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Title: NEW INSIGHT INTO SHORT-WAVELENGTH SOLAR WIND FLUCTUATIONS FROM VLASOV THEORY

Abstract

The nature of solar wind (SW) turbulence below the proton gyroscale is a topic that is being investigated extensively nowadays, both theoretically and observationally. Although recent observations gave evidence of the dominance of kinetic Alfven waves (KAWs) at sub-ion scales with {omega} < {omega}{sub ci}, other studies suggest that the KAW mode cannot carry the turbulence cascade down to electron scales and that the whistler mode (i.e., {omega} > {omega}{sub ci}) is more relevant. Here, we study key properties of the short-wavelength plasma modes under limited, but realistic, SW conditions, typically {beta}{sub i} {approx}> {beta}{sub e} {approx} 1 and for high oblique angles of propagation 80 Degree-Sign {<=} {Theta}{sub kB} < 90 Degree-Sign as observed from the Cluster spacecraft data. The linear properties of the plasma modes under these conditions are poorly known, which contrasts with the well-documented cold plasma limit and/or moderate oblique angles of propagation ({Theta}{sub kB} < 80 Degree-Sign ). Based on linear solutions of the Vlasov kinetic theory, we discuss the relevance of each plasma mode (fast, Bernstein, KAW, whistler) in carrying the energy cascade down to electron scales. We show, in particular, that the shear Alfven mode (known in the magnetohydrodynamic limit) extends at scalesmore » k{rho}{sub i} {approx}> 1 to frequencies either larger or smaller than {omega}{sub ci}, depending on the anisotropy k{sub ||}/k . This extension into small scales is more readily called whistler ({omega} > {omega}{sub ci}) or KAW ({omega} < {omega}{sub ci}), although the mode is essentially the same. This contrasts with the well-accepted idea that the whistler branch always develops as a continuation at high frequencies of the fast magnetosonic mode. We show, furthermore, that the whistler branch is more damped than the KAW one, which makes the latter the more relevant candidate to carry the energy cascade down to electron scales. We discuss how these new findings may facilitate resolution of the controversy concerning the nature of the small-scale turbulence, and we discuss the implications for present and future spacecraft wave measurements in the SW.« less

Authors:
;  [1]
  1. Laboratoire de Physique des Plasmas, CNRS-Ecole Polytechnique-UPMC, Observatoire de Saint-Maur, 4 avenue de Neptune, 94107 Saint-Maur-des-Fosses (France)
Publication Date:
OSTI Identifier:
22016101
Resource Type:
Journal Article
Journal Name:
Astrophysical Journal
Additional Journal Information:
Journal Volume: 748; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA); Journal ID: ISSN 0004-637X
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ALFVEN WAVES; COLD PLASMA; MAGNETOHYDRODYNAMICS; SOLAR WIND; TURBULENCE

Citation Formats

Sahraoui, F, Belmont, G, and Goldstein, M. L., E-mail: fouad.sahraoui@lpp.polytechnique.fr. NEW INSIGHT INTO SHORT-WAVELENGTH SOLAR WIND FLUCTUATIONS FROM VLASOV THEORY. United States: N. p., 2012. Web. doi:10.1088/0004-637X/748/2/100.
Sahraoui, F, Belmont, G, & Goldstein, M. L., E-mail: fouad.sahraoui@lpp.polytechnique.fr. NEW INSIGHT INTO SHORT-WAVELENGTH SOLAR WIND FLUCTUATIONS FROM VLASOV THEORY. United States. https://doi.org/10.1088/0004-637X/748/2/100
Sahraoui, F, Belmont, G, and Goldstein, M. L., E-mail: fouad.sahraoui@lpp.polytechnique.fr. Sun . "NEW INSIGHT INTO SHORT-WAVELENGTH SOLAR WIND FLUCTUATIONS FROM VLASOV THEORY". United States. https://doi.org/10.1088/0004-637X/748/2/100.
@article{osti_22016101,
title = {NEW INSIGHT INTO SHORT-WAVELENGTH SOLAR WIND FLUCTUATIONS FROM VLASOV THEORY},
author = {Sahraoui, F and Belmont, G and Goldstein, M. L., E-mail: fouad.sahraoui@lpp.polytechnique.fr},
abstractNote = {The nature of solar wind (SW) turbulence below the proton gyroscale is a topic that is being investigated extensively nowadays, both theoretically and observationally. Although recent observations gave evidence of the dominance of kinetic Alfven waves (KAWs) at sub-ion scales with {omega} < {omega}{sub ci}, other studies suggest that the KAW mode cannot carry the turbulence cascade down to electron scales and that the whistler mode (i.e., {omega} > {omega}{sub ci}) is more relevant. Here, we study key properties of the short-wavelength plasma modes under limited, but realistic, SW conditions, typically {beta}{sub i} {approx}> {beta}{sub e} {approx} 1 and for high oblique angles of propagation 80 Degree-Sign {<=} {Theta}{sub kB} < 90 Degree-Sign as observed from the Cluster spacecraft data. The linear properties of the plasma modes under these conditions are poorly known, which contrasts with the well-documented cold plasma limit and/or moderate oblique angles of propagation ({Theta}{sub kB} < 80 Degree-Sign ). Based on linear solutions of the Vlasov kinetic theory, we discuss the relevance of each plasma mode (fast, Bernstein, KAW, whistler) in carrying the energy cascade down to electron scales. We show, in particular, that the shear Alfven mode (known in the magnetohydrodynamic limit) extends at scales k{rho}{sub i} {approx}> 1 to frequencies either larger or smaller than {omega}{sub ci}, depending on the anisotropy k{sub ||}/k . This extension into small scales is more readily called whistler ({omega} > {omega}{sub ci}) or KAW ({omega} < {omega}{sub ci}), although the mode is essentially the same. This contrasts with the well-accepted idea that the whistler branch always develops as a continuation at high frequencies of the fast magnetosonic mode. We show, furthermore, that the whistler branch is more damped than the KAW one, which makes the latter the more relevant candidate to carry the energy cascade down to electron scales. We discuss how these new findings may facilitate resolution of the controversy concerning the nature of the small-scale turbulence, and we discuss the implications for present and future spacecraft wave measurements in the SW.},
doi = {10.1088/0004-637X/748/2/100},
url = {https://www.osti.gov/biblio/22016101}, journal = {Astrophysical Journal},
issn = {0004-637X},
number = 2,
volume = 748,
place = {United States},
year = {2012},
month = {4}
}