Turbulent heating in space plasmas: theory and observations

Abstract

A turbulent system transfers energy from large scales to progressively smaller scales until it is ultimately dissipated as heat. At intermediate lengthscales, this energy transfer mostly occurs from larger scales to smaller scales, without any loss of energy. This process is known as the energy cascade. Most space and astrophysical plasmas are considered to exist in a turbulent state. Turbulent energy cascade and dissipation have significant effects on the dynamics of the plasma. However, the nature of energy dissipation is not well understood in weakly-collisional plasmas. Several mechanisms have been proposed as candidates for energy dissipation in these systems. Examples include magnetic reconnection, Landau damping, damping of waves, and heating by microinstabilities, all of which can contribute to plasma heating. A complementary point of view treats the plasma as a statistically homogeneous system with all the aforementioned processes embedded ab inito in an ensemble. From this perspective, an important question is how to quantitatively estimate the average rates of energy transfer and dissipation. In this dissertation, we attempt to answer this and related questions, with a focus on heliospheric plasmas, although the same understandings apply in other turbulent plasmas in laboratory, geophysical, and astrophysical systems.