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Numerical Study on the Validity of the Taylor Hypothesis in Space Plasmas
Univ Calabria, Dipartimento Fis, Via P Bucci, I-87036 Arcavacata Di Rende, Italy..
Univ Calabria, Dipartimento Fis, Via P Bucci, I-87036 Arcavacata Di Rende, Italy..ORCID iD: 0000-0001-8184-2151
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.ORCID iD: 0000-0003-1654-841x
Univ Calabria, Dipartimento Fis, Via P Bucci, I-87036 Arcavacata Di Rende, Italy..
2017 (English)In: Astrophysical Journal Supplement Series, ISSN 0067-0049, E-ISSN 1538-4365, Vol. 231, no 1, article id 4Article in journal (Refereed) Published
Abstract [en]

In situ heliospheric measurements allow us to resolve fluctuations as a function of frequency. A crucial point is to describe the power spectral density as a function of the wavenumber, in order to understand the energy cascade through the scales in terms of plasma turbulence theories. The most favorable situation occurs when the average wind speed is much higher than the phase speed of the plasma modes, equivalent to the fact that the fluctuations' dynamical times are much longer than their typical crossing period through the spacecraft (frozen-in Taylor approximation). Using driven compressible Hall-magneothydrodynamics simulations, in which an "imaginary" spacecraft flies across a time-evolving turbulence, here we explore the limitations of the frozen-in assumption. We find that the Taylor hypothesis is robust down to sub-proton scales, especially for flows with mean velocities typical of the fast solar wind. For slow mean flows (i.e., speeds of the order of the Alfven speed) power spectra are subject to an amplitude shift throughout the scales. At small scales, when dispersive decorrelation mechanisms become significant, the frozen-in assumption is generally violated, in particular for k-vectors almost parallel to the average magnetic field. A discussion in terms of the spacetime autocorrelation function is proposed. These results might be relevant for the interpretation of the observations, in particular for existing and future space missions devoted to very high-resolution measurements.

Place, publisher, year, edition, pages
2017. Vol. 231, no 1, article id 4
Keywords [en]
interplanetary medium, methods: numerical, plasmas, turbulence
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
URN: urn:nbn:se:uu:diva-341635DOI: 10.3847/1538-4365/aa755aISI: 000415144100001OAI: oai:DiVA.org:uu-341635DiVA, id: diva2:1182025
Available from: 2018-02-12 Created: 2018-02-12 Last updated: 2018-02-12Bibliographically approved

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Vaivads, Andris

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