Revisiting the November 2004 Superstorm: Lessons from the TIMED/GUVI Limb Observation

We revisited the November 2004 superstorm by analyzing data from TIMED/GUVI, a FUV spectrograph imager. The GUVI 135.6 nm limb radiances at 520-km tangent altitude are mainly due to the O+ and electron radiative recombination and represent the daytime ionosphere density at the altitude. The 135.6 nm radiances clearly showed a signature of ionospheric equatorial arcs and their variations during the November 2004 magnetic superstorm. When an intense eastward Interplanetary Electric Field (IEF) occurred, the dayside equatorial arcs were enhanced and their latitude separation increased. The enhanced equatorial arcs were hemispherically symmetric or asymmetric in the region with non-depleted O/N2 or hemispherically asymmetric O/N2 depletion, respectively. When the O/N2 depletion reached the magnetic equator, there was no observable enhancement in the equatorial arcs regardless of the IEF conditions, indicating O/N2 conditions significantly modulated the variations in storm-time equatorial arcs.