Thermospheric global average density trends, 1967–2007, derived from orbits of 5000 near-Earth objects

• Published in: Geophysical research letters Vol. 35; no. 5; pp. L05101 - n/a
• Main Authors: Emmert, J. T., Picone, J. M., Meier, R. R.
• Format: Journal Article
• Language: English
• Published: Washington, DC American Geophysical Union 01.03.2008; Blackwell Publishing Ltd
• Subjects: Atmosphere; Atmospheric Composition and Structure; composition and chemistry; Earth sciences; Earth, ocean, space; Exact sciences and technology; Global Change; greenhouse cooling; Pressure, density, and temperature; Space Plasma Physics; Spacecraft/atmosphere interactions; Thermosphere; thermosphere density; global change; thermosphere density; greenhouse cooling; models; Thermosphere; trend-surface analysis; Minimum solar activity; density; Orbit; Bias; solar radiation; concentration; global; Long term; Earth; prediction; solar cycles; Geomagnetic activity
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2007GL032809

We use orbit data on ∼5000 near‐Earth space objects to investigate long‐term trends in thermospheric total mass density, which has been predicted to decrease with time due to increasing CO2 concentrations. We refine and extend to 2007 previous density trend estimates, and investigate solar cycle‐dependent bias in empirical density models previously used to filter out solar irradiance effects. We find that the bias is caused in part by the solar cycle dependence of the long‐term trends, and we develop a new representation of solar cycle, seasonal, and geomagnetic activity effects. At 400 km, we estimate an overall trend of –2.68 ± 0.49 % per decade and trends of ∼–5 and –2 % per decade at solar minimum and maximum, respectively, in fair quantitative agreement with theoretical predictions. The global average density trends also depend on the phase of the year, with the strongest trends around October and weak trends in January.