Sensitivity of solar wind mass flux to coronal temperature

Stansby, David; Berčič, Laura; Matteini, Lorenzo; Owen, C. J.; French, Ryan J.; Baker, D.; Badman, S. T.

doi:10.1051/0004-6361/202039789

Cited by 6 publications

(6 citation statements)

References 68 publications

(46 reference statements)

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“…The modeled values are within the range of the observed values, even though the BiCoP boundary parameters-electron and proton temperature at 3 R S set to 121 eV-differ from the expected coronal temperatures. Electrons in the corona are observed to be colder, T e ∼ 86 eV (1 MK; Cranmer 2002;Berčič et al 2020;Stansby et al 2021), while the proton temperature is expected to be greater. This difference in temperature between the two species and the preferential perpendicular heating of solar wind protons potentially result in the observed Φ r,∞ , even when the electron temperature at the origin is less than the electron temperature assumed in BiCoP simulations.…”

Section: Ambipolar Electric Potential (φ R∞ )mentioning

confidence: 99%

“…These can be estimated remotely through spectroscopy and multifrequency radio imaging (Mercier & Chambe 2015). In coronal holes, which are regions of open magnetic field lines along which plasma can flow freely in the radial direction, the typical electron temperature is 0.79 MK (David et al 1998;Cranmer 2002), while much higher temperatures are found on the edges of coronal holes and in active regions (Stansby et al 2021).…”

Section: Introductionmentioning

confidence: 99%

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Ambipolar Electric Field and Potential in the Solar Wind Estimated from Electron Velocity Distribution Functions

Berčič

Maksimović

Halekas

et al. 2021

ApJ

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The solar wind escapes from the solar corona and is accelerated, over a short distance, to its terminal velocity. The energy balance associated with this acceleration remains poorly understood. To quantify the global electrostatic contribution to the solar wind dynamics, we empirically estimate the ambipolar electric field (E ∥) and potential (Φr,∞). We analyze electron velocity distribution functions (VDFs) measured in the near-Sun solar wind between 20.3 R S and 85.3 R S by the Parker Solar Probe. We test the predictions of two different solar wind models. Close to the Sun, the VDFs exhibit a suprathermal electron deficit in the sunward, magnetic-field-aligned part of phase space. We argue that the sunward deficit is a remnant of the electron cutoff predicted by collisionless exospheric models. This cutoff energy is directly linked to Φr,∞. Competing effects of E ∥ and Coulomb collisions in the solar wind are addressed by the Steady Electron Runaway Model (SERM). In this model, electron phase space is separated into collisionally overdamped and underdamped regions. We assume that this boundary velocity at small pitch angles coincides with the strahl break-point energy, which allows us to calculate E ∥. The obtained Φr,∞ and E ∥ agree well with theoretical expectations. They decrease with radial distance as power-law functions with indices α Φ = −0.66 and α E = −1.69. We finally estimate the velocity gained by protons from electrostatic acceleration, which equals 77% calculated from the exospheric models, and 44% from the SERM model.

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Section: Ambipolar Electric Potential (φ R∞ )mentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Ambipolar Electric Field and Potential in the Solar Wind Estimated from Electron Velocity Distribution Functions

Berčič

Maksimović

Halekas

et al. 2021

ApJ

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“…Backmapping solar wind measured at 1 AU to active region sources identified in EUV shows that active region solar wind is slower than the average solar wind (Fu et al, 2015;Zhao et al, 2017). Active regions are hotter than coronal holes, which drives increased mass fluxes in the corona (Stansby et al, 2020b), but in the case of the Sun the magnetic field expansion almost exactly cancels this difference out, resulting in a remarkably constant solar wind mass flux (Wang, 2010) that is independent of source type. There is still plenty of scope for further investigation of the properties of solar wind originating in active regions.…”

Section: Discussionmentioning

confidence: 98%

Active region contributions to the solar wind over multiple solar cycles

Stansby,

Green,

van Driel-Gesztelyi

et al. 2021

Preprint

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Both coronal holes and active regions are source regions of the solar wind. The distribution of these coronal structures across both space and time is well known, but it is unclear how much each source contributes to the solar wind. In this study we use photospheric magnetic field maps observed over the past four solar cycles to estimate what fraction of magnetic open solar flux is rooted in active regions, a proxy for the fraction of all solar wind originating in active regions. We find that the fractional contribution of active regions to the solar wind varies between 30% to 80% at any one time during solar maximum and is negligible at solar minimum, showing a strong correlation with sunspot number. While active regions are typically confined to latitudes ±30 • in the corona, the solar wind they produce can reach latitudes up to ±60 • . Their fractional contribution to the solar wind also correlates with coronal mass ejection rate, and is highly variable, changing by ±20% on monthly timescales within individual solar maxima. We speculate that these variations are primarily driven by coronal mass ejections causing global reconfigurations of the coronal magnetic field on sub-monthly timescales.

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“…Backmapping solar wind measured at 1 AU to active region sources identified in EUV images shows that active region solar wind is slower than the average solar wind (Fu et al, 2015;Zhao et al, 2017). Active regions are hotter than coronal holes, which drives increased mass fluxes in the corona (Stansby et al, 2020b), but in the case of the Sun the magnetic field expansion almost exactly cancels this difference out, resulting in a remarkably constant solar wind mass flux (Wang, 2010) that is independent of source type. There is still plenty of scope for further investigation of the properties of solar wind originating in active regions.…”

Section: Discussionmentioning

confidence: 98%

Active Region Contributions to the Solar Wind over Multiple Solar Cycles

et al. 2021

Self Cite

View full text Add to dashboard Cite

Both coronal holes and active regions are source regions of the solar wind. The distribution of these coronal structures across both space and time is well known, but it is unclear how much each source contributes to the solar wind. In this study we use photospheric magnetic field maps observed over the past four solar cycles to estimate what fraction of magnetic open solar flux is rooted in active regions, a proxy for the fraction of all solar wind originating in active regions. We find that the fractional contribution of active regions to the solar wind varies between 30% to 80% at any one time during solar maximum and is negligible at solar minimum, showing a strong correlation with sunspot number. While active regions are typically confined to latitudes ±30∘ in the corona, the solar wind they produce can reach latitudes up to ±60∘. Their fractional contribution to the solar wind also correlates with coronal mass ejection rate, and is highly variable, changing by ±20% on monthly timescales within individual solar maxima. We speculate that these variations could be driven by coronal mass ejections causing reconfigurations of the coronal magnetic field on sub-monthly timescales.

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Sensitivity of solar wind mass flux to coronal temperature

Cited by 6 publications

References 68 publications

Ambipolar Electric Field and Potential in the Solar Wind Estimated from Electron Velocity Distribution Functions

Ambipolar Electric Field and Potential in the Solar Wind Estimated from Electron Velocity Distribution Functions

Active region contributions to the solar wind over multiple solar cycles

Active Region Contributions to the Solar Wind over Multiple Solar Cycles

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