Bibliography

Radiative transfer modeling of the OI 135.6~nm emission in the nighttime ionosphere

Remote sensing of the nighttime OI 135.6\ nm emissions has been a widely used method for measuring the\ F\ region ionospheric plasma densities. In this work, we first develop a comprehensive radiative transfer model from first principles to investigate the effects of different physical processes on the production and transport of the 135.6\ nm photons in the ionosphere and then propose a new approach for estimating electron densities from the nightglow. The forward modeling investigation indicates that under certain conditions mutual neutralization can contribute up to \~38\% of the total production of the nighttime 135.6\ nm emissions. Moreover, depending on the ionospheric conditions, resonant scattering by atomic oxygen and pure absorption by oxygen molecules can reduce the limb brightness observed by satellite-borne instruments by up to \~40\% while enhancing the brightness viewing in the nadir direction by typically \~25\%. Further analysis shows that without properly addressing these effects in the inversion process, the peak electron density in the\ F\ region (NmF2) obtained using limb observations can be overestimated by up to \~24\%. For accurate estimation of the ionospheric electron density, we develop a new type of inverse model that accounts for the effects of mutual neutralization, resonant scattering, and pure absorption. This inversion method requires the knowledge of O and O₂\ densities in order to solve the radiative transfer equations. Application of the inverse model to the nighttime ionosphere in the noiseless cases demonstrates that the electron density can be accurately quantified with only \~1\% error in NmF2 and hmF2.

Qin, Jianqi; Makela, Jonathan; Kamalabadi, Farzad; Meier, R.;

Published by: Journal of Geophysical Research: Space Physics      Published on: 11/2015

YEAR: 2015     DOI: 10.1002/jgra.v120.1110.1002/2015JA021687

OI 135.6-nm Emission; onosphere; Radiative transfer; remote sensing

Remote sensing of Earth's limb by TIMED/GUVI: Retrieval of thermospheric composition and temperature

The Global Ultraviolet Imager (GUVI) onboard the Thermosphere-Ionosphere-Mesosphere Energetics and Dynamics (TIMED) satellite senses far ultraviolet emissions from O and N₂ in the thermosphere. Transformation of far ultraviolet radiances measured on the Earth limb into O, N₂, and O₂ number densities and temperature quantifies these responses and demonstrates the value of simultaneous altitude and geographic information. Composition and temperature variations are available from 2002 to 2007. This paper documents the extraction of these data products from the limb emission rates. We present the characteristics of the GUVI limb observations, retrievals of thermospheric neutral composition and temperature from the forward model, and the dramatic changes of the thermosphere with the solar cycle and geomagnetic activity. We examine the solar extreme ultraviolet (EUV) irradiance magnitude and trends through comparison with simultaneous Solar Extreme EUV (SEE) measurements on TIMED and find the EUV irradiance inferred from GUVI averaged (2002\textendash2007) 30\% lower magnitude than SEE version 11 and varied less with solar activity. The smaller GUVI variability is not consistent with the view that lower solar EUV radiation during the past solar minimum is the cause of historically low thermospheric mass densities. Thermospheric O and N₂ densities are lower than the NRLMSISE-00 model, but O₂ is consistent. We list some lessons learned from the GUVI program along with several unresolved issues.

Meier, R.; Picone, J.; Drob, D.; Bishop, J.; Emmert, J.; Lean, J.; Stephan, A.; Strickland, D.; Christensen, A.; Paxton, L.; Morrison, D.; Kil, H.; Wolven, B.; Woods, Thomas; Crowley, G.; Gibson, S.;

Published by: Earth and Space Science      Published on: 01/2015

YEAR: 2015     DOI: 10.1002/2014EA000035

airglow and aurora; remote sensing; thermosphere: composition and chemistry; thermosphere: energy deposition

Remote sensing of neutral temperatures in the Earth\textquoterights thermosphere using the Lyman-Birge-Hopfield bands of N ₂ : Comparisons with satellite drag data

This paper presents remotely sensed neutral temperatures obtained from ultraviolet observations and compares them with temperatures from the NRLMSISE-00 version of the Mass Spectrometer and Incoherent Scatter (MSIS) model (unconstrained and constrained to match the total densities from satellite drag). Latitudinal profiles of the temperatures in the Earth\textquoterights thermosphere are obtained by inversion of high-resolution (\~1.3\ \r A) observations of the (1,1) and (5,4) Lyman-Birge-Hopfield (LBH) bands of N₂. The spectra are from the High resolution Ionospheric and Thermospheric Spectrograph (HITS) instrument aboard the Advanced Research and Global Observation Satellite (ARGOS). The results indicate that on each day examined there was consistency between the remotely sensed thermospheric temperatures, the densities from coincident satellite drag measurements at adjacent altitudes, and the NRLMSISE-00 model.

Krywonos, Andrey; Murray, D.; Eastes, R.; Aksnes, A.; Budzien, S.; Daniell, R.;

Published by: Journal of Geophysical Research      Published on: 09/2012

YEAR: 2012     DOI: 10.1029/2011JA017226

airglow; N2; remote sensing; satellite drag; temperature; thermosphere

First look at the 20 November 2003 superstorm with TIMED/GUVI: Comparisons with a thermospheric global circulation model

The NASA TIMED/GUVI experiment obtained unprecedented far ultraviolet images of thermospheric composition and temperature during the intense geomagnetic storm on 20\textendash21 November 2003. Geographic maps of the atomic oxygen to molecular nitrogen column density ratio show severe depletions that extend to the equator near the peak of the storm. This ratio is a key indicator of how the thermospheric composition is disrupted at high latitudes and how the perturbed air moves globally as a result of dynamical forcing. For example, migrating regions of low oxygen-to-nitrogen air are invariably found to correlate with high thermospheric temperatures. As well, GUVI obtained altitudinal-latitudinal (limb) images of temperature and composition, which show how the disturbances vary at different heights. The ASPEN thermospheric global circulation model was used to test our understanding of these remarkable images. The resulting simulations of thermospheric response show good agreement with GUVI data prior to the peak of the storm on 20 November. During the peak and recovery phases, serious discrepancies between data and model are seen. Although this initial attempt to model the storm is encouraging, much more detailed analysis is required, especially of the high-latitude inputs. The GUVI images demonstrate that far ultraviolet imaging is becoming a crucial component of space weather research and development.

Meier, R.; Crowley, G.; Strickland, D.; Christensen, A.; Paxton, L.; Morrison, D.; Hackert, C.;

Published by: Journal of Geophysical Research      Published on: 09/2005

YEAR: 2005     DOI: 10.1029/2004JA010990

dayglow; geomagnetic storm; GUVI; remote sensing; thermospheric composition; TIMED

Quiet-time seasonal behavior of the thermosphere seen in the far ultraviolet dayglow

The TIMED/GUVI instrument is a far ultraviolet spectrograph that obtains images in five spectrally resolved wavelength channels. These images yield information on the dayside composition, temperature, solar EUV flux, large-scale wave structures, and auroral processes. In this paper we present an overview analysis of Earth-disk images for four seasons (March, July, and September 2002 and January 2003). Days were selected during geomagnetically quiet periods when the Sun was nearly in the orbital plane (noon orbits). Two of GUVI\textquoterights five channels (designated as 135.6 and LBH_S and dominated by OI 135.6 nm and short wavelength N₂ LBH band emission, respectively) are used when the instrument is in its imaging mode. These data are used to derive O/N₂ (column density ratio referenced to an N₂ column density of 10¹⁷ cm^-2). The AURIC model is used to generate a lookup table that relates O/N₂ to the ratio of 135.6 to LBH_S for a given solar zenith angle. Global images of derived O/N₂ (designated as GUVI O/N₂) are presented for the 4 days. The initial validation of the retrieved composition ratio comes from comparison with the NRLMSIS model. Good overall qualitative agreement is obtained between GUVI and NRLMSIS. Both data and model exhibit similar latitudinal behaviors on the near-solstice days, namely a distinct gradient with O/N₂ decreasing from the winter to the summer hemisphere. Reductions in O/N₂ in the vicinity of magnetic poles are seen in both GUVI and NRLMSIS images. Globally, O/N₂ is smaller at the solstices and may be explained by the \textquotedblleftthermospheric spoon\textquotedblright mechanism discussed by Fuller-Rowell [1998]. Alternatively, the greater overall values at the equinoxes may arise in part from global response to greater Joule heating at these times of the year. The sensitivity of O/N₂ to scalings of the N₂ LBH cross section and solar EUV below 20 nm is also addressed in response to recent papers on these topics. This initial look at the GUVI data demonstrates great promise of FUV remote sensing as a way to observe thermospheric composition changes over broad geographic scales.

Strickland, D.; Meier, R.; Walterscheid, R.; Christensen, A.; Paxton, L.; Morrison, D.; Craven, J.; Crowley, G.;

Published by: Journal of Geophysical Research      Published on: 01/2004

YEAR: 2004     DOI: 10.1029/2003JA010220

far ultraviolet; remote sensing; seasonal behavior; thermosphere