Aims of this episode:
- Understand what defines an area as a desert;
- Explain how radiation and convection currents mean that the Sahara Desert is very cold at night;
- Explain how Specific Heat Capacity means that most desert animals are nocturnal.
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Deserts are just sand… right?
Actually, the definition of a desert only mentions how much rain it receives in a year (25 cm). It doesn’t mention temperature or how many plants or animals there are. Therefore, some parts of Antarctica (one of the coldest places on Earth) are classed as deserts because of their lack of rain (or snow).
However, even the ‘hottest’ deserts can be very cold. The Sahara Desert in Africa can reach temperatures of 50 degrees Centigrade during the day, but at night these can fall to below zero! This is because all of the energy that has beaten down on the desert during the day radiates off at night. Since there is no cloud cover at night, there is nothing to reflect this energy back towards the ground, therefore the temperature falls.
In addition to radiation, there are convection currents in the air. The air particles at the surface gain energy from the ground. The particles spread out – reducing the density of the air – which then rises up. This is replaced by cool air, so gradually the energy is taken from the surface of the desert. This rising air can cause problems for aircraft flying overhead and is known as turbulence.
Now, 50 degrees Centigrade is extremely hot when it comes to living things. Therefore animals find it extremely difficult to live in hot deserts during the day. However, at night the temperature becomes a lot more bearable. Therefore, most animals burrow into the sand during the day. The high temperatures don’t reach very far below the surface because the sand will be able to hold a lot of energy without its temperature rising too much.