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.
03/10/97 Chris Davis