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The first observed connection between kinetic instabilities driven by proton temperature anisotropy and estimated energy cascade rates in the turbulent solar wind is reported using measurements from the Wind spacecraft at 1 AU. We find…

At kinetic scales in the solar wind, instabilities transfer energy from particles to fluctuations in the electromagnetic fields while restoring plasma conditions towards thermodynamic equilibrium. We investigate the interplay between…

Solar and Stellar Astrophysics · Physics 2023-04-05 Simon Opie , Daniel Verscharen , Christopher H. K. Chen , Christopher J. Owen , Philip A. Isenberg

In the parts of the solar corona and solar wind that experience the fewest Coulomb collisions, the component proton, electron, and heavy ion populations are not in thermal equilibrium with one another. Observed differences in temperatures,…

Solar and Stellar Astrophysics · Physics 2015-06-05 Steven R. Cranmer , Adriaan A. van Ballegooijen

Motivated by prior remote observations of a transition from striated solar coronal structures to more isotropic ``flocculated'' fluctuations, we propose that the dynamics of the inner solar wind just outside the Alfv\'en critical zone, and…

Past observations show that solar wind (SW) acceleration occurs inside the sub-Alfvenic region, reaching the local Alfven speed at typical distances ~ 10 - 20 Rs (solar radii). Recently, Parker Solar Probe (PSP) traversed regions of…

Current models of the solar wind must approximate (or ignore) the small-scale dynamics within the solar atmosphere, however these are likely important in shaping the emerging wave-turbulence spectrum and ultimately heating/accelerating the…

Solar and Stellar Astrophysics · Physics 2022-09-28 Adam J. Finley , Sacha A. Brun , Mats Carlsson , Mikolaj Szydlarski , Viggo Hansteen , Munehito Shoda

Kinetic plasma processes have been investigated in the framework of solar wind turbulence, employing Hybrid Vlasov-Maxwell (HVM) simulations. The dependency of proton temperature anisotropy T_{\perp}/T_{\parallel} on the parallel plasma…

Spicules, the smallest observable jet-like dynamic features ubiquitous in the chromosphere, are supposedly an important potential source for small-scale solar wind transients, with supporting evidence yet needed. We studied the…

Solar and Stellar Astrophysics · Physics 2025-07-18 Jeongwoo Lee , Haimin Wang , Jiasheng Wang , Meiqi Wang

Near the 10 solar radius perihelion of Parker Solar Probe encounter 24, a confined region containing an enhanced plasma density (25,000 per cubic centimeter) and broadband electrostatic waves was encountered. The solar wind velocity (200…

Space Physics · Physics 2026-02-24 Forrest Mozer , Oleksiy Agapitov , Kyungeun Choi , Andrii Voshchepynets

Protons in the solar corona and heliosphere exhibit anisotropic velocity distributions, violation of magnetic moment conservation, and a general lack of thermal equilibrium with the other particle species. There is no agreement about the…

Solar and Stellar Astrophysics · Physics 2015-06-19 Steven R. Cranmer

The problems of heating and acceleration of solar wind particles are of significant and enduring interest in astrophysics. The interactions between waves and particles are crucial in determining the distributions of proton and alpha…

Although the solar wind flows primarily outward from the Sun to interplanetary space, there are times when small-scale plasma inflows are observed. Inward-propagating density fluctuations in polar coronal holes were detected by the COR2…

Solar and Stellar Astrophysics · Physics 2021-05-26 Steven R. Cranmer , Craig E. DeForest , Sarah E. Gibson

Parker Solar Probe measurements have recently shown that coherent fast magnetosonic and Alfv\'{e}n ion-cyclotron waves are abundant in the solar wind and can be accompanied by higher-frequency electrostatic fluctuations. In this letter we…

Solar and Stellar Astrophysics · Physics 2024-04-26 I. Y. Vasko , F. S. Mozer , T. Bowen , J. Verniero , X. An , A. V. Artemyev , J. W. Bonnell , J. Halekas , I. V. Kuzichev

After leaving the Sun's corona, the solar wind continues to accelerate and cools, but more slowly than expected for a freely expanding adiabatic gas. We use in situ measurements from the Parker Solar Probe and Solar Orbiter spacecrafts to…

We present a solitary Alfv\'en wave model that exhibits nontrivial three-dimensional twisting of open magnetic field lines while preserving constant $|B|$. Embedded rotational discontinuities sharply deflect the otherwise uniform field…

Space Physics · Physics 2025-12-16 Zesen Huang , Marco Velli , Yuliang Ding

Several studies in the near-Earth environment show that intermittent structures are important sites of energy dissipation and particle energization. Recent Parker Solar Probe (PSP) data, sampled in the near-Sun environment, have shown that…

Solar and Stellar Astrophysics · Physics 2022-11-30 C. Phillips , R. Bandyopadhyay , D. J. McComas , S. D. Bale

Correlations are studied between the power density of transverse waves having frequencies between $0.01$ and $1$ normalized to the proton gyrofrequency in the plasma frame and the ratio of the perpendicular and parallel temperature of the…

Solar and Stellar Astrophysics · Physics 2010-08-04 Sofiane Bourouaine , Eckart Marsch , Fritz M. Neubauer

Partially-ionized plasmas consist of charged and neutral particles whose mutual collisions modify magnetic reconnection compared with the fully-ionized case. The collisions alter the rate and locations of the magnetic dissipation heating…

Solar and Stellar Astrophysics · Physics 2024-05-16 Fulvia Pucci , Alkendra Singh , Uma Gorti , Marco Velli , Neal Turner , Disha Varshney , Maria Elena Innocenti

Observations by the Parker Solar Probe mission of the solar wind at about 35.7 solar radii reveal the existence of whistler wave packets with frequencies below 0.1 f/fce (20-80 Hz in the spacecraft frame). These waves often coincide with…

We report small-scale magnetic flux ropes via the Parker Solar Probe in situ measurements during the first six encounters and present additional analyses to supplement our prior work in Chen et al. 2021. These flux ropes are detected by the…

Space Physics · Physics 2022-01-19 Yu Chen , Qiang Hu