Abstract
Line-of-sight Doppler velocities from the SuperDARN CUTLASS HF radar pair have been combined to produce the first two-dimensional vector measurements of the convection pattern throughout the ionospheric footprint of a flux transfer event (a pulsed ionospheric flow, or PIF). Very stable and moderate interplanetary magnetic field conditions, along with a preceding prolonged period of northward interplanetary magnetic field, allow a detailed study of the spatial and the temporal evolution of the ionospheric response to magnetic reconnection. The flux tube footprint is tracked for half an hour across six hours of local time in the auroral zone, from magnetic local noon to dusk. The motion of the footprint of the newly reconnected flux tube is compared with the ionospheric convection velocity. Two primary intervals in the PIF's evolution have been determined. For the first half of its lifetime in the radar field of view the phase speed of the PIF is highly variable and the mean speed is nearly twice the ionospheric convection speed. For the final half of its lifetime the phase velocity becomes much less variable and slows down to the ionospheric convection velocity. The evolution of the flux tube in the magnetosphere has been studied using magnetic field, magnetopause and magnetosheath models. The data are consistent with an interval of azimuthally propagating magnetopause reconnection, in a manner consonant with a peeling of magnetic flux from the magnetopause, followed by an interval of anti-sunward convection of reconnected flux tubes.Key words: Magnetospheric physics (magnetosphere · ionosphere interactions; plasma convection; solar wind · magnetosphere interactions)
Highlights
The nature of reconnection at the dayside magnetopause is fundamental to comprehending the primary means of energy input into the terrestrial magnetosphere
Chisham et al (2000) studied data from three high-time resolution beams from two overlapping SuperDARN radars in the Southern Hemisphere. They examined the large-scaleows associated with PIF activity and their relationship to the changing orientation of the interplanetary magnetic ®eld (IMF), focusing on convection velocities measured by the overlapping high-time resolution beams. Their measurements were obtained in the noon sector in the region of the initial ionospheric response to theux transfer events
The Cooperative UK Twin Located Auroral Sounding System (CUTLASS) radars are expected to monitor an isolated ionospheric response to the southward turning of the IMF, which is expected to aect the ionosphere at 10:59 UT
Summary
The nature of reconnection at the dayside magnetopause is fundamental to comprehending the primary means of energy input into the terrestrial magnetosphere. The bipolar signature in the normal component of the magnetic ®eld at the magnetopause is interpreted as that of a newly reconnectedux tube passing very near to the spacecraft and has been studied quite extensively (Haerendel et al, 1978; Russell and Elphic, 1978, 1979; Lockwood and Wild, 1993; Kuo et al, 1995) These bursts of reconnection have come to be known asux transfer events, or FTEs. They examined the large-scaleows associated with PIF activity and their relationship to the changing orientation of the interplanetary magnetic ®eld (IMF), focusing on convection velocities measured by the overlapping high-time resolution beams Their measurements were obtained in the noon sector in the region of the initial ionospheric response to theux transfer events. The backscattered power, the mean Doppler velocity, an estimate of the line-of-sight (LOS) plasma drift velocity, and the width of the Doppler spectrum are determined for each radar range gate
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