Electrostatic Fields in Ionospheric Density Cavities and Their Effect on Ion Dynamics

Details Electrostatic Fields in Ionospheric Density Cavities and Their Effect on Ion Dynamics Electrostatic Fields in Ionospheric Density Cavities and Their Effect on Ion Dynamics

Dec 2003

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003agufmsm11c1179r&link_type=abstract

American Geophysical Union, Fall Meeting 2003, abstract #SM11C-1179

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Computation

2407 Auroral Ionosphere (2704), 2451 Particle Acceleration, 2471 Plasma Waves And Instabilities, 2483 Wave/Particle Interactions, 7839 Nonlinear Phenomena

Scientific paper

In auroral ionospheric plasmas, intense electrostatic fields in density depleted regions and associated transverse energization of ions are observed. We have been studying, theoretically and computationally, the generation of fields in density cavities and the energization of ions by electrostatic fields. Intense localized electric fields can be generated in regions where plasma resonances (e.g., the lower hybrid or the upper hybrid resonances) exist. An appropriate description of the fields is obtained from Maxwell's equations for a cold plasma with a spatial profile. We will discuss the characteristic features of the fields obtained from such a description. We are further studying the interaction of ionospheric ions with electrostatic fields to understand the observed transverse energization of ions. The electrostatic fields are assumed to be represented either by a set of plane waves propagating obliquely to the geomagnetic field or localized field structures whose spatial dimensions are small compared to the thermal Larmor radii of the ionospheric ions. The ion dynamics are compared and contrasted in the two cases. For obliquely propagating waves, nonlinear, coherent, transverse energization of low energy ions can take place for certain conditions that depend on the frequency spectrum, wavenumbers, and amplitudes of the waves [1,2]. The interaction of low energy ions with localized field structures is significantly different from that with an obliquely propagating spectrum of electrostatic waves. We find that the phase space of the energized ions is chaotic, and, for long-time interactions, the ions can undergo large energy gains akin to Levy flights. Detailed analytical and numerical results describing the ion dynamics, and a comparison between the interaction of ions with localized field structures and with plane waves will be discussed. This work is supported by NSF Grant No. ATM-98-06328. [1] A.K. Ram, A. Bers, and D. Benisti, J. Geophys. Res. 103, 9431 (1998). [2] D.J. Strozzi, A.K. Ram, and A. Bers, Physics of Plasmas 10, 2722 (2003).

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