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Ann. Geophys., 24, 2543-2552, 2006
www.ann-geophys.net/24/2543/2006/
© European Geosciences Union 2006
First ground-based optical analysis of Hβ Doppler profiles close to local noon in the cusp
S. C. Robertson1,2, B. S. Lanchester1, M. Galand3, D. Lummerzheim4, A. B. Stockton-Chalk1, A. D. Aylward2, I. Furniss2, and J. Baumgardner5
1Space Environment Physics, University of Southampton, UK
2Atmospheric Physics Laboratory, University College London, UK
3Space and Atmospheric Physics Group, Imperial College London, UK
4Geophysical Institute, University of Alaska, USA
5Centre for Space Physics, Boston University, MA, USA
Abstract. Observations of hydrogen emissions along the magnetic zenith at
Longyearbyen (78.2 N, 15.8 E geographic) are used to investigate
the energy and source of protons precipitating into the high
latitude region. During the hours around local solar noon (11:00 UT),
measurements of the hydrogen Balmer β line are severely
affected by sunlight, such that most data until now have been
disregarded during these times. Here we use a simple technique to
subtract sunlight contamination from such spectral data. An
example is shown in which the removal of twilight contamination
reveals a brightening of Hβ aurora over Svalbard on 27
November 2000 between 08:00 UT and 10:00 UT, which is centred on
magnetic noon (08:48 UT). These data were measured by the High
Throughput Imaging Echelle Spectrograph (HiTIES), one instrument
on the Southampton-UCL Spectrographic Imaging Facility (SIF). Data
from the IMAGE satellite confirms the location of a cusp "spot"
over Svalbard at the time of the ground-based measurements, which
moved in response to changes in the IMF conditions. A coincident
pass of the DMSP F12 satellite provided input spectra for
modelling studies of the Hβ profiles, which confirm that
the method for removing the twilight contamination is robust. The
results described here are the first ground-based optical
measurements of Hβ Doppler profiles from the cusp region
close to local solar noon, when scattered sunlight swamps the raw
data.
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