O<sup>+</sup> heating associated with strong wave activity in the high altitude cusp and mantle
We use the Cluster spacecraft to study three events with intense waves and energetic oxygen ions (O<sup>+</sup>) in the high altitude cusp and mantle. The ion energies considered are of the order 1000 eV and higher, observed above an altitude of 8 earth radii together with high wave p...
| Main Authors: | , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2011-05-01
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| Series: | Annales Geophysicae |
| Online Access: | https://www.ann-geophys.net/29/931/2011/angeo-29-931-2011.pdf |
| Summary: | We use the Cluster spacecraft to study three events with intense waves and
energetic oxygen ions (O<sup>+</sup>) in the high altitude cusp and mantle. The ion
energies considered are of the order 1000 eV and higher, observed above an
altitude of 8 earth radii together with high wave power at the O<sup>+</sup>
gyrofrequency. We show that heating by waves can explain the observed high
perpendicular energy of O<sup>+</sup> ions, using a simple gyroresonance model and
25–45% of the observed wave spectral density at the gyrofrequency. This is
in contrast to a recently published study where the wave intensity was too
low to explain the observed high altitude ion energies. Long lasting cases
(>10 min) of high perpendicular-to-parallel temperature ratios are
sometimes associated with low wave activity, suggesting that high
perpendicular-to-parallel temperature ratio is not a good indicator of local
heating. Using multiple spacecraft, we show that the regions of enhanced wave
activity are at least one order of magnitude larger than the gyroradius of
the heated ions. |
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| ISSN: | 0992-7689 1432-0576 |