Bibliography

The anomalous ionosphere between solar cycles 23 and 24

The solar minimum period during 2008\textendash2009 was characterized by lower thermospheric density than the previous solar minimum and lower than any previously measured. Recent work used the NCAR Thermosphere-Ionosphere-Electrodynamics General Circulation Model to show that the primary cause of density changes from 1996 to 2008 was a small reduction in solar extreme ultraviolet (EUV) irradiance, causing a decrease in thermospheric temperature and hence a contracted thermosphere. There are similar effects in the ionosphere, with most measurements showing an F region ionosphere that is unusually low in density, and in peak altitude. This paper addresses the question of whether model simulations previously conducted, and their solar, geomagnetic, and anthropogenic inputs, produce ionospheric changes commensurate with observations. We conducted a 15 year model run and obtained good agreement with observations of the global mean thermospheric density at 400 km throughout the solar cycle, with a reduction of ~30\% from the 1996 solar minimum to 2008\textendash2009. We then compared ionosonde measurements of the midday peak density of the ionospheric F region (N_mF₂) to the model simulations at various locations. Reasonable agreement was obtained between measurements and the model, supporting the validity of the neutral density comparisons. The global average N_mF₂ was estimated to have declined between the two solar minima by ~15\%. In these simulations, a 10\% reduction of solar EUV plays the largest role in causing the ionospheric change, with a minor contribution from lower geomagnetic activity and a very small additional effect from anthropogenic increase in CO₂.

Solomon, Stanley; Qian, Liying; Burns, Alan;

Published by: Journal of Geophysical Research: Space Physics      Published on: 10/2013

YEAR: 2013     DOI: 10.1002/jgra.v118.1010.1002/jgra.50561

climate; Ionosphere; irradiance; solar; thermosphere; ultraviolet

Initial observations with the Global Ultraviolet Imager (GUVI) in the NASA TIMED satellite mission

The Global Ultraviolet Imager (GUVI) instrument carried aboard the NASA TIMED satellite measures the spectral radiance of the Earth\textquoterights far ultraviolet airglow in the spectral region from 120 to 180 nm using a cross-track scanning spectrometer design. Continuous operation of the instrument provides images of the Earth\textquoterights disk and limb in five selectable spectral bands. Also, spectra at fixed scanning mirror position can be obtained. Initial results demonstrate the quantitative functionality of the instrument for studies of the Earth\textquoterights dayglow, aurora, and ionosphere. Moreover, through forward modeling, the abundance of the major constituents of the thermosphere, O, N₂, and O₂\ and thermospheric temperatures can be retrieved from observations of the limb radiance. Variations of the column O/N₂\ ratio can be deduced from sunlit disk observations. In regions of auroral precipitation not only can the aurora regions be geographically located and the auroral boundaries identified, but also the energy flux Q, the characteristic energy E_o, and a parameter f_o\ that scales the abundance of neutral atomic oxygen can be derived. Radiance due to radiative recombination in the ionospheric F region is evident from both dayside and nightside observations of the Earth\textquoterights limb and disk, respectively. Regions of depleted F-region electron density are evident in the tropical Appleton anomaly regions, associated with so-called ionospheric \textquotedblleftbubbles.\textquotedblright Access to the GUVI data is provided through the GUVI website\ www.timed.jhuapl.edu\guvi.

Christensen, AB; Paxton, LJ; Avery, S; Craven, J; Crowley, G; Humm, DC; Kil, H; Meier, RR; Meng, C-I; Morrison, D; , others;

Published by: Journal of Geophysical Research: Space Physics (1978\textendash2012)      Published on:

YEAR: 2003     DOI: 10.1029/2003JA009918

airglow; AURORA; ultraviolet; imaging; satellite; atmosphere