New Observations of Solar Wind 1/f Turbulence Spectrum from Parker Solar Probe

Abstract

The trace magnetic power spectrum in the solar wind is known to be characterized by a double power law at scales much larger than the proton gyro-radius, with flatter spectral exponents close to −1 found at the lower frequencies below an inertial range with indices closer to [−1.5, −1.67]. The origin of the 1/f range is still under debate. In this study, we selected 109 magnetically incompressible solar wind intervals (δ∣ B ∣/∣ B ∣ ≪ 1) from Parker Solar Probe encounters 1–13 that display such double power laws, with the aim of understanding the statistics and radial evolution of the low-frequency power spectral exponents from Alfvén point up to 0.3 au. New observations from closer to the Sun show that in the low-frequency range solar wind, turbulence can display spectra much shallower than 1/f, evolving asymptotically to 1/f as advection time increases, indicating a dynamic origin for the 1/f range formation. We discuss the implications of this result on the Matteini et al. conjecture for the 1/f origin as well as example spectra displaying a triple power law consistent with the model proposed by Chandran et al., supporting the dynamic role of parametric decay in the young solar wind. Our results provide new constraints on the origin of the 1/f spectrum and further show the possibility of the coexistence of multiple formation mechanisms.

A two-dimensional numerical study of ion-acoustic turbulence

“…At such a scale, the corresponding can be estimated using the Alfvén velocity at the outer scale and the observed magnetic power spectrum; a value of seems reasonable (Huang et al. 2023). Assuming a fast reconnection rate of , can easily extend beyond .…”

“…There is a range of potential values of that one may consider; a reasonable lower bound appears to be the scale at which the turbulent inertial range starts: around at distances of this order (Coles & Harmon 1988; Huang et al. 2023; Lotz et al. 2023).…”

On Calculating Diffusion Coefficients Numerically in Synthetic Turbulence Using Particle Pushers

“…approach to generating synthetic turbulence also remains highly relevant. The many recent studies of turbulence as observed by, e.g., Parker Solar Probe (see, e.g., Adhikari et al 2020;Telloni 2021;Parashar & Matthaeus 2022;Huang et al 2023;Lotz et al 2023) provide valuable inputs whereby the transport coefficients of solar energetic particles, for example, may be investigated in the very inner heliosphere. Lastly, it has been shown that cosmic-ray transport coefficients in different astrospheres can potentially play a significant role in the habitability of exoplanets (see, e.g., Herbst et al 2020;Engelbrecht et al 2024).…”

Solar Flare 1/f Fluctuations from Amplitude-Modulated Five-Minute Oscillation

“…For instance, if magnetic reconnection induces solar wind through jetlets [28], triggered by SFO, then the solar wind [29] may also exhibit pink noise. Indeed, 1/f fluctuation in the solar wind has been observed over many years [30][31][32]. SFO has been detected in the solar corona [33], suggesting the potential observation of 1/f fluctuation in that context as well.…”