The Unstable atmosphere encourages vertical motion. Which term completes this description?

• A. Unstable
• B. Stable
• C. Advection
• D. Arctic

Answer: (A)

Vertical motion in the atmosphere is driven by buoyancy. When the air is unstable, a displaced parcel remains lighter than its surroundings and continues to rise, so vertical motion is encouraged and gravity-driven convection can develop. That makes the term that completes the sentence Unstable, because it describes the condition that allows the air to keep rising. A stable atmosphere would resist vertical motion, keeping the parcel from ascending; advection refers to horizontal transport rather than vertical buoyancy effects; and Arctic is simply a location, not a descriptor of atmospheric stability.