Evolution of Proton and Alpha Particle Velocities through the Solar Cycle

Ďurovcová, Tereza; Šafránková, Jana; Němeček, Zdenek; Richardson, J. D.

doi:10.3847/1538-4357/aa9618

Cited by 25 publications

(21 citation statements)

References 36 publications

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“…1 shows. We see very few cases of H + faster than He 2+ , which could occur in the pristine solar wind at large heliocentric distances ( Ďurovcová et al 2017;Steinberg et al 1996). Figure 1 strongly supports the samespeed assumption and that at least the majority of the observed speed difference is due to the solar wind interaction with the coma.…”

Section: Validation Of the Same-speed Assumptionsupporting

confidence: 72%

Upstream solar wind speed at comet 67P

Nilsson

Moslinger

Williamson

et al. 2022

A&A

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Context. Rosetta followed comet 67P at heliocentric distances from 1.25 to 3.6 au. The solar wind was observed for much of this time, but was significantly deflected and to some extent slowed down by the interaction with the coma. Aims. We use the different changes in the speed of H+ and He2+ when they interact with the coma to estimate the upstream speed of the solar wind. The different changes in the speed are due to the different mass per charge of the particles, while the electric force per charge due to the interaction is the same. A major assumption is that the speeds of H+ and He2+ were the same in the upstream region. This is investigated. Methods. We derived a method for reconstructing the upstream solar wind from H+ and He2+ observations. The method is based on the assumption that the interaction of the comet with the solar wind can be described by an electric potential that is the same for both H+ and He2+. This is compared to estimates from the Tao model and to OMNI and Mars Express data that we propagated to the observation point. Results. The reconstruction agrees well with the Tao model for most of the observations, in particular for the statistical distribution of the solar wind speed. The electrostatic potential relative to the upstream solar wind is derived and shows values from a few dozen volts at large heliocentric distances to about 1 kV during solar events and close to perihelion. The reconstructed values of the solar wind for periods of high electrostatic potential also agree well with propagated observations and model results. Conclusions. The reconstructed upstream solar wind speed during the Rosetta mission agrees well with the Tao model. The Tao model captures some slowing down of high-speed streams as compared to observations at Earth or Mars. At low solar wind speeds, below 400 km s−1, the agreement is better between our reconstruction and Mars observations than with the Tao model. The magnitude of the reconstructed electrostatic potential is a good measure of the slowing-down of the solar wind at the observation point.

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Section: Validation Of the Same-speed Assumptionsupporting

confidence: 72%

Upstream solar wind speed at comet 67P

Nilsson

Moslinger

Williamson

et al. 2022

A&A

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“…4 and Tu and Marsch, 1995), and has a higher proton temperature (Neugebauer, 1976;Wilson et al, 2018). Importantly for its multi-scale evolution, fast wind is also less collisional (both in terms of the local collisional relaxation times and the cumulative time for collisions to act) than slow wind (Marsch et al, 1982b;Marsch and Goldstein, 1983;Livi et al, 1986;Kasper et al, 2008;Bourouaine et al, 2011;Ďurovcová et al, 2017), which allows for more kinetic non-equilibrium features to survive the thermalizing action of Coulomb collisions. Fast wind, therefore, exhibits more non-Maxwellian structure in its distribution functions (Marsch, 2006(Marsch, , 2018 as we discuss in the next section.…”

Section: Categorization Of Solar Windmentioning

confidence: 99%

The multi-scale nature of the solar wind

Verscharen¹,

Klein²,

Maruca³

2019

Living Rev Sol Phys

336

285

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The solar wind is a magnetized plasma and as such exhibits collective plasma behavior associated with its characteristic spatial and temporal scales. The characteristic length scales include the size of the heliosphere, the collisional mean free paths of all species, their inertial lengths, their gyration radii, and their Debye lengths. The characteristic timescales include the expansion time, the collision times, and the periods associated with gyration, waves, and oscillations. We review the past and present research into the multi-scale nature of the solar wind based on in-situ spacecraft measurements and plasma theory. We emphasize that couplings of processes across scales are important for the global dynamics and thermodynamics of the solar wind. We describe methods to measure in-situ properties of particles and fields. We then discuss the role of expansion effects, non-equilibrium distribution functions, collisions,

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“…Due to the lack of alpha particle observations, we make an assumption that V α ≈ V p . In fact, the differential speed between protons and alpha particles is also typically on the order of the local Alfvén speed (e.g., Steinberg et al 1996;Ďurovcová et al 2017;Alterman et al 2018), so that it may affect the energy flux closer to the Sun. We await more data that are to come in the future PSP encounters, with the recovery of the well calibrated alpha parameters.…”

Section: Discussionmentioning

confidence: 99%

Solar wind energy flux observations in the inner heliosphere: First results from Parker Solar Probe

Liu,

Issautier,

Meyer-Vernet

et al. 2021

Preprint

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Aims. We investigate the solar wind energy flux in the inner heliosphere using 12-day observations around each perihelion of Encounter One (E01), Two (E02), Four (E04), and Five (E05) of Parker Solar Probe (PSP), respectively, with a minimum heliocentric distance of 27.8 solar radii (R ). Methods. Energy flux was calculated based on electron parameters (density n e , core electron temperature T c , and suprathermal electron temperature T h ) obtained from the simplified analysis of the plasma quasi-thermal noise (QTN) spectrum measured by RFS/FIELDS and the bulk proton parameters (bulk speed V p and temperature T p ) measured by the Faraday Cup onboard PSP, SPC/SWEAP. Results. Combining observations from E01, E02, E04, and E05, the averaged energy flux value normalized to 1 R plus the energy necessary to overcome the solar gravitation (W R ) is about 70±14 W m −2 , which is similar to the average value (79±18 W m −2 ) derived by Le Chat et al from 24-year observations by Helios, Ulysses, and Wind at various distances and heliolatitudes. It is remarkable that the distributions of W R are nearly symmetrical and well fitted by Gaussians, much more so than at 1 AU, which may imply that the small heliocentric distance limits the interactions with transient plasma structures.

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Evolution of Proton and Alpha Particle Velocities through the Solar Cycle

Cited by 25 publications

References 36 publications

Upstream solar wind speed at comet 67P

Upstream solar wind speed at comet 67P

The multi-scale nature of the solar wind

Solar wind energy flux observations in the inner heliosphere: First results from Parker Solar Probe

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