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Annales Geophysicae An interactive open-access journal of the European Geosciences Union
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Volume 23, issue 5
Ann. Geophys., 23, 1797-1806, 2005
https://doi.org/10.5194/angeo-23-1797-2005
© Author(s) 2005. This work is distributed under
the Creative Commons Attribution 3.0 License.
Ann. Geophys., 23, 1797-1806, 2005
https://doi.org/10.5194/angeo-23-1797-2005
© Author(s) 2005. This work is distributed under
the Creative Commons Attribution 3.0 License.

  28 Jul 2005

28 Jul 2005

Statistics of a parallel Poynting vector in the auroral zone as a function of altitude using Polar EFI and MFE data and Astrid-2 EMMA data

P. Janhunen1, A. Olsson2, N. A. Tsyganenko3, C. T. Russell4, H. Laakso5, and L. G. Blomberg6 P. Janhunen et al.
  • 1Finnish Meteorological Institute, Geophysical Research, Helsinki, Finland
  • 2Unaffiliated, previously at Swedish Institute of Space Physics, Uppsala, Sweden
  • 3Universities Space Research Association, Code 695.1, NASA Goddard Space Flight Centre, Greenbelt, MD 20771, USA
  • 4Institute of Geophysics and Planetary Physics, UCLA, Los Angeles, CA 90024-1567, USA
  • 5ESTEC, Space Science Department, Noordwijk, The Netherlands
  • 6Alfvén Laboratory, Royal Institute of Technology, Stockholm, Sweden

Abstract. We study the wave-related (AC) and static (DC) parallel Poynting vector (Poynting energy flux) as a function of altitude in auroral field lines using Polar EFI and MFE data. The study is statistical and contains 5 years of data in the altitude range 5000–30000 km. We verify the low altitude part of the results by comparison with earlier Astrid-2 EMMA Poynting vector statistics at 1000 km altitude. The EMMA data are also used to statistically compensate the Polar results for the missing zonal electric field component. We compare the Poynting vector with previous statistical DMSP satellite data concerning the electron precipitation power. We find that the AC Poynting vector (Alfvén-wave related Poynting vector) is statistically not sufficient to power auroral electron precipitation, although it may, for Kp>2, power 25–50% of it. The statistical AC Poynting vector also has a stepwise transition at R=4 RE, so that its amplitude increases with increasing altitude. We suggest that this corresponds to Alfvén waves being in Landau resonance with electrons, so that wave-induced electron acceleration takes place at this altitude range, which was earlier named the Alfvén Resonosphere (ARS). The DC Poynting vector is ~3 times larger than electron precipitation and corresponds mainly to ionospheric Joule heating. In the morning sector (02:00–06:00 MLT) we find that the DC Poynting vector has a nontrivial altitude profile such that it decreases by a factor of ~2 when moving upward from 3 to 4 RE radial distance. In other nightside MLT sectors the altitude profile is more uniform. The morning sector nontrivial altitude profile may be due to divergence of the perpendicular Poynting vector field at R=3–4 RE.

Keywords. Magnetospheric physics (Auroral phenomena; Magnetosphere-ionosphere interactions) – Space plasma physics (Wave-particle interactions)

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