Anomalously low solar extreme-ultraviolet irradiance and thermospheric density during solar minimum

• Published in: Geophysical research letters Vol. 37; no. 16
• Main Authors: Solomon, Stanley C., Woods, Thomas N., Didkovsky, Leonid V., Emmert, John T., Qian, Liying
• Format: Journal Article
• Language: English
• Published: Washington, DC Blackwell Publishing Ltd 01-08-2010; American Geophysical Union; John Wiley & Sons, Inc
• Subjects: Astronomy; Astrophysics; Atmospheric sciences; Carbon dioxide; Climate change; density; Earth; Earth sciences; Earth, ocean, space; EUV; Exact sciences and technology; Greenhouse gases; Ionosphere; Physics; solar; Solar activity; Spacecraft; Sun; thermosphere; Upper atmosphere; carbon dioxide; Electrodynamics; Minimum solar activity; density; General circulation models; satellite orbit; digital simulation; climate; ionosphere; greenhouse gas; instruments; Drag; extreme value; solar activity; irradiance; Upper atmosphere; age
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2010GL044468

Solar activity during 2007–2009 was very low, and during this protracted solar minimum period, the terrestrial thermosphere was cooler and lower in density than expected. Measurements from instruments on the SOHO and TIMED spacecraft, and by suborbital rocket flights, indicate that solar extreme‐ultraviolet irradiance levels were lower than they were during the previous solar minimum. Analysis of atmospheric drag on satellite orbits indicate that the thermosphere was lower in density, and therefore cooler, and than at any time since the beginning of the space age. However, secular change due to increasing levels of carbon dioxide and other greenhouse gases, which cool the upper atmosphere, also plays a role in thermospheric climate. Simulations by the NCAR Thermosphere‐Ionosphere‐Electrodynamics General Circulation Model are compared to thermospheric density measurements, yielding evidence that the primary cause of the low thermospheric density was the unusually low level of solar extreme‐ultraviolet irradiance.