Auroras during extreme geomagnetic storms: Some features of mid-latitude aurora on February 11, 1958

This paper discusses peculiarities of the great mid-latitude aurora that occurred during the extreme magnetic storm on February 11, 1958. This mid-latitude aurora had unusual optical and spectral characteristics, among which, first of all, were very high (10⁵–10⁸ R) intensities of atomic oxygen [OI] 630.0 nm emission and an unusually high ratio of the intensities of two forbidden lines of oxygen [OI] 630.0 nm and 557.7 nm (I₆₃₀/I₅₅₇.₇). In some points, this ratio was as high as 10³–10⁴. Analysis of I₆₃₀ dynamics during other extreme geomagnetic storms and associated geophysical conditions and physical processes in Earth’s ionosphere and magnetosphere allows us to assume that great mid-latitude auroras are formed during intense substorms in main phases of magnetic storms. In order to interpret the observed features of the February 11, 1958 mid-latitude aurora, we propose to examine the mechanism of level [OI] ¹D selective filling in which reactions of resonance recharge of oxygen ions O⁺(²D)+O (³P)→O⁺(⁴S)+O(³P, ¹D) and/or reactions of oxygen atom and molecule collisions with excited components of odd nitrogen can be implemented.