PLASMA-FIELD COUPLING AT SMALL LENGTH SCALES IN SOLAR WIND NEAR 1 au

• Published in: The Astrophysical journal Vol. 829; no. 2; pp. 88 - 101
• Main Authors: Livadiotis, G., Desai, M. I.
• Format: Journal Article
• Language: English
• Published: Philadelphia The American Astronomical Society 01.10.2016; IOP Publishing
• Subjects: ACCURACY; ALFVEN WAVES; Astrophysics; ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; Charged particles; COLLISIONLESS PLASMA; Collisionless plasmas; Coupling; DATA ANALYSIS; DISPERSIONS; EFFICIENCY; LANGMUIR FREQUENCY; MAGNETIC FIELDS; methods: data analysis; Plasma; Plasma frequencies; plasmas; Solar energy; SOLAR WIND; Solar wind velocity; VELOCITY; waves
• DOI: 10.3847/0004-637X/829/2/88
• ISSN: 0004-637X

ABSTRACT In collisionless plasmas such as the solar wind, the coupling between plasma constituents and the embedded magnetic field occurs on various temporal and spatial scales, and is primarily responsible for the transfer of energy between waves and particles. Recently, it was shown that the transfer of energy between solar wind plasma particles and waves is governed by a new and unique relationship: the ratio between the magnetosonic energy and the plasma frequency is constant, Ems/ pl ∼ *. This paper examines the variability and substantial departure of this ratio from * observed at ∼1 au, which is caused by a dispersion of fast magnetosonic (FMS) waves. In contrast to the efficiently transferred energy in the fast solar wind, the lower efficiency of the slow solar wind can be caused by this dispersion, whose relation and characteristics are derived and studied. In summary, we show that (i) the ratio Ems/ pl transitions continuously from the slow to the fast solar wind, tending toward the constant *; (ii) the transition is more efficient for larger thermal, Alfvén, or FMS speeds; (iii) the fast solar wind is almost dispersionless, characterized by quasi-constant values of the FMS speed, while the slow wind is subject to dispersion that is less effective for larger wind or magnetosonic speeds; and (iv) the constant * is estimated with the best known precision, * (1.160 0.083) × 10−22 Js.