The Implications of Simple Estimates of the 2D Outerscale Based on Measurements of Magnetic Islands for the Modulation of Galactic Cosmic-Ray Electrons

Engelbrecht, N. Eugene

doi:10.3847/1538-4357/aafe7f

Cited by 24 publications

(12 citation statements)

References 75 publications

(145 reference statements)

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“…This was usually done by comparing computed with measured electron intensities at Earth during periods of good or bad magnetic connection. Furthermore, given the demonstrated sensitivity of computed low-energy galactic electron intensities to various turbulence quantities (see Engelbrecht & Burger 2010Engelbrecht 2019), it may be possible to draw conclusions from Jovian electrons to better understand the behaviour of those quantities in regions of the heliosphere where spacecraft observations of this character do not exist (see, e.g., Engelbrecht 2017). Since these transport parameters and the diffusion coefficients they depend on are spatially dependent, the time that particles reside in a certain part of the heliosphere may yield significant insights to the modulation of GCRs as well.…”

Section: Jovian Electrons As Test Particlesmentioning

confidence: 99%

The residence-time of Jovian electrons in the inner heliosphere

Vogt

Engelbrecht

Strauss

et al. 2020

A&A

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Context. Jovian electrons serve an important role in test-particle distribution in the inner heliosphere. They have been used extensively in the past to study the (diffusive) transport of cosmic rays in the inner heliosphere. With new limits on the Jovian source function, that is, the particle intensity just outside the Jovian magnetosphere, and a new set of in-situ observations at 1 AU for cases of both good and poor magnetic connection between the source and observer, we revisit some of these earlier simulations. Aims. We aim to find the optimal numerical set-up that can be used to simulate the propagation of 6 MeV Jovian electrons in the inner heliosphere. Using such a setup, we further aim to study the residence (propagation) times of these particles for different levels of magnetic connection between Jupiter and an observer at Earth (1 AU). Methods. Using an advanced Jovian electron propagation model based on the stochastic differential equation approach, we calculated the Jovian electron intensity for different model parameters. A comparison with observations leads to an optimal numerical setup, which was then used to calculate the so-called residence (propagation) times of these particles. Results. Through a comparison with in-situ observations, we were able to derive transport parameters that are appropriate for the study of the propagation of 6 MeV Jovian electrons in the inner heliosphere. Moreover, using these values, we show that the method of calculating the residence time applied in the existing literature is not suited to being interpreted as the propagation time of physical particles. This is due to an incorrect weighting of the probability distribution. We applied a new method, where the results from each pseudo-particle are weighted by its resulting phase-space density (i.e. the number of physical particles that it represents). We thereby obtained more reliable estimates for the propagation time.

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Section: Jovian Electrons As Test Particlesmentioning

confidence: 99%

The residence-time of Jovian electrons in the inner heliosphere

Vogt

Engelbrecht

Strauss

et al. 2020

A&A

Self Cite

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“…The 2D turbulence power spectrum behavior at the lowest wavenumber, i.e., the outer scale, has an important impact on the perpendicular diffusion coefficients of charged particles in the heliosphere [146,193,194], including galactic cosmic ray proton and electron intensities. Engelbrecht et al [193] calculated the galactic cosmic ray electron intensities using the observed size of magnetic islands [195,196], and different outer scales [136,145], finding that galactic cosmic ray electron differential intensities above kinetic energy 0.1 GeV are closer to the observed electron differential intensities, and lower than that below 0.1 GeV. Similarly, Engelbrecht et al [194] proposed a new method to calculate the perpendicular diffusion coefficients by using the random ballistic decorrelation interpretation of the NLGC theory proposed by Ruffolo et al [197].…”

Section: Cr Perpendicular Mean Free Pathmentioning

confidence: 99%

The Transport and Evolution of MHD Turbulence throughout the Heliosphere: Models and Observations

Adhikari

Zank

Zhao

2021

Fluids

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A detailed study of solar wind turbulence throughout the heliosphere in both the upwind and downwind directions is presented. We use an incompressible magnetohydrodynamic (MHD) turbulence model that includes the effects of electrons, the separation of turbulence energy into proton and electron heating, the electron heat flux, and Coulomb collisions between protons and electrons. We derive expressions for the turbulence cascade rate corresponding to the energy in forward and backward propagating modes, the fluctuating kinetic and magnetic energy, the normalized cross-helicity, and the normalized residual energy, and calculate the turbulence cascade rate from 0.17 to 75 au in the upwind and downwind directions. Finally, we use the turbulence transport models to derive cosmic ray (CR) parallel and perpendicular mean free paths (mfps) in the upwind and downwind heliocentric directions. We find that turbulence in the upwind and downwind directions is different, in part because of the asymmetric distribution of new born pickup ions in the two directions, which results in the CR mfps being different in the two directions. This is important for models that describe the modulation of cosmic rays by the solar wind.

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“…For the purposes of the present study, these simplified transport parameters serve to qualitatively emulate the behaviour in the inner heliosphere of more theoretically-motivated expressions for the same employed in ab initio particle transport studies (see, e.g., Engelbrecht & Burger 2013;Engelbrecht 2019). For instance, the energy-independence of λ over the range of (low) energies considered in this study reflects the behaviour of electron parallel mean free paths derived from quasilinear theory (see, e.g., Teufel & Schlickeiser 2003;Engelbrecht & Burger 2010;Dempers & Engelbrecht 2020), as well as what is expected from observations (e.g.…”

Section: The Numerical Setupmentioning

confidence: 99%

Numerical and experimental evidence for a new interpretation of residence times in space

Vogt,

Engelbrecht,

Heber

et al. 2021

Preprint

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Aims. We investigate the energy dependence of Jovian electron residence times, which allows for a deeper understanding of adiabatic energy changes that occur during charged particle transport, as well as of their significance for simulation approaches. Thereby we seek to further validate an improved approach to estimate residence times numerically by investigating the implications on previous analytical approaches, and possible effects detectable by spacecraft data. Methods. Utilizing a propagation model based on a Stochastic Differential Equation (SDE) solver written in CUDA, residence times for Jovian electrons are calculated over the whole energy range dominated by the Jovian electron source spectrum. We analyse the interdependences both with the magnetic connection between observer and the source as well as between the the distribution of the exit (simulation) times and the resulting residence times. Results. We point out a linear relation between the residence time for different kinetic energies and the longitudinal shift of the 13 month periodicity typically observed for Jovian electrons and discuss the applicability of these findings to data. Furthermore, we utilize our finding that the simulated residence times are approximately linearly related to the energy loss for Jovian and Galactic electrons, and develop an improved analytical estimation in agreement with the numerical residence time and the longitudinal shift observed by measurements.

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The Implications of Simple Estimates of the 2D Outerscale Based on Measurements of Magnetic Islands for the Modulation of Galactic Cosmic-Ray Electrons

Cited by 24 publications

References 75 publications

The residence-time of Jovian electrons in the inner heliosphere

The residence-time of Jovian electrons in the inner heliosphere

The Transport and Evolution of MHD Turbulence throughout the Heliosphere: Models and Observations

Numerical and experimental evidence for a new interpretation of residence times in space

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