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.
The use of SF6 releases to excite the airglow from atomic oxygen in the ionosphere is demonstrated by experiment and by theory. Enhanced 777.4‐nm emissions from O(5P) states were measured during the AFGL‐sponsored Ionospheric Modification Studies campaign at Wallops Island, Virginia. For this rocket campaign, 8×1025 molecules of SF6 were released at 350‐km altitude into the midnight ionosphere on November 9, 1983. The 777.4‐nm airglow increased by over 150 R. The temporal evolution of the airglow is simulated using an ion chemistry model involving six positive and negative ion species and 16 reactions. The model indicates that substantial enhancements in 844.6 nm and 135.6 nm will be triggered by SF6 injections into the ionosphere. The model also demonstrates that the intensity of the 777.4‐nm line is strongly dependent on the temperature of the neutral atmosphere.
[1] A new spectrograph instrument, called the Continuous High-resolution Instrument for Multiwavelength Echelle Spectroscopy (CHIMES), has been designed to make simultaneous and spatially overlapping ground-based measurements of the green line and red line airglow emissions (5577 Å and 6300 Å) continuously, 24 hours-a-day. The spectrograph uses a 50 mm long, 50 mm wide slit, and varies the exposure time at different times of day (daytime, twilight, and nighttime), from 2 s in daytime to 10 min at night. It utilizes an Echelle grating to achieve dispersion of 0.05 Å/pixel at 5577 Å. Daytime 6300 Å and 5577 Å airglow from this instrument are extracted by comparing the measured spectra to direct solar spectra and extracting small increases in flux in the Fraunhofer absorption lines at those wavelengths, after compensating for the Ring effect contribution. We present the first ground-based measurements of the daytime 5577 Å airglow, as well as example measurements of daytime, twilight, and nighttime airglow signatures.
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