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The solar wind is typically categorized as fast and slow based on the measured speed ($v_\mathrm{sw}$). The separation between these two regimes is often set between 400 and 600 km/s without a rigorous definition. Observations of the solar…

Solar and Stellar Astrophysics · Physics 2025-02-19 B. L. Alterman , Y. J. Rivera , S. T. Lepri , R. M. Raines

Connecting the solar wind observed throughout the heliosphere to its origins in the solar corona is one of the central aims of heliophysics. The variability in the magnetic field, bulk plasma, and heavy ion composition properties of the…

Solar and Stellar Astrophysics · Physics 2023-05-26 B. J. Lynch , N. M. Viall , A. K. Higginson , L. Zhao , S. T. Lepri , X. Sun

Switchbacks are Aflv\'enic fluctuations in the solar wind, which exhibit large rotations in the magnetic field direction. Observations from Parker Solar Probe's (PSP's) first two solar encounters have formed the basis for many of the…

Space Physics · Physics 2022-09-14 R. Laker , T. S. Horbury , L. Matteini , S. D. Bale , J. E. Stawarz , L. D. Woodham , T. Woolley

Solar coronal jets are small, transient, collimated ejections most easily observed in coronal holes (CHs). The upcoming Parker Solar Probe (PSP) mission provides the first opportunity to encounter CH jets in situ near the Sun and examine…

Solar and Stellar Astrophysics · Physics 2018-10-17 Merrill A Roberts , Vadim M Uritsky , C Richard DeVore , Judith T Karpen

As fundamental parameters of the Sun, the Alfv\'en radius and angular momentum loss determine how the solar wind changes from sub-Alfv\'enic to super-Alfv\'enic and how the Sun spins down. We present an approach to determining the solar…

Solar and Stellar Astrophysics · Physics 2021-06-23 Ying D. Liu , Chong Chen , Michael L. Stevens , Mingzhe Liu

By using our previous results of magnetohydrodynamical simulations for the solar wind from open flux tubes, I discuss how the solar wind in the past is different from the current solar wind. The simulations are performed in fixed…

Solar and Stellar Astrophysics · Physics 2015-05-27 Takeru K. Suzuki

Parker Solar Probe (PSP) entered a region of the sub-Alfvenic solar wind during encounter 8 and we present the first detailed analysis of low-frequency turbulence properties in this novel region. The magnetic field and flow velocity vectors…

Solar and Stellar Astrophysics · Physics 2022-02-08 G. P. Zank , L. -L. Zhao , L. Adhikri , D. Telloni , J. C. Kasper , M. Stevens , A. Rahmati , S. D. Bale

Parker Solar Probe (PSP) achieved its first orbit perihelion on November 6, 2018, reaching a heliocentric distance of about 0.165 au (35.55 R$_\odot$). Here, we study the evolution of fully developed turbulence associated with the slow…

We present in this Letter the first coordinated radio occultation measurements and ultraviolet observations of the inner corona below 5.5 Rs, obtained during the Galileo solar conjunction in January 1997, to establish the origin of the slow…

Astrophysics · Physics 2009-10-30 S. R. Habbal , R. Woo , S. Fineschi , R. O'Neal , J. Kohl , G. Noci , C. Korendyke

In a previous work we analysed the white-light coronal brightness as a function of elongation and time from Wide-Field Imager (WISPR) observations on board the Parker Solar Probe (PSP) mission when PSP reached a minimum heliocentric…

Solar and Stellar Astrophysics · Physics 2023-08-23 Spiros Patsourakos , Angelos Vourlidas , Alexander Nindos

The fast solar wind that fills the heliosphere originates from deep within regions of open magnetic field on the Sun called coronal holes. The energy source responsible for accelerating the plasma to high speeds is widely debated, however…

Switchbacks -- rapid, large deflections of the solar wind's magnetic field -- have generated significant interest as possible signatures of the key mechanisms that heat the corona and accelerate the solar wind. In this context, an important…

Solar and Stellar Astrophysics · Physics 2022-11-23 Jonathan Squire , Zade Johnston , Alfred Mallet , Romain Meyrand

The elemental composition of the Sun's hot atmosphere, the corona, shows a distinctive pattern that is different than the underlying surface, or photosphere (Pottasch 1963). Elements that are easy to ionize in the chromosphere are enhanced…

Solar and Stellar Astrophysics · Physics 2022-05-18 David H. Brooks , Deborah Baker , Lidia van Driel-Gesztelyi , Harry P. Warren , Stephanie L. Yardley

Magnetic switchbacks are fluctuations in the solar wind in which the interplanetary magnetic field sharply deflects away from its background direction so as to create folds in magnetic field lines while remaining of roughly constant…

The motion of faint propagating disturbances (PD) in the solar corona reveals an intricate structure which must be defined by the magnetic field. Applied to quiet Sun observations by the Atmospheric Imaging Assembly (AIA)/Solar Dynamics…

Solar and Stellar Astrophysics · Physics 2022-07-20 Huw Morgan , Marianna Korsos

Empirical solar wind speed models play an important role in enabling space weather forecasting with low computational cost. Among these, one model called WS model is based on the asymptotic expansion factor. However, it is known that it…

Solar and Stellar Astrophysics · Physics 2026-01-30 Kyogo Tokoro , Munehito Shoda , Shinsuke Imada

We use dual-site radio observations of interplanetary scintillation (IPS) with extremely long baselines (ELB) to examine meridional flow characteristics of the ambient fast solar wind at plane-of-sky heliocentric distances of 24-85 solar…

Solar and Stellar Astrophysics · Physics 2015-06-05 Gareth Dorrian , Andy Breen , Richard Fallows , Mario Bisi

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

The solar corona has been revealed in the past decade to be a highly dynamic nonequilibrium plasma environment. Both the loop-filled coronal base and the extended acceleration region of the solar wind appear to be strongly turbulent, but…

Astrophysics · Physics 2008-11-26 Steven R. Cranmer

We analyze magnetic field data from the first six encounters of PSP, three Helios fast streams and two Ulysses south polar passes covering heliocentric distances $0.1\lesssim R\lesssim 3$ au. We use this data set to statistically determine…

Solar and Stellar Astrophysics · Physics 2021-10-13 Anna Tenerani , Nikos Sioulas , Lorenzo Matteini , Olga Panasenco , Chen Shi , Marco Velli