Detecting Mirror Mode Waves at Mars with MAVEN: from Case Study to Statistical Occurrence Maps
Abstract
Mirror mode waves are highly compressional structures arising from an ion temperature anisotropy in a high-β plasma; they play an important role in the generation of particle acceleration and in the energy transfer from solar wind particles to planetary magnetospheres. The detection of mirror mode waves at Mars and Venus have historically relied on magnetic measurements only, because magnetometers on space missions are common and have a high temporal resolution. The NASA/MAVEN spacecraft, which arrived at Mars in October 2014, uniquely possesses both a fluxgate magnetometer (MAG) and a suite of plasma instruments such as the Solar Wind Ion Analyser (SWIA), capable of measuring the in-situ ion plasma moments --density, velocity and pressure tensor-- up to a resolution of 4 s.
In this study we present spatial occurrence maps of mirror mode waves detected around Mars with the NASA/MAVEN spacecraft. First, mirror mode candidates are detected with magnetic-field-only criteria (large amplitude, linearly polarised compressional signatures) by applying the minimum variance analysis to the 1-Hz magnetic field components. In a second step, these candidate detections are validated against calculated plasma moments given by SWIA: several test cases illustrating bow shock crossings and magnetosheath conditions are discussed, which make it possible to fine-tune the B-field-only criteria. In a third step, spatial occurrence maps are built for the 2014-2020 period using these refined criteria, and occurrence rates are studied with respect to Martian year (MY32 to MY35), solar longitude and solar activity. These structures appear to be delimited by the bow shock on one side and by the magnetic pile-up boundary on the other, with occurrence probabilities below 5-6% on average.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2020
- Bibcode:
- 2020AGUFMP049...04S
- Keywords:
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- 6026 Ionospheres;
- PLANETARY SCIENCES: COMETS AND SMALL BODIES;
- 5405 Atmospheres;
- PLANETARY SCIENCES: SOLID SURFACE PLANETS;
- 5435 Ionospheres;
- PLANETARY SCIENCES: SOLID SURFACE PLANETS;
- 5443 Magnetospheres;
- PLANETARY SCIENCES: SOLID SURFACE PLANETS