Unit 21
Atmosphere and weather.
The air above us: its layers, thunderstorms, the Coriolis effect, the ozone hole, and the auroras.
The unit, lesson by lesson
Lessons
5 lessons · 35 practice questions · about 2 hours
Layers of the atmosphere
Rise through the air from the ground to 200 km: it cools, warms, cools again and turns hot. Measure how fast it cools, find where half the air lies, and see why each layer is warm or cold.
Storms and weather
One afternoon ends with a few white puffs, another in a thunderstorm. See how the ground's heat, the moisture and the wind decide what grows: thermals, the cloud base, the latent heat that feeds a storm, and the wind shear that sets how long it lives.
The Coriolis effect
Throw a ball straight across a turning carousel and it misses. On the Earth the ground turns about its upright at a rate set by the latitude, which bends winds and spins storms: right in the north, left in the south, and not at all at the equator.
The ozone layer
A layer of gas that would be a few millimetres thick if squeezed down shields life from ultraviolet light. Measure how thin it is, see how ozone absorbs light without running out, and how chlorine, a catalyst, tore a hole in it over Antarctica every spring.
Auroras
The Earth's magnetic field holds off the solar wind and steers electrons into rings round the poles. See how a storm brings the aurora nearer the equator, and why it glows green and red.