Statistics – Computation
Scientific paper
Dec 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002agufmsm21b0554r&link_type=abstract
American Geophysical Union, Fall Meeting 2002, abstract #SM21B-0554
Statistics
Computation
2407 Auroral Ionosphere (2704), 2451 Particle Acceleration, 2483 Wave/Particle Interactions, 7815 Electrostatic Structures, 7839 Nonlinear Phenomena
Scientific paper
We extend our previous analysis of transverse energization of ionospheric ions by electrostatic lower hybrid waves, propagating perpendicular to the geomagnetic field [1], to waves propagating obliquely to the field. The analysis in [1] showed that low energy ions can undergo nonlinear coherent energization from their initial ambient low energies to gravitational escape energies if the bandwidth of the frequency spectrum of the waves extends beyond twice the ion cyclotron frequency. While the rocket observations of the upper auroral ionosphere indicate that electrostatic waves are propagating essentially across the geomagnetic field, a small parallel component of the wave vector cannot be ruled out. We determine the effect of oblique propagation of the waves on the nonlinear coherent energization of ions and obtain conditions for which this energization can persist. In the auroral ionospheric plasmas, intense electrostatic fields in density depleted regions and associated transverse energization of ions are also observed. We have been studying, theoretically and computationally, the generation of fields in density cavities. 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. The characteristic features of the fields obtained from this description will be presented. In contrast to a spectrum of plane waves, the fields in density gradients are localized to spatial scales that are small compared to the ion Larmor radius. Also, the interaction of ions with these localized fields is significantly different from that with obliquely propagating electrostatic waves. We find that the phase space of the energized ions can be chaotic, and, for long-time interactions, the ions can undergo large energy gains akin to Levy flights. Detailed analytical and numerical results of the comparison between the interaction of ions with localized field structures and with plane waves will be presented. This work is supported by NSF Grant No. ATM-98-06328 and by NSF-DOE Grant No. DE-FG02-99ER-54555. [1] A.K. Ram, A. Bers, and D. Benisti, J. Geophys. Res. 103, 9431 (1998).
Bers Abraham
Ram Abhay K.
Strozzi David J.
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