The Winter Solstice
21st December 1998 |
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As Christmas approaches, the northern hemisphere moves towards its shortest day and the 'official' start of winter on December 21st - the Winter Solstice. In
the north, days are short and the winter nights are long. Temperatures fall as the weak sunlight attempts to warm the northern landmasses. Southern latitudes
experience their summer - with hot dry conditions across Australia and continuous hours of daylight in the far south of Antarctica.
Images of the Solstice: Meteosat 7Visible light band
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Image acquired at 12:00 UTC (12 noon, London time) in the visible light band. The central and southern parts of the image show clear and strong
illumination from the Sun. To the north, the light intensity decreases until, just to the north of the UK, there appears the dark band of night. Northern
Norway and Sweden, Finland and Iceland are all now experiencing the long winter night with just a glimmer of sunlight appearing over the horizon
at midday.
Look south at the Southern Atlantic Ocean. There is a horizontal band of cloud at the Tropic of Capricorn - directly below the Sun. The strong heating of the Sun's rays is evaporating water in the Atlantic - the water is rising in the hot air and cooling to form clouds. There are more clouds over the Southern ocean than the north - but notice the clear skies over the desert regions of South West Africa. |
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| Thermal Infra-Red band | |
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Image acquired at 12:00 UTC (12 noon, London time) in the thermal infra-red band. This image shows temperature variations - with the hottest parts
being darkest. Cold icy clouds show up as white whilst the hot land mass is dark - almost black! Notice the differences in temperature between Africa
and Europe. Europe is much much cooler - the most southerly parts have a darker hint but Europe gets colder quickly as you move north. Across northern
Britain and Scandinavia (Norway, Sweden etc.) temperatures were down to 0 C (freezing!) and snow was falling.
Now look at the colour of southern Africa. Under the intense heating of the almost overhead Sun, the land has become very hot and appears almost black. The land is much hotter than the surrounding sea which is cold - cold water currents from the Antarctic flow up the west coast of Africa. Compare the sea temperatures off the west coast of southern Africa with those off the east coast. To the south of Africa, a deep depression is swirling over the southern ocean. Look at the cloud pattern - air is moving around the depression in a clockwise direction - in the north it rotates in the opposite direction. Can you see a northern depression rotating in an anti-clockwise manner? |
The December solstice |
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Compare these images of the winter solstice with images taken on June 21st - the Summer Solstice. Summer images show the
landmass of Europe in clear bright sunlight - extending right up to the North Pole.
Page update: December 1998 |
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