Abstract
Abstract. We statistically study various properties of low-frequency waves such as frequencies, wave numbers, phase velocities, and polarization in the plasma rest frame in the terrestrial foreshock. Using Cluster observations the wave telescope or k-filtering is applied to investigate wave numbers and rest frame frequencies. We find that most of the foreshock waves propagate upstream along the magnetic field at phase velocity close to the Alfvén velocity. We identify that frequencies are around 0.1xΩcp and wave numbers are around 0.1xΩcp/VA, where Ωcp is the proton cyclotron frequency and VA is the Alfvén velocity. Our results confirm the conclusions drawn from ISEE observations and strongly support the existence of Alfvén waves in the foreshock.
Highlights
Waves upstream of the Earth’s bow shock have been widely studied since early observations in the 1960s
Backstreaming ions and associated low-frequency waves were discovered by Asbridge et al (1968), Greenstadt et al (1968), and Fairfield (1969). They led to speculation that the waves were driven by backstreaming ions. These phenomena were studied in more detail using the ISEE dual spacecraft in various methods: morphology or wave form study, frequency analysis, polarization analysis, and estimating wavelengths
We identify this position as the wave number associated with the given frequency and obtain (k, k⊥)=(−1.4 ×10−3, −0.4×10−3) km−1 and=(−1.1×10−3, 0.6×10−3, −0.7×10−3) km−1 in GSE
Summary
Waves upstream of the Earth’s bow shock have been widely studied since early observations in the 1960s. Y. Narita et al.: Alfven waves in the foreshock propagating upstream in the plasma rest frame. Russell (1971) discussed that the foreshock waves were left-hand polarized in the spacecraft frame but intrinsically right-hand polarized, resulting from a reversal of phase speed direction. Such waves should have phase velocities in the plasma rest frame less than the solar wind velocity. Applying the wave analysis method for dual spacecraft data, Dudok de Wit et al (1995), Balikhin et al (1997a, b) presented experimental dispersion relations They combined wave numbers projected into the spacecraft separation line with wave propagation direction derived from the minimum variance analysis.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
