image: Dean Evans, Halley Research Station, AntarcticaTamsin Gray works for the British Antarctic Survey as a meteorological observer. Here she tells us a bit about her job, and weather observation in Antarctica. To find out more, join Tamsin on the Above The Poles Live Event.
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Every day, at the same time, a weather balloon is launched at more than 800 sites around the world. Sixteen of those sites are in or around Antarctica where daily weather balloon launches have been carried out at many bases since the IGY in 1956/7.
Last year it was my job to launch the daily balloon at Halley Research Station on the Brunt Ice Shelf on the coast of Antarctica (that's me in the photo). This year I’ll be launching balloons from Rothera base on the Antarctic Peninsula. Each day, I attach a small package of instruments called a radiosonde to the balloon. The radiosonde measures the temperature, pressure and humidity of the air it passes through and sends the data back to a ground station every second. We can track the balloon throughout its flight using Global Positioning System satellites (GPS) and then convert the GPS track into information about the wind speed and direction at different heights in the atmosphere. It's pretty incredible that a tiny package the size of your fist can provide so much useful information. Data from radiosondes tells us how the atmosphere changes with height - vital information for accurate weather forecasting. Weather balloon data is also capable of shedding light on some of the questions at the very heart of the climate change debate
image: Preparing a radiosonde, Halley Research Station, AntarcticaWeather balloons provide evidence that the warming we have measured on the surface of the earth is linked to carbon dioxide and other greenhouse gases. As greenhouse gases provide a blanket that traps heat, we expect to see warming under the blanket, but cooling above and this is what weather balloon data shows. The British Antarctic Survey reports,
Analysis of weather balloon data collected over the past 30 years has shown that the Antarctic atmosphere has warmed below 8 km and cooled above this height. This pattern of warming in the troposphere and cooling in the stratosphere is seen globally and is the expected signature of increases in greenhouse gases, such as carbon dioxide. However, the 30-year warming at 5 km over the Antarctic during winter (0.75°C) is over three times the average rate of warming at this level for the globe as a whole.
Over Antarctica, even in regions where no warming has been recorded at the surface, a very dramatic rise in temperature can be observed when you look further up in the atmosphere.
For me, launching a weather balloon is one of the highlights of my job as an Antarctic Meteorologist. I find it a privilege to play a part in collecting such unique and important data. When you launch your virtual weather balloon on December 4th, think about the people in the Arctic and the Antarctic who are doing exactly the same as you, providing us with the knowledge to help us predict our weather and understand our climate and the effect we’re having upon it.
Data from Weather Ballons
Below are three screen shots showing information collected from a weather balloon launched from halley on October 14th, 2008.
Balloon trajectory, Halley 14 Oct 2008
The green line marks the path of the balloon from its starting point at Halley. Balloons can travel up to 200km and reach heights up to 35km before expanding to the size of a double decker bus, bursting and falling back to earth. In populated areas, the balloons are equipped with a small parachute to stop them causing too much damage if they hit something. In Antarctica, that's not really necessary but occasionally we find balloons that have landed in the local area.
Sometimes the balloon goes round and round in circles as the winds change direction as it rises. By following the path of the balloon, we can tell the speed and direction of the winds at different heights.
Wind Speed and Direction from Balloon, Halley 14 Oct 2008
These graphs show wind speed. The one on the left shows how fast the balloon has been blown around: the wind speed. On the right you can see how the wind direction changes with height.
What happens to the wind speed high up in the path of the balloon? Planes sometimes use these winds high up around 10km above us to help them on their way.
The winds aren’t the only thing that change as the balloon rises. The temperature and humidity of the air changes too. At first the temperature falls as the air expands (pressure decreases). This is just the same as climbing a mountain and feeling it getting colder the higher you go (about 1 degree C for every 100m you climb). Below, the red line shows the temperature and the blue line is humidity.
Temperature & Humidity from Balloon, Halley 14 Oct 2008
When the balloon passes into a cloud, the temperature rises briefly. This is due to the heat released as the water vapour condenses into droplets. We call the heat associated with a change in state latent heat. You can see the cloud layers on this graph. I have already said that the temperature stops falling and briefly rises but what happens to the humidity? Can you spot a cloud layer?
Facts:
Released twice a day midday and midnight UTC all around the world
At sea, automated systems launch weather balloons from the decks of ships
A radiosonde can reach 35 km (115,000 feet) and drift 200 km (125 miles) from the release point
Temperatures as low as -90 °C, with pressures only thousandths of that found at the surface, are found routinely
Useful links:
UK Met office timeline and facts about weather balloons
UK Met office list of current weather observations from sites around the world
Met office teachers guide to cloud observing
Ozone monitoring balloon being launched at IPY launch in Sweden.