MAVEN Observations of Steepened Ultra-Low Frequency Waves in the Upstream Martian Foreshock Region
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Author/Creator ORCID
Date
2023-04-03
Type of Work
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Citation of Original Publication
Poh, Gangkai, et al. "MAVEN Observations of Steepened Ultra-Low Frequency Waves in the Upstream Martian Foreshock Region" EGU General Assembly 2023, EGU23-10536 (Vienna, Austria & Online, 23–28 April 2023). https://doi.org/10.5194/egusphere-egu23-10536.
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This work was written as part of one of the author's official duties as an Employee of the United States Government and is therefore a work of the United States Government. In accordance with 17 U.S.C. 105, no copyright protection is available for such works under U.S. Law.
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Abstract
In this study, we present the analysis of steepened ultra-low frequency (ULF) waves in the
foreshock region upstream of Mars’ bow shock observed by the Mars Atmosphere and Volatile
EvolutioN (MAVEN) spacecraft at Mars. A survey of MAVEN magnetic field and plasma
measurements shows quasi-periodic gradual increases followed by a sharp decrease in the
magnetic field magnitude (Btotal). Higher frequency waves were also commonly, but not always,
observed at the trailing edge of the large-amplitude increase in Btotal. These observations are
consistent with the signatures of shocklets observed in the solar wind region upstream of Earth’s
and planetary bow shocks. Shocklets are believed to be formed as a result of the steepening of
fast magnetosonic waves generated by reflected ions in the quasi-parallel foreshock region. We
also performed the minimum variance analysis (MVA) and statistical analysis technique to
determine the wave properties (e.g. polarization, wave propagation, amplitude and frequency) of
the shocklets and higher frequency waves observed in its trailing edge. Our results showed that
these shocklets are left-handed polarized in the spacecraft frame, with mean amplitude δB/B of
~3.5 and time separation between adjacent shocklet events of ~40s. We also analyzed
measurements (ions and electrons) from MAVEN’s plasma instruments to investigate the
energization process of the particles during the observations of shocklets. We will discuss the
possible generation mechanisms for these steepened ultra-low frequency waves at Mars, and any
implications for the martian plasma environment downstream of Mars’ bow shock.