Abstract
Abstract. Ps 6 disturbances and associated omega bands are often considered to be part of the phenomenology of the recovery phase of substorms. We note cases of the initiation of Ps 6 activity at or very near the time of onset, either of a substorm expansive phase, a pseudobreakup, or a poleward border intensification. Thus, we claim that Ps 6 disturbances need not be viewed primarily as phenomena of the recovery phase. This produces both the challenge of explaining Ps 6 within a broader context and the opportunity to use Ps 6 observations to better understand magnetospheric phenomenology, including expansive phase onsets. We further examine the position of the causative currents for Ps 6 and find that they may be located at either the equatorward or poleward border of the auroral oval, or within it. In the first case, the relationship of expansive phase onset and time delay to Ps 6 initiation appears to be very short. In the latter case, there is an association with poleward border intensification, but with a measurable time delay. We present HF radar data to discuss how the electric field at onset time favors the growth of Ps 6 current systems.Key words. Magnetospheric physics (Storms and substorms; Electric fields; MHD waves and instabilities)
Highlights
Ps 6 disturbances and associated omega bands are often considered to be part of the phenomenology of the recovery phase of substorms
It is reasonable to infer that increased electric fields in the morning sector during periods of enhanced convection favors growth of the Kelvin-Helmholtz instability (KHI) and that this is associated with the Ps 6 current systems (Connors and Rostoker, 1993)
We have presented here evidence that Ps 6 initiation and onsets, both of substorm expansive phases and at the poleward border, may be linked in at least some cases
Summary
We have provided several examples in which Ps 6 initiation or change of character coincided temporally with expansive phase (EP) onset, as detected either nearby or to the west, in some cases many time zones westward In these latter cases, at least, any initiation front travelling at the speed suggested by Saito (1978) would have taken many minutes to arrive, yet we find the Ps 6 activation to coincide with onset. In the cases of strong Ps 6 signal near the centre of the oval, it is likely that the current systems extend to near the equatorward border, we have not shown this here This would be consistent with imaging observations (Connors and Rostoker, 1993), where localized patches of UV emission associated with upward field-aligned current were observed at the equatorward border of the auroral oval. This is consistent with the claim of Saito, it is not easy to determine whether the cases he studied, dealt with PBI onsets or EP onsets
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