First ground-based optical analysis of Hβ Doppler profiles close to local noon in the cusp

• Published in: Annales Geophysicae
• Main Authors: Robertson, S. C., Lanchester, B. S., Galand, M., Lummerzheim, D., Stockton-Chalk, A. B., Aylward, A. D., Furniss, I., Baumgardner, J.
• Format: Text
• Language: English
• Published: 2018
• Subjects: Longyearbyen; Svalbard
• Online Access: https://doi.org/10.5194/angeo-24-2543-2006; https://angeo.copernicus.org/articles/24/2543/2006/

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 (11:00UT), 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 H β aurora over Svalbard on 27 November 2000 between 08:00UT and 10:00UT, which is centred on magnetic noon (08:48UT). 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 β 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 β Doppler profiles from the cusp region close to local solar noon, when scattered sunlight swamps the raw data.