Journal article
Localized Ionization Hypothesis for Transient Ionospheric Layers
Journal of geophysical research. Space physics, Vol.124(6), pp.4870-4880
06/2019
DOI: 10.1029/2018JA026251
Abstract
The persistent two‐peaked vertical structure of the Martian ionosphere is created by extreme and far ultraviolet radiation whose energies, respectively, determine their ionization altitude. A third low‐altitude transient layer (previously referred to as M3 or Mm) has been observed by radio occultation techniques and attributed to meteor ablation. However, recent remote sensing and in situ observations disfavor a meteoric origin. Here we propose an alternative hypothesis for these apparent layers associated with impact ionization from penetrating solar wind ions, previously observed as proton aurora. Localized ionization, occurring nonglobally at a given altitude range, breaks the symmetry assumed by the radio occultation technique, and creates electron layers apparently lower in the ionosphere than their true altitude. This may occur when the upstream bow shock is altered by a radial interplanetary magnetic field configuration, which allows the solar wind to penetrate directly into the thermosphere. This localized ionization hypothesis provides an explanation for apparent layers' wide variation in heights and their transient behavior. Moreover, this hypothesis is testable with new observations by the Mars Atmospheric and Volatile EvolutioN Radio Occultation Science Experiment in future Mars years. This hypothesis has implications for the ionospheres of Venus and Titan, where similar transient layers have been observed.
Plain Language Summary
The ionosphere of a planet couples the neutral atmosphere to the exosphere and solar wind. Created by solar ionizing radiation, the ionosphere on the dayside of planet is expected to be hemispherically symmetric. When Mars Express discovered transient low‐altitude ionospheric layers in 2005, they were initially predicted to be due to meteor ablation. However, recent observations indicate that they are due to a geometric observational effect related to local, not hemispheric, ionization. Observations from three instruments on Mars Atmospheric and Volatile EvolutioN are used concurrently to understand this phenomenon. These transient layers have been observed at Venus and Titan as well, and this hypothesis indicates novel physics for those ionospheric systems.
Key Points
Low‐altitude transient ionospheric layers may be explained by a geometric observational effect from localized, not hemispheric, ionization
A radio occultation of a transient ionospheric layer was obtained with observations of variable proton aurora and penetrating solar wind
Transient layers observed at Mars, Venus, and Titan are consistent with the presence of solar wind impact ionization at those planets
Details
- Title: Subtitle
- Localized Ionization Hypothesis for Transient Ionospheric Layers
- Creators
- M. M. J. Crismani - Goddard Space Flight CenterJ. Deighan - University of Colorado BoulderN. M. Schneider - University of Colorado BoulderJ. M. C. Plane - University of LeedsP. Withers - Boston UniversityJ. Halekas - University of IowaM. Chaffin - Laboratory for Atmospheric and Space PhysicsS. Jain - Laboratory for Atmospheric and Space Physics
- Resource Type
- Journal article
- Publication Details
- Journal of geophysical research. Space physics, Vol.124(6), pp.4870-4880
- DOI
- 10.1029/2018JA026251
- ISSN
- 2169-9380
- eISSN
- 2169-9402
- Number of pages
- 11
- Grant note
- European Research Council (291332) Universities Space Research Association (USRA)
- Language
- English
- Date published
- 06/2019
- Academic Unit
- Physics and Astronomy
- Record Identifier
- 9984428796702771
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