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Annales Geophysicae An interactive open-access journal of the European Geosciences Union
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Discussion papers | Copyright
https://doi.org/10.5194/angeo-2018-89
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Regular paper 28 Aug 2018

Regular paper | 28 Aug 2018

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This discussion paper is a preprint. It is a manuscript under review for the journal Annales Geophysicae (ANGEO).

A new scenario applying traffic flow analogy to poleward expansion of auroras

Osuke Saka Osuke Saka
  • Office Geophysik, Ogoori, Japan

Abstract. An auroral ionosphere is generally incompressive and non-uniform medium with anisotropic conductivities. Compressibility may occur, however, following the onset of field line dipolarization. This behavior can happen when; (1) Westward directing electric fields transmitted from the dipolarization region accumulate both electrons and ions in equatorward latitudes in F region. (2) The mobility difference of electrons and ions in E region produces electrostatic potential in a quasi-neutral condition, positive in higher latitudes and negative in lower latitudes. (3) Density modulation in F region excites ion acoustic wave propagating along the field lines towards the magnetosphere. (4) The ion acoustic wave stops in the ionosphere for about 4min because of a low phase velocity (~1.6km/s). During this compressive interval, density accumulation in equatorward latitudes expands upstream to form a poleward expansion of auroras analogous to upstream propagation of a shock in traffic flow on crowded roads. Electrostatic potential produced in the E region generates field-aligned currents and closing Pedersen currents to retain electrostatic potential in a quasi-neutral ionosphere. The ion acoustic wave produces upward electric fields along the field lines in accordance with the Boltzmann relation which contributed to the ion upflow at topside ionosphere.

Osuke Saka
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Osuke Saka
Osuke Saka
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Latest update: 13 Nov 2018
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Short summary
During a short interval (~ 4 min) following the dipolarization, a local accumulation of ionospheric plasmas by convection surge induced compressibility of the auroral ionosphere. Compressibility generated electrostatic potential, field-aligned currents and parallel electric fields by exciting ion acoustic wave. Density accumulations in equatorward latitudes expand poleward because of their nonlinear evolution analogous to an upstream propagation of a shock in traffic flow.
During a short interval (~ 4 min) following the dipolarization, a local accumulation of...
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