Waves with frequencies in the vicinity of the oxygen cyclotron frequency and its harmonics have been regularly observed on the Van Allen Probes satellites during geomagnetic storms. We focus on properties of these waves and present events from the main phase of two storms on 1 November 2012 and 17 March 2013 and associated dropouts of a few MeV electron fluxes. They are electromagnetic, in the frequency range ~0.5 to several Hz, and amplitude ~0.1 to a few nT in magnetic and ~0.1 to a few mV/m in electric field, with both the wave velocity and the Poynting vector directed almost parallel to the background magnetic field. These properties are very similar to those of electromagnetic ion cyclotron waves, which are believed to contribute to loss of ring current ions and radiation belt electrons and therefore can be also important for inner magnetosphere dynamics.
Bibliographical noteFunding Information:
We wish to thank the Van Allen Probes EMFISIS and HOPE instrument team for data. We thank Brian Anderson and Richard Denton for insightful conversations. We acknowledge CDAWeb, SSCWeb, and Kyoto observatory for the use of their resources. M.E.U. would like to thank Yuri Khotyaintsev for his wavelet transformation and wave analysis routine. M.E.U. is supported by NASA awards NAS5-01072 and NNX16AF91G. Van Allen Probes data are publicly available and can be accessed at http://rbsp.space.umn.edu/data/rbsp (EFW), https://emfisis.physics.uiowa.edu/data/index (EMFISIS), and https://www.rbsp-ect.lanl.gov (HOPE and REPT).
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- Van Allen Probes
- cyclotron harmonic waves
- energetic particle loss
- geomagnetic storms
- inner magnetosphere