O+ 4P-4D0 Lines in Aurora over Svalbard

Spectrographic Imaging Facility (SIF) at the auroral station near Longyearbyen, in Svalbard, Norway, measures auroral spectra in three wavelength intervals (H_β , N_2⁺ 1N(0,2) and N_2⁺ 1N(1,3)), and images the aurora in the field aligned direction. Oxygen ion ⁴P-⁴D⁰ multiplet (4639-4696~Å) is blended with the N_2⁺ 1N(1,3) band. SIF observations of the intensity of this multiplet, and its relation to the other emissions are presented. The spectral data are used together with the images, and the incoherent scatter radar, to study the multiplet in context of different types of aurora. Typically, the intensity of the multiplet is about 0.1 of the N_2⁺ 1N(0,2) band. This ratio is enhanced when the ionisation in the upper E-layer (140-190~km) is significant with respect to the E-layer peak below 130~km. Rayed arcs were observed on one such occasion, whereas on other occasions the intensity was below the threshold of the imager. The occurrence of the multiplet lines in proton aurora is discussed as well.