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Ann. Geophys., 20, 1617-1630, 2002
www.ann-geophys.net/20/1617/2002/
© European Geosciences Union 2002
Signatures of the midnight open-closed magnetic field line boundary during balanced dayside and nightside reconnection
M. L. Parkinson1, P. L. Dyson1, M. Pinnock2, J. C. Devlin3, M. R. Hairston4, E. Yizengaw1, and P. J. Wilkinson5
1Department of Physics, La Trobe University, Victoria 3086, Australia
2British Antarctic Survey, Natural Environment Research Council, Cambridge CB3 0ET, UK
3Department of Electronic Engineering, La Trobe University, Victoria 3086, Australia
4William B. Hanson Center for Space Sciences, University of Texas at Dallas, Richardson, Texas, USA
5IPS Radio and Space Services, Sydney, New South Wales 1240, Australia
Correspondence to: M. L. Parkinson
(m.parkinson@latrobe.edu.au)
Abstract. The geomagnetic conditions were moderately
disturbed (Kp = 2) during magnetic midnight on 10 December
1999, when the Tasman International Geospace Environment Radar (TIGER), a
Southern Hemisphere HF SuperDARN radar, observed a persistent, sharp
latitudinal decrease (~ 90 km) in spectral width near - 69°L.
The line-of-sight Doppler velocity also rapidly declined across this spectral
width boundary (SWB). The region poleward of the SWB was characterized by high
spectral widths (>200 m/s), and the start of bursty equatorward and eastward
flows (>500 m/s), which rapidly expanded equatorward. The relationships
between familiar ionospheric and magnetospheric regions were inferred by
comparing TIGER data with spectrograms calculated from precipitating particles
measured on board the Defence Meteorology Satellite Program (DMSP) F14
satellite. The high spectral width scatter is often observed, and on this
evening it was associated with irregularities forming on the open (but soon to
be reconnected) field lines threading the polar cap ionosphere to the southern
tail lobe. The region equatorward of the SWB was characterized by very low
spectral widths (<50 m/s) and generally slower, more zonal flows (<300
m/s). This kind of scatter is more transient, and was associated with
irregularities residing on the closed field lines threading the discrete and
diffuse auroral oval to the plasma sheet boundary layer (PSBL) and central
plasma sheet (CPS). Hence, the SWB was a reasonable proxy for the open-closed
field line boundary, and the equatorward limit of the region, with low spectral
width, was probably aligned with the poleward wall of the main ionospheric
trough. The SWB was observed to contract poleward and expand equatorward on
time scales of ~10 min, much as would be expected during balanced dayside and
nightside reconnection. Total electron content (TEC) measurements made at
Macquarie Island (- 65°L) and Hobart (- 54°L),
and the ionograms recorded at the same stations, as well as at Bundoora (- 49°L),
also helped to validate the interpretation.
Key words. Ionosphere (auroral ionosphere; electric
fields and currents; ionosphere-magnetosphere interactions)
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