EGU23-10536
https://doi.org/10.5194/egusphere-egu23-10536
EGU General Assembly 2023
© Author(s) 2023. This work is distributed under
the Creative Commons Attribution 4.0 License.

MAVEN Observations of Steepened Ultra-Low Frequency Waves in the Upstream Martian Foreshock Region

Gangkai Poh1,2, Jared Espley1, Shaosui Xu3, Guan Le1, Norberto Romanelli1,4, Jasper Halekas5, Gina DiBraccio1, and Jacob Gruesbeck1
Gangkai Poh et al.
  • 1Solar System Exploration Division, NASA Goddard Space Flight Center, Greenbelt, Maryland, USA
  • 2Center for Research and Exploration in Space Sciences and Technology II, Catholic University of America, Washington DC, USA
  • 3Space Sciences Laboratory, University of California, Berkeley, Berkeley, CA, USA,
  • 4Center for Research and Exploration in Space Sciences and Technology II, University of Maryland Baltimore County, Baltimore, MD, USA
  • 5Department of Physics and Astronomy, University of Iowa, Iowa City, IA, USA

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. 

How to cite: Poh, G., Espley, J., Xu, S., Le, G., Romanelli, N., Halekas, J., DiBraccio, G., and Gruesbeck, J.: MAVEN Observations of Steepened Ultra-Low Frequency Waves in the Upstream Martian Foreshock Region, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-10536, https://doi.org/10.5194/egusphere-egu23-10536, 2023.