Probing Alfvenic turbulence in numerical simulations in preparation for Solar Probe Plus

Abstract:

This work presents results from numerical simulations of Alfvenic turbulence in the inner heliosphere designed to understand the nature of turbulent fluctuations similar to those that will be measured by Solar Probe Plus (SPP). The simulations are performed inside a narrow magnetic flux tube that models a coronal hole extending from the solar surface into the solar corona to about 40+ solar radii. The simulations describe broad-spectrum, non-compressive turbulence in an inhomogeneous background, including the outflow velocity, without approximating the nonlinear terms in the governing equations. The turbulence is driven by injecting random velocity fluctuations at the photosphere, which are observationally constrained to emulate photospheric motions on the solar surface. These motions in turn drive Alfvenic fluctuations that propagate out into the solar-corona producing non-WKB reflections in the inhomogeneous background and triggering a turbulence cascade from the interaction between outward and inward (reflected) propagating fluctuations. Several diagnostics are used to probe various turbulence properties such as turbulent power spectra, correlation times and lengths, energy dissipation rates, as well as other turbulence characteristics. These simulations are uniquely positioned to investigate and make physics-based predictions of the kind of measurements that are expected from SPP. We will discuss the results in the context of the upcoming measurements by both missions.