References

ANGEO

Annales Geophysicae

ANGEO

Ann. Geophys.

1432-0576

Copernicus Publications

Göttingen, Germany

10.5194/angeo-24-2543-2006

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

Robertson

S. C.

¹ ² Lanchester

B. S.

¹ Galand

³ Lummerzheim

⁴ Stockton-Chalk

A. B.

¹ Aylward

A. D.

² Furniss

² Baumgardner

⁵

Space Environment Physics, University of Southampton, UK

Atmospheric Physics Laboratory, University College London, UK

Space and Atmospheric Physics Group, Imperial College London, UK

Geophysical Institute, University of Alaska, USA

Centre for Space Physics, Boston University, MA, USA

20 10 2006

24 10 2543 2552

2006

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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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