The International Standard Atmosphere

A standard atmosphere can be regarded as an average pressure, temperature, and air density for various altitudes.

The International Standard Atmosphere (ISA) is a static atmospheric model of how the pressure, temperature, density, and viscosity of the Earth's atmosphere change over a wide range of altitudes.

Units of pressure

Atm is a unit of pressure defined as 101,325 Pa. It is sometimes used as a reference pressure or standard pressure.

Applications

The ISA is used as a reference for many purposes, including:

• Aircraft performance calculations
• Weather forecasting
• Climate modeling
• Balloon flights

The ISA is not a perfect representation of the actual atmosphere, but it provides a useful starting point for many calculations.