Spectral modelling of molecular nitrogen in Aurora

Abstract

A custom made five panel filter mosaic window was designed, installed and operated with the HiTIES (High Throughput Imaging Echelle Spectrograph) at the Nordlysstasjonen in Svalbard, Norway (78.2025N and 15.829E). The filter provides images of the resonant scattered spectra of N+2 1N (0,1), (1,2), (2,3) bands and a neutral N2 2P (0,3) band. Ab initio models were created for describing the populations of vibrational and rotational energy levels in both excited and ionised N2 molecules in the ionosphere. In the rotational profiles the species are treated to be in thermal equilibrium, whereas the vibrational levels assume a non-thermal steady state time independent model.

Rotational temperatures were evaluated for different auroral forms for the N+ 2 (0,2) band from the magnetic zenith and along the meridian slit in HiTIES data from winter. A clear trend in neutral temperature is found, with higher values for times of lower energy precipitation. The relationship between resonant scattering of solar photons via N+2 and direct emission from electron impact on N2 was evaluated qualitatively and quantitatively with HiTIES data from January-March 2007. A relationship was found that clearly indicates the emission profiles are a function of primary electron energy
and solar shadow height when auroral arcs are partially sunlit during events of electron precipitation.

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