Interpreting magnetic variance anisotropy measurements in the solar wind

The magnetic variance anisotropy (A_m) of the solar wind has been used widely as a method to identify the nature of solar wind turbulent fluctuations; however, a thorough discussion of the meaning and interpretation of the A_m has not appeared in the literature. This paper explores the implications and limitations of using the A_m as a method for constraining the solar wind fluctuation mode composition and presents a more informative method for interpreting spacecraft data. The paper also compares predictions of the A_m from linear theory to nonlinear turbulence simulations and solar wind measurements. In both cases, linear theory compares well and suggests that the solar wind for the interval studied is dominantly Alfvénic in the inertial and dissipation ranges to scales of kρ_i ≃5.