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Annales Geophysicae An interactive open-access journal of the European Geosciences Union
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Volume 18, issue 1
Ann. Geophys., 18, 47–55, 2000
© European Geosciences Union 2000
Ann. Geophys., 18, 47–55, 2000
© European Geosciences Union 2000

  31 Jan 2000

31 Jan 2000

Modeling of occurrence frequencies of ion conics as a function of altitude and conic angle

W. Miyake1, T. Mukai2, and N. Kaya3 W. Miyake et al.
  • 1Communications Research Laboratory, 4-2-1 Koganei, Tokyo 184-8795, Japan
  • E-mail:
  • 2The Institute of Space and Astronautical Science, Yoshinodai, Sagamihara 229-8510, Japan
  • 3Kobe University, 1-1, Rokkodai, Nada, Kobe 657-8501, Japan

Abstract. The occurrence frequencies of dayside ion conics with various conic angles are obtained as a function of altitude from Exos-D (Akebono) observations. We made a model calculation of ion conic evolution to match the observation results. The observed occurrence frequencies of ion conics with 80° to 90° conic angle are used as an input to the model and the occurrence frequencies of ion conics with smaller conic angles are numerically calculated at higher altitudes. The calculated occurrence frequencies are compared with the observed ones of ion conics with smaller conic angles. We take into account conic angle variation with altitude in both adiabatic and non-adiabatic cases, horizontal extension of ion conics due to E×B drift, and evolution to elevated conics and ion beams in the model. In the adiabatic case, the conic angle decreases with increasing altitude much faster than was observed. The occurrence frequency of small-angle conics is much larger than the observed value without E×B drift and evolution to the other UFIs. An agreement is obtained by assuming non-adiabatic variation of conic angles with altitude and an ion E×B drift to gyro velocity ratio of 0.08 to 0.6, depending on geomagnetic activities.

Key words. Ionosphere (particle acceleration) · Magnetospheric physics (auroral phenomena; magnetopause, cusp, and boundary layers).

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