Periodic Mesoscale Density Structures Comprise a Significant Fraction of the Solar Wind and Are Formed at the Sun

Kepko, L.; Viall, N. M.; DiMatteo, S.

doi:10.1029/2023ja031403

Cited by 5 publications

(1 citation statement)

References 85 publications

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“…There is still debate on the generation mechanisms of PDSs, but there is increasing evidence toward processes involving magnetic reconnection in the solar corona (Kepko et al 2024). For example, Réville et al (2020) showed in MHD simulations that periodic variations on timescales of a few hours might result from the periodic release of flux ropes from the tip of helmet streamers via a tearing mode.…”

Section: Introductionmentioning

confidence: 99%

Azimuthal Size Scales of Solar Wind Periodic Density Structures

Di Matteo,

Katsavrias,

Kepko

et al. 2024

ApJ

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Periodic density structures (PDSs) are quasiperiodic variations of solar wind density ranging from a few minutes to a few hours. PDSs advect with the solar wind and have radial length scales (L x ) of tens to several thousand megameters, thus belonging to the class of “mesoscale structures.” Current interplanetary multispacecraft observations are not at spatial separations capable of directly measuring the 3D size scale of PDSs or other mesoscale structures. Instead, previous investigations estimated characteristic spatial scales in solar wind parameters using cross-correlation and/or coherence analysis applied to multispacecraft observations. For the solar wind density and interplanetary magnetic field (IMF) intensity, the reported size scales perpendicular to the Sun–Earth line (L y ) ranged between ≈30 and ≈200 Earth Radii (R E). Here, we implemented a similar approach for the same parameters, but focused on high-density, slow-solar-wind intervals with PDSs observed by the Wind and ARTEMIS-P1 spacecraft. Additionally, this is the first statistical study of the IMF intensity periodicities in relation to PDSs. We identified intervals in which the two spacecraft observed the same periodicity, obtaining two PDS groups based on their radial length scale: L x1 ≈ 86R E and L x2 ≈ 35R E. Then, we classified the events based on the periodic variations’ coherence level. Reproducing the results with simulations of the PDSs’ transit, we inferred the L y order of magnitudes for the two PDS groups: L y1 ≈ 340R E and L y2 ≈ 187R E. Knowing the PDSs’ size scales is fundamental for constraining models aimed at reproducing these structures and is critical for better understanding the PDS–magnetosphere coupling.

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Section: Introductionmentioning

confidence: 99%

Azimuthal Size Scales of Solar Wind Periodic Density Structures

Di Matteo,

Katsavrias,

Kepko

et al. 2024

ApJ

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Identification of a single plasma parcel during a radial alignment of the Parker Solar Probe and Solar Orbiter

Berriot,

Démoulin,

Alexandrova

et al. 2024

A&A

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Configurations in which two spacecraft, such as the Parker Solar Probe (PSP) and Solar Orbiter, are radially aligned provide opportunities for studying the evolution of a single solar wind parcel during so-called plasma line-ups. The most critical part of these studies arguably is the identification of what can be considered the same plasma crossing both spacecraft. We present here a method that allowed us to determine what we think to be the same plasma parcel that passed through PSP ($ 0.075$ au) and Solar Orbiter ($ 0.9$ au) after their radial alignment on April 29 2021. We started by modeling the plasma propagation in order to obtain a first estimation of the plasma line-up intervals. The identification of the same density structure (with a crossing duration $ 1.5$ h) that passed through the two spacecraft allowed us to specify and confirm this estimate. Our main finding is that the density structure was very stable and remained well recognizable from PSP to Solar Orbiter despite its journey of $ 137$ hours in the inner heliosphere. We found, moreover, that the slow solar wind plasma parcel was significantly accelerated (from $ 200$ to $ 300$ km/s) during its propagation.

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Proton polytropic behavior of periodic density structures in the solar wind

Katsavrias,

Nicolaou,

Di Matteo

et al. 2024

A&A

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In recent years, mesoscales have gained scientific interest because they have been determined to be important in a broad range of phenomena throughout heliophysics. The solar wind mesoscale structures include periodic density structures (PDSs), which are quasi-periodic increases in the density of the solar wind that range from a few minutes to a few hours. These structures have been extensively observed in remote-sensing observations of the solar corona and in in situ observations out to 1 AU, where they manifest as radial length scales greater than or equal to the size of the Earth's dayside magnetosphere, that is, from tens to hundreds of Earth radii (R$_E$). While the precise mechanisms that form PDSs are still debated, recent studies confirmed that most PDSs are of solar origin and do not form through dynamics during their propagation in the interplanetary space. We further investigate the origin of PDSs by exploring the thermodynamic signature of these structures. To do this, we estimate the values of the effective polytropic index (gamma ) and the entropy of protons, which in turn are compared with the corresponding values found for the solar wind. We used an extensive list of PDS events spanning more than two solar cycles of Wind measurements (the entire Wind dataset from 1995 to 2022) to investigate the thermodynamic signatures of PDSs. With the use of wavelet methods, we classified these PDSs as coherent or incoherent, based on the shared periodic behavior between proton density and alpha-to-proton ratio, and we derive the proton polytropic index. Our results indicate that the coherent PDSs exhibit lower gamma values ($ on average and a higher entropy than the values in the entire Wind dataset ($ but also exhibit similarities with the magnetic cloud of an interplanetary coronal mass ejection. In contrast, incoherent PDSs exhibit the same gamma values as those of the entire Wind dataset.

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Periodic Mesoscale Density Structures Comprise a Significant Fraction of the Solar Wind and Are Formed at the Sun

Cited by 5 publications

References 85 publications

Azimuthal Size Scales of Solar Wind Periodic Density Structures

Azimuthal Size Scales of Solar Wind Periodic Density Structures

Identification of a single plasma parcel during a radial alignment of the Parker Solar Probe and Solar Orbiter

Proton polytropic behavior of periodic density structures in the solar wind

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