Dual site observations of dayside Doppler-shifted hydrogen profiles: preliminary results

Simultaneous optical ground-based observations of auroral Balmer excited hydrogen atoms were performed during the boreal winters of 2002–2003 and 2003–2004 at Ny-Alesund, Svalbard (NYA 76.26°N 110.98°E geomagnetic) and Longyearbyen, Svalbard (LYR 75.31°N 111.88°E geomagnetic). Balmer α (Hα) with a natural wavelength of 6563A was detected at Ny-Alesund, while Balmer β (Hβ) at 4861A was measured at Longyearbyen. The emissions are well known to originate from precipitating protons whose charge exchanges with the neutral atmosphere lead to a diffuse, Doppler-shifted emission region. Measurements are made using Ebert–Fastie spectrometers that are located 118 km apart on a line of roughly constant geomagnetic longitude, thus making this configuration suitable for studying the variation of proton energy with geomagnetic latitude, the so-called “velocity filter” effect. For two different days, analysis of the spectrometer data sets was performed, yielding in both cases positive energy differences between LYR and ...