Cross Helicity Reversals in Magnetic Switchbacks

McManus, Michael D.; Bowen, T. A.; Mallet, Alfred; Chen, Christopher H. K.; Chandran, Benjamin D. G.; Bale, S. D.; Larson, D. E.; Wit, T. Dudok de; Kasper, J. C.; Stevens, Michael L.; Whittlesey, P. L.; Livi, R.; Korreck, K. E.; Goetz, K.; Harvey, P.; Pulupa, M.; MacDowall, R. J.; Malaspina, D.; Case, A. W.; Bonnell, J. W.

doi:10.3847/1538-4365/ab6dce

Cited by 85 publications

(60 citation statements)

References 31 publications

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“…respectively, marked as solid black lines. In general, it can be seen that in both cases the fluctuations are highly Alfvénic (σ c ≈ 1, σ r ≈ 0, r E 1, r A ≈ 1), more so than in previous encounters (Chen et al 2020;McManus et al 2020;Parashar et al 2020), but the near-HCS wind is less Alfvénic than the wind far from the HCS. The averages for these different regions are given in Table 1.…”

Section: Hcs Proximity Dependencementioning

confidence: 66%

The near-Sun streamer belt solar wind: turbulence and solar wind acceleration

Chen

Chandran

Woodham

et al. 2021

A&A

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The fourth orbit of Parker Solar Probe (PSP) reached heliocentric distances down to 27.9 R , allowing solar wind turbulence and acceleration mechanisms to be studied in situ closer to the Sun than previously possible. The turbulence properties were found to be significantly different in the inbound and outbound portions of PSP's fourth solar encounter, which was likely due to the proximity to the heliospheric current sheet (HCS) in the outbound period. Near the HCS, in the streamer belt wind, the turbulence was found to have lower amplitudes, higher magnetic compressibility, a steeper magnetic field spectrum (with a spectral index close to -5/3 rather than -3/2), a lower Alfvénicity, and a '1/ f ' break at much lower frequencies. These are also features of slow wind at 1 au, suggesting the near-Sun streamer belt wind to be the prototypical slow solar wind. The transition in properties occurs at a predicted angular distance of ≈ 4 • from the HCS, suggesting ≈ 8 • as the full-width of the streamer belt wind at these distances. While the majority of the Alfvénic turbulence energy fluxes measured by PSP are consistent with those required for reflection-driven turbulence models of solar wind acceleration, the fluxes in the streamer belt are significantly lower than the model predictions, suggesting that additional mechanisms are necessary to explain the acceleration of the streamer belt solar wind.

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Section: Hcs Proximity Dependencementioning

confidence: 66%

The near-Sun streamer belt solar wind: turbulence and solar wind acceleration

Chen

Chandran

Woodham

et al. 2021

A&A

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“…D' Amicis et al (2019) reported that the slow solar wind with high Alfvénicity share common characteristics with the fast wind, and Perrone et al (2020) further observed that Alfvénic slow wind shows a break between the inertial range and large scales where the magnetic fluctuations saturate. It seems plausible that this −1 frequency range is related to the observations of Alfvénic switchbacks (de Wit et al 2020;Horbury et al 2020;Mozer et al 2020;McManus et al 2020), close the Sun, that provide most of the energy-containing range in the slow wind. Later on other processes such as stream interactions and reconnection could furnish the large scales and the cascade (even at lower rates).…”

Section: Discussionmentioning

confidence: 83%

Energy Supply for Heating the Slow Solar Wind Observed by Parker Solar Probe between 0.17 and 0.7 au

Wang

et al. 2020

ApJL

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Energy supply sources for the heating process in the slow solar wind remain unknown. The Parker Solar Probe (PSP) mission provides a good opportunity to study this issue. Recently, PSP observations have found that the slow solar wind experiences stronger heating inside 0.24 au. Here for the first time we measure in the slow solar wind the radial gradient of the low-frequency breaks on the magnetic trace power spectra and evaluate the associated energy supply rate. We find that the energy supply rate is consistent with the observed perpendicular heating rate calculated based on the gradient of the magnetic moment. Based on this finding, one could explain why the slow solar wind is strongly heated inside 0.25 au but expands nearly adiabatically outside 0.25 au. This finding supports the concept that the energy added from the energy-containing range is transferred by an energy cascade process to the dissipation range, and then dissipates to heat the slow solar wind. The related issues for further study are discussed.

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“…However we feel that the above method of fitting to both the contaminant protons and alpha particles at the same time, using fitted parameters from the SF00 channel, better accounts for overlap between the proton and alpha distributions, especially in slow solar wind. This is also important during the ubiquitous magnetic field reversals or switchbacks observed so far by PSP (de Wit et al 2020;McManus et al 2020), because the associated speed enhancements in the protons causes greater overlap of the proton and alpha VDFs in velocity space. Finally, spacecraft motion is removed from the fitted proton and alpha parameters to obtain plasma velocities in RTN coordinates.…”

Section: Alpha Channel Contaminationmentioning

confidence: 95%

The contribution of alpha particles to the solar wind angular momentum flux in the inner heliosphere

Finley

McManus

Kasper

et al. 2021

A&A

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Context. An accurate assessment of the Sun's angular momentum (AM) loss rate is an independent constraint for models that describe the rotation evolution of Sun-like stars. Aims. In-situ measurements of the solar wind taken by Parker Solar Probe (PSP), at radial distances of ∼ 28 − 55R , are used to constrain the solar wind AM-loss rate. For the first time with PSP, this includes a measurement of the alpha particle contribution. Methods. The mechanical AM flux in the solar wind protons (core and beam), and alpha particles, is determined as well as the transport of AM through stresses in the interplanetary magnetic field. The solar wind AM flux is averaged over three hour increments, so that our findings more accurately represent the bulk flow. Results. During the third and fourth perihelion passes of PSP, the alpha particles contain around a fifth of the mechanical AM flux in the solar wind (the rest is carried by the protons). The proton beam is found to contain ∼ 10 − 50% of the proton AM flux. The sign of the alpha particle AM flux is observed to correlate with the proton core. The slow wind has a positive AM flux (removing AM from the Sun as expected), and the fast wind has a negative AM flux. As with previous works, the differential velocity between the alpha particles and the proton core tends to be aligned with the interplanetary magnetic field. Conclusions. In future, by utilising the trends in the alpha-proton differential velocity, it may be possible to estimate the alpha particle contribution when only measurements of the proton core are available. Based on the observations from this work, the alpha particles contribute an additional 10 − 20% to estimates of the solar wind AM-loss rate which consider only the proton and magnetic field contributions. Additionally, the AM flux of the proton beam can be just as significant as the alpha particles, and so should not be neglected in future studies.

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Cross Helicity Reversals in Magnetic Switchbacks

Cited by 85 publications

References 31 publications

The near-Sun streamer belt solar wind: turbulence and solar wind acceleration

The near-Sun streamer belt solar wind: turbulence and solar wind acceleration

Energy Supply for Heating the Slow Solar Wind Observed by Parker Solar Probe between 0.17 and 0.7 au

The contribution of alpha particles to the solar wind angular momentum flux in the inner heliosphere

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