What is the standard dry adiabatic lapse rate, i.e., the rate at which temperature decreases with altitude per 1000 meters?

What is the standard dry adiabatic lapse rate, i.e., the rate at which temperature decreases with altitude per 1000 meters?

• A. 6.5°C per 1000 meters
• B. 3.0°C per 1000 meters
• C. 15.0°C per 1000 meters
• D. 9.8°C per 1000 meters

Answer: (D)

The rate tested is how fast a rising, unsaturated air parcel cools when it expands without exchanging heat with its surroundings. For dry air, this adiabatic cooling is about 9.8°C per kilometer of ascent, or 9.8°C per 1,000 meters. This comes from the thermodynamic relation dT/dz ≈ -g/cp, using g ≈ 9.81 m/s² and cp for dry air ≈ 1005 J/(kg·K). So, as you climb 1,000 meters, the parcel’s temperature drops roughly 9.8°C. This value is higher than the standard environmental lapse rate (about 6.5°C/km) and higher than typical moist-adiabatic rates (which are around 5–6°C/km due to latent heat release). The other numbers listed do not match the dry adiabatic mechanism.

The rate tested is how fast a rising, unsaturated air parcel cools when it expands without exchanging heat with its surroundings. For dry air, this adiabatic cooling is about 9.8°C per kilometer of ascent, or 9.8°C per 1,000 meters. This comes from the thermodynamic relation dT/dz ≈ -g/cp, using g ≈ 9.81 m/s² and cp for dry air ≈ 1005 J/(kg·K). So, as you climb 1,000 meters, the parcel’s temperature drops roughly 9.8°C. This value is higher than the standard environmental lapse rate (about 6.5°C/km) and higher than typical moist-adiabatic rates (which are around 5–6°C/km due to latent heat release). The other numbers listed do not match the dry adiabatic mechanism.