Dissipation of magnetic fluctuations in the solar wind

Robert J. Leamon

Ph.D. Dissertation, University of Delaware, Newark(1999)

Abstract:

The dissipation range for interplanetary magnetic field fluctuations is formed by those fluctuations with spatial scales comparable to the gyroradius of a thermal ion. The dissipation range represents the final fate of magnetic energy that is transferred from the largest spatial scales via nonlinear processes until resonance with the thermal ions removes the energy from the spectrum and heats the background distribution. Typically, the dissipation range at 1 AU sets in at spacecraft frame frequencies of a few tenths of a Hertz. It is characterized by a steepening of the power spectrum and often demonstrates a bias of the polarization or magnetic helicity spectrum. We examine WIND observations of inertial and dissipation range spectra in an attempt to better understand the processes that form the dissipation range and how these processes depend on the ambient solar wind parameters (e.g., IMF intensity, ambient proton density and temperature, etc.). Despite the commonly held belief that parallel-propagating waves such as Alfvén waves form the bulk of inertial range fluctuations, we argue that such waves are inconsistent with spectral break location data. Instead, we show that kinetic Alfvén waves propagating at large angles to the background magnetic field are consistent with the observations, and we describe some possible motivations for this solution. We also show that MHD turbulence consisting of a slab/2-D composite geometry is consistent with the observations and may form the dissipation range, thereby being responsible for heating the background ions. Lastly, we demonstrate that heating of the background electrons is a likely, or possibly necessary, byproduct of magnetic dissipation.