Bibliography

Proton aurora observed from the ground

Auroral keV proton precipitation is a significant-energy particle input upon the high-latitude ionosphere, often dominating in the polar cusp and the dusk sector of the equatorward auroral oval. A unique signature of proton precipitation is the Doppler-shifted H Balmer lines (Hα, Hβ) observable from the ground. These lines are emitted by energetic H atoms produced within the proton beam through charge-exchange processes. Their observations allow one to assess the location, dynamic evolution especially during magnetospheric substorms, and spectral characteristics of the source regions of the energetic protons projected to the high-latitude ionosphere. They also allow to identify the associated magnetospheric processes and to evaluate ionospheric perturbations induced by the energetic protons. The source regions include the cusp, the low-latitude boundary layer, the mantle, and the plasma sheet, including its dayside extension. If qualitative studies of proton aurora morphology and time variability are possible with photometric observations of hydrogen lines, quantitative assessment of H-emission brightness, and incident proton mean energy and flux, requires spectroscopic measurements of the H-emission profile. In this review paper, we report on the tremendous progress made in the past 20 years in the observational capability applied to proton aurora and in the modeling of energetic proton transport in the upper atmosphere, which is needed for quantitative analysis of the spectroscopic measurements of H emission. The current issues in the field are also discussed and suggestions for future directions are proposed. They include the deployment of chains of instruments dedicated to proton aurora studies along magnetic local time and geomagnetic latitude, such as high-spectral-resolution-imaging spectrographs and spectral imagers. Such campaigns would improve our understanding of the topology and dynamics of the magnetosphere, and provide, at dayside, the azimuthal extent of the reconnection region. Magnetically conjugate experiments and optical instruments dedicated to proton aurora observations in Antarctica are greatly encouraged. The contribution of atmospheric scattering to the H-spectral profiles needs to be further assessed and additional laboratory measurements of differential cross sections are required for a comprehensive understanding of the physics of proton aurora.

Galand, Marina; Chakrabarti, Supriya;

Published by: Journal of Atmospheric and Solar-Terrestrial Physics      Published on:

YEAR: 2006     DOI: https://doi.org/10.1016/j.jastp.2005.04.013

Proton aurora; H. Balmer; Auroral spectroscopy

Contribution of proton precipitation to space-based auroral FUV observations

Imaging from space offers a unique way to access the global picture, and its temporal variability, of the particle energy input over the auroral ovals. Electron characteristics are inferred from the analysis of auroral images taken from space in two different spectral bands in UV or visible. Usually, only the electron component of the precipitation is considered, as most of the particle energy is carried by electrons. However, at some locations and certain times protons are a major energy source, that is, a major ionization and excitation source of the atmosphere. The response of POLAR/UVI, IMAGE/WIC and SI13, and TIMED/GUVI (used for retrieving the electron components) to proton precipitation is estimated. Secondary electrons produced within the proton beam also contribute to auroral emissions. Since they are less energetic than the secondary electrons produced in electron aurora, they have a different spectral signature. In addition, for a given energy flux, protons are usually more efficient at ionizing than electrons and yield larger values of the Pedersen ionospheric conductance. Therefore the difference between proton and electron aurora can lead to misinterpretation when brightness ratios are used to derive ionospheric conductances with parameterizations that are based on electron aurora. The validation and limitations of auroral analysis are discussed, especially at the equatorward edge of the afternoon oval, where protons are a significant energy source. In regions of \>4 keV electron precipitation, the presence of proton precipitation, even modest (\~10\%), yields a large underestimation of both the electron mean energy and the energy flux. Overall, the presence of proton precipitation yields a poor estimation of the electron mean energy. In proton-dominated aurora, the Pedersen and Hall conductances are always underestimated with a large discrepancy for POLAR/UVI. However, in location where the protons are not dominant and the electron precipitation is not too hard, it is legitimate to estimate the particle characteristics and ionospheric conductances from the FUV brightnesses assuming pure electron precipitation. This is true in particular for the period around midnight (1900\textendash0400 MLT), at a magnetic latitude of 65\textendash67\textdegree.

Galand, M.; Lummerzheim, D.;

Published by: Journal of Geophysical Research      Published on: 03/2004

YEAR: 2004     DOI: 10.1029/2003JA010321

auroral protons; FUV

SA52A-0395

Galand, Marina; Lummzheim, Dirk; Frey, HU; Paxton, LJ; Christensen, AB;

Published by:       Published on:

YEAR: 2003     DOI: