It consists of a set of tables of average air pressures, altitudes and temperatures.
The CIRA models are developed by the Committee on Space Research (COSPAR) and have been important for the planning of spaceflight.
[1][2] Orbit determinations and flight planning of the very first satellites proved to be more complicated than expected due to a lack of knowledge on the upper atmosphere.
The Committee on Space Research therefore set up a long lasting special project to elaborate a reference model of the most important parameters of the upper atmosphere.
Presently "CIRA 1986" or CIRA-86 covers the height range up to 120 km as a set of tables.