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Australian Weather Calendar 2012

The Bureau of Meteorology in Australia runs a photographic competition each year. The winning pictures go into a calendar, alongside their stories. Here are the pictures in the 2012 calendar.

January: Double rainbow over Wombarra beach, New South Wales. Matt Smith, a warehouse supervisor of Wollongong, NSW, risked his $15,000 medium-format camera to capture this double rainbow at Wombarra beach in January 2011. It survived the rain. Rainbows are formed when light from the sun passes through raindrops in the atmosphere. As the light shines on the surface of the droplets, it is refracted, or bent. It then reflects off the back of the drop and is refracted again as it passes back through the surface of the droplet. Blue light refracts at a greater angle than red light, resulting in white light being separated into its spectrum of colours. A rainbow is an optical effect dependent on the position of the observer. If you travel towards a rainbow, it appears to move further away. Similarly, a rainbow viewed from above, such as from an aircraft, appears as a full circle rather than the semicircle when viewed from the ground.
The Bureau of Meteorology in Australia runs a photographic competition each year. The winning pictures go into a calendar, alongside their stories. Here are the pictures in the 2012 calendar, available to buy here. The full-colour, spiral-bound wall calendar is available in a large (A2) format, and a compact (A4) format. Credit: Matt Smith
February: A dust storm descends on Warralong, northwest Western Australia. Suzanne Pollard, who calls herself 'a gypsy, a bush girl, a weather freak', was caretaking at an Aboriginal community at Warralong, 110 km southeast of Port Hedland, when she photographed this dust storm in January 2010. The strong and gusty winds associated with a thunderstorm picked up the loose red dust characteristic of the region.
February: A dust storm descends on Warralong, northwest Western Australia. Credit: Suzanne Pollard
March: A flood palette, Channel Country, Queensland. Photographing from a mustering helicopter with doors removed, Helen Commens of Ourdel Station, near Windorah, Queensland, took this shot in December of the 2010-11 floods in the channel country. Frequent heavy rain in late 2010 - associated with a strong La Niña in the Pacific Ocean - led to widespread flooding across much of eastern Australia. La Niña, when sea-surface temperatures in the central/eastern equatorial Pacific Ocean are cooler than normal, usually results in increased rainfall across eastern Australia. In the week preceding the photograph, a low pressure trough over eastern Australia had directed a humid northerly airstream over central Queensland, leading to widespread rainfall.
March: A flood palette, Channel Country, Queensland. Credit: Helen Commens
A call from a friend alerted storm chaser Steph Hall to this storm front at Undertow Bay near her home at Inverloch in southeast Victoria. The thunderstorm was generated as a low pressure trough crossed Victoria. A low pressure trough is an area of low atmospheric pressure that marks a boundary between different air masses. Warm moist air is usually on one side of the trough and cooler, drier air is on the other. This leads to instability in the atmosphere and can initiate the formation of thunderstorms. In the photograph, shelf clouds (arcus) are formed by the thunderstorm's outflow. They are best described as low, horizontal, wedge-shaped clouds attached to the base of the parent cloud.
April: Thunderstorm approaches Undertow Bay, near Inverloch, southeast Victoria. Credit: Steph Hall
May: Balcony lightshow, Darwin, Northern Territory. When Mark Percival lived at Palmerston in the Northern Territory, inland of Darwin, he enjoyed photographing tropical thunderstorms from his second-floor balcony. Northern parts of the Territory experience two distinct seasons, the Dry (May to September), and the Wet (October to April the following year).The Wet is characterised by more thunderstorms and monsoon activity due to higher rainfall, temperature and humidity. A shift in the prevailing wind also directs more moisture into the Darwin region from warm oceans north of Australia. On average, Darwin experiences 20 days with thunder each December.
May: Balcony lightshow, Darwin, Northern Territory. Credit: Mark Percival
June: Snow streaks in the Blue Mountains, New South Wales. Keen photographer and bushwalker John Martyn followed a Bureau of Meteorology forecast and drove for two hours from his home at Turramurra in northern Sydney to photograph 'a full-on snow storm, with winds around 50 km/hr' at Hargraves Lookout in the Blue Mountains, west of Sydney. Snow is common during the winter months in the elevated alpine areas of Victoria and NSW. In the winter of 2008, the year the photograph was taken, the Blue Mountains experienced 20 to 40 days with snow.
June: Snow streaks in the Blue Mountains, New South Wales. Credit: John Martyn
July: A frosty shroud, Rosewhite, northeast Victoria. Melbourne IT consultant Paul Burgess snapped this frost-encased willow tree near Happy Valley Creek while visiting his parents' property at Rosewhite, near Myrtleford in northeast Victoria. On average, Rosewhite experiences 15 June days when the temperature drops below 2 degrees, making frost a possibility.
July: A frosty shroud, Rosewhite, northeast Victoria. Credit: Paul Burgess
August: Roll clouds off Cape Tourville, Tasmania. Persistence paid off for enthusiastic photographer Susan Mace, who captured this image of unusual roll-cloud formations off Cape Tourville, near Coles Bay, Tasmania, after colleagues on a photographic workshop had proceeded to breakfast after a dawn expedition. The roll clouds were generated by a land breeze trapped under a low-level inversion (a warmer layer above colder air). A land breeze may blow from the land to open water when sea temperatures are higher than the land surface temperature.
August: Roll clouds off Cape Tourville, Tasmania. Credit: Susan Mace
September: Storm front over Brinard Station, Queensland. Gina Harrington's children called her out from the Brinard Station homestead in Queensland's Gulf Country at sunset on 2 February 2011 to photograph 'a weird, big rolling cloud'. It proved to be their first sign of severe tropical cyclone Yasi. Yasi crossed the coast as a marginal category 5 cyclone near Mission Beach on 3 February 2011, between midnight and 1 am. Yasi was one of the most powerful cyclones to have affected Queensland in recorded history. Cyclones of comparable intensity include cyclone Mahina in Princess Charlotte Bay in 1899, and cyclones at Mackay (January) and Innisfail (March) in 1918.
September: Storm front over Brinard Station, Queensland. Credit: Gina Harrington
October: Distinctive lenticular clouds, northern Tasmania. Meteorologist Barend Becker was on duty on the Bureau of Meteorology's stand at Agfest at Carrick, near Launceston, in northern Tasmania, when a farmer interrupted his discussions to ask him to identify some distinctive clouds. They were lenticular clouds, near stationary lens-shaped clouds that usually form downwind of a mountain range or elevated area. As wind passes over a mountain range it becomes turbulent due to the disruption to the flow. This sometimes produces a wave pattern in the flow beyond the mountains and, under certain conditions, moisture in the air will condense as it moves up towards the crest of the wave, forming cloud. As the moist air descends towards the trough of the wave, the cloud particles may evaporate again.
October: Distinctive lenticular clouds, northern Tasmania. Credit: Barend Becker
November: Fog at McKay Reserve, Palm Beach, Sydney. Prompted by a forecast for fog, Sydneysider Kathryn Lynch got up to greet the dawn in the pristine bushland of McKay Reserve at Palm Beach on Sydney's North Shore in April 2010. By definition, fog occurs when visibility is less than one kilometre. Mist occurs when visibility is more than one kilometre.
November: Fog at McKay Reserve, Palm Beach, Sydney. Credit: Kathryn Lynch
December: Reflections at Lake Eyre, South Australia. When South Australia's Lake Eyre started filling in July 2010, photographers from around the world came to Australia's largest salt lake to capture the infrequent phenomenon. Wollongong photographer Matt Smith was among them and captured altocumulus cloud reflected in the waters of the lake. The volume of water in Lake Eyre varies substantially each year - large portions are often dry - and is linked to the cycle of El Niño and La Niña, a major driver of rainfall in the lake's catchment areas.
December: Reflections at Lake Eyre, South Australia. Credit: Matt Smith
Cover photo: An aurora shimmers over Mawson base, Antarctica. Chris Wilson, deputy station leader at Australia's Mawson Base in Antarctica, photographed this aurora at 11.06 pm on 24 April 2011. The broad swathe of green light is a space-weather phenomenon known as aurora australis, or the southern lights. The name comes from the Roman goddess of dawn, Aurora. Auroras are a complex interaction of the earth's magnetic field with the solar wind, a stream of charged particles from the sun.Although auroras are most commonly seen from the polar regions, under the right conditions they can be visible from as far north as the Australian mainland.
Cover photo: An aurora shimmers over Mawson base, Antarctica. Credit: Chris Wilson