The Radial Dependence of Proton-scale Magnetic Spectral Break in Slow Solar Wind during <i>PSP</i> Encounter 2

Duan, Die; Bowen, T. A.; Chen, Christopher H. K.; Mallet, Alfred; He, Jie; Bale, S. D.; Vech, Daniel; Kasper, J. C.; Pulupa, M.; Bonnell, J. W.; Case, A. W.; Wit, T. Dudok de; Goetz, K.; Harvey, P.; Korreck, K. E.; Larson, D. E.; Livi, R.; MacDowall, R. J.; Malaspina, D.; Stevens, Michael L.; Whittlesey, P. L.

doi:10.3847/1538-4365/ab672d

Cited by 46 publications

(40 citation statements)

References 64 publications

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“…According to Figure 4, on the other hand, there appears an increasing trend of kρ p with β ‖ p for a given slope or | σ k |. Such a trend may be related to the increasing trend of k b ρ p (dimensionless spectral break position) with β ‖ p , as found by Duan et al (2020).…”

Section: Statistical Resultssupporting

confidence: 59%

Observational Evidence for Solar Wind Proton Heating by Ion‐Scale Turbulence

Zhao

Lin

Wang

et al. 2020

Geophysical Research Letters

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Based on in situ measurements by Wind spacecraft from 2005 to 2015, this letter reports for the first time a clearly scale-dependent connection between proton temperatures and the turbulence in the solar wind. A statistical analysis of proton-scale turbulence shows that increasing helicity magnitudes correspond to steeper magnetic energy spectra. In particular, there exists a positive power law correlation (with a slope ∼0.4) between the proton perpendicular temperature and the turbulent magnetic energy at scales 0.3 ≲ k p ≲ 1, with k being the wave number and p being the proton gyroradius. These findings present evidence of solar wind heating by the proton-scale turbulence. They also provide insight and observational constraint on the physics of turbulent dissipation in the solar wind. Plain Language Summary The solar wind is a tenuous magnetized plasma that serves as a natural laboratory of nearly collisionless turbulence. It is streaming outward from the Sun and has temperatures much higher than those from a spherically expanding ideal gas, implying a heating process must occur. The heating has been extensively discussed in past decades, but still not well understood. Based on in situ measurements, we reveal a scale-dependent connection between proton temperatures and the turbulence with enhanced magnetic helicity signature. The connection is particularly strong for the proton temperature in the direction perpendicular to the background magnetic field. These observations provide implications for the physics of turbulent dissipation and heating in a collisionless plasma.

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Section: Statistical Resultssupporting

confidence: 59%

Observational Evidence for Solar Wind Proton Heating by Ion‐Scale Turbulence

Zhao

Lin

Wang

et al. 2020

Geophysical Research Letters

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“…Duan et al. (2020) have shown that in the Alfvénic slow wind the break manifests a radial dependence similar to fast wind, with the spectral break occurring around the ion cyclotron resonance scales (Bruno & Trenchi, 2014; D’Amicis, Matteini, & Bruno, 2019). A similarity between fast and Alfvénic slow wind is also recovered in the relation between β ∥ and T ⊥ / T ∥ , suggesting that Alfvénic slow wind is characterized by more anisotropic distribution functions than non‐Alfvénic slow wind, as is also seen in the fast solar wind (J. Huang, et al., 2020), and in agreement with observations at 1 AU (D’Amicis, Matteini, & Bruno, 2019).…”

Section: In Situ Observationsmentioning

confidence: 99%

On Alfvénic Slow Wind: A Journey From the Earth Back to the Sun

et al. 2021

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Introduction"Asking for the average solar wind might appear as silly as asking for the taste of an average drink. What is the average between wine and beer? Obviously mere mixing-and averaging means mixing-does not lead to a meaningful result. Better taste and judge separately and then compare, if you wish." (Reiner Schwenn, Solar Wind 5, 1982) Following this basic idea, the quasi-stationary solar wind observed in the heliosphere has been traditionally categorized into two types based on particle bulk speed (Borovsky, 2012a;Stakhiv et al., 2015;Zurbuchen, 2007), namely fast (V sw > 600 km/s) and slow (V sw < 500 km/s) wind, also characterized by different features ranging from large to small scales. Indeed, slow wind has lower proton temperature and higher density, and in general much more variable properties, with respect to fast wind (Bruno et al., 1986;Lopez & Freeman, 1986;Schwenn, 2006). Moreover, the variability in the observed relative abundance of different charge-states of solar wind ions implies an anti-correlation of the freezing-in temperature with wind speed (Geiss et al., 1995;Kasper et al., 2012), and the thermodynamics of electrons, protons and heavy ions has also been observed to vary with speed (

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“…The statistical properties of the solar wind generally vary with speed, location, and type of source region and heliocentric distance (Bavassano et al 1982;Tu et al 1989;He et al 2013;Matteini et al 2014;Horbury et al 2018;Perrone et al 2019;Wang et al 2019;Bandyopadhyay et al 2020;Chen et al 2020;Chhiber et al 2020;Duan et al 2020;Qudsi et al 2020). Tu et al (1989) contrast the properties of magnetohydrodynamic (MHD) turbulence between highspeed and low-speed solar wind at 0.3 au using the spectra of Elsässer variables, cross helicity, residual energy, Alfvén ratio, and Elsässer ratio.…”

Section: Introductionmentioning

confidence: 99%

Wave Composition, Propagation, and Polarization of Magnetohydrodynamic Turbulence within 0.3 au as Observed by Parker Solar Probe

Zhu

Duan

et al. 2020

ApJL

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Turbulence, a ubiquitous phenomenon in interplanetary space, is crucial for the energy conversion of space plasma at multiple scales. This work focuses on the propagation, polarization, and wave composition properties of the solar wind turbulence within 0.3 au, and its variation with heliocentric distance at magnetohydrodynamic scales (from 10 s to 1000 s in the spacecraft frame). We present the probability density function of propagation wavevectors (PDF (k P , k ⊥ )) for solar wind turbulence within 0.3 au for the first time: (1) wavevectors cluster quasi-(anti-)parallel to the local background magnetic field for kd i <0.02, where d i is the ion inertial length;(2) wavevectors shift to quasi-perpendicular directions for kd i >0.02. Based on our wave composition diagnosis, we find that: the outward/anti-sunward Alfvén mode dominates over the whole range of scales and distances, the spectral energy density fraction of the inward/sunward fast mode decreases with distance, and the fractional energy densities of the inward and outward slow mode increase with distance. The outward fast mode and inward Alfvén mode represent minority populations throughout the explored range of distances and scales. On average, the degree of anisotropy of the magnetic fluctuations defined with respect to the minimum variation direction decreases with increasing scale, with no trend in distance at any scale. Our results provide comprehensive insight into the scenario of transport and transfer of the solar wind fluctuations/turbulence in the inner heliosphere.

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The Radial Dependence of Proton-scale Magnetic Spectral Break in Slow Solar Wind during PSP Encounter 2

Cited by 46 publications

References 64 publications

Observational Evidence for Solar Wind Proton Heating by Ion‐Scale Turbulence

Observational Evidence for Solar Wind Proton Heating by Ion‐Scale Turbulence

On Alfvénic Slow Wind: A Journey From the Earth Back to the Sun

Wave Composition, Propagation, and Polarization of Magnetohydrodynamic Turbulence within 0.3 au as Observed by Parker Solar Probe

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