Resonance scattering by auroral N<sub>2</sub><sup>+</sup>: steady state theory and observations from Svalbard

Abstract

Abstract. Studies of auroral energy input at high latitudes often depend on observations of emissions from the first negative band of ionised nitrogen. However, these emissions are affected by solar resonance scattering, which makes photometric and spectrographic measurements difficult to interpret. This work is a statistical study from Longyearbyen, Svalbard, Norway, during the solar minimum between January and March 2007, providing a good coverage in shadow height position and precipitation conditions. The High Throughput Imaging Echelle Spectrograph (HiTIES) measured three bands of N It is shown that in sunlit aurora, the brightness of the (0,1) band is enhanced, with the scattered contribution increasing with decreasing energy of precipitation (10-fold enhancements for energies of 100 eV). The higher vibrational bands are enhanced even more significantly. In sunlit aurora the observed 1N (1,2)/(0,1) and (2,3)/(0,1) ratios increase as a function of decreasing precipitation energy, as predicted by theory. In non-sunlit aurora the N

Neutral temperature and atmospheric water vapour retrieval from spectral fitting of auroral and airglow emissions

“…Following the methods of Jokiaho et al (2008Jokiaho et al ( , 2009), synthetic N 2 1P line spectra are produced for vibrational levels 0 to 12 at different rotational temperatures. These spectra are convolved with a Gaussian instrument function of full width at half maximum (FWHM) equal to 0.12 nm to produce the synthetic N 2 1P spectra plotted in Fig.…”

“…It has also been possible to measure rotational temperatures from N + 2 ions observed during aurorae (e.g. Koehler et al, 1981;Jokiaho et al, 2008).…”

Neutral temperature and atmospheric water vapour retrieval from spectral fitting of auroral and airglow emissions

“…These emission doublets are shown in orange in the spectrum of Fig. 2 Following the methods of Jokiaho et al (2008Jokiaho et al ( , 2009, synthetic N 2 1P line spectra are produced for vibrational levels 0 to 12 at different rotational temperatures. These spectra are convolved with a Gaussian instrument function of Full Width at Half Maximum (FWHM) equal to 0.12 nm to produce the synthetic N 2 1P spectra plotted in Fig.…”

RELATIVE BRIGHTNESS OF THE O+(2D-2P) DOUBLETS IN LOW-ENERGY AURORAE

“…In order to be certain that the contribution from N 2 has been removed correctly from the remaining spectra, synthetic N 2 1P(5, 3) band emissions have been modeled as a function of rotational temperature, following the methods of Jokiaho et al (2008Jokiaho et al ( , 2009. These synthetic spectra are then used with a combination of nine Gaussian peaks, representing the four lines of the O + doublets and five OH lines (P 1 (2), P 2 (3), P 1 (3), P 2 (4), and P 1 (4)), and a straight line for the continuum background, all of which are fitted to the measured spectra between 730.7 nm and 738.7 nm.…”