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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

Review status
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.

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Osuke Saka
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Latest update: 18 Sep 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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