Considerations Limiting Cyclotron-Resonant Damping of Cascading Interplanetary Turbulence and why the `Slab' Approximation Fails

Robert J. Leamon, William H. Matthaeus, Charles W. Smith and Hung K. Wong

Proceedings, Ninth International Solar Wind Conference (Nantucket, MA), 465-468, AIP, New York (1999)

Abstract:

In attempting to understand the dissipation of MHD scale fluctuation energy in the solar wind, the challenge is to harness kinetic theory [1,2] effects in a way that is consistent with the presence of an active spectral cascade in a collisionless plasma. Recent observational studies [3,4] have begun the task of sorting out constraints that spacecraft observations place on dissipation range dynamical processes. Here we examine some implications of dissipation range and inertial range correlation and spectral analyses extracted [4] from 33 intervals of Wind magnetic field data. There are strong suggestions of magnetic fluctuations having highly oblique wave vectors, but when field polarity and signatures of cross helicity and magnetic helicity are examined, most of the data sets suggest some role of resonant dissipative processes involving thermal protons. Here we seek an explanation for this effect by postulating that an active spectral cascade into the dissipation range is balanced by a combination of resonant and non resonant kinetic dissipation mechanisms. By solving a pair of rate equations, and employing constraints from the data, this theory suggests that the ratio of the two types of effects is of order unity. With an additional assumption that mixed cross helicity corresponds to random directional sweeping, the theory approximates the relationship between magnetic and cross helicities seen in the Wind datasets. Although highly simplified, this approach appears to account for several observed features, and explains why complete absorption, and the corresponding pure signature in the magnetic helicity spectrum, is usually not observed.

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[4] R J Leamon, C W Smith, N F Ness, W H Matthaeus and H K Wong, J. Geophys. Res., 103, 4775 (1998)