ANTARCTIC



WELCOME TO THE COLDEST PLACES ON EARTH
	WEBCAMS Halley Rothera Research Station St Georgia RSS St James Ross Research Ship RRS Ernest Shackleton Research Ship Mawson Station Casey Station Davis Station Macquarie Island
		ANTARCTIC




	The weather at Antarctic stations can change very quickly from brilliant sunshine to raging storm. Spectacular weather phenomena are often visible, ranging from halos round the Sun to the brockenspectre, whilst the aurora lights up the night sky. The southern lights, or aurora australis, are one of nature's light-shows in the night sky. They are often seen from Halley, but less often from Rothera and much less often from South Georgia. The aurora is created when charged particles from disturbances on the Sun interact with the Earth's magnetosphere. High energy particles then cascade into the highest parts of the Earth's atmosphere, ionising gasses and creating a glow much as in a neon advertising sign. Particles with different energies ionise different gasses and hence create different colours to the aurora.

Atmospheric conditions in Antarctica mean that many unusual weather phenomena can be seen.
In particular halo displays are often exceptionally brilliant and mirages are frequent.

Brockenspectre

When the shadow of an
observer is cast onto a
fog bank below it often
appears unusually shaped and of large proportions this is the

Corona

Pastel colours in clouds
close to the Sun or Moon reveal the presence of water droplets in the cloud. These shades are

Diamond dust

The air temperature in Antarctica is often low enough for water vapour to condense directly out of the atmosphere and form

Spectre of the Broken, firstnoted by climbers in the Harz mountains of northern Germany.

called the corona and the physics is similar to that seen
when a drop of oil falls onto the surface
of a puddle.

tiny ice crystals which then fall. On a sunny day these catch the sunlight and shine like a sprinkling of diamonds in the sky, hence the name diamond dust. If the crystals are orientated in exactly the right way they can give rise to brilliant halos.

Fogbow

A fogbow is formed in exactly the same way as a rainbow, but the colours overlap in the tiny droplets of water in fog and convert the

Halo

A halo is a ring or pillar
of light around the Sun
or the Moon. Halo
displays are frequent in
Antarctica and are particularly bright

Mirage

When there is a strong temperature contrast near the ground, light can be bent or reflected, thus distorting the shape of

rainbow back to a colourless bow.

when they form in diamond dust. There are many different types of halo, ranging in simple rings with diameters of 22° or 46°, pillars above the sun or moon, sun dogs or parhelia on either side of the Sun or Moon and arcs like rainbows high in the sky.

distant objects. Mirages can extend ice floes into huge icebergs, and even give images of ships upside down.

SNOW

The distribution of precipitation over Antarctica is very marked, with several metres of snow falling each year near the coast but the interior only getting an annual snowfall of a few centimetres, thus officially making much of the continent a desert. After the snow has fallen it will be redistributed by the winds, particularly in the coastal areas where the downslope katabic winds can be in excess of 40 kts for long periods of time.

When the snow first falls its density will be relatively low at around 300 kgm^-3 (compared to solid ice which is around 900 kgm^-3). With the passage of time it slowly becomes denser as the ice crystals grow and eventually it becomes solid glacier ice.

ICE

The Antarctic ice sheet is the largest single mass of ice on Earth. It covers an area of almost 14 million km² and contains 30 million km³ of ice. Around 90 per cent of the fresh water on the Earth's surface is held in the ice sheet, an amount equivalent to 70 m of water in the world's oceans. In East Antarctica the ice sheet rests on a major land mass, but in West Antarctica the bed is in places more than 2500 m below sea level. It would be seabed if the ice sheet were not there.

Even in summer Antarctic temperatures are below 0°C and so frost and snow crystals that gather on the surface of the ice sheet do not melt but accumulate year-by-year. As these crystals are buried the weight of the crystals above presses them together. Eventually, they are transformed into dense and impermeable glacial ice.

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