We study the plasma flows in the solar photosphere during the emergence of two small active regions, NOAA 9021 and 10768. Using SOHO/MDI data, we find that the strong plasma upflows appear at the initial stage of active region formation, with maximum upflow velocities of -1650 and -1320 m/s. The structures with enhanced upflows have size about 8 Mm in diameter, and they exist for 1-2 hr. The parameters of the enhanced upflows are consistent with those of the large active region NOAA 10488, which may suggest the possibility that the elementary emerging magnetic loops that appear at the earliest phase of active region formation have similar properties, irrespective of scales of active regions. Comparison between the observations and a numerical simulation of magnetic flux emergence shows a striking consistency. We find that the driving force of the plasma upflow is at first the gas pressure gradient and later the magnetic pressure gradient.
In a force-free magnetic field, there is no interaction of field and the plasma in the surrounding atmosphere i.e., electric currents are aligned with the magnetic field, giving rise to zero Lorentz force. The computation of many magnetic parameters like magnetic energy, gradient of twist of sunspot magnetic fields (computed from the force-free parameter $α$), including any kind of extrapolations heavily hinge on the force-free approximation of the photospheric magnetic fields. The force-free magnetic behaviour of the photospheric sunspot fields has been examined by \cite{metc95} and \cite{moo…
In this review, our present day understanding of the Sun's global photospheric and coronal magnetic fields is discussed from both observational and theoretical viewpoints. Firstly, the large-scale properties of photospheric magnetic fields are described, along with recent advances in photospheric magnetic flux transport models. Following this, the wide variety of theoretical models used to simulate global coronal magnetic fields are described. From this, the combined application of both magnetic flux transport simulations and coronal modeling techniques to describe the phenomena of coronal hol…
We study the magnetic field evolution in the active region (AR) 12673 that produced the largest solar flare in the past decade on 2017 September 6. Fast flux emergence is one of the most prominent features of this AR. We calculate the magnetic helicity from photospheric tangential flows that shear and braid field lines (shear-helicity), and from normal flows that advect twisted magnetic flux into the corona (emergence-helicity), respectively. Our results show that the emergence-helicity accumulated in the corona is $-1.6\times10^{43}~Mx^2$ before the major eruption, while the shear-helicity ac…
MHD simulations of sunspots have successfully reproduced many aspects of sunspot fine structure as consequence of magneto convection in inclined magnetic field. We study how global sunspot properties and penumbral fine structure depend on the magnetic top boundary condition as well as on grid spacing. The overall radial extent of the penumbra is subject to the magnetic top boundary condition. All other aspects of sunspot structure and penumbral fine structure are resolved at an acceptable level starting from a grid resolution of 48 [24] km (horizontal [vertical]). We find that the amount of in…
A magnetic field is force-free if there is no interaction between the magnetic field and plasma in surrounding atmosphere i.e., electric currents are aligned with the magnetic field, giving rise to zero Lorentz force. Computation of various magnetic parameters such as magnetic energy, gradient of twist of sunspot fields and any kind of extrapolations, heavily hinge on the force-free approximation of the photospheric sunspot magnetic fields. Thus it is important to inspect the force-freeness of sunspot fields. The force-freeness of sunspot magnetic fields has been examined earlier by some resea…
A recent study carried out on high sensitivity SUNRISE/IMAX data has reported about the existence of areas of limited flux emergence in the quiet Sun. By exploiting an independent and longer (4 hours) data set acquired by HINODE/SOT, we further investigate these regions by analysing their spatial distribution and relation with the supergranular flow. Our findings, while confirming the presence of these calm areas, also show that the rate of emergence of small magnetic elements is largely suppressed at the locations where the divergence of the supergranular plasma flows is positive. This means …
We present observational evidence for the presence of MHD waves in the solar photosphere deduced from SOHO/MDI Dopplergram velocity observations. The magneto-acoustic perturbations are observed as acoustic power enhancement in the sunspot umbra at high-frequency bands in the velocity component perpendicular to the magnetic field. We use numerical modelling of wave propagation through localised non-uniform magnetic field concentration along with the same filtering procedure as applied to the observations to identify the observed waves. Guided by the results of the numerical simulations we class…
We studied flux emergence events of sub-granular scale in a solar active region. New Solar Telescope (NST) of Big Bear Solar Observatory made it possible to clearly observe the photospheric signature of flux emergence with very high spatial (0".11 at 7057Å) and temporal (15 s) resolution. From TiO observations with the pixel scale of 0".0375, we found several elongated granule-like features (GLFs) stretching from the penumbral filaments of a sunspot at a relatively high speed of over 4 km s-1. After a slender arched darkening appeared at a tip of a penumbral filament, a bright point (BP) devel…
We investigate the ratio of the vertical and horizontal velocities of the photospheric plasma flows in the region of emerging magnetic fields on the Sun. We carried out a study of photospheric velocities during the first hours of the appearance of 83 active regions with magnetic flux more than 10^21 Mx with data acquired by the Michelson Doppler Imager (MDI) on board the Solar and Heliospheric Observatory (SOHO). The emerging magnetic fluxes under investigation were isolated from extended concentrations of existing magnetic fields; they have different spatial scales and are located at differen…
The Helioseismic and Magnetic Imager provides 45 s cadence intensity images and 720 s cadence vector magnetograms. These unprecedented high-cadence and high-resolution data give us a unique opportunity to study the change of photospheric flows and sunspot rotations associated with flares. By using the differential affine velocity estimator method and the Fourier local correlation tracking method separately, we calculate velocity and vorticity of photospheric flows in the flaring NOAA AR 11158, and investigate their temporal evolution around the X2.2 flare on 2011 February 15. It is found that …
We used photospheric intensity images and magnetic field measurements from the New Solar Telescope in Big Bear and Helioseismic Magnetic Imager on board Solar Dynamics Observatory (SDO) to study the the effect that the new small-scale emerging flux induces on solar granulation. We report that emerging flux appears to leave different types of footprint on solar granulation: i) diffuse irregular patches of increased brightness, ii) well defined filament-like structures and accompanied bright points, and iii) bright point-like features that appear inside granules. We suggest that the type of the …
Many jets are detected at X-ray wavelengths in the Sun's polar regions, and the ejected plasma along the jets has been suggested to contribute mass to the fast solar wind. From in-situ measurements in the magnetosphere, it has been found that the fast solar wind has photospheric abundances while the slow solar wind has coronal abundances. Therefore, we investigated the abundances of polar jets to determine whether they are the same as that of the fast solar wind. For this study, we selected 22 jets in the polar region observed by Hinode/EIS (EUV Imaging Spectrometer) and XRT (X-Ray Telescope) …
We study the variability of solar activity using new photospheric proxies originally developed for the analysis of stellar magnetism with the CoRoT and Kepler photometric observations. These proxies are obtained by tracking the temporal modulations in the observations associated to the spots and magnetic features as the Sun rotates. We analyze here 21 years, spanning solar cycles 23 and 24, of the observations collected by the space-based photometric VIRGO and radial velocity GOLF instruments on board the SoHO satellite. The photospheric activity proxy Sph is then calculated for each of the th…
Recently, there have been some reports of unusually strong photospheric magnetic fields (which can reach values of over 7 kG) inferred from Hinode SOT/SP sunspot observations within penumbral regions. These superstrong penumbral fields are even larger than the strongest umbral fields on record and appear to be associated with supersonic downflows. The finding of such fields has been controversial since they seem to show up only when spatially coupled inversions are performed. Here, we investigate and discuss the reliability of those findings by studying in detail observed spectra associated wi…
Recent studies of NOAA active region 10953, by Okamoto {\it et al.} ({\it Astrophys. J. Lett.} {\bf 673}, 215, 2008; {\it Astrophys. J.} {\bf 697}, 913, 2009), have interpreted photospheric observations of changing widths of the polarities and reversal of the horizontal magnetic field component as signatures of the emergence of a twisted flux tube within the active region and along its internal polarity inversion line (PIL). A filament is observed along the PIL and the active region is assumed to have an arcade structure. To investigate this scenario, MacTaggart and Hood ({\it Astrophys. J. Le…
The dynamics of horizontal plasma flows during the first hours of the emergence of active region magnetic flux in the solar photosphere have been analyzed using SOHO/MDI data. Four active regions emerging near the solar limb have been considered. It has been found that extended regions of Doppler velocities with different signs are formed in the first hours of the magnetic flux emergence in the horizontal velocity field. The flows observed are directly connected with the emerging magnetic flux; they form at the beginning of the emergence of active regions and are present for a few hours. The D…
Various theoretical and observational results have been reported regarding the presence/absence of net electric currents in the sunspots. The limited spatial resolution of the earlier observations perhaps obscured the conclusions. We have analyzed 12 sunspots observed from Hinode (SOT/SP) to clarify the issue. The azimuthal and radial components of magnetic fields and currents have been derived. The azimuthal component of the magnetic field of sunspots is found to vary in sign with azimuth. The radial component of the field also varies in magnitude with azimuth. While the latter pattern is a c…
The solar magnetic field is responsible for all aspects of solar activity. Sunspots are the main manifestation of the ensuing solar activity. Combining high-resolution and synoptic observations has the ambition to provide a comprehensive description of the sunspot growth and decay processes. Active region NOAA 12396 emerged on 2015 August 3 and was observed three days later with the 1.5-meter GREGOR solar telescope on 2015 August 6. High-resolution spectropolarimetric data from the GREGOR Infrared Spectrograph (GRIS) are obtained in the photospheric Si I $λ$ 1082.7 nm and Ca I $λ$1083.9 nm lin…
We investigated the role of photospheric plasma motions in the formation and evolution of polar magnetic patches using time-sequence observations with high spatial resolution. The observations were obtained with the spectropolarimeter on board the Hinode satellite. From the statistical analysis using 75 magnetic patches, we found that they are surrounded by strong converging, supergranulation associated flows during their apparent life time and that the converging flow around the patch boundary is better observed in the Doppler velocity profile in the deeper photosphere. Based on our analysis …
A statistical study has been carried out of the relationship between plasma flow Doppler velocities and magnetic field parameters during the emergence of active regions at the solar photospheric level with data acquired by the Michelson Doppler Imager (MDI) onboard the Solar and Heliospheric Observatory (SOHO). We have investigated 224 emerging active regions with different spatial scales and positions on the solar disc. The following relationships for the first hours of the emergence of active regions have been analysed: i) of peak negative Doppler velocities with the position of the emerging…
Observational power spectra of the photospheric magnetic field turbulence, of the quiet-sun, were presented in a recent paper by Abramenko and Yurchyshyn. Here I focus on the power spectrum derived from the observations of the Near InfraRed Imaging Spectrapolarimeter (NIRIS) operating at the Goode Solar Telescope. The latter exhibits a transition from a power law with index $-1.2$ to a steeper power law with index $-2.2$, for smaller spatial scales. The present paper presents an interpretation of this change. Furthermore, this interpretation provides an estimate for the effective width of the …
Polarity imbalance of the photospheric magnetic field was studied using synoptic maps of NSO Kitt Peak (1976-2016). Imbalance of positive and negative fluxes was considered for the fields with strength B>50 G in the sunspot zone (5 deg - 40 deg) and for the fields with strength B<50 G at higher latitudes (40 deg - 90 deg). The 22-year periodicity in the imbalance of positive and negative fields was found which maintained itself during four solar cycles. While for the sunspot zone the sign of the imbalance always coincides with the northern hemisphere polarity, for the high latitudes the sign o…
Magnetic reconnection in the low atmosphere, e.g. chromosphere, is investigated in various physical environments. Its implications for the origination of explosive events (small--scale jets) are discussed. A 2.5-dimensional resistive magnetohydrodynamic (MHD) model in Cartesian coordinates is used. It is found that the temperature and velocity of the outflow jets as a result of magnetic reconnection are strongly dependent on the physical environments, e.g. the magnitude of the magnetic field strength and the plasma density. If the magnetic field strength is weak and the density is high, the te…
We observed an elongated filamentary bright structure inside the umbra of the big sunspot in active region NOAA 12529, which differs from the light bridges usually observed in sunspots for its morphology, magnetic configuration, and velocity field. We used observations taken with the Solar Dynamic Observatory satellite to characterize this feature. Its lifetime is 5 days, during which it reaches a maximum length of about 30". In the maps of the vertical component of the photospheric magnetic field, a portion of the feature has a polarity opposite to that of the hosting sunspot. At the same tim…
We investigate the vertical gradient of the magnetic field of sunspots in the photospheric layer. Independent observations were obtained with the SOT/SP onboard the Hinode spacecraft and with the TIP-2 mounted at the VTT. We apply state-of-the-art inversion techniques to both data sets to retrieve the magnetic field and the corresponding vertical gradient. In the sunspot penumbrae we detected patches of negative vertical gradients of the magnetic field strength, i.e.,the magnetic field strength decreases with optical depth in the photosphere. The negative gradient patches are located in the in…
We studied the dynamics of the solar atmosphere in the region of a large quiet-Sun filament, which erupted on 21 October 2010. The filament eruption started at its northern end and disappeared from the H$α$ line-core filtergrams line within a few hours. The very fast motions of the northern leg were recorded in ultraviolet light by AIA. We aim to study a wide range of available datasets describing the dynamics of the solar atmosphere for five days around the filament eruption. This interval covers three days of the filament evolution, one day before the filament growth and one day after the er…
Element abundance ratios of magnesium to neon (Mg/Ne) and neon to oxygen (Ne/O) in the transition region of the quiet Sun have been derived by re-assessing previously published data from the Coronal Diagnostic Spectrometer on board the Solar and Heliospheric Observatory in the light of new atomic data. The quiet Sun Mg/Ne ratio is important for assessing the effect of magnetic activity on the mechanism of the first ionization potential (FIP) effect, while the Ne/O ratio can be used to infer the solar photospheric abundance of neon, which can not be measured directly. The average Mg/Ne ratio is…
Solar active regions contain electric currents. Information on the distribution of currents is important for understanding the processes of energy release on the surface of the Sun and in the overlying layers. The paper presents an analysis of the probability density function (PDF) of the absolute value of the photospheric vertical electric current density ($|j_z|$) in 48 active regions before and after flares in 2010--2017. Calculation of $|j_z|$ is performed by applying the differential form of Ampere's circuital law to photospheric vector magnetograms obtained from observations of the Helio…
The distribution of magnetic fields of positive and negative polarities over the surface of the Sun was studied. Synoptic maps of the photospheric magnetic field (NSO Kitt Peak, 1978--2016) were used for the analysis. In the time-latitude diagram for weak magnetic fields ($B \leq 5 G$), inclined bands are clearly visible, indicating the alternating dominance of magnetic fields with positive or negative polarity drifting towards the poles of the Sun. Analysis of the time-latitude diagram using the method of empirical orthogonal functions (EOF) made it possible to establish a cyclic change in th…
Following Couvidat (2013), we analyze data from the Helioseismic and Magnetic Imager (HMI) and the Atmospheric Imaging Assembly (AIA) instruments onboard the Solar Dynamics Observatory: Doppler velocity and continuum intensity at 6173 A as well as intensity maps at 1600 A and 1700 A. Datasets of 14 active regions and four quiet-Sun regions are studied at four heights in the solar photosphere. An Hankel-Fourier analysis is performed around these regions of interest. Outgoing-ingoing scattering phase shifts at a given atmospheric height are computed, as well as ingoing-ingoing and outgoing-outgo…
Some models for the topology of the magnetic field in sunspot penumbrae predict the existence of field-free or dynamically weak-field regions in the deep Photosphere. To confirm or rule out the existence of weak-field regions in the deepest photospheric layers of the penumbra. The magnetic field at $\logτ_5=0$ is investigated by means of inversions of spectropolarimetric data of two different sunspots located very close to disk center with a spatial resolution of approximately 0.4-0.45 arcsec. The data have been recorded using the GRIS instrument attached to the 1.5-meters GREGOR solar telesco…
By focusing on the oscillations of the cross-sectional area and the intensity of magnetic waveguides located in the lower solar atmosphere, we aim to detect and identify magnetohydrodynamic (MHD) sausage waves. Capturing several series of high-resolution images of pores and sunspots and employing wavelet analysis in conjunction with empirical mode decomposition (EMD) makes the MHD wave analysis possible. For this paper, two sunspots and one pore (with a light bridge) were chosen as representative examples of MHD waveguides in the lower solar atmosphere. The sunspots and pore display a range of…
From the inversion of a time series of high resolution slit spectrograms obtained from the quiet sun, the spatial and temporal distribution of the thermodynamical quantities and the vertical flow velocity is derived as a function of logarithmic optical depth and geometrical height. Spatial coherence and phase shift analyzes between temperature and vertical velocity depict the height variation of these physical quantities for structures of different size. An average granular cell model is presented, showing the granule-intergranular lane stratification of temperature, vertical velocity, gas pre…
In June 2013, the two scientific instruments onboard the second Sunrise mission witnessed, in detail, a small-scale magnetic flux emergence event as part of the birth of an active region. The Imaging Magnetograph Experiment (IMaX) recorded two small (~5 arcsec) emerging flux patches in the polarized filtergrams of a photospheric Fe I spectral line. Meanwhile, the Sunrise Filter Imager (SuFI) captured the highly dynamic chromospheric response to the magnetic fields pushing their way through the lower solar atmosphere. The serendipitous capture of this event offers a closer look at the inner wor…
Chromospheric and photospheric properties of sunspots as inferred from Stokes inversions under magneto-hydrostatic and non-local-thermodynamic equilibrium
Institut für Sonnenphysik（太阳物理研究所）；Institute for Solar Physics, Department of Astronomy, Stockholm University（斯德哥尔摩大学天文学系太阳物理研究所）；Leibniz-Institut für Astrophysik Potsdam (AIP)（波茨坦阿诺德·爱因斯坦天文 Leibniz 研究所）；ETH Zürich, Institute for Particle Physics and Astrophysics（苏黎世联邦理工学院粒子物理与天体物理研究所）；Istituto ricerche solari Aldo e Cele Daccò (IRSOL), Faculty of Informatics, Università della Svizzera italiana（意大利瑞士大学信息学院阿尔多和塞莱达科太阳研究所以及研究所）
Advances in understanding of the white light faculae measured at the Royal Greenwich Observatory from 1874 to 1976 suggest that they offer a more direct measure of solar brightening by small diameter photospheric magnetic flux tubes than do chromospheric proxies. Proxies such as the area of Ca K plages, the Mg index or the microwave flux include many dark photospheric structures as well as pores and sunspots. Our reconstruction of variation in total solar irradiance,TSI,based on the faculae indicates that the sun dimmed by almost 0.1 percent in the mid- twentieth century rather than brightenin…
Spectra of the cellular photospheric flows are determined from full-disk Doppler velocity observations acquired by the Helioseismic and Magnetic Imager (HMI) instrument on the Solar Dynamics Observatory (SDO) spacecraft. Three different analysis methods are used to separately determine spectral coefficients representing the poloidal flows, the toroidal flows, and the radial flows. The amplitudes of these spectral coefficients are constrained by simulated data analyzed with the same procedures as the HMI data. We find that the total velocity spectrum rises smoothly to a peak at a wavenumber of …
Solar flares abruptly release the free energy stored as a non-potential magnetic field in the corona and may be accompanied by eruptions of the coronal plasma. Formation of a non-potential magnetic field and the mechanisms for triggering the onset of flares are still poorly understood. In particular, photospheric dynamics observed near those polarity inversion lines that are sites of major flare production have not been well observed with high spatial resolution spectro-polarimetry. This paper reports on a remarkable high-speed material flow observed along the polarity inversion line located b…
Strongly Doppler-shifted Stokes $V$ profiles have been detected in the quiet Sun with the IMaX instrument on-board the SUNRISE stratospheric balloon-borne telescope. High velocities are required in order to produce such signals, hence these events have been interpreted as jets, although other sources are also possible. We aim to characterize the variation of the main properties of these events (occurrence rate, lifetime, size and velocities) with their position on the solar disk between disk centre and the solar limb. These events have been identified in Sunrise/IMaX data according to the same…
We analyzed spectropolarimetric data from the Swedish 1-meter Solar Telescope to investigate physical properties of small-scale magnetic cancellations in the quiet Sun photosphere. Specifically, we looked at the full Stokes polarization profiles along the Fe I 557.6 nm and of the Fe I 630.1 nm lines measured by CRisp Imaging SpectroPolarimeter (CRISP) to study temporal evolution of the line-of-sight (LOS) magnetic field during 42.5 minutes of quiet Sun evolution. From this magnetogram sequence, we visually identified 38 cancellation events. We then used Yet Another Feature Tracking Algorithm (…
We use the historic record of sunspot groups compiled by the Royal Greenwich Observatory together with the sunspot number to derive the statistical properties of sunspot group emergence in dependence of cycle phase and strength. In particular we discuss the latitude, longitude, area and tilt angle of sunspot groups as functions of the cycle strength and of time during the solar cycle. Using these empirical characteristics the time-latitude diagram of sunspot group emergence (butterfly diagram) is reconstructed from 1700 onward on the basis of the Wolf and group sunspot numbers. This reconstruc…
Understanding the nature and evolution of the photospheric helicity flux transfer is a key to reveal the role of magnetic helicity in coronal dynamics of solar active regions. Using SDO/HMI photospheric vector magnetograms and the derived flow velocity field, we computed boundary driven helicity flux with a 12 minute cadence during the emergence of AR 11928. Accounting the foot point connectivity defined by non-linear force-free magnetic extrapolations, we derived and analyzed the corrected distribution of helicity flux maps. The photospheric helicity flux injection is found to changes sign du…
Simulating the photospheric to coronal plasma using magnetohydrodynamic characteristics III: validation including gravity, flux emergence, and an eruption
National Solar Observatory（国家太阳观测台）；NASA Goddard Space Flight Center（美国宇航局戈达德太空飞行中心）；U.S. Naval Research Laboratory（美国海军研究实验室）
Context. Stellar spectral variability on timescales of a day and longer, arising from magnetic surface features such as dark spots and bright faculae, is an important noise source when characterising extra-solar planets. Current 1D models of faculae do not capture the geometric properties and fail to reproduce observed solar facular contrasts. Magnetoconvection simulations provide facular contrasts accounting for geometry. Aims. We calculate facular contrast spectra from magnetoconvection models of the solar photosphere with a view to improve (a) future parameter determinations for planets wit…
Bright small-scale magnetic elements found mainly in intergranular lanes at the solar surface are named bright points (BPs). They show high contrasts in Fraunhofer G-band observations and are described by nearly vertical slender flux tubes or sheets. A recent comparison between BP observations in the ultraviolet (UV) and visible spectral range recorded with the balloon-borne observatory SUNRISE and state-of-the-art magnetohydrodynamical (MHD) simulations revealed a kiloGauss magnetic field for 98% of the synthetic BPs. Here we address the opposite question, namely which fraction of pixels host…
Photospheric magnetic fields were studied using the Kitt Peak synoptic maps for 1976-2003. Only strong magnetic fields (B>100 G) of the equatorial region were taken into account. The north-south asymmetry of the magnetic fluxes was considered as well as the imbalance between positive and negative fluxes. The north-south asymmetry displays a regular alternation of the dominant hemisphere during the solar cycle: the northern hemisphere dominated in the ascending phase, the southern one in the descending phase during Solar Cycles 21-23. The sign of the imbalance did not change during the 11 years…
Recent dedicated Hinode polar region campaigns revealed the presence of concentrated kilogauss patches of magnetic field in the polar regions of the Sun which are also shown to be correlated with facular bright points at the photospheric level. In this work, we demonstrate that this spatial intermittency of the magnetic field persists even up to the chromospheric heights. The small-scale bright elements visible in the bright network lanes of solar network structure as seen in the Ca ii H images are termed as network bright points. We use special Hinode campaigns devoted to observe polar region…
Our aim is to study the photospheric flux distribution of a twisted flux tube that emerges from the solar interior. We also report on the eruption of a new flux rope when the emerging tube rises into a pre-existing magnetic field in the corona. To study the evolution, we use 3D numerical simulations by solving the time-dependent and resistive MHD equations. We qualitatively compare our numerical results with MDI magnetograms of emerging flux at the solar surface. We find that the photospheric magnetic flux distribution consists of two regions of opposite polarities and elongated magnetic tails…
The X9.3 flare of September 6, 2017, was the most powerful flare of Solar Cycle 24. It generated strong white-light emission and multiple helioseismic waves (sunquakes). By using data from Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamics Observatory (SDO) as well as hard X-ray data from KONUS instrument onboard WIND spacecraft, and Anti-Coincidence System (ACS) onboard the INTERGRAL space observatory, we investigate spatio-temporal dynamics of photospheric emission sources, identify sources of helioseismic waves and compare the flare photospheric dynamics with the hard X-ray (…
Context. Observations of flux emergence indicate that rotational velocities may develop within sunspots. However, the dependence of this rotation on sub-photospheric field strength and twist remains largely unknown. Aims. We investigate the effects of varying the initial field strength and twist of an emerging sub-photospheric magnetic flux tube on the rotation of the sunspots at the photosphere. Methods. We consider a simple model of a stratified domain with a sub-photospheric interior layer and three overlying atmospheric layers. A twisted arched flux tube is inserted in the interior and is …
A new model has been proposed for magnetic field determination at different distances from the Sun during different solar cycle phases. The model depends on the observed large-scale non-polar photospheric magnetic fields and that measured at polar regions from 55N to 90N and from 55S to 90S,which are the visible manifestations of cyclic changes in the toroidal and poloidal components of the global magnetic field of the Sun. The modeled magnetic field is determined as the superposition of the non-polar and the polar photospheric magnetic field cycle variations. The agreement between the model p…
A 50 min time series of one-dimensional slit-spectrograms, taken in quiet sun at disk center, observed at the German Vacuum Tower Telescope (Observatorio del Teide), was used to study the global and spatial variations of different line parameters. In order to determine the vertical structure of the photosphere two lines with well separated formation heights have been considered. The data have been filtered of p-modes to isolate the pure convective phenomenon. From our studies of global correlation coefficients and coherence and phase shift analyzes between the several line parameters, the foll…
A sunspot penumbra is observationally examined to reveal properties of small-scale flow structures and how they are related to the filamentary magnetic structures and the Evershed flow. We also study how the photospheric dynamics is related to chromospheric activities. The study is based on data analysis of spectro-polarimetric observations of photospheric Fe I lines with the Solar Optical Telescope aboard Hinode in a sunspot penumbra at different heliocentric angles. Vector magnetic fields and velocities are derived using the spectro-polarimetric data and a Stokes inversion technique. An obse…
Within the coronae of stars, abundances of those elements with low first ionization potential (FIP) often differ from their photospheric values. The coronae of the Sun and solar-type stars mostly show enhancements of low- FIP elements (the FIP effect) while more active stars such as M-dwarfs have coronae generally characterized by the inverse-FIP effect (I-FIP). Here we observe patches of I-FIP effect solar plasma in AR 12673, a highly complex beta/gamma/delta active region. We argue that the umbrae of coalescing sunspots and more specifically strong light bridges within the umbrae, are prefer…
Aims. We aim to characterise the magnetism of a large fraction of the north polar region close to a maximum of activity, when the polar regions are reversing their dominant polarity. Methods. We make use of full spectropolarimetric data from the CRisp Imaging Spectro-Polarimeter installed at the Swedish Solar Telescope. The data consist of a photospheric spectral line, which is used to infer the various physical parameters of different quiet Sun regions by means of the solution of the radiative transfer equation. We focus our analysis on the properties found for the north polar region and thei…
The flux-injection hypothesis for driving coronal mass ejections (CMEs) requires the transport of substantial magnetic energy and helicity flux through the photosphere concomitant with the eruption. Under the magnetohydrodynamics approximation, these fluxes are produced by twisting magnetic field and/or flux emergence in the photosphere. A CME trajectory, observed 2000 September 12 and fitted with a flux-rope model constrains energy and helicity budgets for testing the flux-injection hypothesis. Optimal velocity profiles for several driving scenarios are estimated by minimizing the photospheri…
Magnetic field and radial velocity fluxes at the initial stages of the evolution of solar active regions based on measurements at the photospheric level
Magnetic fields emerging from the Sun's interior carry information about physical processes of magnetic field generation and transport in the convection zone. Soon after appearance on the solar surface the magnetic flux gets concentrated in sunspot regions and causes numerous active phenomena on the Sun. This paper discusses some properties of the emerging magnetic flux observed on the solar surface and in the interior. A statistical analysis of variations of the tilt angle of bipolar magnetic regions during the emergence shows that the systematic tilt with respect to the equator (the Joy's la…
