The Impact of Energetic Particles on the Martian Ionosphere During a Full Solar Cycle of Radar Observations: Radar Blackouts - Archive ouverte HAL Access content directly
Journal Articles Journal of Geophysical Research: Space Physics Year : 2022

The Impact of Energetic Particles on the Martian Ionosphere During a Full Solar Cycle of Radar Observations: Radar Blackouts

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Mark Lester
Beatriz Sanchez-Cano
Daniel Potts
  • Function : Author
Rob Lillis
  • Function : Author
Marco Cartacci
  • Function : Author
Fabrizio Bernardini
  • Function : Author
Roberto Orosei
Matthew Perry
  • Function : Author
Nathaniel Putzig
  • Function : Author
Bruce Campbell
  • Function : Author
Steve Milan
  • Function : Author
Hermann Opgenoorth
Olivier Witasse
Elena M. M. Redrojo
  • Function : Author
Aaron Russell
  • Function : Author

Abstract

We present the first long-term characterization of ionization layers in the lower ionosphere of Mars (below ∼90 km), a region inaccessible to orbital in-situ observations, based on an analysis of radar echo blackouts observed on Mars Express and the Mars Reconnaissance Orbiter from 2006 to 2017. A blackout occurs when the expected surface reflection is partly or totally attenuated for portions of an observation. Enhanced ionization at altitudes of 60-90 km, below the main ionospheric electron density peak, leads to increased absorption of the radar signal, resulting in the blackouts. We find that (a) MARSIS, operating at frequencies between 1.8 and 5 MHz, suffered more blackouts than SHARAD, which has a higher carrier frequency (20 MHz), (b) there is a clear correlation of blackout occurrence with solar cycle, (c) there is no apparent relationship between blackout occurrence and crustal magnetic fields, and (d) blackouts occur during both nightside and dayside observations, although the peak occurrence is deep on the nightside. Analysis of Mars Atmosphere and Volatile EvolutioN Solar Energetic Particle electron counts between 20 and 200 keV demonstrates that these electrons are likely responsible for attenuating the radar signals. We investigate the minimum SEP electron fluxes required to ionize the lower atmosphere and produce measurable attenuation. When both radars experience a blackout, the SEP electron fluxes are at their highest. Based on several case studies, we find that the average SEP spectrum responsible for a blackout is particularly enhanced at its higher energy end, that is, above 70 keV.
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Dates and versions

insu-03672052 , version 1 (19-05-2022)

Licence

Attribution - CC BY 4.0

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Mark Lester, Beatriz Sanchez-Cano, Daniel Potts, Rob Lillis, Marco Cartacci, et al.. The Impact of Energetic Particles on the Martian Ionosphere During a Full Solar Cycle of Radar Observations: Radar Blackouts. Journal of Geophysical Research: Space Physics, 2022, 127, ⟨10.1029/2021JA029535⟩. ⟨insu-03672052⟩
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