Coordinated Cluster, ground-based instrumentation and low-altitude satellite observations of transient poleward-moving events in the ionosphere and in the tail lobe

Abstract

Abstract. During the interval between 8:00-9:30 on 14 January 2001, the four Cluster spacecraft were moving from the central magnetospheric lobe, through the dusk sector mantle, on their way towards intersecting the magnetopause near 15:00 MLT and 15:00 UT. Throughout this interval, the EIS-CAT Svalbard Radar (ESR) at Longyearbyen observed a series of poleward-moving transient events of enhanced F-region plasma concentration ("polar cap patches"), with a repetition period of the order of 10 min. Allowing for the estimated solar wind propagation delay of 75 (±5) min, the interplanetary magnetic field (IMF) had a southward component during most of the interval. The magnetic footprint of the Cluster spacecraft, mapped to the ionosphere using the Tsyganenko T96 model (with input conditions prevailing during this event), was to the east of the ESR beams.Correspondence to: M. Lockwood (M.Lockwood@rl.ac.uk) Around 09:05 UT, the DMSP-F12 satellite flew over the ESR and showed a sawtooth cusp ion dispersion signature that also extended into the electrons on the equatorward edge of the cusp, revealing a pulsed magnetopause reconnection. The consequent enhanced ionospheric flow events were imaged by the SuperDARN HF backscatter radars. The average convection patterns (derived using the AMIE technique on data from the magnetometers, the EISCAT and Super-DARN radars, and the DMSP satellites) show that the associated poleward-moving events also convected over the predicted footprint of the Cluster spacecraft. Cluster observed enhancements in the fluxes of both electrons and ions. These events were found to be essentially identical at all four spacecraft, indicating that they had a much larger spatial scale than the satellite separation of the order of 600 km. Some of the events show a correspondence between the lowest energy 1590 M. Lockwood et al.: Coordinated observations of transient poleward-moving events magnetosheath electrons detected by the PEACE instrument on Cluster (10-20 eV) and the topside ionospheric enhancements seen by the ESR (at 400-700 km). We suggest that a potential barrier at the magnetopause, which prevents the lowest energy electrons from entering the magnetosphere, is reduced when and where the boundary-normal magnetic field is enhanced and that the observed polar cap patches are produced by the consequent enhanced precipitation of the lowest energy electrons, making them and the low energy electron precipitation fossil remnants of the magnetopause reconnection rate pulses.

Simultaneous observations of magnetopause flux transfer events and of their associated signatures at ionospheric altitudes

“…More recently, Cluster observations have been combined with a variety of ground-based instruments (e.g. Wild et al, 2001;Lockwood et al, 2001aLockwood et al, , 2001b. Statistically, the distribution of the repetition rates of pulsed ionospheric flows and poleward moving auroral forms is in agreement with the distribution of times between FTEs at the magnetopause (McWilliams et al, 2000).…”

Ground-based observations of the auroral zone and polar cap ionospheric responses to dayside transient reconnection

“…In the work of Davis and Lockwood (1996), the authors simulated a series of such features in ESR data by imposing episodic precipitation on a model ionosphere, such as would be expected to result from a series of FTEs. Lockwood et al (2001) have observed recently polar patches associated with enhancements in the fluxes of ions and electrons observed by Cluster in the mantle. During that part of the interval over which patches are observed, the Y component of the IMF remains approximately constant (see Fig.…”

“…Weber et al, 1984;Sojka et al, 1993;Rodger et al, 1994), although this term does encompass features with a large range of scale sizes. Although polar patches are a ubiquitous feature of the polar F-region under conditions of southward IMF, the exact physical mechanism by which they are created is the subject of continuing debate (see Lockwood et al, 2001). What is generally accepted though is that once formed, they can migrate for great distances across the polar cap, preserved by the long lifetime of plasma in the F-region.…”

“…Foster and Doupnik (1984) observed poleward-moving density structures with the Chatanika radar in Alaska, while Lockwood and Carlson (1992) detected their presence with the EISCAT UHF radar system. Recent authors, for example Lockwood et al (2000Lockwood et al ( , 2001, have documented EISCAT Svalbard radar (ESR) observations of such features. Such plasma density structures fall under the remit of what has been termed "polar cap patches" (e.g.…”

The dynamics and relationships of precipitation, temperature and convection boundaries in the dayside auroral ionosphere

“…2a. These are signatures expected of reconnection pulses or "flux transfer events" (FTEs; Moen et al, 2001;Lockwood et al, 2001), indicating that the radar experienced plasma convecting away from the cusp region.…”