A modified version of taylor's hypothesis for solar probe plus observations

Kristopher G. Klein, Jean C. Perez, Daniel Verscharen, Alfred Mallet, Benjamin D.G. Chandran

Research output: Contribution to journalArticle

12 Scopus citations

Abstract

The Solar Probe Plus (SPP) spacecraft will explore the near-Sun environment, reaching heliocentric distances less than 10 R?. Near Earth, spacecraft measurements of fluctuating velocities and magnetic fields taken in the time domain are translated into information about the spatial structure of the solar wind via Taylors frozen turbulence hypothesis. Near the perihelion of SPP, however, the solar-wind speed is comparable to the Alfvn speed, and Taylors hypothesis in its usual form does not apply. In this paper, we show that under certain assumptions, a modified version of Taylors hypothesis can be recovered in the near-Sun region. We consider only the transverse, non-compressive component of the fluctuations at length scales exceeding the proton gyroradius, and we describe these fluctuations using an approximate theoretical framework developed by Heinemann and Olbert. We show that fluctuations propagating away from the Sun in the plasma frame obey a relation analogous to Taylors hypothesis when ⊥ Vsc蠑 z- and z+ 蠑 z-, where Vsc⊥ is the component of the spacecraft velocity perpendicular to the mean magnetic field and z+ (z-) is the Elsasser variable corresponding to transverse, non-compressive fluctuations propagating away from (toward) the Sun in the plasma frame. Observations and simulations suggest that, in the near-Sun solar wind, the above inequalities are satisfied and z+ fluctuations account for most of the fluctuation energy. The modified form of Taylors hypothesis that we derive may thus make it possible to characterize the spatial structure of the energetically dominant component of the turbulence encountered by SPP.

Original languageEnglish (US)
Article numberL18
JournalAstrophysical Journal Letters
Volume801
Issue number1
DOIs
StatePublished - Mar 1 2015
Externally publishedYes

Keywords

  • Sun: corona
  • plasmas
  • solar wind
  • turbulence

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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