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Ann. Geophys., 26, 1431-1437, 2008
www.ann-geophys.net/26/1431/2008/
© European Geosciences Union 2008
An interpretation for the bipolar electric field structures parallel to the magnetic field observed in the auroral ionosphere
Jiankui Shi1, M. N. S. Qureshi2, K. Torkar3, M. Dunlop4, Zhenxing Liu1, and T. L. Zhang3
1State Key Laboratory for Space Weather, CSSAR, Chinese Academy of Sciences, Beijing 100080, China
2Department of Physics, Government College University, Lahore 54000, Pakistan
3Space Research Institute, Austrian Academy of Sciences, 8042, Graz, Austria
4SSTD, Rutherford Appleton Laboratory, Chilton, Didcot, UK
Abstract. A physical model for the existence of bipolar structures in the electric
field that are parallel to the magnetic field and observed in the auroral
ionosphere, is established by deriving the "Sagdeev potential" from the
two-fluid equations in a cylindrical coordinate system. The model shows that
the bipolar electric field structure can develop not only from an ion
acoustic wave, but also from an ion cyclotron wave, when the Mach number and
the initial electric field satisfy certain conditions. Moreover, in the
auroral region, it shows that the polarity of this electric field structure
can be oriented either negative to positive or the reverse polarity, its
amplitude can be varied from 35 to 330 mV/m, and its duration can be 7 ms to 23 ms.
These results are in agreement with observation. Therefore, our
two-fluid model can interpret the bipolar structures observed in the auroral
ionosphere.
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