Articles | Volume 28, issue 5
Ann. Geophys., 28, 1107–1120, 2010
Ann. Geophys., 28, 1107–1120, 2010

ANGEO Communicates 10 May 2010

ANGEO Communicates | 10 May 2010

On the fine structure of medium energy electron fluxes in the auroral zone and related effects in the ionospheric D-region

J. K. Hargreaves1,2, M. J. Birch2,3, and D. S. Evans4 J. K. Hargreaves et al.
  • 1Department of Communication Systems, Lancaster University, UK
  • 2Jeremiah Horrocks Institute for Astrophysics and Supercomputing, University of Central Lancashire, Preston, UK
  • 3John Tyndall Institute for Nuclear Research, University of Central Lancashire, Preston, UK
  • 4Space Environment Centre, NOAA, Boulder, USA

Abstract. This study is based on measurements of trapped and precipitated electrons of energy >30 keV and >100 keV observed by polar orbiting environmental satellites during overpasses of the imaging riometer at Kilpisjärvi, Finland. The satellites are in sun-synchronous orbits of about 850 km altitude, recording the electron fluxes at 2-s time resolution. The riometer measures the radiowave absorption at 38.2 MHz, showing the spatial pattern within a 240 km field of view.

The analysis has focussed on two areas. Having found a close correlation between the radiowave absorption and the medium-energy electron fluxes during satellite overpasses, empirical relationships are derived, enabling one quantity to be predicted from the other for three sectors of local time. It is shown that small-scale variations observed during a pass are essentially spatial rather than temporal.

Other properties, such as the spectra and the relation between precipitated and trapped components, are also considered in the light of the theory of pitch angle scattering by VLF waves. It is found that the properties and behaviour depend strongly on the time of day. In the noon sector, the precipitated and trapped fluxes are highly correlated through a square law relationship.