Statistical evidence for O<sup>+</sup> energization and outflow caused by wave-particle interaction in the high altitude cusp and mantle
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Published:2011-05-30
Issue:5
Volume:29
Page:945-954
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ISSN:1432-0576
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Container-title:Annales Geophysicae
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language:en
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Short-container-title:Ann. Geophys.
Author:
Waara M.,Slapak R.,Nilsson H.,Stenberg G.,André M.,Barghouthi I. A.
Abstract
Abstract. We present a statistical study of the low (<1 Hz) frequency electric and magnetic field spectral densities observed by Cluster spacecraft in the high altitude cusp and mantle region. At the O+ gyrofrequency (0.02–0.5 Hz) for this region the electric field spectral density is on average 0.2–2.2 (mV m−1)2 Hz−1, implying that resonant heating at the gyrofrequency can be intense enough to explain the observed O+ energies of 20–1400 eV. The relation between the electric and magnetic field spectral densities results in a large span of phase velocities, from a few hundred km s−1 up to a few thousand km s−1. In spite of the large span of phase velocity, the ratio between the calculated local Alfvén velocity and the estimated phase velocity is close to unity. We provide average values of a coefficient describing diffusion in ion velocity space at different altitudes, which can be used in studies of ion energization and outflow. The observed average waves can explain the average O+ energies measured in the high altitude (8–15 RE) cusp/mantle region of the terrestrial magnetosphere according to our test particle calculations.
Publisher
Copernicus GmbH
Subject
Space and Planetary Science,Earth and Planetary Sciences (miscellaneous),Atmospheric Science,Geology,Astronomy and Astrophysics
Cited by
30 articles.
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