Here, we show that: (1) Sawtooth injections can be produced by the copious production of auroral streamers, without a substorm onset (2) Auroral streamers typically evolve into torches and omega bands rather than leading to onsets (3) Equatorward- moving "inclined arcs" can feed into the onset region. Due to the large separation between the poleward boundary and the onset region during these types of substorms, the interaction between the onset region and poleward boundary intensifications, auroral streamers, inclined arcs, torches and omega bands are more easily determined. This behavior is highly consistent with the Akasofu picture of substorm onset occurring deep within the closed field-line region on the equator-most arc. A new expanded double oval configuration emerges from this expansion phase activity and the cycle repeats itself for the duration of the sawtooth event. This is followed by a localized substorm-like brightening of the auroral distribution in the dusk to midnight sector on the lower branch of the double oval which subsequently expands rapidly poleward and azimuthally. In association with each tooth, the double oval evolves in a repeatable manner in which a wide double-oval configuration gradually thins down in association with an expansion of the polar cap and stretching of the tail field lines.
Substorms, poleward boundary activations and geosynchronous particle injections during sawtooth eventsĭuring sawtooth events, the auroral distribution is typically comprised of an active and dynamic double oval configuration. This statistical study will provide the following results: number of poleward-moving auroral forms that are generated during dayside auroral oval expansions/contractions and during periods of a stable and expanded dayside auroral oval, the average initial and final elevation angle of the dayside auroral oval, time This study examines the dayside auroral oval during periods of expansion, contraction, and during periods of an expanded and stable dayside auroral oval. Poleward-moving auroral forms have also been observed during some dayside oval contractions but have not been discussed much in the literature.
Dayside poleward-moving auroral forms are also observed during periods of an expanded and stable dayside auroral oval for both northern and southern hemisphere observations. and Horwitz and Akasofu attributed these PMAFs to magnetic flux being eroded away from the dayside magnetopause and transported antisunward. The field line merging process is thought to be most efficient when the interplanetary magnetic field (IMF) Bz-component turns southward. During the southward turning of the IMF Bz-component the merging rate on the dayside increases leading to the erosion of the dayside magnetopause. Horwitz and Akasofu noted a one-to-one correspondence of luminous PMAFs associated with an equatorward expansion of the dayside auroral oval. Past studies have shown that poleward-moving auroral forms (PMAFs) are a common feature during equatorward expansions of the dayside auroral oval. The equatorward/ poleward edge of the dayside auroral oval shifts equatorward/ poleward when the IMF Bz-component is negative/positive. The latitude of the equatorial edge of the dayside auroral oval has been shown to vary with the direction of the IMF Bz-component. Generation of poleward moving auroral forms (PMAFs) during periods of dayside auroral oval expansions/contractions and periods when the dayside auroral oval is expanded and stableįasel, G.
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