What is the approximate ELR assumed by ISA?

The International Standard Atmosphere (ISA) assumes an average Environmental Lapse Rate (ELR) of approximately 2°C per 1000 feet. This lapse rate reflects how the temperature of the atmosphere typically decreases with altitude in the troposphere, which is the lowest layer of the Earth's atmosphere where weather events occur.

The 2°C per 1000 feet is a general guideline used in aviation and meteorology to model how temperature changes with elevation under standard atmospheric conditions. Knowing the ELR is essential for pilots and meteorologists to make accurate calculations for flight performance and weather predictions.

Understanding this lapse rate helps in comprehending how temperature variations affect air pressure, humidity, and ultimately, flight dynamics. Therefore, the assumption of 2°C per 1000 feet is foundational in various applications concerning atmospheric science and aviation operations.