Magnetic field spectra of ICMEs observed by Parker Solar Probe and Solar Orbiter

Abstract

A statistical study of magnetic field power spectra in interplanetary coronal mass ejections (ICMEs) observed by Parker Solar Probe and Solar Orbiter has been performed. The ICMEs had characteristically low proton beta, with values well below unity in all cases. The spectral index was typically near –5/3 and radially invariant in the inertial range, similar to solar wind near the heliospheric current sheet, and steepened to values below –3 in the kinetic range. The break frequency between the inertial and kinetic ranges evolved approximately linearly with radial distance and was closer in scale to the proton inertial length than the proton gyroscale. Magnetic compressibility was invariant with radial distance, in contrast to the solar wind generally. Removal of the background flux rope field gives spectra with shallower slopes at low frequencies (i.e. large spatial scales) and reveals shorter correlation lengths in the magnetic field.