasons.

First, the rapid rise of temperatures in the upper atmosphere means the super cold polar stratospheric ice clouds, which are vital for the chemical process that destroys ozone, may not even form.

Secondly, the disrupted winds carry more ozone-rich air from the tropics to the polar region, helping repair the ozone hole.

We also expect an enhanced decline in Antarctic sea ice between October and January, particularly in the eastern Ross Sea and western Amundsen Sea, as more warm water moves towards the poles due to the weaker westerly winds.




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Thanks to improvements in modelling and the Bureau’s new supercomputer, these types of events can be forecast better than ever before. Compared to 2002, when we didn’t know much about the event until after it had happened, this time we’ve had almost three weeks’ notice that a very strong warming event was coming. We also know much more about the process that has been set in train, that will affect our weather over the next one to four months.The Conversation

Harry Hendon, Senior Principal Research Scientist, Australian Bureau of Meteorology; Andrew B. Watkins, Manager of Long-range Forecast Services, Australian Bureau of Meteorology; Eun-Pa Lim, Senior research scientist, Australian Bureau of Meteorology, and Griffith Young, Senior IT Officer, Australian Bureau of Meteorology

This article is republished from The Conversation under a Creative Commons license. Read the original article.