Tomography-like retrieval of auroral volume emission ratios for the 31 January 2008 Hotel Payload 2 event

Abstract. Quantitative tomography-like volume estimates of the N₂⁺(1N) emission at 427.8 nm, the O(¹S) emission at 557.7 nm and the O(¹D) emission at 630.0 nm can be retrieved from data from the Auroral Large Imaging System (ALIS) remote-controlled spectral imagers operated at field stations in northern Sweden and Norway. This paper presents a case study of a quiet auroral arc passing over the common volume of the imagers in the evening of 31 January 2008, before the launch of the Hotel Payload 2 (HotPay 2) rocket from Andøya Rocket Range.

The reconstructed spectroscopic ratios at the lower altitudes close to the mesopause region can be used as indicators of the NO and O profiles, as the atomic oxygen O(¹S) and O(¹D) states are excited partly through chemical reactions. The profiles of the ratios of the volume emission rates ε_557.7 and ε_427.8 observed by ALIS over northern Norway show nothing unambiguously unusual within the accuracy of the calibration and retrieval, whereas HotPay 2 indicated subsidence of lower thermospheric air, with higher NO concentrations. This is consistent with observations of NO and CO by satellite instruments, which indicate subsidence in vortex filaments only in the NW as seen from the Scandinavian mainland.