Observational constraints on the dynamics of the interplanetary magnetic field dissipation range

TLDR

The interplanetary magnetic field dissipation range occurs at scales comparable to the ion gyroradius or inertial length, appears at ~0.1 Hz at 1 AU, steepens the power spectrum, and often shows polarization or helicity bias, representing the final stage of magnetic energy transfer and plasma heating. We examine Wind observations of inertial and dissipation range spectra to better understand the processes that form the dissipation range and how these processes depend on ambient solar wind parameters. We focus on stationary intervals with well‑defined inertial and dissipation range spectra. Our analysis shows that parallel‑propagating Alfvén waves are inconsistent with the data, while MHD turbulence with a partly slab and partly 2‑D composite geometry—possibly involving thermal particle interactions with the 2‑D component—and kinetic Alfvén waves at large angles to the background field are consistent with observations and may contribute to the dissipation range.

Abstract

The dissipation range for interplanetary magnetic field fluctuations is formed by those fluctuations with spatial scales comparable to the gyroradius or ion inertial length of a thermal ion. It is reasonable to assume that the dissipation range represents the final fate of magnetic energy that is transferred from the largest spatial scales via nonlinear processes until kinetic coupling with the background plasma 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 (interplanetary magnetic field intensity, ambient proton density and temperature, etc.). We focus on stationary intervals with well‐defined inertial and dissipation range spectra. Our analysis shows that parallel‐propagating waves, such as Alfvén waves, are inconsistent with the data. MHD turbulence consisting of a partly slab and partly two‐dimensional (2‐D) composite geometry is consistent with the observations, while thermal paxticle interactions with the 2‐D component may be responsible for the formation of the dissipation range. Kinetic Alfvén waves propagating at large angles to the background magnetic field are also consistent with the observations and may form some portion of the 2‐D turbulence component.