About Atmospheric Models at SPDF
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).
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,
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.
Go to the Atmospheric Models index
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If you have questions/comments about the various models, contact:
Dr. Dieter K. Bilitza, email@example.com,
Mail Code 612.4, NASA/Goddard Space Flight Center, Greenbelt, MD 20771
NASA Official: Dr. Robert McGuire, Head of the Space Physics Data Facility