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The atmosphere can roughly be characterized as the region from sea level to about 1000 km altitude around the globe, where neutral gases can be detected. Below 50 km the atmosphere can be assumed to be homogeneously mixed and can be treated as a perfect gas. Above 80 km the hydrostatic equilibrium gradually breaks down as diffusion and vertical transport become important. The major species in the upper atmosphere are N2, O, O2, H, He. Temperature-oriented nomenclature differentiates the strata of the atmosphere as follows: the troposphere, from sea level up to about 10 km, where the temperature decreases; the stratosphere, from 10 km up to about 45 km, where the temperature increases; the mesosphere, from 45 km up to about 95 km, where the temperature decreases again; the thermosphere, from 95 km to about 400 km, where the temperature increases again; and the exosphere, above about 400 km, where the temperature is constant. The first global models of the upper atmosphere were developed by L. G. Jacchia in the early sixties based on theoretical considerations and satellite drag data. Since the launch of Sputnik 1 in 1957, orbit decay of artificial satellites has been used to derive atmospheric data.

Several national and international organizations have established committees for the development of atmospheric reference models, e.g., the International Civil Aviation Organization (ICAO), the Committee on Space Research (COSPAR), and the Committee on Extension to the Standard Atmosphere (COESA). Probably the most widely used and well established model is the COSPAR International Reference Atmosphere (CIRA), an effort that started in 1961 with the publication of CIRA-61. CIRA-72, the third generation of this model, CIRA-86, includes Jacchia's 1971 model.

With the launch of the OGO 6 satellite in 1969, in situ measurements of atmospheric parameters by mass spectrometer became available. At about the same time, ground-based incoherent scatter radars started to monitor the thermospheric temperature. A. E. Hedin and his co-workers combined data from these two data sources to establish the Mass Spectrometer Incoherent Scatter (MSIS) models: MSIS-77, -83, -86. The CIRA and MSIS groups joined forces in 1986 and MSIS-86 became the upper part of CIRA-86.

Description of storm effects remains one of the most challenging topics in thermospheric modeling. DE-2 wind measurements have shown characteristic high- latitude wind signatures caused by similar IMF (Interplanetary Magnetic Field)- dependent signatures in ionospheric convection.


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