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The Effects Of Kinetic Instabilities On Small-Scale Turbulence In Earth's Magnetosheath
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
LESIA Observ Paris Meudon, Meudon, France..
2016 (English)In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 829, no 1, article id 54Article in journal (Refereed) Published
Abstract [en]

The Earth's magnetosheath is the region delimited by the bow shock and the magnetopause. It is characterized by highly turbulent fluctuations covering all scales from MHD down to kinetic scales. Turbulence is thought to play a fundamental role in key processes such as energy transport and dissipation in plasma. In addition to turbulence, different plasma instabilities are generated in the magnetosheath because of the large anisotropies in plasma temperature introduced by its boundaries. In this study we use high-quality magnetic field measurements from Cluster spacecraft to investigate the effects of such instabilities on the small-scale turbulence (from ion down to electron scales). We show that the steepening of the power spectrum of magnetic field fluctuations in the magnetosheath occurs at the largest characteristic ion scale. However, the spectrum can be modified by the presence of waves/structures at ion scales, shifting the onset of the small-scale turbulent cascade toward the smallest ion scale. This cascade is therefore highly dependent on the presence of kinetic instabilities, waves, and local plasma parameters. Here we show that in the absence of strong waves the small-scale turbulence is quasi-isotropic and has a spectral index alpha approximate to 2.8. When transverse or compressive waves are present, we observe an anisotropy in the magnetic field components and a decrease in the absolute value of alpha. Slab/2D turbulence also develops in the presence of transverse/compressive waves, resulting in gyrotropy/non-gyrotropy of small-scale fluctuations. The presence of both types of waves reduces the anisotropy in the amplitude of fluctuations in the small-scale range.

Place, publisher, year, edition, pages
2016. Vol. 829, no 1, article id 54
Keywords [en]
Earth, instabilities, turbulence, waves
National Category
Astronomy, Astrophysics and Cosmology Other Earth and Related Environmental Sciences
Identifiers
URN: urn:nbn:se:uu:diva-307749DOI: 10.3847/0004-637X/829/1/54ISI: 000385374500054OAI: oai:DiVA.org:uu-307749DiVA, id: diva2:1048356
Funder
EU, European Research Council, 313038/STORMAvailable from: 2016-11-21 Created: 2016-11-21 Last updated: 2017-11-29Bibliographically approved

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