%0 Journal Article
%T First ground-based optical analysis of H¦Â Doppler profiles close to local noon in the cusp
%A S. C. Robertson
%A B. S. Lanchester
%A M. Galand
%A D. Lummerzheim
%A A. B. Stockton-Chalk
%A A. D. Aylward
%A I. Furniss
%A J. Baumgardner
%J Annales Geophysicae (ANGEO)
%D 2006
%I Copernicus Publications
%X 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 ¦Â 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 H¦Â 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 H¦Â 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 H¦Â Doppler profiles from the cusp region close to local solar noon, when scattered sunlight swamps the raw data.
%U http://www.ann-geophys.net/24/2543/2006/angeo-24-2543-2006.html