On the Origin of the Photospheric Magnetic Field

Schuck, P. W.; Linton, M. G.; Knizhnik, K. J.; Leake, James E.

doi:10.3847/1538-4357/ac739a

“…The presented results support the recent predictions ofAslanyan et al (2022), and provide strong evidence that interchange reconnection dynamics could occur at small scales in the corona. One fascinating possibility for these small-scale changes relates to the new findings bySchuck et al (2022): the stresses commonly known to create current sheets in the tiny…”

mentioning

confidence: 99%

Statistical Evidence for Small-scale Interchange Reconnection at a Coronal Hole Boundary

Mason¹,

Uritsky²

2022

ApJL

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Much of coronal hole (CH) research is focused upon determining the boundary and calculating the open flux as accurately as possible. However, the observed boundary itself is worthy of investigation, and holds important clues to the physics transpiring at the interface between the open and closed fields. This Letter reports a powerful new method, an application of the correlation integral which we call correlation dimension mapping, by which the irregularity of a CH boundary can be objectively quantified. This method highlights the most important spatial scales involved in boundary dynamics, and also allows for easy temporal analysis of the boundary. We apply this method to an equatorial CH bounded on two sides by helmet streamers and on the third by a small pseudostreamer, which we observed at maximum cadence for an hour on 2015 June 4. We argue that the relevant spatial scales are in the range of ∼5–20 Mm, and we find that the boundary complexity depends measurably upon the nature of the neighboring closed structure. The boundary along the pseudostreamer shows signs of highly localized, intermittent-complexity variability, likely associated with abrupt changes in the magnetic topology, which would be elegantly explained by interchange reconnection. By contrast, the helmet streamer boundary supports long-lived, high-complexity regions. These findings support the recent predictions of interchange reconnection occurring at very small scales in the corona.

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“…Near the PIL, the horizontal field vectors display clear counterclockwise and clockwise rotational patterns in the northern and southern umbrae, respectively. According to Schuck et al (2022), this pattern is unambiguously associated with electric currents through the photosphere. Third, the redshift signal is co-located with the central penumbra with a median v l of −0.8 km s −1 and a maximum of −3.2 km s −1 .…”

Section: Photospheric Magnetic and Velocity Fieldsmentioning

confidence: 98%

Large Photospheric Doppler Shift in Solar Active Region 12673. I. Field-aligned Flows

Liu 刘,

Sun 孙,

Schuck

et al. 2023

ApJ

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Delta (δ) sunspots sometimes host fast photospheric flows along the central magnetic polarity inversion line (PIL). Here we study the strong Doppler shift signature in the central penumbral light bridge of solar active region NOAA 12673. Observations from the Helioseismic and Magnetic Imager (HMI) indicate highly sheared and strong magnetic fields. Large Doppler shifts up to 3.2 km s−1 appeared during the formation of the light bridge and persisted for about 16 hr. A new velocity estimator, called DAVE4VMwDV, reveals fast converging and shearing motion along the PIL from HMI vector magnetograms, and recovers the observed Doppler signal much better than an old version of the algorithm. The inferred velocity vectors are largely (anti-)parallel to the inclined magnetic fields, suggesting that the observed Doppler shift contains a significant contribution from the projected field-aligned flows. High-resolution observations from the Hinode/Spectro-Polarimeter further exhibit a clear correlation between the Doppler velocity and the cosine of the magnetic inclination, which is in agreement with HMI results and consistent with a field-aligned flow of about 9.6 km s−1. The complex Stokes profiles suggest significant gradients of physical variables along the line of sight. We discuss the implications on the δ-spot magnetic structure and the flow-driving mechanism.

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“…in  may be defined as zero in a simply connected domain (Berger 1999). However, as noted in Schuck et al (2022) and Sections 1 and 2 here, the physical origin of the potential field may be in the currents supported in  . Thus, the potential field P can misattribute the origin of flux threading the bounding surface to external current sources.…”

Section: Relative Helicity With Attribution For Magnetically Open Sys...mentioning

confidence: 99%

“…This potential field, shown in Figure 1(b), is represented by an image current ŷ I outside the volume of interest  at x/a = 0 and z/a = −1 in *  , as ∇×P = 0 must be zero inside  . Thus, the representation of flux threading the boundary by a potential field P misattributes the origin of this flux to a current source outside the volume of interest  (Schuck et al 2022). Similarly, the magnetic component that closes in  , defined as B cl ≡ B − P and shown in Figure 1(c), is represented by two antiparallel currents: one corresponds to the physical current ŷ I in  and the other corresponds to its image current y I in *  .…”

Section: Introductionmentioning

confidence: 99%

Disentangling the Entangled Linkages of Relative Magnetic Helicity

Schuck,

Linton

2024

ApJ

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Magnetic helicity, H, measures magnetic linkages in a volume. The early theoretical development of helicity focused on magnetically closed systems in V bounded by ∂ V . For magnetically closed systems, V ∈ R 3 = V + V ∗ , no magnetic flux threads the boundary, n ˆ · B ∣ ∂ V = 0 . Berger & Field and Finn & Antonsen extended the definition of helicity to relative helicity, H , for magnetically open systems where magnetic flux may thread the boundary. Berger expressed this relative helicity as two gauge-invariant terms that describe the self-helicity of the magnetic field that closes inside V and the mutual helicity between the magnetic field that threads the boundary ∂ V and the magnetic field that closes inside V . The total magnetic field that permeates V entangles magnetic fields that are produced by current sources J in V with magnetic fields that are produced by current sources J ∗ in V ∗ . Building on this fact, we extend Berger's expressions for relative magnetic helicity to eight gauge-invariant quantities that simultaneously characterize both of these self and mutual helicities and attribute their origins to currents J in V and/or J ∗ in V ∗ , thereby disentangling the domain of origin for these entangled linkages. We arrange these eight terms into novel expressions for internal and external helicity (self) and internal-external helicity (mutual) based on their domain of origin. The implications of these linkages for interpreting magnetic energy are discussed and new boundary observables are proposed for tracking the evolution of the field that threads the boundary.

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On the Origin of the Photospheric Magnetic Field

Cited by 6 publications

References 95 publications

Statistical Evidence for Small-scale Interchange Reconnection at a Coronal Hole Boundary

Statistical Evidence for Small-scale Interchange Reconnection at a Coronal Hole Boundary

Large Photospheric Doppler Shift in Solar Active Region 12673. I. Field-aligned Flows

Disentangling the Entangled Linkages of Relative Magnetic Helicity

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