Abstract. Ring effect refers to the 'filling-in' of the Fraunhofer absorption lines in the day sky spectrum as compared to the solar spectrum. Rotational Raman scattering is believed to be the main cause for this excess in the sky spectrum. Earlier measurements showed contradictory behavior of this effect with solar zenith angle and wavelength. It is important to take proper account of this effect as it otherwise results in overestimating the dayglow emission intensities and underestimating the number densities of atmospheric trace gases. The present study details the results obtained from a simultaneous 11-wavelength investigation carried out using a newly built daytime spectrograph. This data demonstrates that the absorption line strength (normalized depth x half width) has a major control on the Ring effect contribution irrespective of the solar zenith angle and the wavelength.
Abstract. Measurements in the visible wavelength range at high spectral resolution (1.3Å) have been made at Longyearbyen, Svalbard (15.8 E,78.2 N) during an interval of intense proton precipitation. The shape and Doppler shift of hydrogen Balmer beta line profiles have been compared with model line profiles, using as input ion energy spectra from almost coincident passes of the FAST and DMSP spacecraft. The comparison shows that the simulation contains the important physical processes that produce the profiles, and confirms that measured changes in the shape and peak wavelength of the hydrogen profiles are the result of changing energy input. This combination of high resolution measurements with modeling provides a method of estimating the incoming energy and changes in flux of precipitating protons over Svalbard, for given energy and pitch-angle distributions. Whereas for electron precipitation, information on the incident particles is derived from brightness and brightness ratios which require at least two spectral windows, for proton precipitation the Doppler profile of resulting hydrogen emission is directly related to the energy and energy flux of the incident energetic protons and can be used to gather information about the source region. As well as the expected Doppler shift to shorter wavelengths, the measured profiles have a significant red-shifted component, the result of upward flowing emitting hydrogen atoms.
Abstract. We present the ground-based oxygen 630.0 nm daytime optical measurements of a discrete auroral arc from $ondre Stromfjord, Greenland. The optical measurements were made using an imaging echelle spectrograph built at Boston University. We show that the auroral optical signature extracted from the blue-sky background agrees closely in both space and time with the aurorMly enhanced electron densities at 200 km altitude obtained simultaneously by the incoherent scatter radar. The dayglow measurements are also in good agreement with the integrated emission rates modeled using the measured N,, T,, and Ti profiles from the radar. The results reported in this paper demonstrate the potential of this spectrograph to observe aurora during daytime, and it promises to be a valuable complement to the existing tools for the investigation of upper atmospheric phenomena.
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