The development of thermals depends upon which factor?

• A. Solar heating
• B. Wind shear
• C. Moisture content
• D. Adiabatic cooling

Answer: (A)

Thermals form because solar heating of the Earth's surface makes the near-surface air rise. When the ground is warmed by the sun, some air parcels become unusually buoyant and start to climb, creating a vertical column of rising air. As these parcels rise, they cool because of expansion (adiabatic cooling), and if there is enough moisture, condensation can occur and clouds may form.

Wind shear can influence how a thermal looks or persists, and moisture content affects whether you see visible clouds, but the fundamental driver of thermal lift is the heating of the surface by the sun.