Nonradial and nonpolytropic astrophysical outflows

Sauty, C.; Lima, J. J. G.; Iro, Nicolas; Tsinganos, K.

doi:10.1051/0004-6361:20041606

Cited by 9 publications

(5 citation statements)

References 25 publications

(32 reference statements)

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“…A combination of Ulysses measurements with a self-similar solar-wind model finds a scaled Alfvén Mach number MA of about 10 to 20 (Sauty et al 2005) consistent with our simpler scaling estimate in Section 3.3. The earlier self-similar model, however, suffered from inconsistencies in reproducing observed magneticfield values at 1 au, which could be resolved in a later update (Aibéo et al 2007).…”

Section: Discussionsupporting

confidence: 83%

Flux conservation, radial scalings, Mach numbers, and critical distances in the solar wind: magnetohydrodynamics and Ulysses observations

Verscharen,

Bale,

Velli

2021

Preprint

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One of the key challenges in solar and heliospheric physics is to understand the acceleration of the solar wind. As a super-sonic, super-Alfvénic plasma flow, the solar wind carries mass, momentum, energy, and angular momentum from the Sun into interplanetary space. We present a framework based on two-fluid magnetohydrodynamics to estimate the flux of these quantities based on spacecraft data independent of the heliocentric distance of the location of measurement. Applying this method to the Ulysses dataset allows us to study the dependence of these fluxes on heliolatitude and solar cycle. The use of scaling laws provides us with the heliolatitudinal dependence and the solar-cycle dependence of the scaled Alfvénic and sonic Mach numbers as well as the Alfvén and sonic critical radii. Moreover, we estimate the distance at which the local thermal pressure and the local energy density in the magnetic field balance. These results serve as predictions for observations with Parker Solar Probe, which currently explores the very inner heliosphere, and Solar Orbiter, which will measure the solar wind outside the plane of the ecliptic in the inner heliosphere during the course of the mission.

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Section: Discussionsupporting

confidence: 83%

Flux conservation, radial scalings, Mach numbers, and critical distances in the solar wind: magnetohydrodynamics and Ulysses observations

Verscharen,

Bale,

Velli

2021

Preprint

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“…Not only are the fluctuations in the AM flux comparable to the average value, but from an instrument standpoint, small errors in determining the wind velocity translate to large errors in the AM flux (because the radial wind speed is 2-3 orders of magnitude larger than the typical tangential speed of 1-10km/s at 1au). The latter problem appears to be the main reason why data from most spacecraft have not been used to measure AM (see Figure 6 of Sauty et al 2005, which shows data from the Ulysses spacecraft; there is an approximately 1-year periodicty in the observations that is likely due to spacecraft pointing). The magnetic field direction is generally more accurately determined because it is not as radial as the flow, and the instruments used are less sensitive to spacecraft pointing than the particle detectors (which get different exposures as the spacecraft pointing changes).…”

Section: Spacecraft Selectionmentioning

confidence: 99%

Direct Detection of Solar Angular Momentum Loss with the Wind Spacecraft

Finley

Hewitt

Matt

et al. 2019

ApJL

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The rate at which the solar wind extracts angular momentum from the Sun has been predicted by theoretical models for many decades, and yet we lack a conclusive measurement from in-situ observations. In this letter we present a new estimate of the time-varying angular momentum flux in the equatorial solar wind, as observed by the Wind spacecraft from 1994-2019. We separate the angular momentum flux into contributions from the protons, alpha particles, and magnetic stresses, showing that the mechanical flux in the protons is ∼3 times larger than the magnetic field stresses. We observe the tendency for the angular momentum flux of fast wind streams to be oppositely signed to the slow wind streams, as noted by previous authors. From the average total flux, we estimate the global angular momentum loss rate of the Sun to be 3.3 × 10 30 erg, which lies within the range of various MHD wind models in the literature. This angular momentum loss rate is a factor of ∼2 weaker than required for a Skumanich-like rotation period evolution (Ω * ∝ stellar age −1/2 ), which should be considered in studies of the rotation period evolution of Sun-like stars.

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“…Moreover, observations of the solar wind by Ulysses also show that in situ rotation measurements are delicate. Sauty et al (2005) have plotted in Fig. 1 of their paper, the latitudinal variation of the rotation velocity of the flow, the absolute value of which is very small.…”

Section: Introductionmentioning

confidence: 99%

Counterrotation in Magnetocentrifugally Driven Jets and Other Winds

Sauty

Cayatte

Lima

et al. 2012

ApJ

Self Cite

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Rotation measurements in jets from T Tauri stars is a rather difficult task.Some jets seem to be rotating in a direction opposite to that of the underlying disk, although it is not yet clear if this affects the totality or part of the outflows.On the other hand, Ulysses data also suggest that the solar wind may rotate in two opposite ways between the northern and southern hemispheres. We show that this result is not surprising as it may seem and that it emerges naturally from the ideal MHD equations. Specifically, counter rotating jets do not contradict the magneto-centrifugal driving of the flow nor prevent extraction of angular momentum from the disk. The demonstration of this result is shown by combining the ideal MHD equations for steady axisymmetric flows. Provided that the jet is decelerated below some given threshold beyond the Alfvén surface, the flow will change its direction of rotation locally or globally. Counter-rotation is also possible for only some layers of the outflow at specific altitudes along the jet axis. We conclude that the counter rotation of winds or jets with respect to the source, star or disk, is not in contradiction with the magneto-centrifugal driving paradigm. This phenomenon may affect part of the outflow, either in one hemisphere, or only in some of the outflow layers. From a time dependent simulation, we illustrate this effect and show that it may not be permanent.

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Nonradial and nonpolytropic astrophysical outflows

Cited by 9 publications

References 25 publications

Flux conservation, radial scalings, Mach numbers, and critical distances in the solar wind: magnetohydrodynamics and Ulysses observations

Flux conservation, radial scalings, Mach numbers, and critical distances in the solar wind: magnetohydrodynamics and Ulysses observations

Direct Detection of Solar Angular Momentum Loss with the Wind Spacecraft

Counterrotation in Magnetocentrifugally Driven Jets and Other Winds

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