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Galand et al. 2004
Galand, M., Baumgardner, J., Pallamraju, D., Chakrabarti, S., Løvhaug, U.P., Lummerzheim, D., Lanchester, B.S. and Rees, M.H. (2004). Spectral imaging of proton aurora and twilight at Tromsø, Norway. Journal of Geophysical Research 109: doi: 10.1029/2003JA010033. issn: 0148-0227.

An imaging Echelle spectrograph designed for high-resolution studies of selected spectral features located in the visible spectrum was deployed from November 2001 until April 2003 in Troms¿, Norway. For moderately disturbed magnetic conditions, Troms¿ is located on the equatorial edge of the evening auroral oval for several hours. Energetic protons are frequently the dominant particle energy source in this region. For this experiment, four spectral windows were selected, each around different emission features: Hα (656.3 nm), H¿ (486.1 nm), N2+1NG 427.8 nm, and OI 777.4 nm. The 8¿ long slit of the spectrograph was centered on the magnetic zenith. This instrument provided simultaneous, high-resolution (~0.1 nm) spectra of Hα and H¿ emissions, which offers a unique opportunity to investigate the Hα to H¿ Balmer decrement in proton aurora. Information on the cloud cover and on the overall auroral activity was provided by a large field of view (70¿) conventional imaging spectrograph that spans the 350--800 nm spectral range. In this paper we describe both instruments and demonstrate their capabilities for the study of the H Balmer emissions in twilight and during auroral activity. Our high-resolution spectra taken in twilight could be used to observe the variability of the geocoronal component over time and to compare the derived variability with midlatitude sites. We conclude that the 0.1 nm spectral resolution is sufficient to identify and take into account contaminating OH and N2 1PG features in Hα emission profiles. Comparison of H¿ Doppler profiles observed at different locations (Troms¿, Poker Flat, Svalbard) in proton aurora is presented. Lummerzheim and Galand <2001> find that the shape of the violet wing of the Balmer profile is a more suitable indicator of the mean energy of the incident protons than the Doppler shift of the peak. Numerous uncertainties in measured and modeled Hα and H¿ line profiles preclude using the Balmer decrement as an indicator of the precipitating proton flux.

BACKGROUND DATA FILES

Abstract

Keywords
Ionosphere, Auroral ionosphere, Ionosphere, Particle precipitation, Ionosphere, Instruments and techniques, Ionosphere, Ionosphere/magnetosphere interactions, proton aurora, auroral spectroscopy, geocoronal emission, calibration technique, H Balmer lines, Balmer decrement
Journal
Journal of Geophysical Research
http://www.agu.org/journals/jb/
Publisher
American Geophysical Union
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