posted on 2017-01-24, 11:40authored byE. E. Woodfield, J. A. Davies, M. Lester, T. K. Yeoman, P. Eglitis, M. Lockwood
A previous case study found a relationship between high spectral width measured by the CUTLASS Finland HF radar and elevated electron temperatures observed by the EISCAT and ESR incoherent scatter radars in the post-midnight sector of magnetic local time. This paper expands that work by briefly re-examining that interval and looking in depth at two further case studies. In all three cases a region of high HF spectral width (>200 ms-1) exists poleward of a region of low HF spectral width (<200 ms-1). Each case, however, occurs under quite different geomagnetic conditions. The original case study occurred during an interval with no observed electrojet activity, the second study during a transition from quiet to active conditions with a clear band of ion frictional heating indicating the location of the flow reversal boundary, and the third during an isolated sub-storm. These case studies indicate that the relationship between elevated electron temperature and high HF radar spectral width appears on closed field lines after 03:00 magnetic local time (MLT) on the nightside. It is not clear whether the same relationship would hold on open field lines, since our analysis of this relationship is restricted in latitude. We find two important properties of high spectral width data on the nightside. Firstly the high spectral width values occur on both open and closed field lines, and secondly that the power spectra which exhibit high widths are both single-peak and multiple-peak. In general the regions of high spectral width (>200 ms-1) have more multiple-peak spectra than the regions of low spectral widths whilst still maintaining a majority of single-peak spectra. We also find that the region of ion frictional heating is collocated with many multiple-peak HF spectra. Several mechanisms for the generation of high spectral width have been proposed which would produce multiple-peak spectra, these are discussed in relation to the data presented here. Since the regions of high spectral width are observed both on closed and open field lines the use of the boundary between low and high spectral width as an ionospheric proxy for the open/closed field line boundary is not a simple matter, if indeed it is possible at all.
Funding
The authors wish to thank those involved in
the deployment and operation of the CUTLASS HF radars run by
the University of Leicester with joint funding from the UK Particle
Physics and Astronomy Research Council (PPARC) grant number
PPA/R/R/1997/00256, the Swedish Institute for Space Physics,
Uppsala and the Finnish Meteorological Institute, Helsinki, the institutes
who maintain the IMAGE magnetometer array, R. Lepping
at NASA/GSFC and CDAWeb for WIND data. EEW is indebted
to PPARC for a research studentship. JAD is supported by
PPARC grant number PPA/G/O/1999/00181. EISCAT is an international
facility funded collaboratively by the research councils of
Finland (SA), France (CNRS), the Federal Republic of Germany
(MPG), Japan (NIPR), Norway (NAVF), Sweden (NFR) and the
UK. (PPARC).
History
Citation
Annales Geophysicae, 2002, 20 (9), pp. 1399-1413 (15)
Author affiliation
/Organisation/COLLEGE OF SCIENCE AND ENGINEERING/Department of Physics and Astronomy
Source
10th International EISCAT Workshop, TOKYO, JAPAN
Version
VoR (Version of Record)
Published in
Annales Geophysicae
Publisher
European Geosciences Union (EGU), Copernicus Publications, Springer Verlag (Germany)