Question

What is the value of the Dry Adiabatic Lapse Rate (DALR) in the Earth's atmosphere?

• A. \(6.5^\circ \text{C/km}\)
• B. \(9.8^\circ \text{C/km}\)
• C. \(12^\circ \text{C/km}\)
• D. \(4^\circ \text{C/km}\)

Hint:

\textbf{DALR = \(9.8^\circ \text{C/km}\)} (dry air).
Moist air has a lower lapse rate (~\(4\text{–}7^\circ \text{C/km}\)).

Answer 1

The Correct Option is B

Concept: The Dry Adiabatic Lapse Rate (DALR) refers to the rate at which the temperature of a rising or descending dry air parcel changes with altitude, without heat exchange with the surroundings.
Step 1: Understanding adiabatic process.
In an adiabatic process, no heat is exchanged. As dry air rises, it expands and cools due to decreasing pressure.
Step 2: Standard value of DALR.
The Dry Adiabatic Lapse Rate is approximately: \[ 9.8^\circ \text{C per km} \]
Step 3: Eliminating incorrect options.

• \(6.5^\circ \text{C/km}\) is the Environmental Lapse Rate (average).
• \(12^\circ \text{C/km}\) and \(4^\circ \text{C/km}\) are not standard values.

Conclusion:
Thus, the correct value is \( \boxed{9.8^\circ \text{C/km}} \).