The effect of sunlight on the upper atmosphere
Heating and the generation of global winds
Sunlight is absorbed by the atmosphere which heats up and expands. Since
only one side of the earth is sunlit at any one time, the atmosphere on
that side is warmer than the nightside. This temperature difference
causes winds to blow from the dayside to the nightside. Although other
effects, such as the Coriolis force, will alter the movement of the air,
the day/night temperature difference has the largest effect. As the earth
rotates, an observer on the ground will see the wind change sinusoidally
over the course a day.
The creation of the ionosphere
Some specific wavelengths of light are sufficiently energetic to
ionise a small percentage of the gas in the upper atmosphere.
The resulting ions will survive until they collide with an electron
again to form a neutral particle. The amount of ionisation in the
atmosphere is therefore a delicate balance between production (by
sunlight) and loss (by collision). Different wavelengths of light
penetrate the atmosphere to different depths, forming ionisation in
distinct layers.
- The F layer The highest, formed above 200 km by ultra violet
radiation.
- The E layer Formed at 100 km from Extreme-Ultra Violet radiation.
- The D layer Formed at around 70 km by X-rays.
Home
03/10/97 Chris Davis