MEASUREMENT OF GEOCORONAL BALMER-ALPHA IN THE AURORAL-ZONE

A Fabry-Perot spectrometer is used at Sondre Stromfjord Greenland, dur ing periods of quiet auroral conditions to isolate the resonant fluore scent component of the geocoronal atomic hydrogen Balmer alpha emissio n. The data demonstrate that we can detect a weak, 8-rayleigh emission with signal-to-noise ratio of 6 using 25-min of integration. Moreover , these observations have sufficient spectral resolution to determine effective exospheric temperatures with statistical uncertainties of ab out 35%. Energetic neutral hydrogen, due presumably to neutralized pro ton precipitation, appears in the line profile background, and as such , is distinct from the quiescent, less energetic, geocoronal component excited by resonant fluorescence of solar Lyman beta photons.