The COSPAR International Reference Atmosphere (abbreviated CIRA) is a series of empirical and semi-empirical reference models of the Earth's atmosphere, developed under the auspices of the Committee on Space Research (COSPAR), an international scientific body. The models provide standardized specifications of atmospheric parameters—principally temperature, pressure, total and constituent density, geopotential height, and neutral winds—and are used as international standards for atmospheric and aerospace applications.
Purpose and rationale
CIRA was established because early orbit determination and flight planning for the first artificial satellites proved more difficult than anticipated, owing to limited knowledge of the upper atmosphere. To address this, COSPAR initiated a long-term project to produce accepted reference models of the most important upper-atmosphere parameters. The resulting models have been important for spaceflight planning and for satellite drag calculation and related operational applications.
Content and scope
A reference atmosphere of this kind consists of sets of tables and associated formulations giving average (climatological) values of atmospheric properties. Typical quantities included are mean air pressure, temperature, altitude, geopotential height, and zonal (east–west) wind speed. Depending on the version, the models span the middle atmosphere and the upper atmosphere, covering altitudes from the ground up to the thermosphere.
The CIRA models are prepared by an international working group jointly sponsored by COSPAR and URSI (Union of Radio Science). Within COSPAR's organizational structure the relevant body is the COSPAR/URSI Task Group on Reference Atmospheres, which also liaises with the International Organization for Standardization (ISO) as Working Group 4 (ISO WG4). The task group aims to develop and improve atmosphere models compatible with operational use, notably for satellite drag calculations, and it periodically reviews newer data.
History and versions
CIRA first appeared in 1961 as "CIRA-1961," a set of tables that was reconsidered and updated on a recurring basis by the Task Group on the CIRA, originally chaired by Hildegard Kallmann-Bijl. It was subsequently supplemented by work published in 1965 and 1972.
CIRA-1986 (commonly "CIRA-86"), the fourth in the series, was published in parts. Part I addressed thermosphere models; Part II presented middle-atmosphere models (approximately 20–100 km); and Part III addressed trace constituent reference models. In the thermosphere (above roughly 100 km), CIRA-86 is consistent with the NASA MSIS-86 model, while the lower portion (0–120 km) consists of tabulations of monthly mean temperature and zonal wind, generally extending over latitudes from about 80° N to 80° S. These tables were derived from combinations of satellite, radiosonde, and ground-based measurements and model data, with the lower portion merged with MSIS-86 at 120 km altitude.
Later editions include CIRA-2012, described as the fifth in the series, which presents updated semi-empirical models developed in part from space-based instrument data collected from the 1980s through the 2000s. A subsequent version, sometimes designated CIRA-2014, has also been reported. Intermediate planning documents, such as the draft outline for a "CIRA-08," indicate that proposed editions may be revised or superseded before publication. The task group meets at intervals, typically in connection with COSPAR assemblies, to take account of more recent data.
Use and limitations
CIRA models serve as reference standards in atmospheric science and aerospace engineering. Specific implementations exist in engineering software; for example, the CIRA-86 model has been implemented in the MATLAB Aerospace Blockset, where it supplies mean temperature, pressure, and zonal wind speed for a given geopotential altitude. Such implementations inherit the limitations of the underlying model, including restricted latitude coverage (approximately 80° S to 80° N) and altitude ranges, and missing data points at certain levels and latitudes.
See also
- Committee on Space Research (COSPAR)
- International Reference Ionosphere (IRI)
- MSIS (Mass Spectrometer Incoherent Scatter) atmospheric models
References
- "COSPAR International Reference Atmosphere," Wikipedia.
- COSPAR/URSI Task Group on Reference Atmospheres, Scientific Commission C, Committee on Space Research.
- D. Rees (ed.), "COSPAR International Reference Atmosphere: 1986, Part I: Thermosphere," Advances in Space Research, Vol. 8, Nos. 5–6, Pergamon Press, 1988.
- D. Rees, J. J. Barnett, and K. Labitzke, "COSPAR International Reference Atmosphere: 1986, Part II: Middle Atmosphere Models," Advances in Space Research, Vol. 10, No. 12, Pergamon Press, 1990.
- G. M. Keating, "COSPAR International Reference Atmosphere: 1986, Part III: Trace Constituent Reference Models," Advances in Space Research, Vol. 10, Nos. 9–10, Pergamon Press, 1990.
- E. L. Fleming, S. Chandra, M. R. Schoeberl, and J. J. Barnett, "Monthly Mean Global Climatology of Temperature, Wind, Geopotential Height and Pressure for 0–120 km," NASA TM-100697, February 1988.
- NERC/CEDA Data Catalogue, "COSPAR International Reference Atmosphere (CIRA-86)"; NCAS British Atmospheric Data Centre.
