|
|
 |
|
|
Ann. Geophys., 20, 781-794, 2002
www.ann-geophys.net/20/781/2002/
© European Geosciences Union 2002
Ground-based observations of the auroral zone and polar cap ionospheric responses to dayside transient reconnection
J. A. Davies1, T. K. Yeoman1, I. J. Rae1,*, S. E. Milan1, M. Lester1, M. Lockwood2, and A. McWilliams1
1Department of Physics and Astronomy, University of Leicester, Leicester, UK
2Rutherford Appleton Laboratory, Oxfordshire, UK/Department of Physics and Astronomy, Southampton University, Southampton, UK
*now at Department of Physics, University of Alberta, Edmonton, Alberta, Canada
Correspondence to: J. A. Davies (jaq@ion.le.ac.uk)
Abstract. Observations from the
EISCAT VHF incoherent scatter radar system in northern Norway, during a run of
the common programme CP-4, reveal a series of poleward-propagating F-region
electron density enhancements in the pre-noon sector on 23 November 1999. These
plasma density features, which are observed under conditions of a strongly
southward interplanetary magnetic field, exhibit a recurrence rate of under 10
min and appear to emanate from the vicinity of the open/closed field-line
boundary from where they travel into the polar cap; this is suggestive of their
being an ionospheric response to transient reconnection at the day-side
magnetopause (flux transfer events). Simultaneous with the density structures
detected by the VHF radar, poleward-moving radar auroral forms (PMRAFs) are
observed by the Finland HF coherent scatter radar. It is thought that PM-RAFs,
which are commonly observed near local noon by HF radars, are also related to
flux transfer events, although the specific mechanism for the generation of the
field-aligned irregularities within such features is not well understood. The
HF observations suggest, that for much of their existence, the PMRAFs trace
fossil signatures of transient reconnection rather than revealing the footprint
of active reconnection itself; this is evidenced not least by the fact that the
PMRAFs become narrower in spectral width as they evolve away from the region of
more classical, broad cusp scatter in which they originate. Interpretation of
the HF observations with reference to the plasma parameters diagnosed by the
incoherent scatter radar suggests that as the PMRAFs migrate away from the
reconnection site and across the polar cap, entrained in the ambient
antisunward flow, the irregularities therein are generated by the presence of
gradients in the electron density, with these gradients having been formed
through structuring of the ionosphere in the cusp region in response to
transient reconnection.
Key words. Magnetospheric physics
(magnetosphere-ionosphere interaction) – ionosphere (ionospheric
irregularities; plasma density and temperature)
Full Article in PDF (1290 KB) |
|
|
