First simultaneous observations of flux transfer events at the high-latitude magnetopause by the Cluster spacecraft and pulsed radar signatures in the conjugate ionosphere by the CUTLASS and EISCAT radars

Abstract

Abstract. Cluster magnetic field data are studied during an outbound pass through the post-noon high-latitude magnetopause region on 14 February 2001. The onset of several minute perturbations in the magnetospheric field was observed in conjunction with a southward turn of the interplanetary magnetic field observed upstream by the ACE spacecraft and lagged to the subsolar magnetopause. These perturbations culminated in the observation of four clear magnetospheric flux transfer events (FTEs) adjacent to the magnetopause, together with a highly-structured magnetopause boundary layer containing related field features. Furthermore, clear FTEs were observed later in the magnetosheath. The magnetospheric FTEs were of essentially the same form as the original "flux erosion events" observed in HEOS-2 data at a similar location and under similar interplanetary conditions by Haerendel et al. (1978). We show that the nature of the magnetic perturbations in these events is consistent with the formation of open flux tubes connected to the northern polar ionosphere via pulsed reconnection in the dusk sector magnetopause. The magnetic footprint of the Cluster spacecraft during the boundary passage is shown to map centrally within the fields-of-view of the CUTLASS SuperDARN radars, and to pass across the field-aligned beam of the EISCAT Svalbard radar (ESR) system. It is shown that both the ionospheric flow and the backscatter power in the CUTLASS data pulse are in synchrony with the magnetospheric FTEs and boundary layer structures at the latitude of the Cluster footprint. These flow and power features are subsequently found to propagate poleward, forming classic "pulsed ionospheric flow" and "poleward-moving radar auroral form" structures at higher latitudes. The combined Cluster-CUTLASS observations thus represent a direct demonstration of the coupling of momentum and energy Correspondence to: J. A. Wild (j.wild@ion.le.ac.uk) into the magnetosphere-ionosphere system via pulsed magnetopause reconnection. The ESR observations also reveal the nature of the structured and variable polar ionosphere produced by the structured and time-varying precipitation and flow.

Excitation of twin-vortex flow in the nightside high-latitude ionosphere during an isolated substorm

“…Even the substructure of characteristically pulsed dayside reconnection on 5-10 min time scales (i.e. flux transfer events) are well-resolved in dayside flow data as pulsed ionospheric flows (Lockwood et al, 1989(Lockwood et al, , 1993Elphic et al, 1990;Pinnock et al, 1993Pinnock et al, , 1995Moen et al, 1995;Provan et al, 1998;Neudegg et al, 1999Neudegg et al, , 2000Milan et al, 2000;Wild et al, 2001). As a consequence, there is now little uncertainty about the central role of magnetopause reconnection in magnetospheric dynamics and flow excitation.…”

“…This latitude is close to the equatorward edge of the SuperDARN field of view (in normal scan mode), so that the substorm-effected region may only be partially imaged. Third, it is very often the case that SuperDARN radar backscatter drops out during intervals of magnetic disturbance due to precipitation-induced D-region radio absorption (Milan et al, 1996;Yeoman and Lühr, 1997). In this case the evolution of the flow during the substorm cannot be properly followed after the onset of the expansion phase.…”

“…These events, termed poleward boundary intensifications (PBIs) by Lyons et al (1999), have been found to occur in all phases of the substorm cycle, including during long intervals of magnetic quiet, though they appear to be more frequent during substorm expansion phases. They are associated with azimuthally-localized bursty bulk flows (BBFs) in the near-Earth plasma sheet (Baumjohann et al, 1990;Angelopoulos et al, 1992;Yeoman et al, 1998;Lyons et al, 1999) and the excitation of equatorward flow in the ionosphere (Sergeev et al, 1990;de la Beaujardire et al, 1994;Yeoman and Lühr, 1997;Watanabe et al, 1998), together with relatively weak structured magnetic disturbances in the high-latitude ionosphere, Pi2 signals, and particle injections at geosynchronous orbit (Hsu and McPherron, 1996;Henderson et al, 1998;Lyons et al, 1999;Sergeev et al, 1999Sergeev et al, , 2000. As discussed, for example, by Cowley (1998), and Cowley et al (1998), these features are strongly suggestive of the occurrence of localized impulsive reconnection in the tail leading to plasma injection and flow excitation.…”

A decade of the Super Dual Auroral Radar Network (SuperDARN): scientific achievements, new techniques and future directions

“…In a study of 87 FTEs measured by the Equator-S spacecraft, 69 (77%) of these had a measurable convection flow burst signature and hence the two signatures were statistically associated with greater than 99% confidence. Wild et al (2001Wild et al ( , 2003 later presented coincident observations of highlatitude magnetopause FTEs measured by the Cluster spacecraft and convection flow transients measured at conjugate locations in both hemispheres by SuperDARN. The flow transients were found to pulse in close synchronization with the occurrence of the FTEs observed by Cluster.…”

Pulsed flows at the high-altitude cusp poleward boundary, and associated ionospheric convection and particle signatures, during a Cluster - FAST - SuperDARN- Søndrestrøm conjunction under a southwest IMF

“…Individual signatures include: poleward-moving auroral forms (PMAFs; Sandholt et al, 1986Sandholt et al, , 1990Sandholt et al, , 2003, pulsed ionospheric flows/flow channels (PIFs; Pinnock et al, 1993Pinnock et al, , 1995Rodger and Pinnock, 1997;Neudegg et al, 1999;Provan et al, 2002), poleward-moving radar auroral forms (PMRAFs; Wild et al, 2001), an ion energy-latitude dispersion signature in the cusp of the staircase variety ("stepped cusp"; Cowley et al, 1991;Newell et al, 1989;Escoubet et al, 1992). The reliable and unique association of these signatures to transient reconnection requires in general multi-point observations.…”