Sunspot Penumbra Research Articles

The Decay of α-configuration Sunspots

Abstract To better understand the decay of different types of sunspots, we studied the decay of eight α-configuration sunspots by using the data that were acquired by the Helioseismic and Magnetic Imager on board the Solar Dynamic Observatory. We followed their decay for about four days and analyzed the evolution of their photospheric area and magnetic field parameters. We found that the area and total magnetic flux of α sunspots show a near-linear decrease during their decay. Meanwhile, the area decay rate of an individual sunspot is not constant. The area decay of a sunspot can be divided into two stages, a slow and a rapid decay process. Moreover, according to the difference of the area decay of the penumbra and umbra, the α sunspots decay can be classified in three ways: the penumbra and umbra decay synchronously, the penumbra decays first, and the umbra decays first. In addition, the flux decay of the penumbra is lagging behind the decay of the penumbral area. This finding suggests that the vertical magnetic field of the sunspot penumbra increases significantly in the early stage of sunspot decay.

Signatures of ubiquitous magnetic reconnection in the deep atmosphere of sunspot penumbrae

Context. Ellerman bombs are regions with enhanced Balmer line wing emission and mark magnetic reconnection in the deep solar atmosphere in active regions and the quiet Sun. They are often found in regions where opposite magnetic polarities are in close proximity. Recent high-resolution observations suggest that Ellerman bombs are more prevalent than previously thought. Aims. We aim to determine the occurrence of Ellerman bombs in the penumbra of sunspots. Methods. We analyzed high spatial resolution observations of sunspots in the Balmer Hα and Hβ lines as well as auxiliary continuum channels obtained with the Swedish 1-m Solar Telescope and applied the k-means clustering technique to systematically detect and characterize Ellerman Bombs. Results. Features with all the defining characteristics of Ellerman bombs are found in large numbers over the entire penumbra. The true prevalence of these events is only fully appreciated in the Hβ line due to the highest spatial resolution and lower chromospheric opacity. We find that the penumbra hosts some of the highest Ellerman bomb densities, surpassed only by the moat in the immediate surroundings of the sunspot. Some penumbral Ellerman bombs show flame morphology and rapid dynamical evolution. Many penumbral Ellerman bombs are fast moving with typical speed of 3.7 km s−1 and sometimes more than 10 km s−1. Many penumbral Ellerman bombs migrate from the inner to the outer penumbra over hundreds of km, and some continue moving beyond the outer penumbral boundary into the moat. Many penumbral Ellerman bombs are found in the vicinity of regions with opposite magnetic polarity. Conclusions. We conclude that reconnection is a near continuous process in the low atmosphere of the penumbra of sunspots that manifest in the form of penumbral Ellerman bombs. These are so prevalent that they may be a major sink of sunspot magnetic energy.

Effects of erupting magnetic flux rope on running penumbral waves

Context. It is widely known that solar flares have a substantial impact on the low atmosphere but the matter of how they affect sunspot waves and oscillations is generally unknown. In addition, there are ongoing debates on whether the flare-induced photospheric changes are due to the momentum conservation with coronal mass ejections or to magnetic reconnection. Aims. To shed light on the so-called “back reaction” of solar eruptions, we investigated how running penumbral waves (RPWs) at one foot of an erupting magnetic flux rope (MFR) respond to the rope buildup and subsequent erosion. Methods. We used UV/EUV images from the Atmospheric Imaging Assembly on board the Solar Dynamics Observatory (SDO) to explore the changing behaviors of RPWs in response to the MFR evolution, as well as 135-s vector magnetograms from the SDO Helioseismic and Magnetic Imager to analyze the changes in photospheric magnetic field during the eruption. Results. During the rope buildup stage, the western foot of the rope, which is completely enclosed by a hooked ribbon, expands rapidly and consequently ends up overlapping a sunspot penumbra. This converts the original penumbral field into the rope field, which is associated with a transient increase in electric currents flowing through the ribbon-swept penumbral region. During the rope erosion stage, the rope foot shrinks as the eastern section of the hooked ribbon slowly sweeps the same penumbral region, where the rope field is converted into flare loops. This conversion induces mixed effects on the photospheric field inclination but heats up the low atmosphere at the footpoints of these flare loops to transition-region temperatures, therefore resulting in the post-eruption RPWs with an enhanced contrast in the 1600 Å passband and an extended bandwidth to low frequencies at 3–5 mHz, compared with the pre-eruption RPWs that peak at 6 mHz. Conclusions. This observation clearly demonstrates that it is the magnetic reconnection in the corona that impacts the low atmosphere and leads to the changing behaviors of RPWs, which, in turn, offer a new window onto diagnosing flare reconnections.

On the Decay of Sunspot Groups and Their Internal Parts in Detail

Abstract The decay of sunspot groups is a relatively unknown field since most studies have focused mainly on the decay of sunspots or sunspot groups, but only on small samples. As an extension of the recent work of Muraközy (2020), which is based on a large verified sample, this study investigates not only the long-term behavior of the decay of sunspot groups but also the dynamics of their parts. The aim of the present work is to search for dependencies of the decay process in order to find physical conditions that modify or contribute to the decay. The investigations are based on the catalog of the SoHO Debrecen Sunspot Database (SDD) and the Greenwich Photoheliographic Results as well as the Debrecen Photoheliographic Data. Altogether more than 750 sunspot groups were considered. The decay rates have been calculated for the total, umbral, and penumbral area of the groups and in the case of the SDD’s groups they have been calculated for both the leading and the following parts. The decay rates depend linearly on the maximum areas and ranged from 30 to 50 millionths of the solar hemisphere (MSH) day−1 for the sunspot groups and penumbrae and 5–10 MSH day−1 for the umbrae throughout the cycle. The decay rates fall significantly during the Gnevyshev gap and show 4 + 4 Schwabe cyclical variations in the ascending/descending phases, but it is always higher in the northern hemisphere. There is a slight decrease in the decay rates in the activity range toward higher latitudes.

Solitary Facular Knot: Fountain Magnetic Structure and Temperature Profile

Based on the previously proposed steady-state 3D model of a solar facular knot, we have developed its modified version in which the solitary nature of the facular object is reflected: its magnetic field is sharply bounded in the radial direction. The facula temperature profile calculated for the steady state of such a magnetic structure is compared with the high-resolution filtergram taken in the photospheric TiO 7057 A line at Big Bear Solar Observatory on June 19, 2017, at the New Solar Telescope (with a 1.6-m aperture). The image shows two closely spaced very dark micropores with a diameter $${\sim}300$$ km each. The micropores are surrounded by a fan of thin, light, radially elongated fibrils resembling a sunspot penumbra. The theoretically calculated $$T$$ profile of the facular knot completely reproduces these morphological features of the object being modeled.

Temporal evolution of short-lived penumbral microjets

Context. Penumbral microjets (PMJs) is the name given to elongated jet-like brightenings observed in the chromosphere above sunspot penumbrae. They are transient events that last from a few seconds to several minutes, and their origin is presumed to be related to magnetic reconnection processes. Previous studies have mainly focused on their morphological and spectral characteristics, and more recently on their spectropolarimetric signals during the maximum brightness stage. Studies addressing the temporal evolution of PMJs have also been carried out, but they are based on spatial and spectral time variations only. Aims. Here we investigate, for the first time, the temporal evolution of the polarization signals produced by short-lived PMJs (lifetimes < 2 min) to infer how the magnetic field vector evolves in the upper photosphere and mid-chromosphere. Methods. We use fast-cadence spectropolarimetric observations of the Ca II 854.2 nm line taken with the CRisp Imaging Spectropolarimeter at the Swedish 1 m Solar Telescope. The weak-field approximation (WFA) is used to estimate the strength and inclination of the magnetic field vector. By separating the Ca II 854.2 nm line into two different wavelength domains to account for the chromospheric origin of the line core and the photospheric contribution to the wings, we infer the height variation of the magnetic field vector. Results. The WFA reveals larger magnetic field changes in the upper photosphere than in the chromosphere during the PMJ maximum brightness stage. In the photosphere, the magnetic field inclination and strength undergo a transient increase for most PMJs, but in 25% of the cases the field strength decreases during the brightening. In the chromosphere, the magnetic field tends to be slightly stronger during the PMJs. Conclusions. The propagation of compressive perturbation fronts followed by a rarefaction phase in the aftershock region may explain the observed behavior of the magnetic field vector. The fact that such behavior varies among the analyzed PMJs could be a consequence of the limited temporal resolution of the observations and the fast-evolving nature of the PMJs.

Restoring Process of Sunspot Penumbra

Abstract We describe the disappearance of a sector of sunspot penumbra and its restoring process observed in the preceding sunspot of active region NOAA 12348. The evolution of the magnetic field and the plasma flows supports the idea that the penumbra forms due to a change of inclination of the magnetic field of the canopy. Moving magnetic features have been observed during the disintegration phase of that sector of sunspot penumbra. During the restoring phase we have not observed any magnetic flux emergence around the sunspot. The restoring process of the penumbra sector completed in about 72 hr and it was accompanied by the transition from the counter-Evershed flow to the classical Evershed flow. The inversion of photospheric spectropolarimetric measurements taken by the Interferometric Bidimensional Spectroscopic Instrument (IBIS) allowed us to reconstruct how the uncombed configuration of the magnetic field forms during the new settlement of the penumbra, i.e., the vertical component of the magnetic field seems to be progressively replaced by some horizontal field lines, corresponding to the intraspines.

No universal connection between the vertical magnetic field and the umbra-penumbra boundary in sunspots

Context. It has been reported that the boundary between the umbra and the penumbra of sunspots occurs at a canonical value of the strength of the vertical magnetic field, independently of the size of the spot. This critical field strength is interpreted to be the threshold for the onset of magnetoconvection. Aims. Here we investigate the reasons why this criterion, also called the Jurčák criterion in the literature, does not always identify the boundary between the umbra and the penumbra. Methods. We performed a statistical analysis of 23 sunspots observed with Hinode/SOT. We compared the properties of the continuum intensity and the vertical magnetic field between filaments and spines and how they vary between spots of different sizes. Results. We find that the inner boundary of the penumbra is not related to a universal value of the vertical magnetic field. The properties of spines and filaments vary between spots of different sizes. Both components are darker in larger spots and the spines exhibit a stronger vertical magnetic field. These variations of the properties of filaments and spines with the spot size are also the reason for the reported invariance in the averaged vertical magnetic field at 50% of the mean continuum intensity. Conclusions. The formation of filaments and the onset of magnetoconvection are not related to a canonical value of the strength of the vertical magnetic field. The seemingly unique magnetic field strength is rather an effect of the filling factor of spines and penumbral filaments.

A multi-diagnostic spectral analysis of penumbral microjets

Context. Penumbral microjets (PMJs) are short-lived, jet-like objects found in the penumbra of sunspots. They were first discovered in chromospheric lines and have later also been shown to exhibit signals in transition region (TR) lines. Their origin and manner of evolution is not yet settled. Aims. We perform a comprehensive analysis of PMJs through the use of spectral diagnostics that span from photospheric to TR temperatures to constrain PMJ properties. Methods We employed high-spatial-resolution Swedish 1-m Solar Telescope observations in the Ca II 8542 Å and H α lines, IRIS slit-jaw images, and IRIS spectral observations in the Mg II h & k lines, the Mg II 2798.75 Å & 2798.82 Å triplet blend, the C II 1334 Å & 1335 Å lines, and the Si IV 1394 Å & 1403 Å lines. We derived a wide range of spectral diagnostics from these and investigated other secondary phenomena associated with PMJs. Results. We find that PMJs exhibit varying degrees of signal in all of our studied spectral lines. We find low or negligible Doppler velocities and velocity gradients throughout our diagnostics and all layers of the solar atmosphere associated with these. Dark features in the inner wings of H α and Ca II 8542 Å imply that PMJs form along pre-existing fibril structures. We find evidence for upper photospheric heating in a subset of PMJs through emission in the wings of the Mg II triplet lines. There is little evidence for ubiquitous twisting motion in PMJs. There is no marked difference in onset-times for PMJ brightenings in different spectral lines. Conclusions. PMJs most likely exhibit only very modest mass-motions, contrary to earlier suggestions. We posit that PMJs form at upper photospheric or chromospheric heights at pre-existing fibril structures.

Characterization of the umbra–penumbra boundary by the vertical component of the magnetic field

Context. The vertical component of the magnetic field was found to reach a constant value at the boundary between penumbra and umbra of stable sunspots in a recent statistical study of Hinode/SP data. This finding has profound implications as it can serve as a criterion to distinguish between fundamentally different magneto-convective modes operating in the sun. Aims. The objective of this work is to verify the existence of a constant value for the vertical component of the magnetic field (B⊥) at the boundary between umbra and penumbra from ground-based data in the near-infrared wavelengths and to determine its value for the GREGOR Infrared Spectrograph (GRIS@GREGOR) data. This is the first statistical study on the Jurčák criterion with ground-based data, and we compare it with the results from space-based data (Hinode/SP and SDO/HMI). Methods. Eleven spectropolarimetric data sets from the GRIS@GREGOR slit-spectograph containing fully-fledged stable sunspots were selected from the GRIS archive. SIR inversions including a polarimetric straylight correction are used to produce maps of the magnetic field vector using the Fe I 15648 Å and 15662 Å lines. Averages of B⊥ along the contours between penumbra and umbra are analyzed for the 11 data sets. In addition, contours at the resulting B⊥const are drawn onto maps and compared to intensity contours. The geometric difference between these contours, ΔP, is calculated for each data set. Results. Averaged over the 11 sunspots, we find a value of B⊥const = (1787 ± 100) gauss. The difference from the values previously derived from Hinode/SP and SDO/HMI data is explained by instrumental differences and by the formation characteristics of the respective lines that were used. Contours at B⊥ = B⊥const and contours calculated in intensity maps match from a visual inspection and the geometric distance ΔP was found to be on the order of 2 pixels. Furthermore, the standard deviation between different data sets of averages along umbra–penumbra contours is smaller for B⊥ than for B∥ by a factor of 2.4. Conclusions. Our results provide further support to the Jurčák criterion with the existence of an invariable value B⊥const at the umbra–penumbra boundary. This fundamental property of sunspots can act as a constraining parameter in the calibration of analysis techniques that calculate magnetic fields. It also serves as a requirement for numerical simulations to be realistic. Furthermore, it is found that the geometric difference, ΔP, between intensity contours and contours at B⊥ = B⊥const acts as an index of stability for sunspots.

Temporal Evolution of the Inverse Evershed Flow

Abstract The inverse Evershed flow (IEF) is an inflow of material into the penumbra of sunspots in the solar chromosphere that occurs along dark, elongated super-penumbral fibrils extending from about the outer edge of the moat cell to the sunspot. The IEF channels exhibit brightenings in the penumbra, where the supersonic IEF descends to the photosphere causing shock fronts with localized heating. We used an 1 hr time series of spectroscopic observations of the chromospheric spectral lines of Ca ii IR at 854 nm and Hα at 656 nm taken with the Interferometric Bidimensional Spectrometer at the Dunn Solar Telescope to investigate the temporal evolution of IEF channels. Complementary information on the photospheric magnetic field was obtained from observations with the Facility Infrared Spectropolarimeter at 1083 nm and the Helioseismic and Magnetic Imager. We find that individual IEF channels are long-lived (10–60 minutes) and only show minor changes in position and flow speed during their lifetime. Initiation and termination of IEF channels takes several minutes. The IEF channels with line-of-sight velocities of about 10 km s−1 show no lasting impact from transient or oscillatory phenomena with maximal velocity amplitudes of only about 1 km s−1 that run along them. We could not detect any clear correlation of the location and evolution of IEF channels to local magnetic field properties in the photosphere in the penumbra or moving magnetic features in the sunspot moat. Our results support a picture of the IEF as a field-aligned siphon flow along arched loops. From our data we cannot determine if their evolution is controlled by events at the outer end in the moat or at the inner end in the penumbra.

The Formation and Decay of Sunspot Penumbrae in Active Region NOAA 12673

Abstract To better understand the formation and decay of sunspot penumbrae, we studied the evolution of sunspots in three regions of the active region NOAA 12673 in detail. The evolution of sunspots in the three regions was involved in the interaction of two magnetic field systems: the preexisting magnetic field system and the later-emerging magnetic field system. Through analyzing the photospheric magnetic field properties, it is found that the formation of the penumbra originated from newly emerging magnetic bipoles that were trapped in the photosphere. The change in magnetic field in a penumbra from horizontal to vertical can cause the disappearance of the penumbra. A transformation of the magnetic field between the umbra and the penumbra is found, and the outward moat flow around the sunspot gradually decreased and vanished during decay of the sunspot. In addition, we found that the mean longitudinal magnetic strength in the penumbra decreased and the mean transverse magnetic strength in the penumbra increased with the increasing penumbral area during the formation of sunspots. However, during the decay of sunspots, the mean longitudinal magnetic strength in the penumbra increased, and the mean transverse magnetic strength in the penumbra decreased with decreasing penumbral area. Comparatively, the dependence of the area and the mean transverse/longitudinal magnetic field strength in the umbra is not remarkable. These results reveal that the formation and decay process of umbra are different from penumbra.

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.

Opposite Polarity Magnetic Fields and Convective Downflows in a Simulated Sunspot Penumbra

Abstract Recent numerical simulations and observations of sunspots show a significant amount of opposite polarity magnetic fields within the sunspot penumbra. Most of the opposite polarity fields are associated with convective downflows. We present an analysis of 3D MHD simulations through forward modeling of synthetic Stokes profiles of the Fe i 6301.5 Å and Fe i 6302.5 Å lines. The synthetic Stokes profiles are spatially and spectrally degraded considering typical instrument properties. Line bisector shifts of the Fe i 6301.5 Å line are used to determine line-of-sight velocities. Far wing magnetograms are constructed from the Stokes V profiles of the Fe i 6302.5 Å line. While we find an overall good agreement between observations and simulations, the fraction of opposite polarity magnetic fields, the downflow filling factor, and the opposite polarity-downflow association are strongly affected by spatial smearing and presence of strong gradients in the line-of-sight magnetic fields and velocity. A significant fraction of opposite polarity magnetic fields and downflows is hidden in the observations due to typical instrumental noise. Comparing simulations that differ by more than a factor of two in grid spacing, we find that these quantities are robust within the simulations.

Semi-empirical model atmospheres for the chromosphere of the sunspot penumbra and umbral flashes

Context. The solar chromosphere and the lower transition region are believed to play a crucial role in the heating of the solar corona. Models that describe the chromosphere (and the lower transition region), accounting for its highly dynamic and structured character are, so far, found to be lacking. This is partly due to the breakdown of complete frequency redistribution (CRD) in the chromospheric layers and also because of the difficulty in obtaining complete sets of observations that adequately constrain the solar atmosphere at all relevant heights. Aims. We aim to obtain semi-empirical model atmospheres that reproduce the features of the Mg II h&k line profiles that sample the middle chromosphere with focus on a sunspot. Methods. We used spectropolarimetric observations of the Ca II 8542 Å spectra obtained with the Swedish 1 m Solar Telescope and used NICOLE inversions to obtain semi-empirical model atmospheres for different features in and around a sunspot. These were used to synthesize Mg II h&k spectra using the RH1.5D code, which we compared with observations taken with the Interface Region Imaging Spectrograph (IRIS). Results. Comparison of the synthetic profiles with IRIS observations reveals that there are several areas, especially in the penumbra of the sunspot, where most of the observed Mg II h&k profiles are very well reproduced. In addition, we find that supersonic hot down-flows, present in our collection of models in the umbra, lead to synthetic profiles that agree well with the IRIS Mg II h&k profiles, with the exception of the line core. Conclusions. We put forward and make available four semi-empirical model atmospheres. Two for the penumbra, reflecting the range of temperatures obtained for the chromosphere, one for umbral flashes, and a model representative of the quiet surroundings of a sunspot.

Study of Sunspot Penumbra to Umbra Area Ratio Using Kodaikanal White-light Digitised Data

We study the long-term behaviour of sunspot penumbra to umbra area ratio by analyzing the recently digitized Kodaikanal white-light data (1923-2011). We implement an automatic umbra extraction method and compute the ratio over eight solar cycles (Cycles 16-23). Although the average ratio doesn't show any variation with spot latitudes, cycle phases and strengths, it increases from 5.5 to 6 as the sunspot size increases from 100 $\mu$hem to 2000 $\mu$hem. Interestingly, our analysis also reveals that this ratio for smaller sunspots (area $<$ 100 $\mu$hem) does not have any long-term systematic trend which was earlier reported from the Royal Observatory, Greenwich (RGO) photographic results. To verify the same, we apply our automated extraction technique on Solar and Heliospheric Observatory (SOHO)/Michelson Doppler Imager (MDI) continuum images (1996-2010). Results from this data not only confirm our previous findings, but also show the robustness of our analysis method.

A New Small Satellite Sunspot Triggering Recurrent Standard and Blowout Coronal Jets

Abstract In this paper, we report a detailed analysis of recurrent jets originated from a location with emerging, canceling, and converging negative magnetic field at the east edge of NOAA active region AR11166 from 2011 March 9 to 10. The event presented several interesting features. First, a satellite sunspot appeared and collided with a pre-existing opposite polarity magnetic field and caused a recurrent solar jet event. Second, the evolution of the jets showed blowout-like nature and standard characteristics. Third, the satellite sunspot exhibited a motion toward the southeast of AR11166 and merged with the emerging flux near the opposite polarity sunspot penumbra, which afterward, due to flux convergence and cancellation episodes, caused recurrent jets. Fourth, three of the blowout jets associated with coronal mass ejections (CMEs), were observed from the field of view of the Solar Terrestrial Relations Observatory. Fifth, almost all the blowout jet eruptions were accompanied with flares or with more intense brightening in the jet base region, while almost standard jets did not manifest such obvious features during eruptions. The most important feature, the blowout jets, were inclined to faster and larger scales than the standard jets. The standard jets instead were inclined to be relatively longer-lasting. The obvious shearing and twisting motions of the magnetic field may be interpreted as due to the shearing and twisting motions for a blowout jet eruption. The statistical results show that ~30% of the blowout jets directly developed into CMEs. This suggests that the blowout jets and CMEs should have a close relationship.

A Statistical Study of the Magnetic Imprints of X-class Solar Flares

Abstract Magnetic imprints, the rapid and irreversible evolution of photospheric magnetic fields as feedback from flares in the corona, have been confirmed by many previous studies. These studies showed that the horizontal field will permanently increase at the polarity inversion line (PIL) after eruptions, indicating that a more horizontal geometry of the photospheric magnetic field is produced. In this study, we analyze 20 X-class flares since the launch of the Solar Dynamics Observatory in 15 active regions with heliographic angles no greater than 45°. We observe clear magnetic imprints in 16 flares, whereas 4 flares are exceptional. The imprint regions of the horizontal field are located not only at the PIL but also at sunspot penumbra with strong vertical fields. Making use of the observed mass and speed of the corresponding coronal mass ejections (CMEs), we find that the CMEs with larger momenta are associated with stronger magnetic imprints. Furthermore, a linear relationship, with a Kendall’s Tau-b coefficient 0.54, between the CME momentum and the change of Lorentz force, is revealed. Based on that, we quantify the back reaction time to be ∼70 s, with a 90% confidence interval from about 50 to 90 s.

NVST observations of collision-induced apparent fan-shaped jets

ABSTRACT Using high-quality H α observations from the New Vacuum Solar Telescope, we first report apparent fan-shaped jets (AFJs) generated during the interaction between primary fan-shaped jets (FJs) and nearby facula magnetic structure. The primary FJs were intermittently launched from a sunspot penumbra with negative-polarity magnetic fields in active region 12740 on 2019 May 6, accompanied by impulsive brightenings at the base. While the propagating FJ encountered and collided with the negative-polarity magnetic structure of the west facula, the density of jet material was enhanced to the east of the facula. Meanwhile, the jet structures exhibited a deflection towards the north-west at the jet–facula collision location. Then the primary FJ evolved into two parts, with one part being reflected away from the facula and the other part forming an AFJ. Easily distinguished from the primary FJ, the ejecting AFJ was more ordered and had an apparent end at the facula. The AFJ was impulsively accelerated to speeds of 100 km s−1, and reached lengths of up to 40 Mm. The observed AFJ had a similar morphology to the fan-shaped quasi-separatrix layer (QSL) between the penumbra and facula magnetic systems, implying that the material of the AFJ was mainly guided by the fan plane of the QSL. We suggest that the collision does not cause a change in the field-line connectivity and only leads to the redistribution of jet material.

Automatic Detection of Sunspots on Full-disk Solar Images Using the Simulated Annealing Genetic Method

Sunspots with strong magnetic fields are the most important manifestations of solar activity, appearing as dark features in the photosphere observed in continuum images. We proposed an artificial intelligence technology called the simulated annealing genetic (SAG) method, which combined the genetic algorithm and simulated annealing algorithm to self-adaptively derive dual thresholds for detecting the umbra and penumbra of sunspots simultaneously. Full-disk continuum intensity images obtained from Solar Dynamics Observatory/Helioseismic Magnetic Imager (HMI) at a cadence of four hours from 2010 May to 2016 December were used. The detection results showed that the dual thresholds derived by the SAG method have outstanding performance in segmenting the umbra and penumbra from the photosphere with a satisfactory robustness efficiently. The boundaries of the umbra and penumbra were finely delineated, even for sunspots at the extreme solar limb. The total sunspot areas, umbral areas, and penumbral areas match very well with the data reported from HMI Debrecen Data (HMIDD), with the correlation coefficients reaching 0.99, 0.99, and 0.95, respectively. The mean ratios of umbra to sunspot areas per year ranged from 0.159 to 0.233. The ratios decreased with an increase in solar activity, which implies that the ratio was related to the solar activity level.