Astronomical sky spectra from the 29–31 October 2003 geomagnetic superstorms: Observations of O + ( 2 D o – 4 S o ) and other emissions

High‐resolution spectra of the night sky at near‐equatorial latitudes have been obtained with the Ultraviolet and Visual Echelle Spectrograph on the 8.2 m Kueyen telescope, European Southern Observatory, Cerro Paranal, Chile, during the 29–31 October 2003 geomagnetic superstorms. These spectra show indications of both thermospheric and ionospheric disturbance. Numerous emission features observed in these spectra have behaviors that correlate with the negative magnitude of the disturbance storm time index ( Dst ), a measure of the ring current influence on equatorial magnetic field strength. Specifically, the intensity of the optically forbidden and rarely observed O + ( 2 D o – 4 S o ) doublet lines at 372.6 and 372.9 nm increases with decreasing Dst and have profiles that often possess unusual morphology. Also observed on nights with strong geomagnetic activity is sustained emission after twilight from both the N 2 + first negative system 0‐0 band at 391.4 nm and the He(3 p 3 P o –2 s 3 S ) 388.9 nm line. The intensities of permitted neutral oxygen lines nominally arising from electron radiative recombination are suppressed during active periods relative to levels measured during quiescent periods. The pattern of emission in these spectra may reflect the manifestation of a variety of storm time phenomena, including negative ionospheric storms, energetic neutral auroras, and stable auroral red arcs, and indicates substantial energy deposition at high altitudes.