Cumuliform clouds are formed from unstable air and are commonly associated with what daily solar cycle?

• A. The daily cycle of cooling
• B. Nighttime radiation
• C. Polar air movements
• D. The diurnal cycle of solar heating

Answer: (D)

Cumuliform clouds form when the air is convectively unstable—heated air near the surface rises in buoyant thermals, and moisture condenses as it cools aloft, producing those puffy, vertically developed clouds. The daily cycle that best explains their formation is the diurnal cycle of solar heating. As the sun heats the surface during the day, air near the ground becomes buoyant and rises, fostering cumulus development, often peaking in the afternoon. When solar heating wanes toward evening, convective activity decreases and these clouds tend to dissipate. The other options describe processes not driving daytime convection, so they don’t account for the typical daytime appearance of cumuliform clouds.