Which statement about the environmental lapse rate and stability is true?

Which statement about the environmental lapse rate and stability is true?

• A. If the ELR is steeper than the dry adiabatic rate, the layer is unstable
• B. If the ELR is steeper, stable
• C. If the ELR is shallower than the dry adiabatic rate, unstable
• D. If the ELR equals the dry adiabatic rate, there is full saturation

Answer: (A)

Stability hinges on how quickly air cools with height compared to a rising air parcel. When the environmental lapse rate is steeper than the dry adiabatic lapse rate, the surrounding air cools faster with height than the parcel does as it rises. The parcel stays warmer and less dense than its surroundings, so it continues to rise and the layer is unstable. If the ELR were shallower, the parcel would become cooler and denser than the environment as it ascends, leading to stability. If the ELR equals the dry adiabatic rate, a dry parcel would be neutrally buoyant, and saturation would involve additional factors (the moist adiabatic lapse rate), not automatically implying full saturation.

Stability hinges on how quickly air cools with height compared to a rising air parcel. When the environmental lapse rate is steeper than the dry adiabatic lapse rate, the surrounding air cools faster with height than the parcel does as it rises. The parcel stays warmer and less dense than its surroundings, so it continues to rise and the layer is unstable. If the ELR were shallower, the parcel would become cooler and denser than the environment as it ascends, leading to stability. If the ELR equals the dry adiabatic rate, a dry parcel would be neutrally buoyant, and saturation would involve additional factors (the moist adiabatic lapse rate), not automatically implying full saturation.