Sunspot In Active Region Research Articles

Recurrent 3He-rich solar energetic particle injections observed by Solar Orbiter at ∼0.5 au

We report Solar Orbiter observations of six recurrent solar energetic particle injections in 2022 March 3−6 at ∼0.5 au. All but one were associated with jets emanating from a plage near a large sunspot in active region 12 957. We saw large jets in injections with high 3He and Fe enrichments and minor jets in injections with no or lower enrichments. Furthermore, the event with the highest enrichment showed a more compact configuration of the underlying photospheric magnetic field. The higher fluences as well as harder spectra were seen in the event with a simultaneous jet and wider eruption. However, in this case, the energy buildup time in the source might be required to produce such spectra. Extreme-ultraviolet images from Solar Orbiter revealed a number of intersecting loops at the base of jets not seen from 1 au that might be a precondition for the recurrent events.

Open-field Coronal Structures Neighbouring the Sunspot of AR 8535

We make use of the Potential Field Source Surface (PFSS) model and reveal new details in the strong fields of the dominant sunspot of the active region (AR) 8535. Due to its importance in determining the field line connectivity and topology with resulting consequences for both plasma confinement and dynamics we construct the global magnetic fields with the PFSS model. The coronal emission – observed in the soft X-ray images taken with the Yohkoh Soft X-ray Telescope and 284 A images taken with the Extreme-ultraviolet Imaging Telescope aboard the Solar and HeliosphericObservatory (SOHO/EIT) – is largely asymmetric owing to two dark coronal lanes, which are traceable across the sunspot. The modelled open-field structures overlap with the observed coronal dark lanes and include two narrow coronal corridors that persist for days in the large sunspot. Since the open-field structures overlap also with the plasma upflow observed in the sunspot as Doppler blue-shifts in a set of EUV emission lines (SOHO/Coronal Diagnostic Spectrometer) on 9 May and 13 May 1999, we examine the plasma outflow from the AR 8535. From near-Earth measurements aboard the Advanced Composition Explorer (ACE) spacecraft we estimate the solar-wind speed $V _{\mathrm{p}} \approx 400~\mbox{km}\,\mbox{s}^{-1}$ and the charge state ratio $\mbox{O}^{7+}/\mbox{O}^{6+} = 0.4$ (corresponding to coronal “freezing-in temperature” $T _{\mathrm{e}} = 1.7 \times 10^{6}~\mbox{K}$). However, the abnormally low proton temperature of solar wind, $T _{\mathrm{p}} = 3 \times 10^{4}~\mbox{K}$, implies some impact of the interplanetary coronal mass ejection (ICME) on the plasma flow. The evidence in favour of the outflow from AR 8535 is given by the semi-empirical Wang–Sheeley–Arge model, as it predicts the ACE measurements of solar wind and the relevant features in the tomographic velocity map resulted from the Solar-Terrestrial Environment Laboratory observations of the interplanetary scintillations. Finally, we propose constructing a model atmosphere of the sunspot with the narrow coronal corridors included in order to further elaborate the magnetic-field structure through its effect on the observed microwave radiation.

Sunspot proper motion of individual sunspot in active region 11429 during X5.4 solar flare on March 7, 2012

Based on high resolution images obtained from Helioseismic and Magnetic Imager (HMI) instrument onboard Solar Dynamic Observatory (SDO) satellite at visual wavelength, we traced several individual umbral sunspots to find drift motion during flare occurrences within Active Region (AR) 11429 (N17, E15) at 00:00 to 05:00 UT on March 7, 2012. AR11429 was a large sunspot group with 1270 millionth solar hemisphere in area and complex magnetic morphology with beta-gamma-delta class. We measured relative motion of 22 umbral sunspots positions during eruptive and post-flare phases for about 5 hours. Some sunspots showed faster motion during eruptive phase at about 10% than decay phase and they moved nearly along the magnetic field polarity inversion line that showed shear motion. Flare outburst which is occurred in corona layer affected sunspot motion and area, as seen for their changing configuration and morphology, before and after peaked X-ray intensity. This result indicates that there is a strong connection between X-ray solar flare at corona layer and its foot points motion at photosphere.

Comparison of Features of the Generation of Coronal Mass Ejections with Variable Velocity in the Field of View of LASCO Coronagraphs

This paper compares features of the generation of coronal mass ejections (CMEs) with the lowest, intermediate, and highest velocities in the field of view of LASCO C2 and C3 coronagraphs found from an analysis of multi-wavelength data with high temporal and spatial resolution. The dynamics of the field characteristics in the umbra of sunspots of active regions (ARs) in which variable-velocity CMEs occur are compared based on SDO/HMI vector magnetic field measurements. It is found that there are almost no noticeable changes in field characteristics in the AR sunspots in which slow CMEs occur after the onset of the eruptive event. However, there are noticeable changes in the field intensity and inclination angles of the flux tube emerging from the umbra of the sunspot in some AR sunspots in which CMEs occur after the onset of the eruptive event. Thus, for the fast CME detected on January 7, 2014, the inclination angle of the flux tube from the umbra of one of the sunspots before the flare onset reached a maximum value of ≈4°. After the flare onset, it was less than 1°.

Some Features of the Variation of the Magnetic Field Characteristics in the Umbra of Sunspots During Flares and Coronal Mass Ejections

The observed variations of the magnetic properties of sunspots during eruptive events (solar flares and coronal mass ejections (CMEs)) are discussed. Variations of the magnetic field characteristics in the umbra of the sunspots of active regions (ARs) recorded during eruptive events on August 2, 2011, March 9, 2012, April 11, 2013, January 7, 2014, and June 18, 2015, are studied. The behavior of the maximum of the total field strength Bmax, the minimum inclination angle of the field lines to the radial direction from the center of the Sun αmin (i.e., the inclination angle of the axis of the magnetic tube from the sunspot umbra), and values of these parameters Bmean and αmean mean within the umbra are analyzed. The main results of our investigation are discussed by the example of the event on August 2, 2011, but, in general, the observed features of the variation of magnetic field properties in AR sunspots are similar for all of the considered eruptive events. It is shown that, after the flare onset in six AR sunspots on August 2, 2011, the behavior of the specified magnetic field parameters changes in comparison with that observed before the flare onset.

Modeling the Subsurface Structure of Sunspots

While sunspots are easily observed at the solar surface, determining their subsurface structure is not trivial. There are two main hypotheses for the subsurface structure of sunspots: the monolithic model and the cluster model. Local helioseismology is the only means by which we can investigate subphotospheric structure. However, as current linear inversion techniques do not yet allow helioseismology to probe the internal structure with sufficient confidence to distinguish between the monolith and cluster models, the development of physically realistic sunspot models are a priority for helioseismologists. This is because they are not only important indicators of the variety of physical effects that may influence helioseismic inferences in active regions, but they also enable detailed assessments of the validity of helioseismic interpretations through numerical forward modeling. In this article, we provide a critical review of the existing sunspot models and an overview of numerical methods employed to model wave propagation through model sunspots. We then carry out a helioseismic analysis of the sunspot in Active Region 9787 and address the serious inconsistencies uncovered by Gizon et al. (2009a, 2009b). We find that this sunspot is most probably associated with a shallow, positive wave-speed perturbation (unlike the traditional two-layer model) and that travel-time measurements are consistent with a horizontal outflow in the surrounding moat.

The Rotating Sunspot in AR 10930

We study the pattern and behavior of a rotating sunspot in Active Region 10930. The rotational angular speed has been extracted from the apparent motions of the sunspot determined by applying a new optical technique – called non-linear affine velocity estimator (NAVE) – to high-resolution G-band images taken by the Solar Optical Telescope (SOT) onboard the Hinode satellite. The structure and dynamics of coronal loops in this active region have been examined using the images obtained by the X-Ray Telescope (XRT) and the spectral data taken by the Extreme-ultraviolet Imaging Spectrometer (EIS), both also onboard Hinode. Our results are summarized as follows: i) The small sunspot of positive polarity rotated counterclockwise about its center by 540° during the period of five days. ii) Its angular velocity varied with the azimuth angle as well as the radial distance, being affected by the asymmetric shape of the umbra. iii) The angular velocity increased up to 8° h−1 until 13 December as the sunspot grew, and then decreased rapidly down to 3° h−1 on the next day as the sunspot decayed. iv) The coronal loops that connected the two sunspots became sigmoidal in shape. v) The coronal emissions from the regions around the rotating sunspot were blueshifted, which may indicate the expansion of the coronal loops. Our results suggest that the rotation of the sunspot may be closely related to the dynamic development of emerging twisted magnetic fields.

The line‐ratio method applied to vectormagnetographic measurements

AbstractSince solar magnetic fields are inhomogeneous, the averaging of Stokes parameter I within the entrance slit of the magnetograph is different from averaging Stokes Q0 and V, because the former contains also light from non‐magnetic, while the latter only contain light from magnetic regions. If the magnetographic calibration functions are calculated for homogeneous magnetic fields, errors arise, when they are used to reduce measurements of inhomogeneous fields. Therefore, we propose to use the line‐ratio method to transform magnetographic measurements into the parameters of the magnetic vector field. The Q ratios and the V ratios of two carefully selected lines are free from errors of this kind. This is also the case for the Q ratios in line core and line wings in single‐line magnetographs. An iterative method is presented to calculate the magnetic field parameters using the corresponding new calibration functions. An important advantage is, that the influence of scattered light in sunspots is also eliminated in a good approximation and the filling factor in plages can be estimated.This method is now used to determine magnetic vector fields in plages and sunspots of active regions with a new double‐vector magnetograph.