Effect of Spherical Polarization on the Magnetic Spectrum of the Solar Wind

Understand

Magnetic fluctuations in the solar wind are often observed to maintain constant magnitude of the magnetic field in a manner consistent with spherically-polarized large-amplitude Alfv\'en waves.

• We investigate the effect of spherical polarization on the magnetic spectral index through a statistical survey of magnetic fluctuations observed by Parker Solar Probe between 20$R_\odot$ and 200$R_\odot$.
• We find that deviations from spherical polarization, i.e., changes in $|\mathbf{B}|$ (compressive fluctuations) and one-dimensional discontinuities, have a dramatic effect on the scaling behavior of the turbulent fluctuations.
• We show that shallow $k^{-3/2}$ spectra are only observed for constant magnetic field strength, three-dimensional structures, which we identify as large amplitude Alfv\'en waves.