The Ion Transition Range of Solar Wind Turbulence in the Inner Heliosphere: Parker Solar Probe Observations

Abstract

The scaling of the turbulent spectra provides a key measurement that allows to discriminate between different theoretical predictions of turbulence. In the solar wind, this has driven a large number of studies dedicated to this issue using in-situ data from various orbiting spacecraft. While a semblance of consensus exists regarding the scaling in the MHD and dispersive ranges, the precise scaling in the transition range and the actual physical mechanisms that control it remain open questions. Using the high-resolution data in the inner heliosphere from Parker Solar Probe (PSP) mission, we find that the sub-ion scales (i.e., at the frequency f ~ [2, 9] Hz) follow a power-law spectrum f^a with a spectral index a varying between -3 and -5.7. Our results also show that there is a trend toward and anti-correlation between the spectral slopes and the power amplitudes at the MHD scales, in agreement with previous studies: the higher the power amplitude the steeper the spectrum at sub-ion scales. A similar trend toward an anti-correlation between steep spectra and increasing normalized cross helicity is found, in agreement with previous theoretical predictions about the imbalanced solar wind. We discuss the ubiquitous nature of the ion transition range in solar wind turbulence in the inner heliosphere.

Accepted by ApJL

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Cited by in corpus (10)

• Geometry of Magnetic Fluctuations near the Sun from PSP
• The radial variation of the solar wind turbulence spectra near the kinetic break scale from Parker Solar Probe measurements
• The incompressible energy cascade rate in anisotropic solar wind turbulence
• Anisotropy of Magnetic Field Spectra at Kinetic Scales of Solar Wind Turbulence as Revealed by Parker Solar Probe in the Inner Heliosphere
• Evidence for the helicity barrier from measurements of the turbulence transition range in the solar wind
• Taylor microscale and effective Reynolds number near the Sun from PSP
• Direct kinetic Alfvén wave energy cascade in the presence of imbalance
• The effects of finite electron inertia on helicity-barrier-mediated turbulence
• Gyrofluid simulations of turbulence and reconnection in space plasmas
• Turbulent heating in collisionless low-beta plasmas: imbalance, Landau damping, and electron-ion energy partition