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Nightside studies of coherent HF Radar spectral width behaviour

Nightside studies of coherent HF Radar spectral width behaviour
Nightside studies of coherent HF Radar spectral width behaviour
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.
0992-7689
1399-1413
Woodfield, E.E.
5dc376b3-202e-4963-a5b1-1fc0a642cc06
Davies, J.A.
fc7f1e9a-3c20-4d3a-abe3-8a911fae5fea
Lester, M.
f819515b-5011-4d54-9f89-ceea11494c90
Yeoman, T.K.
cc3f7732-a6a5-462e-aa81-289804631314
Eglitis, P.
0e748dda-e360-4751-a119-cb7ac7380c35
Lockwood, M.
32917473-f7d9-4773-9162-6509baad09fa
Woodfield, E.E.
5dc376b3-202e-4963-a5b1-1fc0a642cc06
Davies, J.A.
fc7f1e9a-3c20-4d3a-abe3-8a911fae5fea
Lester, M.
f819515b-5011-4d54-9f89-ceea11494c90
Yeoman, T.K.
cc3f7732-a6a5-462e-aa81-289804631314
Eglitis, P.
0e748dda-e360-4751-a119-cb7ac7380c35
Lockwood, M.
32917473-f7d9-4773-9162-6509baad09fa

Woodfield, E.E., Davies, J.A., Lester, M., Yeoman, T.K., Eglitis, P. and Lockwood, M. (2002) Nightside studies of coherent HF Radar spectral width behaviour. Annales Geophysicae, 20, 1399-1413.

Record type: Article

Abstract

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.

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Published date: 2002

Identifiers

Local EPrints ID: 9152
URI: http://eprints.soton.ac.uk/id/eprint/9152
ISSN: 0992-7689
PURE UUID: ba6a740e-ffb7-42cb-8268-7b44bb57c3c2

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Date deposited: 24 Sep 2004
Last modified: 07 Jan 2022 21:58

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Contributors

Author: E.E. Woodfield
Author: J.A. Davies
Author: M. Lester
Author: T.K. Yeoman
Author: P. Eglitis
Author: M. Lockwood

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