Auroral Morphological Changes to the Formation of Auroral Spiral during
the Late Substorm Recovery Phase: Polar UVI and Ground All-Sky Camera
Polar ultraviolet imager (UVI) and an all-sky camera at Longyearbyen
contemporaneously detected an auroral vortex structure (so-called
“auroral spiral”). Particularly, from space, the auroral spiral was
observed as a “small spot” in the poleward region of the main auroral
oval near midnight, which was formed while the substorm-associated
auroral bulge was subsiding and several poleward-elongated auroral
streak-like structures appeared during the late substorm recovery phase.
To pursue the spiral source region in the magnetotail, we trace each UVI
image along field lines to the magnetic equatorial plane of the
nightside magnetosphere using an empirical magnetic field model.
Interestingly, the magnetotail region corresponding to the auroral
spiral covered a broad region from Xgsm
~ -40 to -70 E at Ygsm
~ 8 to 12 RE. The appearance of this
auroral spiral may suggest that extensive areas of the magnetotail
remain active even during the late substorm recovery phase.