Time-dependent Occurrence Rate of Electromagnetic Cyclotron Waves in the Solar Wind: Evidence for the Effect of Alpha Particles?

G. Q. Zhao, H. Q. Feng, D. J. Wu, Y. H. Chu, J. Huang

Research output: Contribution to journalArticlepeer-review

8 Scopus citations

Abstract

Previous studies revealed that electromagnetic cyclotron waves (ECWs) near the proton cyclotron frequency exist widely in the solar wind, and the majority of ECWs are left-handed (LH) polarized waves. Using the magnetic field data from the STEREO mission, this Letter carries out a survey of ECWs over a long period of 7 years and calculates the occurrence rates of ECWs with different polarization senses. Results show that the occurrence rate is nearly a constant for the ECWs with right-handed polarization, but it varies significantly for the ECWs with LH polarization. Further investigation of plasma conditions reveals that the LH ECWs take place preferentially in a plasma characterized by higher temperature, lower density, and larger velocity. Some considerable correlations between the occurrence rate of LH ECWs and the properties of ambient plasmas are discussed. The present research may provide evidence for the effect of alpha particles on the generation of ECWs.

Original languageEnglish
Article numberL8
JournalAstrophysical Journal Letters
Volume847
Issue number1
DOIs
StatePublished - 20 Sep 2017

Keywords

  • instabilities
  • interplanetary medium
  • solar wind
  • waves

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