Photospheric Level Research Articles

EVIDENCES FOR STRONG MIXED-POLARITY MAGNETIC FIELDS IN AREA OF A SEISMIC SOURCE ASSOCIATED WITH LARGE PROTON SOLAR FLARE

We present in a concise statement the new results based on spectral-polarization measurements of magnetic fields in an extremely powerful proton solar flare on October 28, 2003 of X17.2 / 4B class. The observation material was obtained with Echelle spectrograph of HST AO KNU, which makes it possible to analyze the spectral manifestations of the Zeeman effect in very many lines of the visible region of the spectrum, including the photospheric and chromospheric lines. The I ± V and V profiles of about ten FeI and FeII lines, as well as the Hα, Hβ, Hγ, and Hδ lines were studied in a area of the seismic source of the flare, which was localized in the sunspot penumbra of S magnetic polarity. In this flare, we found an unprecedented Balmer decrement of intensities of Hα and Hβ lines which corresponds to ratio I (Hβ) / I (Hα) = 1.68. In the FeI 5434.5 line with very low Lande factor (g eff = –0.014), a reliable splitting of emission peaks was found, which could indicate superstrong magnetic fields (about 50 kG) of N polarity. Indications for magnetic fields with intensity ≈ 12 kG of S polarity were found too. These indications are based on the study of the Stokes V profile of FeII 5234.6 line. In this line, there were two positive and two negative peaks of profile V, indicating a two- component structure of the magnetic field. According to the simulation data, the small-scale component with the above-mentioned superstrong magnetic field had a filling factor about 0.1 and had narrow (about twice) the half- widths of the line profiles. The close contact of subtelescopic magnetic fields of different magnetic polarity, but of lower intensity (B ≈ 1 kG) was also indicated by the comparison of the half-widths of the FeI 5247.1 and 5250.2 lines. In general, it can be concluded that the necessary conditions for the reconnection of magnetic lines were fulfilled even at the photospheric level, rather than in the corona or chromosphere, as suggested by theoretical models of solar flares.

Long quasi-periodic oscillations of the faculae and pores

Aims. The main goal of this work is to analyze the structural and temporal evolution of small-scale magnetic structures (SSMSs) observed in the solar atmosphere, such as solitary faculae and pores, and reveal long quasi-periodic oscillations of these structures. Methods. The statistical method of regression analysis and the wavelet transform were used to obtain the periods of oscillations and dependences between the parameters of magnetic structures and periods of oscillations. Results. Long-period oscillations with periods in the interval of 18−260 min are found for the structurally stable phase of SSMSs at the level of the solar photosphere. These long-period oscillations were interpreted as natural oscillations of the structurally stable long-lived magnetic structures around their equilibrium position. These oscillations, which are of similar nature, are observed in the chromospheric bright formations associated with photospheric SSMSs. Dependences between the magnetic field and the continuum intensity of the facula elements were found. It is shown that the continuum intensity of a SSMS decreases when its magnetic field increases.

Association of Calcium Network Bright Points with Underneath Photospheric Magnetic Patches

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 regions of the Sun to study the polar network bright points during the phase of last extended solar minimum. We use Ca ii H images of chromosphere observed by Solar Optical Telescope (SOT). For magnetic field information, level 2 data of spectro-polarimeter (SP) is used. We observe a considerable association between the polar network bright points and magnetic field concentrations. The intensity of such bright points is found to be correlated well with the photospheric magnetic field strength underneath with a linear relation existing between them.

Motion of Photospheric Matter within the Active Region Site with Two Ellerman Bombs

Examination results for specific features of variation of line-of-sight plasma velocities in different photosphere layers of the NOAA 11024 active region (AR) under the influence of two evolving Ellerman bombs (EB-1 and EB-2) are presented. Spectroscopic data with high spatial and temporal resolution were obtained with the French–Italian THEMIS solar telescope on July 4, 2009. The observation time was 20 min. The AR was undergoing a sharp increase in activity on the day of observations, and the EBs evolved in the region of one of the three magnetic fluxes that were emerging at the time. The brightness of EB-1 decreased during observations, while EB-2 got brighter. The λ ≈ 630 nm spectral region, which includes Fraunhofer lines forming within a wide range of photospheric heights (neutral iron lines Fe I λ 630.15, 630.25, and 630.35 nm and titanium line Ti I λ 630.38 nm), was used. Changes in the velocity and direction of motion of matter in the region of Ellerman bombs and in their immediate vicinity at different photosphere levels and at different stages of EB evolution were determined and analyzed. It was found that upflows were predominant at all levels of the AR photosphere. At the same time, line-of-sight velocities Vlos and the amplitude of their oscillations decreased considerably in the region of EBs. Apparently, downward matter flows reduced the velocity of upward plasma motion. This suggests that small-scale downward flows induced by magnetic reconnections were superimposed onto the large-scale upward motion of plasma of the new magnetic flux. The profile shape of photospheric lines reinforces this conclusion. The profiles of strong lines had a red asymmetry. The matter velocity determined based on the shift of a prominent component in the red wing of the Fe I λ 630.35 nm line profiles was as high as 2 km/s. Such a Vlos distribution in the EB regions indicates that they consisted of several jets moving with different velocities in different directions. The line-of-sight velocity in the central part of EB-1 and EB-2 varied from –1 to 0 km/s and from –1 to 0.2 km/s in the upper photospheric layer and from –1.6 to –0.2 km/s and from –1.1 to 0.25 km/s in the lower layer of the photosphere, respectively. Vlos variations in the vicinity of these Ellerman bombs were oscillatory, and the interval between oscillations was ~5 min. The pattern of quasiperiodic Vlos oscillations was disturbed in the EB regions: they often occurred in antiphase. It may be concluded that the excitation caused by a pulsed energy release as a result of successive magnetic reconnections associated with the emergence of the new magnetic flux propagated from the EB-1 site along a magnetic loop and triggered the formation of EB-2, and the Ellerman bombs then evolved as a physically connected pair. The studied features of the line-of-sight velocity variation of chromospheric and photospheric matter indicate that during the evolved of EBs differently directed motions of matter there was: it moved upward in the lower chromospheric layer, while downward flows reduced the velocity of ascending plasma at the photospheric level. Magnetic reconnections occurring in the layer between the upper photosphere and the lower chromosphere, where the core of the Hα line was formed, could induce such a velocity distribution.

МАГНІТНІ ПОЛЯ І ТЕРМОДИНАМІЧНІ УМОВИ В ПЕРЕДМАКСИМАЛЬНІЙ ФАЗІ СОНЯЧНОГО СПАЛАХУ БАЛУ M6.4/3N

We present a study of the pre-peak phase of the solar flare of M6.4 / 3N class which arose on July 19, 2000 in the NOAA 9087 active region. The effective magnetic field Beff was measured using the FeI 6301.5 Ǻ, FeI 6302.5 Ǻ, Hα and Hβ spectral lines. It was found that at the brightest place of the flare, which was projected onto a small sunspot of N polarity, Beff was close to each other on all four lines and corresponded to 1.0-1.2 kG. At the same time, the modulus of the magnetic field at the level of FeI 6302.5 formation, determined by the splitting of peaks V of the Stokes parameter and the localization of the σ-components in the I ± V profiles, was in the range 1.6–2.6 kG. The bisectors of the I + V and I – V profiles of the FeI 6301.5 line are parallel to each other, indicating a simple one-component structure of the magnetic field at the level of the middle photosphere under the flare. The Balmer decrement of Imax (Hα) / Imax (Hβ) by Hα and Hβ lines was 1.16. The semi-empirical model of the photospheric layers of the flare was constructed using Stokes I observations of non-magneticsensitive FeI 5123.7 and 5434.5 lines by solving the inverse equilibrium transfer problem using Tikhonov stabilizers. For the distribution of temperature with height, the effects of deviation from the LTE were found to be significant for the layers of the lower photosphere corresponding to the heights h ≥ 0 (i.e. τ 5 ≤ 1). In the entire thickness of the photosphere (h = 0–500 km), the flare temperature is lower compared to the non-perturbed atmosphere, while it is slightly higher for h> 500 km. The micro-turbulent velocity is increased at altitudes h> 200–500 km, while at altitudes h <200 km it is reduced. The obtained results indicate that the upper photosphere and the lower chromosphere are perturbed during solar flares, even when the magnetic field is quasi-homogeneous in the lower layers (middle photosphere).

ЕЛЕКТРОПРОВІДНІСТЬ ПЛАЗМИ В МАГНІТНИХ КОНФІГУРАЦІЯХ СОНЯЧНИХ ПЛЯМ

The main problem of electromagnetic models of flares on the Sun is that in conditions of high electrical conductivity of the solar plasma it is difficult to provide an effective energy release as a result of Joule dissipation of currents in the “kernel of the flare”. In order to explain the rapid dissipation of electric currents in the “kernel of the flare”, we, within the framework of macroscopic magnetohydrodynamics, have considered the effect of reducing the electrical conductivity in a turbulent environment. The idea of redistribution of the electrical conductivity in groups of sunspots with complex magnetic field configuration is proposed. The proposed concept for the redistribution of electrical conductivity is based on the following physical effects and well-known observational conditions in the solar atmosphere. 1. Decreasing of the electrical conductivity (increase in the resistivity) in a turbulent environment. 2. Magnetic inhibition of the turbulence under the influence of magnetic fields. 3. Excitation of a large-scale electric field by macroscopic movements of the plasma in the photosphere in the presence of a weak general magnetic field of the Sun (photosphere dynamo). 4. Observed spatial heterogeneous structure of magnetic configurations in the vicinity of groups of sunspots, which leads to the formation of the current layers with the zero (neutral) magnetic fields. In the places of the zero magnetic field in the photosphere (which correspond to the “kernel of the flare”), where there is no suppression of turbulence by magnetism, the conductivity is turbulent in the nature. At the same time, in the vicinity of the sunspots outside the “kernel of the flare”, turbulent motions are largely suppressed by strong magnetic fields (B ≈ 3000 G), which almost alleviates the effect of the influence of turbulence on the conductivity of the plasma. Therefore, the electrical conductivity here will be gas-kinetic in the nature, the value of which greatly exceeds the turbulent conductivity. The turbulent conductivity calculated by us in the photosphere σ T ≈ 5 ⋅ 108 CGSE turned out to be 2-3 orders of magnitude smaller than the gaskinetic conductivity σ ≈ 1011 CGSE (in the places of strong magnetic fields). The discovered areas of the abnormal reduced turbulent conductivity in the places of the zero magnetic lines of complex configurations of the sunspot groups can contribute to the efficient dissipation of the electric currents, which provides efficient thermal energy release of the flares. The problem of circulation of two currents in the electric circuit of the corona-photosphere is briefly considered. According to the model of the photosphere dynamo, the convective movements on the photosphere level excite an electric field of magnitude E0 ≈ 10-4 CGSE. In this case, in external areas (in relation to the region of the “kernel of the flare”) of the electric circuit of the corona-photosphere in the places of strong magnetic fields, where the turbulence is almost suppressed, the value of the current will be ja = σ E0 ≈ 107 CGSE. At the same time, in the area of the “kernel of the flare”, where neutral magnetic fields do not affect turbulence, the current value will be much smaller: jT ≈ σ T E0 ≈ 5 ⋅ 104 CGSE. The existence of two sections with different currents in the electric circle of the corona-photosphere may contribute to the spatial division of charges, which in turn may be useful in the further development of the electromagnetic models of the flare.

Study of Variations of Some Characteristics of the Giant Coronal Hole of 2015–2017

Analysis of images of the full solar disk obtained by ground-based (BST-2, CrAO RAS) and space-based (SDO/AIA, SDO/HMI) instruments and the potential approximation method revealed some features of the evolution of a long-lived coronal hole (CH) of 2015–2017. Variations in such CH characteristics as the area, intensity, magnetic field (MF) strength, and magnetic flux are studied. The study of the change in the area and average intensity of the CH contour at different heights has shown that changes in its area throughout the entire period occur almost synchronously within the boundaries determined by model calculations at the photospheric level and by observations of the Sun in the chromosphere and corona. The average CH intensity depends on the moment of its evolution: it varies from the intensity of the undisturbed region to the CH maximum intensity. This process lasts about the same time as the increase in the CH area. The intensity of the He I 10830 A (He I) line occurs in antiphase with the decrease in the intensity in the Fe XII 193A (Fe XII) line. This paper shows that this CH has significantly reduced the magnetic flux in a large part of the Sun in a time interval of almost a year and a half. Even when the CH began to collapse noticeably, the magnetic field strength and the magnetic flux continued to decrease.

Differential Rotation of the Solar Corona from Magnetic Field Data

A method for investigating the differential rotation of the solar corona using the coronal magnetic field as a tracer is proposed. The magnetic field is calculated in the potential approximation from observational data at the photospheric level. The time interval from June 24, 1976, to December 31, 2004, is considered. The magnetic field has been calculated for all latitudes from the equator to ±75◦ with a 5◦ step at distances from the base of the corona 1.0 R⊙ to 2.45 R⊙ near the source surface. The coronal rotation periods at 14 distances from the solar center have been determined by the method of periodogram analysis. The coronal rotation is shown to become progressively less differential with increasing heliocentric distance; it does not become rigid even near the source surface. The change in the coronal rotation periods with time is considered. At the cycleminimumthe rotation has been found to bemost differential, especially at small distances from the solar center. The change in coronal rotation with time is consistent with the tilt of the solar magnetic equator. The results from the magnetic field are compared with those obtained from the brightness of the green coronal Fe XIV 530.3 nm line. The consistency between these results confirms the reliability of the proposed method for studying the coronal rotation. Studying the rotation of the coronal magnetic field gives hope for the possibility of using this method to diagnose the differential rotation in subphotospheric layers.

K2 Ultracool Dwarfs Survey. IV. Monster Flares Observed on the Young Brown Dwarf CFHT-BD-Tau 4

Abstract We present photometric measurements of two superflares observed on a very young brown dwarf, CFHT-BD-Tau 4, observed during Campaign 13 of the Kepler K 2 mission. The stronger of the two superflares brightened by a factor of ∼48 relative to the quiescent photospheric level, with an increase in Kepler magnitude . It has an equivalent duration of ∼107 hr, a flare duration of 1.7 days, and an estimated total bolometric (ultraviolet/optical/infrared) energy up to 2.1 × 1038 erg. The weaker of the two superflares is a complex (multipeaked) flare with an estimated total bolometric (UV/optical/IR) energy up to 4.7 × 1036 erg. They are the strongest flares observed on any brown dwarf so far. The flare energies are strongly dependent on the value of the visual extinction parameter A V used for extinction correction. If we apply a solar flare model to interpret the two superflares, we find that the magnetic fields are required to be stronger by as much as an order of magnitude than previous reports of field measurements in CFHT-BD-Tau 4 by Reiners et al. On the other hand, if we interpret our data in terms of accretion, we find that the requisite rate of accretion for the stronger superflare exceeds the rates that have been reported for other young brown dwarfs.

Signatures of quiet Sun reconnection events in Ca ii, Hα, and Fe i

We use observations of quiet Sun (QS) regions in the H$\alpha$ 6563 \AA, Ca~{\sc ii} 8542 \AA\, and Fe~{\sc i} 6302 \AA\ lines. We observe brightenings in the wings of the H$\alpha$ and Ca~{\sc ii} combined with observations of the interacting magnetic concentrations observed in the Stokes signals of Fe~{\sc i}. These brightenings are similar to Ellerman bombs (EBs), i.e. impulsive bursts in the wings of the Balmer lines which leave the line cores unaffected. Such enhancements suggest that these events have similar formation mechanisms to the classical EBs found in active regions, with the reduced intensity enhancements found in the QS regions due to a weaker feeding magnetic flux. The observations also show that the quiet Sun Ellerman bombs (QSEBs) are formed at a higher height in the upper photosphere than the photospheric continuum level. Using simulations, we investigate the formation mechanism associated with the events and suggest that these events are driven by the interaction of magnetic field-lines in the upper photospheric regions. The results of the simulation are in agreement with observations when comparing the light-curves, and in most cases we found that the peak in the Ca~{\sc ii} 8542 \AA\ wing occurred before the peak in H$\alpha$ wing. Moreover, in some cases, the line profiles observed in Ca~{\sc ii} are asymmetrical with a raised core profile. The source of heating in these events is shown by the MURaM simulations and is suggested to occur 430 km above the photosphere.

New disk discovered with VLT/SPHERE around the M star GSC 07396−00759

Debris disks are usually detected through the infrared excess over the photospheric level of their host star. The most favorable stars for disk detection are those with spectral types between A and K, while the statistics for debris disks detected around low-mass M-type stars is very low, either because they are rare or because they are more difficult to detect. Terrestrial planets, on the other hand, may be common around M-type stars. Here, we report on the discovery of an extended (likely) debris disk around the M-dwarf GSC 07396−00759. The star is a wide companion of the close accreting binary V4046 Sgr. The system probably is a member of the β Pictoris Moving Group. We resolve the disk in scattered light, exploiting high-contrast, high-resolution imagery with the two near-infrared subsystems of the VLT/SPHERE instrument, operating in the Y J bands and the H2H3 doublet. The disk is clearly detected up to 1.5′′ (~110 au) from the star and appears as a ring, with an inclination i ~ 83°, and a peak density position at ~70 au. The spatial extension of the disk suggests that the dust dynamics is affected by a strong stellar wind, showing similarities with the AU Mic system that has also been resolved with SPHERE. The images show faint asymmetric structures at the widest separation in the northwest side. We also set an upper limit for the presence of giant planets to 2 MJ. Finally, we note that the 2 resolved disks around M-type stars of 30 such stars observed with SPHERE are viewed close to edge-on, suggesting that a significant population of debris disks around M dwarfs could remain undetected because of an unfavorable orientation.

K2 Ultracool Dwarfs Survey. III. White Light Flares Are Ubiquitous in M6-L0 Dwarfs

Abstract We report the white light flare rates for 10 ultracool dwarfs using Kepler K2 short-cadence data. Among our sample stars, two have spectral type M6, three are M7, three are M8, and two are L0. Most of our targets are old low-mass stars. We identify a total of 283 flares in all of the stars in our sample, with Kepler energies in the range log E Kp ∼ (29–33.5) erg. Using the maximum-likelihood method of line fitting, we find that the flare frequency distribution (FFD) for each star in our sample follows a power law with slope −α in the range −(1.3–2.0). We find that cooler objects tend to have shallower slopes. For some of our targets, the FFD follows either a broken power law, or a power law with an exponential cutoff. For the L0 dwarf 2MASS J12321827-0951502, we find a very shallow slope (−α = −1.3) in the Kepler energy range (0.82–130) × 1030 erg: this L0 dwarf has flare rates which are comparable to those of high-energy flares in stars of earlier spectral types. In addition, we report photometry of two superflares: one on the L0 dwarf 2MASS J12321827-0951502 and another on the M7 dwarf 2MASS J08352366+1029318. In the case of 2MASS J12321827-0951502, we report a flare brightening by a factor of ∼144 relative to the quiescent photospheric level. Likewise, for 2MASS J08352366+1029318, we report a flare brightening by a factor of ∼60 relative to the quiescent photospheric level. These two superflares have bolometric (ultraviolet/optical/infrared) energies 3.6 × 1033 erg and 8.9 × 1033 erg respectively, while the full width half maximum timescales are very short, ∼2 min. We find that the M8 star TRAPPIST-1 is more active than the M8.5 dwarf 2M03264453+1919309, but less active than another M8 dwarf (2M12215066-0843197).

Spectral Study of Ellerman Bombs. Photosphere

The results of analysis of spectral observations of two Ellerman bombs (EB-1 and EB-2), which were formed and have evolved in the area of emerging magnetic flux in active region (AR) NOAA 11024, are presented. Spectral data with high spatial and temporal (approximately 3 s) resolution were obtained using the THEMIS French–Italian solar telescope on July 4, 2009. The observation duration was 20 min. The spectral region of λ ≈ 630 nm with photospheric lines forming in a wide altitude range (neutral iron lines Fe I λ 630.15, 630.25, and 630.35 nm and titanium line Ti I λ 630.38 nm) was examined. The brightness of EB-1 decreased in the process of observations, while the brightness of EB-2 increased. The profiles of metal lines determined at different stages of EBs evolution were asymmetric. This asymmetry was more pronounced in lines that had formed in the lower photospheric layers and often had profiles with several components. The half-width of profiles increased with a reduction in their central depth. The variation of central intensities of Fraunhofer lines in the spectra of EBs and their vicinity at different stages of EB evolution was analyzed. The EBs formed in intergranular lanes. An increase in the core intensity of all the studied photospheric lines was correlated spatially with an increase in the wings intensity of the Hα line. Brightness variations at all photospheric levels were of an oscillatory nature with an interval of 1–5 min. The observed temporal variations of Fraunhofer line intensities in the spectra of the studied AR section suggest that the emergence of the new magnetic flux induced consecutive magnetic reconnections in the EB-1 region, the excitation propagated along a magnetic loop and initiated the formation of EB-2, and the two bombs then evolved as a physically connected pair.

Association of calcium network brightness with polar magnetic fields

AbstractRecent dedicated HINODE polar region campaign revealed the presence of concentrated kilogauss patches of magnetic field in the polar regions of 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. Polar network bright points are the ones which are present in the polar regions of the Sun (above 70° latitudes). We use special HINODE campaigns devoted to observe polar regions of the Sun to study the polar network bright points during the phase of last extended solar minimum. We are able to find a considerable association between the polar network bright points and magnetic field concentrations which led us to conclude that these bright points can serve as a good proxy for polar magnetic fields where the direct and regular measurements of polar magnetic fields are not available (before 1970).

Long term trends in solar photospheric fields and solar wind turbulence levels: Implications to the near-Earth space

AbstractWe re-examined solar polar magnetic fields, using ground based synoptic photospheric magnetograms, during solar cycle 24. IThe signed polar magnetic fields showed an unusual hemispheric asymmetry in the polar field reversal process with a single unambigous reversal in the Southern hemisphere around late 2013 while the polar reversal in the Northern hemisphere started earlier around June 2012, but was completed only by the end of 2014. The examination of the unsigned polar magnetic fields in cycle 24 showed a continuing decline of fields in the Northern hemisphere whereas in the Southern hemisphere, it had partially recovered. However, the overall declining trend in solar polar fields, which began in the mid-1990’s, is still in progress. The continued decline seen in solar photospheric fields raises thequestion of whether we are heading towards a Grand or Maunder like solar minimum.

Power-law Statistics of Driven Reconnection in the Magnetically Closed Corona

Abstract Numerous observations have revealed that power-law distributions are ubiquitous in energetic solar processes. Hard X-rays, soft X-rays, extreme ultraviolet radiation, and radio waves all display power-law frequency distributions. Since magnetic reconnection is the driving mechanism for many energetic solar phenomena, it is likely that reconnection events themselves display such power-law distributions. In this work, we perform numerical simulations of the solar corona driven by simple convective motions at the photospheric level. Using temperature changes, current distributions, and Poynting fluxes as proxies for heating, we demonstrate that energetic events occurring in our simulation display power-law frequency distributions, with slopes in good agreement with observations. We suggest that the braiding-associated reconnection in the corona can be understood in terms of a self-organized criticality model driven by convective rotational motions similar to those observed at the photosphere.

ВИМІРЮВАННЯ ЛОКАЛЬНИХ МАГНІТНИХ ПОЛІВ У СОНЯЧНОГО СПАЛАХУ ЗА РОЗЩЕПЛЕННЯМ ЕМІСІЙНИХ ПІКІВ У ЯДРАХ СПЕКТРАЛЬНИХ ЛІНІЙ

We present study of solar flare of 19 July 2000 which arose in active region NOAA 9087 and had M 5.6 / 3N importance. Observational material was obtained with the Echelle spectrograph of the horizontal solar telescope of the Astronomical Observatory of Taras Shevchenko National University of Kyiv. The local magnetic fields in this flare were measured by the splitting of emissive peaks of the FeI 5269.54, FeII 4923.93, Нα, Нβ, Нγand D3 HeI lines. The basic idea of the method is based on the fact that the flare emission in some spectral lines is clearly divided into two components: (1) wider and unpolarized, and (2) more narrow and polarized, with significant Zeeman splitting. This is indication to the two-component structure of the magnetic field, with substantially different magnetic fields and thermodynamical conditions in these two components. Due to the fact that the polarized emission is quite confidently separated from the unpolarized, it is possible to measure the local magnetic fields directly in the second (strong) component regardless of the filling factor. It was found that in the bright place of this flare, which was projected on the sunspot penumbra, the effective magnetic field Beff in the FeI 6301.5 i 6302.5 lines measured by splitting of the Fraunhofer profiles, was 900 G. However, the splitting of emissive peaks in Нα, Нβ, Нγ and D3 lines corresponds to 1000 G, 1400 G, 1450 G and about zero, respectively, with errors of 30-50 G for abovenamed FeI lines and about 100–150 G for other lines. This difference in the results is probably due to the fact that in the case of FeI 6301.5 i 6302.5 lines, the Beff value represents several parameters, including the value of the background field, the filling factor, and the intensity of the local fields in the strong component. In contrast, data on the Нα, Нβ, Нγ, and D3 lines mainly reflect local fields in the strong component and indicate the nonmonotonous distribution of the magnetic field with height in solar atmosphere, with its maximum at the chromospheric level. Earlier in this flare, when constructing its semi-empirical model, local amplification of the magnetic field at the photospheric level was discovered, and its value reached 1500 G. These data are confirmed by direct measurements of splitting of emissive peaks in FeI 5269.54 and FeII 4923.93 lines, according to which the magnetic field in the flare was 1250 ± 100 G. Thus, in this flare there were at least two regions (possibly two flat layers) of local amplification of the magnetic field.

Detailed analysis of dynamic evolution of three Active Regions at the photospheric level before flare and CME occurrence

We present a combined analysis of the applications of the weighted horizontal magnetic gradient (denoted as WGM in Korsós et al. (2015)) method and the magnetic helicity tool (Berger and Field, 1984) employed for three active regions (ARs), namely NOAA AR 11261, AR 11283 and AR 11429. We analysed the time series of photospheric data from the Solar Dynamics Observatory taken between August 2011 and March 2012. During this period the three ARs produced a series of flares (eight M- and six X-class) and coronal mass ejections (CMEs). AR 11261 had four M-class flares and one of them was accompanied by a fast CME. AR 11283 had similar activities with two M- and two X-class flares, but only with a slow CME. Finally, AR 11429 was the most powerful of the three ARs as it hosted five compact and large solar flare and CME eruptions. For applying the WGM method we employed the Debrecen sunspot data catalogue, and, for estimating the magnetic helicity at photospheric level we used the Space-weather HMI Active Region Patches (SHARP’s) vector magnetograms from SDO/HMI (Solar Dynamics Observatory/Helioseismic and Magnetic Imager). We followed the evolution of the components of the WGM and the magnetic helicity before the flare and CME occurrences. We found a unique and mutually shared behaviour, called the U-shaped pattern, of the weighted distance component of WGM and of the shearing component of the helicity flux before the flare and CME eruptions. This common pattern is associated with the decreasing-receding phases yet reported only known to be a necessary feature prior to solar flare eruption(s) but found now at the same time in the evolution of the shearing helicity flux. This result leads to the conclusions that (i) the shearing motion of photospheric magnetic field may be a key driver for solar eruption in addition to the flux emerging process, and that (ii) the found decreasing-approaching pattern in the evolution of shearing helicity flux may be another precursor indicator for improving the forecasting of solar eruptions.

Observational Evidence of a Flux Rope within a Sunspot Umbra

Abstract 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 time, in the entire feature the horizontal component of the magnetic field is about 2000 G, substantially stronger than in the surrounding penumbral filaments. Doppler velocity maps reveal the presence of both upward and downward plasma motions along the structure at the photospheric level. Moreover, looking at the chromospheric level, we noted that it is located in a region corresponding to the edge of a small filament that seems rooted in the sunspot umbra. Therefore, we interpreted the bright structure as the photospheric counterpart of a flux rope touching the sunspot and giving rise to penumbral-like filaments in the umbra.

Evolution of an equatorial coronal hole structure and the released coronal hole wind stream: Carrington rotations 2039 to 2050

The Sun is a highly dynamic environment that exhibits dynamic behavior on many different timescales. In particular, coronal holes exhibit temporal and spatial variability. Signatures of these coronal dynamics are inherited by the coronal hole wind streams that originate in these regions and can effect the Earth's magnetosphere. Both the cause of the observed variabilities and how these translate to fluctuations in the in situ observed solar wind is not yet fully understood. During solar activity minimum the structure of the magnetic field typically remains stable over several Carrington rotations (CRs). But how stable is the solar magnetic field? Here, we address this question by analyzing the evolution of a coronal hole structure and the corresponding coronal hole wind stream emitted from this source region over 12 consecutive CRs in 2006. To this end, we link in situ observations of Solar Wind Ion Composition Spectrometer (SWICS) onboard the Advanced Composition Explorer (ACE) with synoptic maps of Michelson Doppler imager (MDI) on the Solar and Heliospheric Observatory (SOHO) at the photospheric level through a combination of ballistic back-mapping and a potential field source surface (PFSS) approach. Together, these track the evolution of the open field line region that is identified as the source region of a recurring coronal hole wind stream. We find that the shape of the open field line region and to some extent also the solar wind properties are influenced by surrounding more dynamic closed loop regions. We show that the freeze-in order can change within a coronal hole wind stream on small timescales and illustrate a mechanism that can cause changes in the freeze-in order. The inferred minimal temperature profile is variable even within coronal hole wind and is in particular most variable in the outer corona.