On the origin of the magnetic energy in the quiet solar chromosphere

The presence of magnetic field is crucial in the transport of energy through the solar atmosphere. Recent ground-based and space-borne observations of the quiet Sun have revealed that magnetic field accumulates at photospheric heights, via a local dynamo or from small-scale flux emergence events. However, most of this small-scale magnetic field may not expand into the chromosphere due to the entropy drop with height at the photosphere. Here we present a study that uses a high resolution 3D radiative MHD simulation of the solar atmosphere with non-grey and non-LTE radiative transfer and thermal conduction along the magnetic field to reveal that: 1) the net magnetic flux from the simulated quiet photosphere is not sufficient to maintain a chromospheric magnetic field (on average), 2) processes in the lower chromosphere, in the region dominated by magneto-acoustic shocks, are able to convert kinetic energy into magnetic energy, 3) the magnetic energy in the chromosphere increases linearly in time until the r.m.s. of the magnetic field strength saturates at roughly 4 to 30 G (horizontal average) due to conversion from kinetic energy, 4) and that the magnetic features formed in the chromosphere are localized to this region.Comment: 12 pages, 14 figures, accepted to be published in Ap

Transport of Internetwork Magnetic Flux Elements in the Solar Photosphere

The motions of small-scale magnetic flux elements in the solar photosphere can provide some measure of the Lagrangian properties of the convective flow. Measurements of these motions have been critical in estimating the turbulent diffusion coefficient in flux-transport dynamo models and in determining the Alfvén wave excitation spectrum for coronal heating models. We examine the motions of internetwork flux elements in Hinode/Narrowband Filter Imager magnetograms and study the scaling of their mean squared displacement and the shape of their displacement probability distribution as a function of time. We find that the mean squared displacement scales super-diffusively with a slope of about 1.48. Super-diffusive scaling has been observed in other studies for temporal increments as small as 5 s, increments over which ballistic scaling would be expected. Using high-cadence MURaM simulations, we show that the observed super-diffusive scaling at short increments is a consequence of random changes in barycenter positions due to flux evolution. We also find that for long temporal increments, beyond granular lifetimes, the observed displacement distribution deviates from that expected for a diffusive process, evolving from Rayleigh to Gaussian. This change in distribution can be modeled analytically by accounting for supergranular advection along with granular motions. These results complicate the interpretation of magnetic element motions as strictly advective or diffusive on short and long timescales and suggest that measurements of magnetic element motions must be used with caution in turbulent diffusion or wave excitation models. We propose that passive tracer motions in measured photospheric flows may yield more robust transport statistics. © 2018. The American Astronomical Society. All rights reserved.This paper is based on the data acquired during Hinode Operation Plan 151. We thank the Hinode Chief Observers for their efforts in executing this plan. Hinode was developed and launched by ISAS/JAXA with NAOJ as a domestic partner and NASA and STFC (UK) as international partners. It is operated by these agencies in cooperation with ESA and NSC (Norway). This work has been partially funded by the Spanish Ministerio de Economia y Competitividad through projects ESP2013-47349-C6-1-R and ESP2016-77548-C5-1-R including European FEDER funds. The research has made use of NASA's Astrophysics Data System Bibliographic Services. N.C.A.R. is supported by the National Science Foundation. The authors thank Samuel Van Kooten for magnetic bright points tracking. M.P.R. was partially supported by NASA award NNX12AB35G. P.A. acknowledges the support of the University of Colorado's George Ellery Hale Graduate Student Fellowship

Solar and Interplanetary Turbulence: Lagrangian Coherent Structures

Talk delivered in 22nd EGU General Assembly, held online 4-8 May, 2020, id.4289, https://meetingorganizer.copernicus.org/EGU2020/EGU2020-4289.html.-- https://www.egu2020.eu/The dynamics of solar and interplanetary plasmas is governed by coherent structures such as current sheets and magnetic flux ropes which are responsible for the genesis of intermittent turbulence via magnetic reconnections in solar supergranular junctions, solar coronal loops, the shock-sheath region of an interplanetary coronal mass ejection, and the interface region of two interplanetary magnetic flux ropes. Lagrangian coherent structures provide a new powerful technique to detect time- or space-dependent transport barriers, and objective (i.e., frame invariant) kinematic and magnetic vortices in space plasma turbulence. We discuss the basic concepts of Lagrangian coherent structures in plasmas based on the computation of the finite-time Lyapunov exponent, the Lagrangian averaged vorticity deviation and the integrated averaged current deviation, as well as their applications to numerical simulations of MHD turbulence and space and ground observations.With funding from the Spanish government through the ‘Severo Ochoa Centre of Excellence’ accreditation SEV-2017-070

Persistent magnetic vortex flow at a supergranular vertex

Photospheric vortex flows are thought to play a key role in the evolution of magnetic fields. Recent studies show that these swirling motions are ubiquitous in the solar surface convection and occur in a wide range of temporal and spatial scales. Their interplay with magnetic fields is poorly characterized, however. Aims. We study the relation between a persistent photospheric vortex flow and the evolution of a network magnetic element at a supergranular vertex. Methods. We used long-duration sequences of continuum intensity images acquired with Hinode and the local correlation-tracking method to derive the horizontal photospheric flows. Supergranular cells are detected as large-scale divergence structures in the flow maps. At their vertices, and cospatial with network magnetic elements, the velocity flows converge on a central point. Results. One of these converging flows is observed as a vortex during the whole 24 h time series. It consists of three consecutive vortices that appear nearly at the same location. At their core, a network magnetic element is also detected. Its evolution is strongly correlated to that of the vortices. The magnetic feature is concentrated and evacuated when it is caught by the vortices and is weakened and fragmented after the whirls disappear. Conclusions. This evolutionary behavior supports the picture presented previously, where a small flux tube becomes stable when it is surrounded by a vortex flow. © ESO 2018.This work has been partially funded by the Spanish Ministerio de Economia y Competitividad through Project Nos. ESP2013-47349-C6-1-R, ESP2014-56169-C6-1-R, and ESP2016-77548-C5-1-R, including a percentage from European FEDER funds. The research leading to these results has received funding from the European Union's Horizon 2020 programme under grant agreement no. 739500 (PRE-EST project).Peer reviewe

Lagrangian chaotic saddles and objective vortices in solar plasmas

We report observational evidence of Lagrangian chaotic saddles in plasmas, given by the intersections of finite-time unstable and stable manifolds, using an approximate to 22h sequence of spacecraft images of the horizontal velocity field of solar photosphere. A set of 29 persistent objective vortices with lifetimes varying from 28.5 to 298.3 min are detected by computing the Lagrangian averaged vorticity deviation. The unstable manifold of the Lagrangian chaotic saddles computed for approximate to 11h exhibits twisted folding motions indicative of recurring vortices in a magnetic mixed-polarity region. We show that the persistent objective vortices are formed in the gap regions of Lagrangian chaotic saddles at supergranular junctions. ©2020 American Physical SocietyThis work was supported by Coordenacao de Aperfeicoamento de Pessoal de Nivel Superior (CAPES No. 88882.316962/2019-01 and No. 88881.309066/2018-01, Brazil), Conselho Nacional de Desenvolvimento Cientifico e Tecnologico (CNPq, Brazil), NASA Contract No. NNM07AA01C [Solar-B (Hinode) Focal Plane Package Phase E], Ministerio de Ciencia, Innovacion y Universidades (No. RTI2018-096886-B-C51, Spain), European Regional Development Fund (FEDER), and Center of Excellence Severo Ochoa Award to the Instituto de Astrofisica de Andalucia (No. SEV-2017-0709, Spain).Peer reviewe

The Solar Internetwork. III. Unipolar versus Bipolar Flux Appearance

This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited.Small-scale internetwork (IN) magnetic fields are considered to be the main building blocks of quiet Sun magnetism. For this reason, it is crucial to understand how they appear on the solar surface. Here, we employ a high-resolution, high-sensitivity, long-duration Hinode/NFI magnetogram sequence to analyze the appearance modes and spatiotemporal evolution of individual IN magnetic elements inside a supergranular cell at the disk center. From identification of flux patches and magnetofrictional simulations, we show that there are two distinct populations of IN flux concentrations: unipolar and bipolar features. Bipolar features tend to be bigger and stronger than unipolar features. They also live longer and carry more flux per feature. Both types of flux concentrations appear uniformly over the solar surface. However, we argue that bipolar features truly represent the emergence of new flux on the solar surface, while unipolar features seem to be formed by the coalescence of background flux. Magnetic bipoles appear at a faster rate than unipolar features (68 as opposed to 55 Mx cm−2 day−1), and provide about 70% of the total instantaneous IN flux detected in the interior of the supergranule. © 2022. The Author(s). Published by the American Astronomical Society.The data used here were acquired in the framework of Hinode Operation Plan 151, "Flux replacement in the solar network and internetwork." We thank the Hinode Chief Observers for the efforts they made to accommodate our demanding observations. Hinode is a Japanese mission developed and launched by ISAS/JAXA, with NAOJ as a domestic partner and NASA and STFC (UK) as international partners. It is operated by these agencies in cooperation with ESA and NSC (Norway). M.G. acknowledges a JAE-Pre fellowship granted by Agencia Estatal Consejo Superior de Investigaciones Científicas toward the completion of a PhD. This work has been funded by the State Agency for Research of the Spanish Ministerio de Ciencia e Innovación through grant RTI2018-096886-B-C5 (including FEDER funds) and through a Center of Excellence Severo Ochoa award to Instituto de Astrofísica de Andalucía (SEV-2017-0709). NASA supported this work through contract NNM07AA01C (Solar-B (Hinode) Focal Plane Package Phase E). Use of NASA's Astrophysical Data System is gratefully acknowledged.Peer reviewe

Supergranular turbulence in the quiet Sun: Lagrangian coherent structures

The quiet Sun exhibits a wealth of magnetic activities that are fundamental for our understanding of solar magnetism. The magnetic fields in the quiet Sun are observed to evolve coherently, interacting with each other to form prominent structures as they are advected by photospheric flows. The aim of this paper is to study supergranular turbulence by detecting Lagrangian coherent structures (LCS) based on the horizontal velocity fields derived from Hinode intensity images at disc centre of the quiet Sun on 2010 November 2. LCS act as transport barriers and are responsible for attracting/repelling the fluid elements and swirling motions in a finite time. Repelling/attracting LCS are found by computing the forward/backward finite-time Lyapunov exponent (FTLE), and vortices are found by the Lagrangian-averaged vorticity deviation method. We show that the Lagrangian centres and boundaries of supergranular cells are given by the local maximum of the forward and backward FTLE, respectively. The attracting LCS expose the location of the sinks of photospheric flows at supergranular junctions, whereas the repelling LCS interconnect the Lagrangian centres of neighbouring supergranular cells. Lagrangian transport barriers are found within a supergranular cell and from one cell to other cells, which play a key role in the dynamics of internetwork and network magnetic elements. Such barriers favour the formation of vortices in supergranular junctions. In particular, we show that the magnetic field distribution in the quiet Sun is determined by the combined action of attracting/repelling LCS and vortices.© 2019 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical SocietySSAS acknowledges financial support from agency Coordenacao de aperfeicoamento de Pessoal de nivel Superior (CAPES 88882.316962/2019-01, Brazil). ELR acknowledges financial support from Conselho Nacional de Desenvolvimento Cientifico e Tecnologico (CNPq, Brazil), partial financial support from CAPES (Brazil) and from Fundacao de Amparo a Pesquisa de Sao Paulo (FAPESP, Brazil). LBR acknowledges financial support from the Spanish Ministerio de Ciencia, Innovacion y Universidades through grant RTI2018-096886-B-C51, including a percentage from European Regional Development Fund (FEDER), and through the 'Center of Excellence Severo Ochoa' award to the Instituto de Astrofisica de Andalucia (SEV-2017-0709).Peer reviewe

Firefly: The Case for a Holistic Understanding of the Global Structure and Dynamics of the Sun and the Heliosphere

This white paper is on the HMCS Firefly mission concept study. Firefly focuses on the global structure and dynamics of the Sun's interior, the generation of solar magnetic fields, the deciphering of the solar cycle, the conditions leading to the explosive activity, and the structure and dynamics of the corona as it drives the heliosphere