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Proton Temperature Anisotropies in the Plasma Environment of Venus
Luleå University of Technology. Swedish Institute of Space Physics, Kiruna, Sweden. Physics, Lancaster University, Lancaster, United Kingdom.
Swedish Institute of Space Physics, Kiruna, Sweden.
Swedish Institute of Space Physics, Uppsala, Sweden.
Swedish Institute of Space Physics, Kiruna, Sweden.
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2019 (English)In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 124, no 5, p. 3312-3330Article in journal (Refereed) Published
Abstract [en]

Velocity distribution functions (VDFs) are a key to understanding the interplay between particles and waves in a plasma. Any deviation from an isotropic Maxwellian distribution may be unstable and result in wave generation. Using data from the ion mass spectrometer IMA (Ion Mass Analyzer) and the magnetometer (MAG) onboard Venus Express, we study proton distributions in the plasma environment of Venus. We focus on the temperature anisotropy, that is, the ratio between the proton temperature perpendicular (T⊥) and parallel (T‖) to the background magnetic field. We calculate average values of T⊥ and T‖ for different spatial areas around Venus. In addition we present spatial maps of the average of the two temperatures and of their average ratio. Our results show that the proton distributions in the solar wind are quite isotropic, while at the bow shock stronger perpendicular than parallel heating makes the downstream VDFs slightly anisotropic (T⊥/T‖ > 1) and possibly unstable to generation of proton cyclotron waves or mirror mode waves. Both wave modes have previously been observed in Venus's magnetosheath. The perpendicular heating is strongest in the near‐subsolar magnetosheath (T⊥/T‖≈3/2), which is also where mirror mode waves are most frequently observed. We believe that the mirror mode waves observed here are indeed generated by the anisotropy. In the magnetotail we observe planetary protons with largely isotropic VDFs, originating from Venus's ionosphere.

Place, publisher, year, edition, pages
John Wiley & Sons, 2019. Vol. 124, no 5, p. 3312-3330
National Category
Fusion, Plasma and Space Physics
Identifiers
URN: urn:nbn:se:ltu:diva-75083DOI: 10.1029/2019JA026619ISI: 000471601500011Scopus ID: 2-s2.0-85066913100OAI: oai:DiVA.org:ltu-75083DiVA, id: diva2:1331948
Available from: 2019-06-27 Created: 2019-06-27 Last updated: 2019-07-01Bibliographically approved

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