1/f Noise in the Heliosphere: A Target for PUNCH Science - Draft review

Sep 15, 2026

Uploaded by James

A broad review examines observational evidence for 1/f noise in the heliosphere and develops the theoretical context of generic 1/f models relevant to NASA’s PUNCH mission. The work summarizes the scale-invariant 1/f spectrum across natural and artificial systems and details solar-wind evidence spanning roughly 2×10−6 Hz to 10−3 Hz at 1 au. It evaluates mechanisms such as superposition of power-law spectra from reconnection and inverse-cascade dynamo scenarios, while addressing causality challenges in purely in situ models.

LanguageEnglish

CategoryResearch & Report

FormatPDF

Pages20

Reading Time50 min

AccessFree to download

ABSTRACT

1/f Noise in the Heliosphere: Target for PUNCH Science

1. INTRODUCTION

Definition and scale invariance of 1/f noise

Historical observations in the solar wind

Motivation for missions and frequency range at 1 au

Role of PUNCH in detecting and characterizing sources

2. BACKGROUND

arXiv :2409 .02255v2 [ astro-ph . SR] 13 Dec 2024 Draft version December 17, 2024 Typeset using LATEX twocolumn style in AASTeX631 1/f Noise in the Heliosphere: A Target for PUNCH Science Jiaming Wang (王嘉明) ,1 William H. Matthaeus ,1 Rohit Chhiber ,1, 2 Sohom Roy ,1 Rayta A. Pradata ,1 Francesco Pecora ,1 and Yan Yang1 1 Department of Physics and Astronomy, University of Delaware 2 Heliophysics Science Division, NASA Goddard Space Flight Center (Dated: December 17, 2024) ABSTRACT We present a broad review of 1/f noise observations in the heliosphere, and discuss and complement the theoretical background of generic 1/f models as relevant to NASA’s Polarimeter to UNify the Corona and Heliosphere (PUNCH) mission. First observed in the voltage fluctuations of vacuum tubes, the scale-invariant 1/f spectrum has since been identified across a wide array of natural and artificial systems, including heart rate fluctuations and loudness patterns in musical compositions. In the solar wind, the interplanetary magnetic field trace spectrum exhibits 1/f scaling within the frequency range from around 2 × 10 −6 Hz to around 10 −3 Hz at 1 au. One compelling mechanism for the generation of 1/f noise is the superposition principle, where a composite 1/f spectrum arises from the superposition of a collection of individual power-law spectra characterized by a scale-invariant distribution of correlation times. In the context of the solar wind, such a superposition could originate from scale-invariant reconnection processes in the corona. Further observations have detected 1/f signatures in the photosphere and corona at frequency ranges compatible with those observed at 1 au, suggesting an even lower altitude origin of 1/f spectrum in the solar dynamo itself. This hypothesis is bolstered by dynamo experiments and simulations that indicate inverse cascade activities, which can be linked to successive flux tube reconnections beneath the corona, and are known to generate 1/f noise possibly through nonlocal interactions at the largest scales. Conversely, models positing in situ generation of 1/f signals face causality issues in explaining the low-frequency portion of the 1/f spectrum. Understanding 1/f noise in the solar wind may inform central problems in heliospheric physics, such as the solar dynamo, coronal heating, the origin of the solar wind, and the nature of interplanetary turbulence. 1. INTRODUCTION 1/f noise, otherwise known as “flicker noise”, refers to a signal in which the amplitude of the spectral density P(f) inversely scales with the frequency f. Such a spectrum has the unique property that the integrated power per octave remains constant across frequencies. Mathematically, the integration of the spectrum over a frequency range f1 to f2 , i.e. R P (f)df ∼ R df/f ∼ log f2 /f1 , depends solely on the ratio f2 /f1 . This total power is insensitive to rescaling of the frequency by an arbitrary factor, a reflection of the scale invariance of the power df/f. The distribution P(f) ∼ 1/f is often referred to as a scale-invariant distribution and is observed across a wide array of physical 2 systems (see, e.g., review by Dutta & Horn 1981), including heliospheric plasmas such as the interplanetary magnetic field (Bavassano et al. 1982; Burlaga & Goldstein 1984; Matthaeus & Goldstein 1986) and elsewhere (Matthaeus et al. 2007; Bemporad et al. 2008) . When the scale-invariant 1/f noise spectrum is observed, it is often fruitful to search for a scale-invariant physical process that produces the observation. In this way the study of 1/f noise can lead to new physical insights. Some examples of such efforts are given in Section 2. The primitive observations of 1/f-like solar wind magnetic field spectra (Coleman 1968; Bavassano et al. 1982; Denskat & Neubauer 1982) revealed a tendency toward spectral indices shallower than the Kolmogorov value of −5/3 at lower frequencies, typically below around a few times 10 −3 Hz to

FAQs

What is 1/f noise and why is it considered scale-invariant?

1/f noise, or flicker noise, has a spectral density that decreases inversely with frequency. The integrated power per octave remains constant, reflecting scale invariance of the spectrum.

What frequency range of 1/f scaling is reported for the solar wind at 1 au?

The solar-wind interplanetary magnetic field trace spectrum shows 1/f scaling from around 2×10−6 Hz to about 10−3 Hz at 1 au.

Which mechanisms does the review discuss for generating heliospheric 1/f noise?

It discusses superposition-based models tied to scale-invariant reconnection, possible inverse-cascade activity in the solar dynamo, and contrasts these with in situ generation models that face causality issues for the low-frequency part.

Sep 15, 2026

Uploaded by James