Nightside studies of coherent HF Radar spectral width behaviour

• Published in: Annales Geophysicae
• Main Authors: Woodfield, E. E., Davies, J. A., Lester, M., Yeoman, T. K., Eglitis, P., Lockwood, M.
• Format: Conference Object
• Language: English
• Published: European Geosciences Union (EGU), Copernicus Publications, Springer Verlag (Germany) 2017
• Subjects: Science & Technology; Physical Sciences; Astronomy & Astrophysics; Geosciences; Multidisciplinary; Meteorology & Atmospheric Sciences; Geology; ionosphere; auroral ionosphere; ionospheric irregularities; HIGH-LATITUDE CONVECTION; EISCAT SVALBARD RADAR; POLAR-CAP BOUNDARY; F-REGION; IONOSPHERIC CUSP; PARTICLE-PRECIPITATION; ISOLATED SUBSTORM; PLASMA; SUPERDARN; SYSTEM; Leicester; Norway; Svalbard; EISCAT
• Online Access: http://www.ann-geophys.net/20/1399/2002/angeo-20-1399-2002.html; http://hdl.handle.net/2381/39286; https://doi.org/10.5194/angeo-20-1399-2002

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. 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). Peer-reviewed Publisher Version 10th International EISCAT Workshop, TOKYO, JAPAN