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Annales Geophysicae An interactive open-access journal of the European Geosciences Union
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Volume 27, issue 1
Ann. Geophys., 27, 121–130, 2009
https://doi.org/10.5194/angeo-27-121-2009
© Author(s) 2009. This work is distributed under
the Creative Commons Attribution 3.0 License.
Ann. Geophys., 27, 121–130, 2009
https://doi.org/10.5194/angeo-27-121-2009
© Author(s) 2009. This work is distributed under
the Creative Commons Attribution 3.0 License.

  07 Jan 2009

07 Jan 2009

The modulation of electromagnetic ion cyclotron waves by Pc 5 ULF waves

T. M. Loto'aniu1,2, B. J. Fraser3, and C. L. Waters3 T. M. Loto'aniu et al.
  • 1Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, CO, USA
  • 2Space Weather Prediction Center, National Oceanic and Atmospheric Administration, Boulder, CO, USA
  • 3Center for Space Physics, School of Mathematical and Physical Sciences, University of Newcastle, NSW, Australia

Abstract. The modulation of electromagnetic ion cyclotron (EMIC) waves by longer-period ULF waves has been proposed as a method for producing pearl structured Pc 1–2 EMIC waves. This study examines frequency and phase relationship between Pc 1 EMIC wavepacket envelopes and simultaneously occurring Pc 5 ULF waves using magnetic data measured by the CRRES spacecraft. Intervals from three days in 1991 where CRRES observed pearls are presented along with simple statistics for 58 EMIC wavepackets. The observations were dominated by EMIC waves propagating away from the equatorial region. Comparisons between pearl wavepacket envelopes and Pc 5 waves show excellent agreement. The pearl wavepacket duration times, τdur, were statistically correlated with Pc 5 wave periods, TPc5, resulting in a correlation coefficient of R=0.7 and best fit equation τdur=0.8·TPc5+6 s. In general, phase differences varied although time intervals of constant in-phase or anti-phase correlation were observed. Anti-phase modulation may be explained by a decreasing background magnetic field due to the negative cycle of the ULF wave decreasing Alfvén velocity and minimum resonant energy. In-phase modulation could be the result of adiabatic modulation of temperature anisotropy in-phase with variations in the background field. Non-adiabatic processes may contribute to intervals that showed varying phase differences with time. Results suggest that future theoretical developments should take into account the full range of possible wave particle interactions inside the magnetosphere.

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