Multispacecraft and ground observations of magnetospheric and ionospheric responses to continuous energy input from the solar wind

On June 28, 1997, Wind spacecraft measurement indicated a long period of mo stly southward interplanetary magnetic field (IMF) B-z while other paramete rs remained overall quasi-steady. This continuous energy input to the magne tosphere over nearly 6 hours has led to large auroral activities in the ion osphere as well as the magnetospheric disturbances. Polar UVI measurement s howed the active auroral substorm brightening over wide area covering a dee p-duskside to local midnight, but the auroral regions with peak intensity w ere clearly separated into three events in longitude. They appear to have i nitiated separately and have developed rather independently at the early st age from the onset. These independent occurrences on three events are furth er evidenced by interpreting the corresponding (three) westward electrojets in the ionosphere along with the Geotail spacecraft observations at near-t ail which show the magnetic field dipolarization, its corresponding current reduction in the central current sheet, and the signature of the field-ali gned current. At later stages of time evolution, on the other hand, auroral brightenings at two events tend to merge and more interestingly spread eas tward. This eastward spreading is likely due to eastward drift of precipita ting auroral electrons under the enhanced convection. Also, the geosynchron ous energetic particle injections though with weak magnitude reveal an oppo site pattern to normal energy-dispersion of the typical substorm, another s ignature of enhanced convection. In conclusion, (1) what was observed here is a spatially multiple occurrence of not fully expanded substorms under th e continuous forcing by the prolonged southward IMF, and (2) this is in str ong superposition with the enhanced convection under the same IMF condition .