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Abstract Switchbacks, defined as Alfvénic reversals in magnetic field polarity, can dissipate their magnetic energy with heliocentric distance. To further investigate this, two distinct solar wind parcels tracing back to a similar solar source region were examined during a radial alignment between Parker Solar Probe (@25.8RS) and Solar Orbiter (@152RS). The one caveat was that the two probes were located on opposite sides of the heliospheric current sheet during the alignment. The two parcels contained a multitude of switchbacks—the parcel closer to the Sun was characterized as a switchback patch (SBP), where background proton velocity (vp) is comparable to the pristine solar wind (vsw), while the parcel farther from the Sun showed characteristics attributable to a microstream (MS;vp > vsw). It was found that (1) MS contains, on average, 30% fewer switchbacks than SBP, and (2) dynamic and thermal pressures decreased by up to 20% across switchback boundaries in SBP and relatively unchanged in MS. Magnetic relaxation can explain the lower number of switchbacks in MS compared to SBP. Switchback relaxation inside SBP can, in turn, accelerate plasma inside SBP over time and heliocentric distance, thus resulting invp>vswin MS. Therefore, it is hypothesized that magnetic relaxation of switchbacks may cause SBPs to evolve into MSs over time and heliocentric distance.
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Heliospheric Diffusion of Stochastic Parker Spirals in Radially Evolving Solar Wind Turbulence
Abstract We present a stochastic field line mapping model where the interplanetary magnetic field lines are described by a density distribution function satisfying a Fokker–Planck equation that is solved numerically. Due to the spiral geometry of the nominal Parker field and to the evolving nature of solar wind turbulence, the heliospheric diffusion of the magnetic field lines is both heterogeneous and anisotropic, including a radial component. The longitudinal distributions of the magnetic field lines are shown to be close to circular Gaussian distributions, although they develop a noticeable skewness. The magnetic field lines emanating from the Sun are found to differ, on average, from the spirals predicted by Parker. Although the spirals remain close to Archimedean, they are here underwound, on average. Our model predicts a spiral angle that is smaller by ∼5° than the Parker spiral angle at Earth’s orbit for the same solar wind speed ofVsw= 400 km s−1. It also predicts an angular position on the solar disk of the best magnetically connected footpoint to an observer at 1 au that is shifted westward by ∼10° with respect to the Parker’s field model. This significantly changes the angle of the most probable magnetic connection between possible sources on the Sun and observers in the inner heliosphere. The results have direct implications for the heliospheric transport of “scatter-free” electrons accelerated in the aftermath of solar eruptions.
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- Award ID(s):
- 2149771
- PAR ID:
- 10493798
- Publisher / Repository:
- ApJ
- Date Published:
- Journal Name:
- The Astrophysical Journal
- Volume:
- 962
- Issue:
- 2
- ISSN:
- 0004-637X
- Page Range / eLocation ID:
- 186
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.3847/1538-4357/ad19dd
