When the reduction in ambient temperature with height r is greater than the change in temperature with height induced by a dry adiabatic process rd​, the atmosphere is said to be:

Correct option is C

The correct answer is (c) absolutely unstable. In meteorology, when the environmental lapse rate (reduction in ambient temperature with height) is greater than the dry adiabatic lapse rate (rd​, which is approximately 9.8°C per kilometer), the atmosphere is absolutely unstable. This means that if an air parcel is displaced vertically, it will continue to rise or sink because it remains warmer (and thus less dense) than the surrounding air.
Explanation of Other Options:
· (a) Absolutely stable: Occurs when the environmental lapse rate is less than the dry adiabatic lapse rate, making vertical motion suppressed.
· (b) Dry neutral: Occurs when the environmental lapse rate equals the dry adiabatic lapse rate (r=rd), making the atmosphere neutral to vertical displacements.
· (d) Conditionally unstable: Occurs when the atmosphere is stable for dry air but can become unstable if the air becomes saturated (moist adiabatic lapse rate applies).
Information Booster: 1. Dry Adiabatic Lapse Rate (DALR): The rate at which an unsaturated parcel of air cools as it rises (~9.8°C/km).
2. Environmental Lapse Rate (ELR): The actual rate at which temperature decreases with height in the atmosphere.
3. Absolutely Unstable: ELR > DALR; parcels continue to rise or fall when displaced.
4. Absolutely Stable: ELR < DALR; displaced parcels return to their original position.
5. Conditional Instability: Stability depends on whether the air is saturated or unsaturated.
6. Stability and Weather: Atmospheric stability affects cloud formation, storms, and turbulence.
Additional Knowledge: · Absolutely Stable:
· Example: Inversions, where warmer air sits above cooler air, suppressing vertical motion.
· Dry Neutral:
· Example: When the environmental lapse rate matches the dry adiabatic lapse rate, parcels neither rise nor sink further.
· Absolutely Unstable:
· Example: During hot afternoons when the ground heats rapidly, causing air to rise quickly.
· Conditionally Unstable:
· Example: Thunderstorms, where rising air becomes unstable once condensation occurs.