What would decrease the stability of an airmass?

• A. Warming from below
• B. Cooling from below
• C. Warming from above
• D. No change

Answer: (A)

When assessing stability, think about how temperature changes with height and how a lifted parcel would behave buoyancy-wise. Warming the lower part of the airmass makes the surface layer warmer than the air above it, so a parcel displaced upward stays warmer and less dense than its surroundings. That buoyancy lets it keep rising, promoting convection and reducing stability.

Cooling from below would make the surface cooler than the air aloft, so a lifted parcel would tend to slow its ascent or sink back, which strengthens stability. Warming from above or no change in temperature structure generally doesn’t encourage the same surface-driven buoyant ascent, so they don’t decrease stability the way surface warming does.