Evolution of Switchbacks in the Inner Heliosphere

Tenerani, Anna; Sioulas, Nikos; Matteini, Lorenzo; Panasenco, O.; Shi, Chen; Velli, Marco

doi:10.3847/2041-8213/ac2606

Cited by 38 publications

(44 citation statements)

References 35 publications

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“…The above models predict different spectral slopes and energy cascade rates, each under specific assumptions. However, solar wind observations cannot be solely explained by any one of the models, and this may be due to the inapplicability of assumptions such as homogeneity and incompressibility: The wind expands spherically, slowing nonlinear interactions and providing a quasi-scale free energy loss in the turbulence; different velocity streams with significant shear are present at meso-scales; and compressible processes such as parametric decay may occur (Primavera et al 2019;Tenerani et al 2020), not to mention the potential role of particle distribution function anisotropies.…”

Section: Introductionmentioning

confidence: 99%

“…Thus, its data provide a unique opportunity to study solar wind turbulence in its early stage of evolution. Initial PSP data have revealed many interesting phenomena, among which the omnipresence of the so-called magnetic switchbacks may be especially important (Bale et al 2019;Dudok de Wit et al 2020;McManus et al 2020;Tenerani et al 2020). There are fluctuations in the solar magnetic field of a sufficient magnitude to invert the local direction with respect to the Sun, that is to say they switch the field backward locally into a fold.…”

Section: Introductionmentioning

confidence: 99%

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Alfvénic versus non-Alfvénic turbulence in the inner heliosphere as observed by Parker Solar Probe

Shi,

Velli,

Panasenco

et al. 2021

Preprint

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Context. Parker Solar Probe (PSP) measures the magnetic field and plasma parameters of the solar wind at unprecedentedly close distances to the Sun. These data provide great opportunities to study the early-stage evolution of magnetohydrodynamic (MHD) turbulence in the solar wind. Aims. In this study, we make use of the PSP data to explore the nature of solar wind turbulence focusing on the Alfvénic character and power spectra of the fluctuations and their dependence on the distance and context (i.e., large-scale solar wind properties), aiming to understand the role that different effects such as source properties, solar wind expansion, and stream interaction might play in determining the turbulent state. Methods. We carried out a statistical survey of the data from the first five orbits of PSP with a focus on how the fluctuation properties at the large MHD scales vary with different solar wind streams and the distance from the Sun. A more in-depth analysis from several selected periods is also presented. Results. Our results show that as fluctuations are transported outward by the solar wind, the magnetic field spectrum steepens while the shape of the velocity spectrum remains unchanged. The steepening process is controlled by the "age" of the turbulence, which is determined by the wind speed together with the radial distance. Statistically, faster solar wind has higher "Alfvénicity," with a more dominant outward propagating wave component and more balanced magnetic and kinetic energies. The outward wave dominance gradually weakens with radial distance, while the excess of magnetic energy is found to be stronger as we move closer toward the Sun. We show that the turbulence properties can significantly vary from stream to stream even if these streams are of a similar speed, indicating very different origins of these streams. Especially, the slow wind that originates near the polar coronal holes has much lower Alfvénicity compared with the slow wind that originates from the active regions and pseudostreamers. We show that structures such as heliospheric current sheets and velocity shears can play an important role in modifying the properties of the turbulence.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Alfvénic versus non-Alfvénic turbulence in the inner heliosphere as observed by Parker Solar Probe

Shi,

Velli,

Panasenco

et al. 2021

Preprint

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“…This is an attempt to remove the first order variation in B R , normalising the switchback amplitude with distance. (Tenerani et al 2020), but it is unclear whether this extends to larger distances, such as the Ulysses observations (Neugebauer & Goldstein 2013). Although switchbacks are the dominant signal in PSP's first encounter, they are not ubiquitous, occurring in 'patches' separated by a 'quiet' radial field (Bale et al 2019;Horbury et al 2020).…”

Section: Introductionmentioning

confidence: 99%

Statistical analysis of orientation, shape, and size of solar wind switchbacks

Laker,

Horbury,

Bale

et al. 2020

Preprint

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Context. One of the main discoveries from the first two orbits of Parker Solar Probe (PSP) was the presence of magnetic switchbacks, whose deflections dominated the magnetic field measurements. Determining their shape and size could provide evidence of their origin, which is still unclear. Previous work with a single solar wind stream has indicated that these are long, thin structures although the direction of their major axis could not be determined Aims. We investigate if this long, thin nature extends to other solar wind streams, while determining the direction along which the switchbacks within a stream were aligned. We try to understand how the size and orientation of the switchbacks, along with the flow velocity and spacecraft trajectory, combine to produce the observed structure durations for past and future orbits. Methods. The direction at which the spacecraft cuts through each switchback depended on the relative velocity of the plasma to the spacecraft and the alignment direction for that stream. We searched for the alignment direction that produced a combination of a spacecraft cutting direction and switchback duration that was most consistent with long, thin structures. The expected form of a long, thin structure was fitted to the results of the best alignment direction, which determined the width and aspect ratio of the switchbacks for that stream. Results. We find that switchbacks consistently demonstrate a non-radial alignment in the same sense as the Parker spiral field, but not the background flow direction within each stream. This alignment direction varied between streams. The switchbacks had a mean width of 50, 000 km, with an aspect ratio of the order of 10. Conclusions. We conclude that switchbacks are not aligned along the background flow direction, but instead aligned along the local Parker spiral, perhaps suggesting that they propagate along the magnetic field. Since the observed switchback duration depends on how the spacecraft cuts through the structure, the duration alone cannot be used to determine the size or influence of an individual event. For future PSP orbits, a larger spacecraft transverse component combined with more radially aligned switchbacks will lead to long duration switchbacks becoming less common.

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“…Parker Solar Probe (PSP; Fox et al 2016) observations during solar encounters have revealed the presence of patches of switchbacks on the scale of hours to days, separated by intervals of 'quieter' radial fields (Bale et al 2019;Kasper et al 2019;Horbury et al 2020). The origin of these structures is still poorly understood and it is not yet clear whether they result from sudden or impulsive events in the chromosphere and corona (Roberts et al 2018;Tenerani et al 2020;Sterling & Moore 2020;Fisk & Kasper 2020) or are steepened waves driven by turbulence and plasma expansion (Squire et al 2020).…”

Section: Introductionmentioning

confidence: 99%

“…Several recent studies have investigated the evolution and nature of switchbacks using PSP observations (Dudok de Wit et al 2020;Farrell et al 2020;Horbury et al 2020;Krasnoselskikh et al 2020;McManus et al 2020;Mozer et al 2020;Tenerani et al 2020). Probing the microphysics of these structures is essential to diagnose their origin and contribution to the total energy and momentum flux of the solar wind.…”

Section: Introductionmentioning

confidence: 99%

Enhanced proton parallel temperature inside patches of switchbacks in the inner heliosphere

Woodham,

Horbury,

Matteini

et al. 2020

Preprint

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Context. Switchbacks are discrete angular deflections in the solar wind magnetic field that have been observed throughout the heliosphere. Recent observations by Parker Solar Probe (PSP) have revealed the presence of patches of switchbacks on the scale of hours to days, separated by 'quieter' radial fields. Aims. We aim to further diagnose the origin of these patches using measurements of proton temperature anisotropy that can illuminate possible links to formation processes in the solar corona. Methods. We fitted 3D bi-Maxwellian functions to the core of proton velocity distributions measured by the SPAN-Ai instrument onboard PSP to obtain the proton parallel, T p, , and perpendicular, T p,⊥ , temperature. Results. We show that the presence of patches is highlighted by a transverse deflection in the flow and magnetic field away from the radial direction. These deflections are correlated with enhancements in T p, , while T p,⊥ remains relatively constant. Patches sometimes exhibit small proton and electron density enhancements. Conclusions. We interpret that patches are not simply a group of switchbacks, but rather switchbacks are embedded within a largerscale structure identified by enhanced T p, that is distinct from the surrounding solar wind. We suggest that these observations are consistent with formation by reconnection-associated mechanisms in the corona.

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Evolution of Switchbacks in the Inner Heliosphere

Cited by 38 publications

References 35 publications

Alfvénic versus non-Alfvénic turbulence in the inner heliosphere as observed by Parker Solar Probe

Alfvénic versus non-Alfvénic turbulence in the inner heliosphere as observed by Parker Solar Probe

Statistical analysis of orientation, shape, and size of solar wind switchbacks

Enhanced proton parallel temperature inside patches of switchbacks in the inner heliosphere

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