Global-scale Observations and Modeling of Far-Ultraviolet Airglow During Twilight. (arXiv:1912.02271v1 [physics.space-ph])
<a href="http://arxiv.org/find/physics/1/au:+Solomon1_S/0/1/0/all/0/1">Stanley C. Solomon1</a>, <a href="http://arxiv.org/find/physics/1/au:+Andersson_L/0/1/0/all/0/1">Laila Andersson</a>, <a href="http://arxiv.org/find/physics/1/au:+Burns_A/0/1/0/all/0/1">Alan G. Burns</a>, <a href="http://arxiv.org/find/physics/1/au:+Eastes_R/0/1/0/all/0/1">Richard W. Eastes</a>, <a href="http://arxiv.org/find/physics/1/au:+Martinis_C/0/1/0/all/0/1">Carlos Martinis</a>, <a href="http://arxiv.org/find/physics/1/au:+McClintock_W/0/1/0/all/0/1">William E. McClintock</a>, <a href="http://arxiv.org/find/physics/1/au:+Richmond_A/0/1/0/all/0/1">Arthur D. Richmond</a>
The NASA Global-scale Observations of the Limb and Disk (GOLD) ultraviolet
imaging spectrograph performs observations of upper-atmosphere airglow from the
sunlit disk and limb of the Earth, in order to infer quantities such as the
composition and temperature of the thermosphere. To interpret the measurements,
the observational and solar illumination geometry must be considered. We use
forward models of upper atmosphere density and composition, photoelectron
impact, airglow emissions, radiative transfer, and line-of-sight integration,
to describe the expected observations, and here test those calculations against
observations near the terminator, and near the limb. On the night side of the
terminator, broad regions of faint airglow are seen, particularly near the
winter solstice. These are caused by photoelectrons that were transported along
field lines from magnetically conjugate areas in the other hemisphere, where
those areas are still illuminated. We perform model calculations to demonstrate
that this process is the source of the emission, and obtain good agreement with
its morphology and intensity. In some regions, the observed emissions are not
as intense as the model simulations. Some of the reductions in electron flux
are explained by changes in magnetic field strength; in other cases,
particularly at high magnetic latitude, the cause is unknown, but must occur
along extended field lines as they reach into the plasma sheet.
The NASA Global-scale Observations of the Limb and Disk (GOLD) ultraviolet
imaging spectrograph performs observations of upper-atmosphere airglow from the
sunlit disk and limb of the Earth, in order to infer quantities such as the
composition and temperature of the thermosphere. To interpret the measurements,
the observational and solar illumination geometry must be considered. We use
forward models of upper atmosphere density and composition, photoelectron
impact, airglow emissions, radiative transfer, and line-of-sight integration,
to describe the expected observations, and here test those calculations against
observations near the terminator, and near the limb. On the night side of the
terminator, broad regions of faint airglow are seen, particularly near the
winter solstice. These are caused by photoelectrons that were transported along
field lines from magnetically conjugate areas in the other hemisphere, where
those areas are still illuminated. We perform model calculations to demonstrate
that this process is the source of the emission, and obtain good agreement with
its morphology and intensity. In some regions, the observed emissions are not
as intense as the model simulations. Some of the reductions in electron flux
are explained by changes in magnetic field strength; in other cases,
particularly at high magnetic latitude, the cause is unknown, but must occur
along extended field lines as they reach into the plasma sheet.
http://arxiv.org/icons/sfx.gif
