Physics
Scientific paper
May 2007
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007agusmsm54a..03s&link_type=abstract
American Geophysical Union, Spring Meeting 2007, abstract #SM54A-03
Physics
2407 Auroral Ionosphere (2704), 2471 Plasma Waves And Instabilities (2772), 2483 Wave/Particle Interactions (7867), 7845 Particle Acceleration
Scientific paper
It is now well established that shear Alfven waves (SAWs) dump a large amount of electrognatic power in the topside auroral ionosphere. How is this energy dissipated? Obervations also show that the SAWs have narrow transverse structures. How are such narrow (filamentary) structures created from SAWs having long transverse wavelengths generated in the distant parts of the magnetosphere? We demonstrate by kinetic simulations that when long wavelength SAWs encounter localized density cavities, they induce electric dipoles in the cavities due to the divergence in the ion polarization current. The dipoles radiate narrow structures of Alfven waves like the inertial Alfven waves detected from Freja, FAST and Polar. The radiated wave patterns are the Alfven wave resonance cones. The existence of Alfven wave resonance cones has already been known theoretically as well as from laboratory experiments. Refined space observations have recently demonstrated that Alfven wave resonance cones do indeed occur and they introduce fine structures in the auroral electron accelerations and hence in the auroral arc structures. Comparing the structures in the Alfven wave resonance cone radiated from the localized cavities with satellite data we find that the transversely narrow structures of the inertial Alfven waves detected from Freja, FAST and Polar are indeed the Alfven wave resonance cones. The localized density cavities themselves are generated by double layers, which are an integral part of the auroaral acceleration processes. Thus we discuss the entire chain of processes involved in the dissipation of SAWs; the chain involves SAWs as the source of energy, the localized plasma density cavities, generation of nature-made electric dipole antennas in the cavities, radiation of short scale inertial Alfven waves, which facilitate the transfer of electromagnetic energy into the kinetic energy of the plasma ions. Thus the Alfven wave cones represent an important plasma phenomenon, which is predicted from theory, has been quantitatively measured in laboratory and now detected in space as well. It is also a strategically important phenomenon because it facilitates in the transfer of Alfven wave power into the ions' kinetic energy and thereby in their outflow.
Khazanov Igor
Singh Navinder
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