Multiple brightenings of transient dayside auroral forms during oval expansions

Abstract

Poleward moving transients have been proposed to be ionospheric signatures of plasma transfer events taking place at the dayside magnetopause. They are usually observed to brighten at the equatorward edge of the dayside auroral oval and fade as they move into the polar cap. This paper reports the observation of a new type of poleward moving dayside auroral transient which has several cycles of intensity variations. Observations of these transients show a series of intensifications in brightness along the arc or rayed band during poleward motion accompanied by a brightening in the auroral oval. As they reach their extreme poleward position they brighten and than fade from view. This brightening sequence may be explained by multiple reconnection of the magnetic flux tube associated with the transient.

Plasma structure within poleward-moving cusp/cleft auroral transients: EISCAT Svalbard radar observations and an explanation in terms of large local time extent of events

“…Because the MSP only samples one meridian, this variation in brightness could be caused by longitudinal structure and eastward motion of the events; however all-sky images (Thorolfsson et al, this issue) do not show any evidence for such structure. The e ect is also consistent with the rebrightening of the entire poleward-moving event, as was noted in many white light all-sky images by Fasel et al (1992). Event a was seen by the ESR before its main brightening, event b was seen just after its initial brightening, events c and d were seen just before they re-brightened and events e, f and g were seen in the middle of their second brightening.…”

“…However, there are features of these events that are still not understood. In particular, it is not known why there are minima in luminosity between events and how events can re-brighten as they propagate (Fasel et al, 1992). Neither of these features were reproduced in the modelling by D&L which was based on the concept that both the convection¯ows and the precipitation on each newly opened ®eld line are a function of only the elapsed time since reconnection.…”

Observations of polar patches generated by solar wind Alfvén wave coupling to the dayside magnetosphere

“…Figure 13 shows the spectral analysis results for the Saskatoon SuperDARN radar (beam 11) LoS velocity. These results were obtained using a two-dimensional analysis technique (Fenrich et al, 1995). Three distinct peaks at about 1, 2 and 2.5 mHz (the same as those identi®ed in Fig.…”

Meridian-scanning photometer, coherent HF radar, and magnetometer observations of the cusp: a case study

“…While the relative importance of quasi-continuous reconnection or more transient and intermittent``¯ux transfer events'' (Russell and Elphic, 1978;Haerendel et al, 1978;Paschmann et al, 1982;Saunders et al, 1984;Lockwood, 1991) is as yet unclear, there is a considerable body of evidence to suggest that the auroral signature of the cusp and the ionospheric convection excited by dayside reconnection are pulsed (e.g. Feldstein and Starkov, 1967;Vorobjev et al, 1975;Horwitz and Akasofu, 1977;van Eyken et al, 1984;Goertz et al, 1985;Lockwood et al, 1989aLockwood et al, , 1989bLockwood et al, , 1993bLockwood et al, , 1993cSandholt et al, 1985Sandholt et al, , 1986Sandholt et al, , 1989Sandholt, 1988;Elphic et al, 1990;Fasel et al, 1992;Pinnock et al, 1993Pinnock et al, , 1995Moen et al, 1995Moen et al, , 1996. Much theoretical work has been published on the ionospheric convection response to transient dayside reconnection (e.g.…”