Weather

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This week at Casey: 18 January 2013

The Bureau of Meteorology provide several staff members to support Australian Antarctic science and operations every year, with meteorological observing staff in place all year round and weather forecasters working the summer seasons.

At Casey this winter there will be two observers who make regular weather observations and release weather balloons twice per day. The balloons carry instrumentation for measuring winds, temperature and relative humidity as they ascend through the atmosphere. The third wintering team member is a meteorological technician who looks after a vast array of instrumentation, from the numerous automatic weather stations to the satellite imagery receiver. Currently joining the winterers are an additional weather observer and two weather forecasters. The forecasters provide daily weather information to all on station.

Balloon releases

Weather balloons are released at 2300 UTC (Universal Coordinated Time) and 1100 UTC everyday by the weather observers. The balloons are inflated with hydrogen gas in which we can achieve a controlled ascent rate of 300 metres per minute by adding a known amount of gas.

The 2300 UTC balloon is released alongside 170 other weather stations around the world as part of the World Meteorological Organisation (WMO) Global Upper Air Network (GUAN), used to analyse current weather conditions through global climate models and weather forecasting. Unfortunately 2300 UTC is 10am Casey station time, which is when morning tea is served, meaning more than often the poor weather observer misses the delicious food the station chefs prepare.  

Weather and safety

The weather determines much of what can and can't happen on a daily basis. Extreme winds, low temperatures and snowfall can disrupt any outdoor operation - from crane work for building the new east wing to whether the aeroplanes can fly for transport or science projects, to whether boats can be taken out on the water. A forecast is produced every day and weather briefings take place for pilots each morning. Everyone is prepared to adapt and rearrange work schedules as the weather dictates.

High winds and blizzards are the main ongoing safety concern for all. When wind speeds are greater than 15 knots boating operations cease and at around 35 knots (gale force winds) aviation operations are affected both for take off and landings as well as moving around on the ski-way. At 60 knots it becomes difficult to walk and so extra caution is required for moving between buildings, such as using blizzard or 'blizz' lines (which are guide ropes between buildings) and only going outside accompanied by another expeditioner and carrying a radio. High winds can also cause snow on the ground to be blown around which can very quickly reduce visibility and produce blizzards. When blizzards occur they suspend all outdoor activities and forecasting those conditions is one of the most important jobs for the weather forecasters.

The weather and climate at Casey

It is January at Casey station, average daytime temperatures reach 2° Celsius with night time minima around -3° Celsius, but in the depths of winter the range is -10° to -18° Celsius. The lowest temperature recorded at Casey was -37° Celsius in August 2005. The wind speed is the most important feature of the weather day to day and windy days a frequent occurrence with gale force being reached on between 100 and 150 days per year. The highest wind gusts have been recorded at 130 knots. Wind chill can significantly modify the apparent temperature as well as high winds being a hazard in their own right.

Casey is at sea level and at the foot of Law Dome, which rises to 1400 metres, 120 kilometres southeast of the station. Law Dome has a significant effect on the climate of Casey. The predominantly easterly flow around the Antarctic coast is often strong as in this region frequent cyclonic storms occur. Easterly winds over Law Dome lead to a rain (snow) shadow on the lee side where Casey is positioned. Winds are often light at the station, especially in summer, but Law Dome can - when easterly winds are already storm force - increase the wind speed further. Such a day of extreme easterly winds occurred on 15th November 2012, just a fortnight after the summer expeditioners arrived, when the anemometer recorded 97 knots before being ripped from the top of the mast just before midnight. A spare was put in as replacement once the winds had died down 36 hours later.
The meteorological staff at Casey station January 2013
The meteorological staff at Casey station - January 2013
(Photo: Michael Salinas)
An expeditioner releases a weather balloon
Balloon release
(Photo: Michael Salinas)
Blowing snow over Casey station blurs out the figure of a male expeditioner at the centre of the photo
Blowing snow over Casey station
(Photo: Luke Pitman)
Cloud associated with strong winds in panorama over water
Cloud associated with strong winds
(Photo: Michael Salinas)
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