Observed Turbulent Properties of Spherically Polarized Alfvénic States
Résumé
Observation of large scale Alfvénic "switchbacks" of the inner-heliospheric magnetic field, made by Parker Solar Probe, leads to renewed interest in the nonlinear dynamics of constant magnitude and spherically polarized states in MHD. Analysis of high cross helicity streams studied by PSP shows that the turbulent fluctuations are largely consistent with outward propagating spherically polarized Alfvén waves. It is well known that such waves are an exact solution to the MHD equations. In this work, we explore the turbulent scaling properties of outward propagating spherically polarized Alfvén waves using an increment analysis of rotation angles of the dominant Elsasser mode. We show the connection between spherical symmetry and the outer scale (1/f) turbulent spectrum. The effects of spherical polarization on the sub-dominant (inward propagating) Alfvén waves, compressive fluctuations are discussed, as well as implications for the generation of solar wind turbulence and magnetic switchbacks.