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Annales Geophysicae An interactive open-access journal of the European Geosciences Union
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Volume 16, issue 8
Ann. Geophys., 16, 948–968, 1998
https://doi.org/10.1007/s00585-998-0948-2
© European Geosciences Union 1998
Ann. Geophys., 16, 948–968, 1998
https://doi.org/10.1007/s00585-998-0948-2
© European Geosciences Union 1998

  31 Aug 1998

31 Aug 1998

Further development in theory/data closure of the photoelectron-driven polar wind and day-night transition of the outflow

S. W. Y. Tam, F. Yasseen, and T. Chang S. W. Y. Tam et al.
  • Center for Space Research, Massachusetts Institute of Technology, Cambridge, MA 02139, USA

Abstract. Recent in situ observations have revealed novel features in the polar wind. Measurements between 5000 and 9000 km altitude by the Akebono satellite indicate that both H+ and O+ ions can have remarkably higher outflow velocities in the sunlit region than on the nightside. Electrons also display an asymmetric behavior: the dayside difference in energy spread, greater for upward-moving than downward-moving electrons, is absent on the nightside. Here, we discuss the further development of a theory by Tam et al. that can explain most of these observed peculiar properties by properly taking into account the global, kinetic, collisional effects of the sunlit photoelectrons, on the background polar wind and the electric field. Quantitative comparisons of the calculated results with actual data will be described. In addition, transition from the daytime photoelectron-driven polar wind to the night-time polar wind will be discussed.

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