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Annales Geophysicae An interactive open-access journal of the European Geosciences Union
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Volume 22, issue 5
Ann. Geophys., 22, 1613–1622, 2004
https://doi.org/10.5194/angeo-22-1613-2004
© Author(s) 2004. This work is distributed under
the Creative Commons Attribution 3.0 License.
Ann. Geophys., 22, 1613–1622, 2004
https://doi.org/10.5194/angeo-22-1613-2004
© Author(s) 2004. This work is distributed under
the Creative Commons Attribution 3.0 License.

  08 Apr 2004

08 Apr 2004

Energy distribution of precipitating electrons estimated from optical and cosmic noise absorption measurements

H. Mori1, M. Ishii1, Y. Murayama1, M. Kubota1, K. Sakanoi1, M.-Y. Yamamoto2, Y. Monzen3, D. Lummerzheim4, and B. J. Watkins4 H. Mori et al.
  • 1Communications Research Laboratory, 4-2-1, Nukui-Kitamachi, Koganei, Tokyo, Japan
  • 2Kochi University of Technology, 185, Miyanokuchi, Tosayamada, Kochi, Japan
  • 3University of Electro-Communications, 1-5-1, Chofugaoka, Chofu, Tokyo, Japan
  • 4Geophysical Institute, University of Alaska Fairbanks, Fairbanks, Alaska 99775-7320, USA

Abstract. This study is a statistical analysis on energy distribution of precipitating electrons, based on CNA (cosmic noise absorption) data obtained from the 256-element imaging riometer in Poker Flat, Alaska (65.11° N, 147.42° W), and optical data measured with an MSP (Meridian Scanning Photometer) over 79 days during the winter periods from 1996 to 1998. On the assumption that energy distributions of precipitating electrons represent Maxwellian distributions, CNA is estimated based on the observation data of auroral 427.8-nm and 630.0-nm emissions, as well as the average atmospheric model, and compared with the actual observation data. Although the observation data have a broad distribution, they show systematically larger CNA than the model estimate. CNA determination using kappa or double Maxwellian distributions, instead of Maxwellian distributions, better explains the distribution of observed CNA data. Kappa distributions represent a typical energy distribution of electrons in the plasma sheet of the magnetosphere, the source region of precipitating electrons. Pure kappas are more likely during quiet times – and quiet times are more likely than active times. This result suggests that the energy distribution of precipitating electrons reflects the energy distribution of electrons in the plasma sheet.

Key words. Ionosphere (auroral ionosphere; particle precipitation; polar ionosphere)

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