Polar cap flow channel events: spontaneous and driven responses

Abstract

Abstract. We present two case studies of specific flow channel events appearing at the dusk and/or dawn polar cap boundary during passage at Earth of interplanetary (IP) coronal mass ejections (ICMEs) on 10 January and 25 July 2004. The channels of enhanced (>1 km/s) antisunward convection are documented by SuperDARN radars and dawn-dusk crossings of the polar cap by the DMSP F13 satellite. The relationship with Birkeland currents (C1-C2) located poleward of the traditional R1-R2 currents is demonstrated. The convection events are manifest in ground magnetic deflections obtained from the IMAGE (International Monitor for Auroral Geomagnetic Effects) Svalbard chain of ground magnetometer stations located within 71-76 • MLAT. By combining the ionospheric convection data and the ground magnetograms we are able to study the temporal behaviour of the convection events. In the two ICME case studies the convection events belong to two different categories, i.e., directly driven and spontaneous events. In the 10 January case two sharp southward turnings of the ICME magnetic field excited corresponding convection events as detected by IMAGE and SuperDARN. We use this case to determine the ground magnetic signature of enhanced flow channel events (the NHdusk/B y < 0 variant). In the 25 July case a several-hour-long interval of steady southwest ICME field (B z < 0; B y < 0) gave rise to a long series of spontaneous convection events as detected by IMAGE when the ground stations swept through the 12:00-18:00 MLT sector. From the ground-satellite conjunction on 25 July we infer the pulsed nature of the polar cap ionospheric flow channel events in this case. The typical duration of these convection enhancements in the polar cap is 10 min.

Investigating the development of double‐peak subauroral ion drift (DSAID)

“…The unusually strong enhancement of SAPS at an earlier time (1100–1200 UT; see shaded interval in grey in Figure c) was investigated by Makarevich et al [] suggesting the important role of convection bursts in SAPS intensification. Convection bursts occur during FTEs [ Southwood , ; Lee , ] when reconnection rates become enhanced briefly and intensively [ Russell and Elphic , ] and leave their signatures in convection flows appearing as various types of FCs [ Sandholt and Farrugia , ; Sandholt et al ., , ]. Adding to the study of Makarevich et al [], we show that during their earlier and our later SAPS detection, the LANL plots tracked the signatures of substorm injections.…”

Substorms and polar cap convection: the 10 January 2004 interplanetary CME case

“…The excitation of FC 1-FC 2 flows (see Fig. 2) during the interval 14:50-15:00 UT on this day can be seen in the IMAGE magnetometer data reported by Sandholt et al (2010) (see their Fig. 3).…”

“…FC 2 is a result of the persistence of open flux tubes previously opened by bursts of reconnection (flux transfer events; FTEs) along the flanks of the polar cap, as predicted by Southwood (1987). The presence of these flows has been documented by Sandholt et al (2010). The IMF B y dependence and the role of conductivity gradients at the polar cap boundary for the formation of these flow channels have been discussed by Sandholt and Farrugia (2009).…”

“…A propagation delay of approx. 50 min from ACE to Earth should be added when comparing ACE data with the low-altitude data reported below (see Sandholt et al, 2010).…”

Polar Cap Energy Deposition Events During the 5–6 August 2011 Magnetic Storm

“…The diagrams illustrate the various flow channel (FC) types in magnetic local time and magnetic latitude coordinates. Modified after Figure 1 of Sandholt et al (), these FCs are shown in the context of the Dungey polar convection operating in a (a) forward or (b) reversed manner. Modified after Figure 3 of Sandholt et al (), the diagrams illustrate the various FCs under IMF B Z < 0 conditions for (c) B Y < 0 and (d) B Y > 0 orientations.…”