In the standard atmosphere (ISA), what is the lapse rate in the troposphere?

• A. 1ºC per 1,000 ft
• B. 3ºC per 1,000 ft
• C. 2ºC per 1,000 ft
• D. 4ºC per 1,000 ft

Answer: (C)

The lapse rate in the troposphere of the standard atmosphere (ISA) is defined as the rate at which temperature decreases with an increase in altitude. In the standard atmosphere model, this rate is specifically set at approximately 2ºC for every 1,000 feet of elevation gained in the troposphere. This means that as you ascend, the air temperature drops consistently by this amount, which is crucial for understanding temperature behavior as altitude changes.

This temperature decrease occurs due to the decreasing air pressure and density as you move higher up in the atmosphere, affecting how heat is retained in the air. This value of 2ºC per 1,000 feet provides a foundational understanding for pilots and meteorologists when planning flights and interpreting weather patterns, ensuring they can anticipate the effects of altitude on atmospheric temperature.