Unit 1 of 12 · 5 of 5 lessons published
The atmosphere
The atmosphere is a thin layer of gas held to the Earth by gravity. Almost all of its mass, and almost all of its weather, lies within about 12 km of the ground. This unit covers the air itself: how it is layered, and the four quantities every weather observation and every later lesson measures, which are pressure, temperature, moisture and cloud.
Each lesson builds on real measurements: weather balloon soundings, surface observations and satellite data. By the end of the unit a reader can say why temperature usually falls with height and where it does not, what a barometer reading means, why a dew point of 70 °F feels different from one of 50 °F, and how a cloud forms and what its name says about it.
The lessons assume no background and are best read in order. Terms are linked to the glossary the first time they appear.
- Layers of the atmosphere
Troposphere to thermosphere, and why weather happens in the lowest layer.
- Air pressure
What pressure is, how it is measured, and why it falls with height.
- Temperature and heat
How the sun heats the ground, the ground heats the air, and the day warms and cools.
- Dew point and humidity
Why dew point, not relative humidity, is the number forecasters watch.
- How clouds form and how to name them
Condensation, cloud bases, and the ten cloud genera.