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Title: Physical interpretation of the angle-dependent magnetic helicity spectrum in the solar wind: The nature of turbulent fluctuations near the proton gyroradius scale

Motivated by recent observations of distinct parallel and perpendicular signatures in magnetic helicity measurements segregated by wave period and angle between the local magnetic field and the solar wind velocity, this paper undertakes a comparison of three intervals of Ulysses data with synthetic time series generated from a physically motivated turbulence model. From these comparisons, it is hypothesized that the observed signatures result from a perpendicular cascade of Alfvénic fluctuations and a local, non-turbulent population of ion-cyclotron or whistler waves generated by temperature anisotropy instabilities. By constraining the model's free parameters through comparison to in situ data, it is found that, on average, ∼95% of the power near dissipative scales is contained in a perpendicular Alfvénic cascade and that the parallel fluctuations are propagating nearly unidirectionally. The effects of aliasing on magnetic helicity measurements are considered and shown to be significant near the Nyquist frequency.
Authors:
;  [1] ;  [2] ;  [3]
  1. Department of Physics and Astronomy, University of Iowa, Iowa City, IA 52242 (United States)
  2. IREAP, University of Maryland, College Park, MD 20742 (United States)
  3. Center for Space Plasma Physics, Space Science Institute, Boulder, CO 80301 (United States)
Publication Date:
OSTI Identifier:
22357095
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 785; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ALFVEN WAVES; ANISOTROPY; COMPARATIVE EVALUATIONS; FLUCTUATIONS; HELICITY; INSTABILITY; MAGNETIC FIELDS; NYQUIST DIAGRAMS; PLASMA; PROTONS; SOLAR WIND; SPECTRA; TURBULENCE; VELOCITY; WHISTLERS