Search arXiv⌕ Search
Home/Archive/arXiv

arXiv · 1911.10923

Co-spatial velocity and magnetic swirls in the simulated solar photosphere

Jiajia Liu·Mats Carlsson·Chris J Nelson·Robert Erdélyi
View original source ↗Read source document ↗Export metadata ↓

Abstract

Context. Velocity or intensity swirls have now been shown to be widely present throughout the photosphere and chromosphere. It has been suggested that these events could contribute to the heating of the upper solar atmosphere, via exciting Alfvén pulses, which could carry significant amounts of energy. However, the conjectured necessary physical conditions for their excitation, that the magnetic field rotates co-spatially and co-temporally with the velocity field, has not been verified. Aims. We aim to understand whether photospheric velocity swirls exist co-spatially and co-temporally with photospheric magnetic swirls, in order to demonstrate the link between swirls and pulses. Methods. The automated swirl detection algorithm (ASDA) is applied to the photospheric horizontal velocity and vertical magnetic fields obtained from a series of realistic numerical simulations using the RMHD code Bifrost. The spatial relationship between the detected velocity and magnetic swirls is further investigated via a well-defined correlation index (CI) study. Results. On average, there are ~63 short-lived photospheric velocity swirls (with lifetimes mostly less than 20 s, and average radius of ~37 km and rotating speeds of ~2.5 km/s) detected in a field of view (FOV) of 6\times6 Mm^{-2}, implying a total population of velocity swirls of ~1.06\times10^7 in the solar photosphere. More than 80% of the detected velocity swirls are found to be accompanied by local magnetic concentrations in intergranular lanes. On average, ~71% of the detected velocity swirls have been found to co-exist with photospheric magnetic swirls with the same rotating direction. Conclusions. The co-temporal and co-spatial rotation in the photospheric velocity and magnetic fields provide evidence that the conjectured condition for the excitation of Alfvén pulses by photospheric swirls is fulfilled.

Explore related subjects

astro-ph.SR

Keep this discovery

Explore connections, maps & timelines

BibTeXRIS

Jiajia Liu, Mats Carlsson, Chris J Nelson, Robert Erdélyi. 2019-11-25. Co-spatial velocity and magnetic swirls in the simulated solar photosphere. https://doi.org/10.1051/0004-6361%2F201936882

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related papers

arXiv2026

Host-star metallicities and kinematics of directly imaged brown-dwarf companions

Brown dwarfs are common as free-floating objects but rare as close companions to Sun-like stars, a disparity known as the "brown-dwarf desert". Host-star metallicity can constrain whether these companions form mainly through metal-sensitive core accretion or through less metal-dependent disc or cloud fragmentation. We extend our homogeneous spectroscopic analysis of directly imaged planet hosts into the brown-dwarf regime and compare their metallicities with those of planet hosts and close-in brown-dwarf hosts. We compiled 54 unique directly imaged brown-dwarf systems selected over an inclusive 13-80 M_Jup interval and projected separations from about 5 au to several thousand au. Objects near the model-dependent 70-75 M_Jup hydrogen-burning boundary may instead be very-low-mass stars. For 31 hosts with archival high-resolution spectra, we derived atmospheric parameters and metallicities using Bayesian spectral synthesis. Literature companion masses and projected separations are heterogeneous and are used only for demographic context. Galactic velocities were calculated for 46 hosts solely to characterise the youth-biased imaging sample. The host stars have a broadly solar metallicity distribution, with a median [Fe/H] of +0.06 dex and a median absolute deviation of 0.11 dex, and show no strong metal-rich bias. No statistically significant metallicity difference is detected between the lower- and higher-mass directly imaged subsamples. The hosts are kinematically cold, as expected from the youth-biased selection of direct-imaging surveys. The absence of a strong metal-rich bias suggests that classical core accretion does not dominate the wide-orbit brown-dwarf population. Disc instability and cloud fragmentation remain plausible, but the current sample and heterogeneous companion properties do not permit object-by-object discrimination between these channels.

astro-ph.SR↗
arXiv2026

Stability Analysis of the Proton Hammerhead Distribution Observed by Parker Solar Probe: Linear Theory and Fully Kinetic Simulations under Idealised Conditions

The non-adiabatic heating of the slow Solar Wind (SW) remains an open problem, with wave--particle interactions as a primary candidate mechanism. Novel in situ Parker Solar Probe (PSP) observations reveal strongly perpendicular anisotropic velocity distribution functions (VDFs), called "hammerhead", correlated with intense wave activity. These VDFs are systematically measured at the Heliospheric Current Sheet (HCS), making the hammerhead an important kinetic signature of the slow SW. In this work, we employ a fully kinetic particle-in-cell approach, complemented by a linear Vlasov solver to cross-validate the simulation results, to investigate the stability of these VDFs, the timescales over which they evolve, and their interaction with plasma waves. Our main findings indicate that the hammerhead distribution is primarily susceptible to drift-type instabilities, while energy is nonlinearly transferred back to the plasma through a combination of Landau and cyclotron resonances, resulting in net heating in the parallel direction, preferentially energizing the beam proton population. Crucially, these nonlinear interactions do not drastically alter the morphology of the distribution. This suggests the possibility that the hammerhead may be generated locally within the HCS in the inner heliosphere and subsequently advected outward, where it is eventually measured by PSP. This work lays the ground for future investigations into the kinetic physics of the HCS.

astro-ph.SR↗
arXiv2026

The independence of the mid-infrared RR Lyrae Period-Luminosity relation from metallicity from a study of three globular clusters in the Large Magellanic Cloud

RR Lyrae are pulsating variable stars tracing old ($>10$ Gyr) stellar populations, and exhibit a strong mid-infrared Period-Luminosity (PL) relation that can be calibrated with known parallaxes to infer distances. Here we present Period-Luminosity relations and distance moduli for three isolated globular clusters in the Large Magellanic Cloud: Reticulum, NGC 1841, and NGC 1466. Our analysis uses legacy \textit{Spitzer Space Telescope} images obtained by the Carnegie RR Lyrae Program, and an internally self-consistent sample restricted to RRab stars, with cluster membership confirmed using Gaia DR3 proper motions and photometry. In the Spitzer 3.6~$μ$m band, we simultaneously fit a PL for these clusters using a slope derived from Galactic Globular Clusters, yielding extinction-corrected distance moduli of $18.47\pm0.09$ mag for Reticulum, $18.29\pm0.09$ mag for NGC 1841, and $18.61\pm0.09$ mag for NGC 1466. The latter two are the first RR Lyrae PL-based distance moduli for these clusters, and all three are consistent with literature values from other techniques. Additionally we fit a PL with slope as a free parameter, and find that this LMC-derived PL is consistent with that derived from Galactic GCs. Simultaneously fitting a PLZ for the three clusters yields a metallicity coefficient $c= -0.03\pm0.05~\mathrm{mag}~\mathrm{dex}^{-1}$ which can be considered a negligible dependence of the PL on metallicity ($|c| <0.1$ mag dex$^{-1}$). Modelling an intrinsic width, $W$, to the PL/ PLZ yields a consistent value $W\approx0.1\pm0.02~\mathrm{mag}$, suggesting intrinsic width is not driven by metallicity.

astro-ph.SR↗