Velocity-space diffusion of solar wind protons in oblique waves and weak turbulence

• Published in: Annales geophysicae (1988) Vol. 29; no. 11; pp. 2089 - 2099
• Main Authors: MARSCH, E, BOUROUAINE, S
• Format: Journal Article
• Language: English
• Published: Göttingen Copernicus 24.11.2011; Copernicus GmbH; Copernicus Publications
• Subjects: Comparative analysis; Earth, ocean, space; Exact sciences and technology; External geophysics; Physics of the ionosphere; Physics of the magnetosphere; Probability distributions; Protons; Turbulence (Fluid dynamics); Wave propagation; Plasma turbulence; Velocity space; Wave interaction; Solar protons; Forecast model; Electrostatic wave; Sun; Velocity distribution function; MHD wave; solar wind; Measurement in situ; Magnetoacoustic wave; Wave propagation; Alfven wave; Solar plasma; Weak turbulence; Diffusion process; Quasi linear theory; Diffusion; Helios satellites; MHD turbulence; Interplanetary physics (MHD waves and turbulence; Plasma waves and turbulence; Solar wind plasma)
• ISSN: 0992-7689; 1432-0576; 1432-0576
• DOI: 10.5194/angeo-29-2089-2011

The fast solar wind is permeated by all kinds of plasma waves which have a broad range of wavelengths and occur on many different scales. Kinetically, a plasma wave induces ion-wave interactions which can within the quasi-linear theory be described as a diffusion process. The impact this diffusion may have on the shape of the proton velocity distribution function (VDF) is studied. We first analyse theoretically some of the possible kinetic effects of the waves on the ions. Then the model predictions are compared with the detailed in-situ plasma measurements made by the Helios spacecraft on 14 April 1976 at 0.3 AU and found to comply favourably with resonant diffusion of protons in obliquely propagating magnetohydrodynamic waves. In particular, the shape at the edges of the VDFs at positive proton velocities in the wind frame can be well explained by cyclotron-resonant diffusion of the protons in oblique fast magnetoacoustic and Alfvén waves propagating away from the Sun.