On the lifetime and extent of an auroral westward flow channel (AWFC) observed during a magnetospheric substorm

Abstract

Abstract.A −190-nT negative bay in the geomagnetic X component measured at Macquarie Island (−65 • ) showed that an ionospheric substorm occurred during 09:58 to 11:10 UT on 27 February 2000. Signatures of an auroral westward flow channel (AWFC) were observed nearly simultaneously in the backscatter power, LOS Doppler velocity, and Doppler spectral width measured using the Tasman International Geospace Environment Radar (TIGER), a Southern Hemisphere HF SuperDARN radar. Many of the characteristics of the AWFC were similar to those occurring during a polarisation jet (PJ), or subauroral ion drift (SAID) event, and suggest that it may have been a precursor to a fully developed, intense westward flow channel satisfying all of the criteria defining a PJ/SAID. A beamswinging analysis showed that the westward drifts (poleward electric field) associated with the flow channel were very structured in time and space, but the smoothed velocities grew to ∼800 m s −1 (47 mV m −1 ) during the 22-min substorm onset interval 09:56 to 10:18 UT. Maximum westward drifts of >1.3 km s −1 (>77 mV m −1 ) occurred during a ∼5-min velocity spike, peaking at 10:40 UT during the expansion phase. The drifts decayed rapidly to ∼300 m s −1 (18 mV m −1 ) during the 6-min recovery phase interval, 11:04 to 11:10 UT. Overall, the AWFC had a lifetime of 74 min, and was located near −65 • in the evening sector west of the Harang discontinuity. The large westward drifts were confined to a geographic zonal channel of longitudinal extent >20 • (>1.3 h magnetic local time), and latitudinal width ∼2 • . Using a half-width of ∼100 km in latitude, the peak electric potential was >7.7 kV. However, a transient velocity of >3.1 km s −1 with potential >18.4 kV was observed further poleward at the end of the recovery phase. Auroral oval boundaries determined using DMSP measurements suggestCorrespondence to: M. L. Parkinson (m.parkinson@latrobe.edu.au) the main flow channel overlapped the equatorward boundary of the diffuse auroral oval. During the ∼2-h interval following the flow channel, an ∼3 • wide band of scatter was observed drifting slowly toward the west, with speeds gradually decaying to ∼50 m s −1 (3 mV m −1 ). The scatter was observed extending past the Harang discontinuity, and had Doppler signatures characteristic of the main ionospheric trough, implicating the flow channel in the further depletion of F-region plasma. The character of this scatter was in contrast with the character of the scatter drifting toward the east at higher latitude.Key words. Ionosphere (auroral ionosphere; electric fields and currents; ionosphere-magnetospehere interactions) Magnetospheric physics (storms and substorms)

Statistical study of high-latitude plasma flow during magnetospheric substorms

“…The auroral flow channel was located at a relatively low latitude of ∼−65 • in the evening sector, had a width of ∼2 • −3 • latitude and had a maximum westward velocity of >1.3 kms −1 during the expansion phase. We suggest that the strong westward flows observed in this study at the equatorward edge of the radars' f-o-v in the post-dusk sector at, and after, substorm onset could well be the poleward edge of the auroral westward flow channel observed by Parkinson et al (2003). The Northern Hemisphere SuperDARN radars are clearly not observing the equatorward edge of the flow channel, which would explain the underestimation of the potential across the return flow region.…”

“…The convection zone moving to lower latitudes is the most likely cause of the plateau of the low-latitude potential around substorm onset. Parkinson et al (2003) presented observations of an auroral westward flow channel observed during a substorm by the TIGER SuperDARN radar in the Southern Hemisphere. The auroral flow channel was located at a relatively low latitude of ∼−65 • in the evening sector, had a width of ∼2 • −3 • latitude and had a maximum westward velocity of >1.3 kms −1 during the expansion phase.…”

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

“…These sub-auroral electric fields play critical roles in energising and transporting ring current ions as well as convecting thermal plasma in the inner magnetosphere and in the mid-to low-latitude ionosphere (Foster and Vo 2002). In SuperDARN observations these phenomena have often been termed auroral westward flow channels (AWFCs) (Parkinson et al 2003(Parkinson et al , 2005 and they appear any time between substorm onset and recovery. Koustov et al (2006) also observed SAPS with the King Salmon SuperDARN radar.…”

An auroral westward flow channel (AWFC) and its relationship to field-aligned current, ring current, and plasmapause location determined using multiple spacecraft observations

“…Galperin et al (1973) originally discovered polarisation jets (PJs), very narrow channels (<1 to 2 • ) of intense westward plasma flow (500 m s −1 to >4 km s −1 ) forming in proximity to SAPS. PJs have been referred to by various terms including sub-auroral ions drifts (SAID) (Spiro et al, 1979), substorm-associated radar auroral surges (SARAS) (Freeman et al, 1992;Shand et al, 1998), sub-auroral electric fields (SAEF) (Karlsson et al, 1998), and auroral westward flow channels (AWFC) (Parkinson et al, 2003a). The diverse SAPS nomenclature has arisen from observations of different aspects of the same phenomena, and the important distinctions need to be reconciled.…”

“…In terms of electric fields, AWFCs are the strongest signature of substorms . Parkinson et al (2003a) suggested AWFCs feed the development of the SAPS. Defining the relationship between AWFCs and the main population of PJ/SAIDs and SAPS occurring further equatorward will require a latitudinal chain of sub-auroral radars making continuous observations throughout the entire substorm cycle.…”