5 research outputs found
Auroral Morphological Changes to the Formation of Auroral Spiral during the Late Substorm Recovery Phase: Polar UVI and Ground All-Sky Camera Observations
The ultraviolet imager (UVI) of the Polar spacecraft and an all-sky camera at
Longyearbyen contemporaneously detected an auroral vortex structure (so-called
"auroral spiral") on 10 January 1997. From space, the auroral spiral was
observed as a "small spot" (one of an azimuthally-aligned chain of similar
spots) in the poleward region of the main auroral oval from 18 h to 24 h
magnetic local time. These auroral spots were formed while the
substorm-associated auroral bulge was subsiding and several poleward-elongated
auroral streak-like structures appeared during the late substorm recovery
phase. During the spiral interval, the geomagnetically north-south and
east-west components of the geomagnetic field, which were observed at several
ground magnetic stations around Svalbard island, showed significant negative
and positive bays caused by the field-aligned currents related with the aurora
spiral appearance. The negative bays were reflected in the variations of local
geomagnetic activity index (SML) which was provided from the SuperMAG
magnetometer network at high latitudes. 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 RE at Ygsm ~ 8 to 12 RE.
The appearance of this auroral spiral suggests that extensive areas of the
magnetotail (but local regions in the ionosphere) remain active even when the
substorm almost ceases, and geomagnetic conditions are almost stable.Comment: 39 Pages, 6 Figures (8 pages), 1 Table, and Supporting Information
file (including 2 Figures (8 pages) and 1 Movie