Relationships Between Fluid Vorticity, Kinetic Helicity, and Magnetic Field on Small-Scales (Quiet-Network) on the Sun

Sangeetha, C. R.; Rajaguru, S. P.

doi:10.3847/0004-637x/824/2/120

Cited by 3 publications

(2 citation statements)

References 42 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Note however, that ζ/N is larger and increases with height in the magnetic model compared to the non-magnetic model, probably because of the generation of vorticity by the magnetic field in the low-β regime (Shelyag et al 2011;Steiner & Rezaei 2012;Wedemeyer-Böhm et al 2012). We also observe that the vortices in the non-magnetic model near the surface are larger compared to the magnetic model as also reported in observations by Sangeetha & Rajaguru (2016). Non-linearity parameter (ζ/N ) as a function of height in the non-magnetic (dashed) and magnetic (solid) models.…”

Section: Non-linear Interactionsupporting

confidence: 82%

Internal Gravity Waves in the Magnetized Solar Atmosphere. I. Magnetic Field Effects

Vigeesh

Jackiewicz

Steiner

2017

ApJ

View full text Add to dashboard Cite

Observations of the solar atmosphere show that internal gravity waves are generated by overshooting convection, but are suppressed at locations of magnetic flux, which is thought to be the result of mode conversion into magneto-acoustic waves. Here, we present a study of the acoustic-gravity wave spectrum emerging from a realistic, self-consistent simulation of solar (magneto-)convection. A magnetic field free, hydrodynamic simulation and a magneto-hydrodynamic (MHD) simulation with an initial, vertical, homogeneous field of 50 G flux density were carried out and compared with each other to highlight the effect of magnetic fields on the internal gravity wave propagation in the Sun's atmosphere. We find that the internal gravity waves are absent or partially reflected back into the lower layers in the presence of magnetic fields and argue that the suppression is due to the coupling of internal gravity waves to slow magneto acoustic waves still within the high-β region of the upper photosphere. The conversion to Alfvén waves is highly unlikely in our model because there is no strongly inclined magnetic field present. We argue that the suppression of internal waves observed within magnetic flux-concentrations may also be due to non-linear breaking of internal waves due to vortex flows that are ubiquitously present in the upper photosphere and the chromosphere.

show abstract

Section: Non-linear Interactionsupporting

confidence: 82%

Internal Gravity Waves in the Magnetized Solar Atmosphere. I. Magnetic Field Effects

Vigeesh

Jackiewicz

Steiner

2017

ApJ

View full text Add to dashboard Cite

show abstract

“…However, an influence of the magnetic fields on the (quiet-Sun) supergranular flows in certain cases cannot be completely excluded. For example, Sangeetha & Rajaguru (2016) found that the vorticity in supergranular inflows is reduced if the magnetic field is strong. According to Kobel et al (2012), in the strongest parts of the magnetic network the convection can be inhibited, causing magnetic elements to appear darker than in regions with a weaker magnetic field.…”

Section: Passive Magnetic Fieldmentioning

confidence: 99%

Evolution and wave-like properties of the average solar supergranule

Langfellner

Birch

Gizon

2018

A&A

View full text Add to dashboard Cite

Context. Solar supergranulation presents us with many mysteries. For example, previous studies in spectral space found that supergranulation has wave-like properties. Aims. Here we study, in real space, the wave-like evolution of the average supergranule over a range of spatial scales (from 10 to 80 Mm). We complement this by characterizing the evolution of the associated network magnetic field. Methods. We use one year of data from the Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamics Observatory to measure horizontal near-surface flows near the solar equator by applying time-distance helioseismology (TD) on Dopplergrams and granulation tracking (LCT) on intensity images. The average supergranule outflow (or inflow) is constructed by averaging over 10,000 individual outflows (or inflows). The contemporaneous evolution of the magnetic field is studied with HMI line-of-sight observations. Results. We confirm and extend previous measurements of the supergranular wave dispersion relation to angular wavenumbers in the range 50 < kR < 270. We find a plateau for kR > 120. In real space, larger supergranules undergo oscillations with longer periods and lifetimes than smaller cells. We find excellent agreement between TD and LCT and obtain wave properties that are independent of the tracking rate. The observed network magnetic field follows the oscillations of the supergranular flows with a six-hour time lag. This behavior can be explained by computing the motions of corks carried by the supergranular flows. Conclusions. Signatures of supergranular waves in surface horizontal flows near the solar equator can be observed in real space. These oscillatory flows control the evolution of the network magnetic field, in particular they explain the recently discovered eastwest anisotropy of the magnetic field around the average supergranule. Background flow measurements that we obtain from Doppler frequency shifts do not favor shallow models of supergranulation.

show abstract

Signatures of Untwisting Magnetic Field in a Small Emerging Bipole in the Solar Photosphere

Sangeetha¹,

Tripathi²,

Rajaguru³

2020

ApJ

View full text Add to dashboard Cite

We perform a study of fluid motions and its temporal evolution in and around a small bipolar emerging flux region using observations made by the Helioseismic and Magnetic Imager on board the Solar Dynamics Observatory. We employ local correlation tracking of the Doppler observations to follow horizontal fluid motions and line-of-sight magnetograms to follow the flux emergence. Changes in vertical vorticity and horizontal divergence are used to derive signatures of evolving twists in the magnetic field. Our analysis reveals that the two polarities of the magnetic flux swirl in opposite directions in the early stages of flux emergence indicating an unwinding of the pre-emergence twists in the magnetic field. We further find that during the emergence, there is an increase in swirly motions in the neighboring nonmagnetic regions. We estimate the magnetic and kinetic energies and find that magnetic energy is about a factor of 10 larger than the kinetic energy. During the evolution, when the magnetic energy decreases, an increase in the kinetic energy is observed indicating transfer of energy from the unwinding of the magnetic flux tube to the surrounding fluid motions. Our results thus demonstrate the presence of pre-emergence twists in an emerging magnetic field that is important in the context of the hemispheric helicity rule warranting a detailed statistical study in this context. Further, our observations point to a possible widespread generation of torsional waves in emerging flux regions due to the untwisting magnetic field with implications for upward energy transport to the corona.

show abstract

Relationships Between Fluid Vorticity, Kinetic Helicity, and Magnetic Field on Small-Scales (Quiet-Network) on the Sun

Cited by 3 publications

References 42 publications

Internal Gravity Waves in the Magnetized Solar Atmosphere. I. Magnetic Field Effects

Internal Gravity Waves in the Magnetized Solar Atmosphere. I. Magnetic Field Effects

Evolution and wave-like properties of the average solar supergranule

Signatures of Untwisting Magnetic Field in a Small Emerging Bipole in the Solar Photosphere

Contact Info

Product

Resources

About