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Cross-scale energy transport in space plasmas

Nature Physics volume 12, pages 11641169 (2016) | Download Citation

Abstract

The solar wind is a supersonic magnetized plasma streaming far into the heliosphere. Although cooling as it flows, it is rapidly heated upon encountering planetary obstacles. At Earth, this interaction forms the magnetosphere and its sub-regions. The present paper focuses on particle heating across the boundary separating the shocked solar wind and magnetospheric plasma, which is driven by mechanisms operating on fluid, ion and electron scales. The cross-scale energy transport between these scales is a compelling and fundamental problem of plasma physics. Here, we present evidence of the energy transport between fluid and ion scales: free energy is provided in terms of a velocity shear generating fluid-scale Kelvin–Helmholtz instability. We show the unambiguous observation of an ion-scale magnetosonic wave packet, inside a Kelvin–Helmholtz vortex, with sufficient energy to account for observed ion heating. The present finding has universal consequences in understanding cross-scale energy transport, applicable to environments experiencing velocity shears during comparable plasma regimes.

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Acknowledgements

The work of T.W.M. and K.N. was supported by National Science Foundation Grants 0847120 and 1502774. The work of A.P.D. was supported by the Academy of Finland Grants 288472 and 267073/2013. The authors would like to thank M. A. Balikhin for valuable discussion. The authors would like to acknowledge the work performed by the Cluster FGM, EFW, CIS and PEACE instrument teams as well as the Cluster Science Archive and the Cluster Active Archive for the use of their data.

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Affiliations

  1. Centre for Space and Atmospheric Research, Physical Sciences Department, Embry-Riddle Aeronautical University, Daytona Beach, Florida 32114, USA

    • T. W. Moore
    •  & K. Nykyri
  2. Department of Radio Science and Engineering, School of Electrical Engineering, Aalto University, Espoo 02150, Finland

    • A. P. Dimmock

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Contributions

K.N. provided the idea, initiated the study and guided the work of graduate student T.W.M., who identified the KH event from Cluster data, screened the data for plasma mixing regions and higher frequency plasma waves, analysed wave properties, created 2.5D MHD simulations of the event and prepared figures for the manuscript. A.P.D. computed the experimental dispersion relation using the two-spacecraft method. All authors contributed to the writing and editing of the manuscript and discussed the methods, results and scientific implications at all stages. All authors discussed the text and commented on the manuscript.

Competing interests

The authors declare no competing financial interests.

Corresponding author

Correspondence to T. W. Moore.

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https://doi.org/10.1038/nphys3869

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