Highly structured slow solar wind emerging from an equatorial coronal hole

Bale, S. D.; Badman, S. T.; Bonnell, J. W.; Bowen, T. A.; Burgess, David; Case, A. W.; Cattell, C. A.; Chandran, Benjamin D. G.; Chaston, C. C.; Chen, C. H. K.; Drake, J. F.; Wit, T. Dudok de; Eastwood, J. P.; Ergun, R. E.; Farrell, W. M.; Fong, Chong Hang; Goetz, K.; Goldstein, M. L.; Goodrich, K.; Harvey, P.; Horbury, T. S.; Howes, G. G.; Kasper, J. C.; Kellogg, P. J.; Klimchuk, J. A.; Korreck, K. E.; Krasnoselskikh, V.; Krucker, S.; Laker, R.; Larson, D. E.; MacDowall, R. J.; Maksimović, M.; Malaspina, D.; Oliveros, J. Martinez; McComas, D. J.; Meyer‐Vernet, N.; Moncuquet, M.; Mozer, F. S.; Phan, T. D.; Pulupa, M.; Raouafi, N. E.; Salem, C. S.; Stansby, David; Stevens, Michael L.; Szabó, Á.; Velli, M.; Woolley, T.; Wygant, J. R.

doi:10.1038/s41586-019-1818-7

Cited by 506 publications

(435 citation statements)

References 51 publications

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“…These findings lead us to conclude that the strahl carries the information about the coronal electron temperature at the point of its origin and can be used as a good proxy for the connectivity studies involving remote sensing and in-situ data. In fact, the origins of the solar wind measured by PSP anticipated from the strahl temperature measurements compare very well to the ones obtained using a PFSS model presented by Bale et al (2019); Badman et al (2019). Even though the measured values of T s agree very well with the coronal electron temperatures measured with the spectroscopes on-board SOHO spacecraft (David et al 1998;Cranmer 2002), we believe further analysis is required to confirm that T s is a direct measure of the electron temperature in corona.…”

Section: Discussionsupporting

confidence: 80%

“…Bi-directional strahls have been observed and related to magnetic field structures like closed magnetic loops and magnetic clouds (Gosling et al 1987). Sunward directed strahls have also been observed and serve as the indicators of magnetic field structures sometimes referred to as the switchbacks (Balogh et al 1999;Yamauchi et al 2004;MacNeil et al 2017), which are frequently observed also during the first perihelion of the PSP Bale et al 2019). In this study we do not consider special cases and focus on the anti- sunward moving strahl electrons in the nominal solar wind.…”

Section: Parker Solar Probementioning

confidence: 99%

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Coronal Electron Temperature Inferred from the Strahl Electrons in the Inner Heliosphere: Parker Solar Probe and Helios Observations

Berčič

Larson

Whittlesey

et al. 2020

ApJ

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The shape of the electron velocity distribution function plays an important role in the dynamics of the solar wind acceleration. Electrons are normally modelled with three components, the core, the halo, and the strahl. We investigate how well the fast strahl electrons in the inner heliosphere preserve the information about the coronal electron temperature at their origin. We analysed the data obtained by two missions, Helios spanning the distances between 65 and 215 R S , and Parker Solar Probe (PSP) reaching down to 35 R S during its first two orbits around the Sun. The electron strahl was characterised with two parameters, pitch-angle width (PAW), and the strahl parallel temperature (T s ). PSP observations confirm the already reported dependence of strahl PAW on core parallel plasma beta (β ec )(Berčič et al. 2019). Most of the strahl measured by PSP appear narrow with PAW reaching down to 30 o . The portion of the strahl velocity distribution function aligned with the magnetic field is for the measured energy range well described by a Maxwellian distribution function. T s was found to be anti-correlated with the solar wind velocity, and independent of radial distance. These observations imply that T s carries the information about the coronal electron temperature. The obtained values are in agreement with coronal temperatures measured using spectroscopy (David et al. 1998), and the inferred solar wind source regions during the first orbit of PSP agree with the predictions using a PFSS model Badman et al. 2019).

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Section: Discussionsupporting

confidence: 80%

Section: Parker Solar Probementioning

confidence: 99%

Coronal Electron Temperature Inferred from the Strahl Electrons in the Inner Heliosphere: Parker Solar Probe and Helios Observations

Berčič

Larson

Whittlesey

et al. 2020

ApJ

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“…4(a). These magnetic field reversals, also known as "switchbacks", have been observed to be pervasive in PSP's initial orbits, but their origin and physical nature remains a mystery Bale et al 2019;Tenerani et al 2020;de Wit et al 2020;Horbury et al 2020). Directly before this 30 minute-duration switchback, Fig.…”

Section: Event 2: April Foolsmentioning

confidence: 98%

Parker Solar Probe Observations of Proton Beams Simultaneous with Ion-scale Waves

Verniero

Larson

Livi

et al. 2020

ApJS

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106

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Parker Solar Probe (PSP), NASA's latest and closest mission to the Sun, is on a journey to investigate fundamental enigmas of the inner heliosphere. This paper reports initial observations made by the Solar Probe Analyzer for Ions (SPAN-I), one of the instruments in the Solar Wind Electrons Alphas and Protons (SWEAP) instrument suite. We address the presence of secondary proton beams in concert with ion-scale waves observed by FIELDS, the electromagnetic fields instrument suite. We show two events from PSP's 2 nd orbit that demonstrate signatures consistent with wave-particle interactions. We showcase 3D velocity distribution functions (VDFs) measured by SPAN-I during times of strong wave power at ion-scales. From an initial instability analysis, we infer that the VDFs departed far enough away from local thermodynamic equilibrium (LTE) to provide sufficient free energy to locally generate waves. These events exemplify the types of instabilities that may be present and, as such, may guide future data analysis characterizing and distinguishing between different wave-particle interactions.

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“…A highly variable streamer belt must exist to explain the small-scale magnetic and density variations in slow wind measured by PSP (e.g. Bale et al 2019), and other spacecraft further from the Sun. Coronal tomography cannot directly show such fine spatial and temporal scales.…”

Section: Summary and Future Workmentioning

confidence: 99%

The Width, Density, and Outflow of Solar Coronal Streamers

Morgan

Cook

2020

ApJ

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Characterising the large-scale structure and plasma properties of the inner corona is crucial to understand the source and subsequent expansion of the solar wind and related space weather effects. Here we apply a new coronal rotational tomography method, along with a method to narrow streamers and refine the density estimate, to COR2A/STEREO observations from a period near solar minimum and maximum, gaining density maps for heights between 4 and 8R . The coronal structure is highly radial at these heights, and the streamers are very narrow, in some regions only a few degrees in width. The mean densities of streamers is almost identical between solar minimum and maximum. However, streamers at solar maximum contain around 50% more total mass due to their larger area. By assuming a constant mass flux, and constraints on proton flux measured by Parker Solar Probe (PSP), we estimate an outflow speed within solar minimum streamers of 50-120 kms −1 at 4R , increasing to 90-250 kms −1 at 8R . Accelerations of around 6 ms −2 are found for streamers at a height of 4R , decreasing with height. The solar maximum slow wind shows a higher acceleration to extended distances compared to solar minimum. To satisfy the solar wind speeds measured by PSP, there must be a mean residual acceleration of around 1-2 ms −2 between 8 and 40R . Several aspects of this study strongly suggest that the coronal streamer belt density is highly variable on small scales, and that the tomography can only reveal a local spatial and temporal average. Subject headings: Sun: corona-sun: CMEs-sun: solar wind 2010), and regions in between (e.g. Kramar et al. 2009); (ii) the short-term (Morgan 2011a; Vibert et al. 2016) and long-term (Morgan & Habbal 2010; Morgan 2011b) time evolution of the corona; and (iii) the relationship between magnetic and plasma structures (Vásquez et al. 2008; Morgan & Habbal 2010; Morgan 2011a; Kramar et al. 2014). Furthermore, estimates of the 3D distribution of density is crucial for interpretation of observations by other instruments (Frazin et al. 2003), and as boundary constraints for large-scale models (Frazin et al. 2005). These methods, and their findings, are described in the review of Aschwanden (2011). Most of the literature is dedicated to descriptions and tests of methods, with application to a number of case studies. Exceptions that look at larger datasets and longer periods are Morgan & Habbal (2010) and Morgan (2011b), where more long-term studies of the streamer distribution are made, albeit based on a qualitative view of density structure. CRT of the solar maximum corona is particularly difficult, and results from these periods are rare (Butala et al. 2005; Morgan & Habbal 2010).Recently, Morgan (2019) (hereafter Paper II) developed a new CRT method based on spherical harmonics. The success of the method depends on the detailed calibration and pre-processing methods described by Morgan (2015) (hereafter Paper I). The method is restricted to heights where the coronal structure is predominantly radial, so at helio...

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Highly structured slow solar wind emerging from an equatorial coronal hole

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Cited by 506 publications

References 51 publications

Coronal Electron Temperature Inferred from the Strahl Electrons in the Inner Heliosphere: Parker Solar Probe and Helios Observations

Coronal Electron Temperature Inferred from the Strahl Electrons in the Inner Heliosphere: Parker Solar Probe and Helios Observations

Parker Solar Probe Observations of Proton Beams Simultaneous with Ion-scale Waves

The Width, Density, and Outflow of Solar Coronal Streamers

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