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 auroral vortex structure (so-called "auroral spiral") on 10 January 1997. From space, spiral was observed as a "small spot" (one azimuthally-aligned chain similar spots) in poleward region main oval from 18 h to 24 magnetic local time. These spots were formed while substorm-associated bulge subsiding several poleward-elongated streak-like structures appeared during late substorm recovery phase. During interval, geomagnetically north-south east-west components geomagnetic field, which ground stations around Svalbard island, showed significant negative positive bays caused by field-aligned currents related with aurora appearance. reflected variations activity index (SML) provided SuperMAG magnetometer network high latitudes. To pursue source magnetotail, we trace each UVI image along field lines equatorial plane nightside magnetosphere using empirical model. Interestingly, magnetotail corresponding covered broad Xgsm ~ -40 -70 RE Ygsm 8 12 RE. appearance this suggests that extensive areas (but regions ionosphere) remain active even when almost ceases, conditions are stable.