How a thermal is born

The sun heats the ground unevenly, and warm air breaks loose as a bubble that rises while it is warmer than the air around it. Where it stops: the inversion that caps the day, and the cumulus whose base you can work out before you fly.

What you learn

• Spot the ground that makes thermals, and what sets them free
• Explain why a bubble rises, and when it stops
• Follow a rising bubble: about 1 °C cooler per 100 m
• Estimate cloud base: 125 m × (temperature − dew point)
• Look upwind of a cumulus when you are low

In playlists

• Weather
• Gliding and soaring

Also on

• Video course: Soaring