Intermittency Scaling Laws in Magnetohydrodynamic Turbulence: Theory, Simulations and Observations

Abstract

The main objective of this dissertation is to investigate intermittency of Magnetohydrodynamic (MHD) plasmas by means of high-resolution numerical simulations and large sets of solar wind data. Understanding intermittency scaling laws is a significant step forward towards understanding the fundamental properties of plasma turbulence and how spatial structures influence dissipation, heating, transport and acceleration of charged particles, which is important in a wide range of laboratory, space and astrophysical plasmas. The current stateof- the art in the theoretical understanding of intermittency in MHD turbulence is based on phenomenological (non-exact) models, numerical simulations and solar wind observations of structure functions of velocity and magnetic field fluctuations, which measure the statistical moments of random field increments characterizing the turbulent flow at each lengthscale. Although velocity and magnetic field are physically intuitive variables to describe a plasma, the so-called Elsasser fields represent a more natural set of variables to describe MHD turbulence. In this work we use state-of-the-art numerical simulations and solar wind observations from the WIND spacecraft to accomplish the following goals: 1) measure probability distribution functions (PDF) of Elsasser fields scale by scale from simulations and large data sets of solar wind data, 2) develop empirical models of the resulting distributions to determine scaling laws, and 3) use the resulting models of PDFs to determine scaling laws of structure functions and compare with phenomenological theories of MHD turbulence.