The high spatial and time resolution data obtained with SDO/AIA for the sunspot in active region NOAA 11131 on 08 December 2010 were analysed with the time-distance plot technique and the pixelised wavelet filtering method. Oscillations in the 3 min band dominate in the umbra. The integrated spectrum of umbral oscillations contains distinct narrowband peaks at 1.9 min, 2.3 min, and 2.8 min. The power significantly varies in time, forming distinct oscillation trains. The oscillation power distribution over the sunspot in the horizontal plane reveals that the enhancements of the oscillation amplitude, or wave fronts, have a distinct structure consisting of an evolving two-armed spiral and a stationary circular patch at the spiral origin, situated near the umbra centre. This structure is seen from the temperature minimum to the corona. In time, the spiral rotates anti-clockwise. The wave front spirality is most pronounced during the maximum amplitude phases of the oscillations. In the low-amplitude phases the spiral breaks into arc-shaped patches. The 2D cross-correlation function shows that the oscillations at higher atmospheric levels occur later than at lower layers. The phase speed is estimated to be about 100 km/s. The fine spectral analysis shows that the central patch corresponds to the high-frequency oscillations, while the spiral arms highlight the lower-frequency oscillations in the 3-min band. The vertical and horizontal radial structure of the oscillations is consistent with the model that interprets umbral oscillations as slow magnetoacoustic waves filtered by the atmospheric temperature non-uniformity in the presence of the magnetic field inclination from the vertical. The mechanism for the polar-angle structure of the oscillations, in particular the spirality of the wave fronts, needs to be revealed.
We report the simultaneous presence of chromospheric umbral flashes and associated umbral waves, and propagating coronal disturbances, in a sunspot and related active region. We have analyzed time-distance maps obtained using the observations from Atmospheric Imaging Assembly (AIA) on-board Solar Dynamics Observatory (SDO). These maps show the simultaneous occurrence of different sunspot oscillation and waves such as umbral flashes, umbral waves, and coronal waves. Analysis of the original light curves, i.e., without implementing any Fourier filtering on them, show that the amplitudes of diffe…
12 stable single sunspots were investigated in two aspects. The outer boundaries of the sunspots umbra were determined by an independent mathematical method and the vertical component of the magnetic field at these boundaries was found. We analyzed data from the SDO station using the segments of the continuum and magnetic field. It is shown that in a wide range of sunspot fields, the field average along the contour changes weakly, while the vertical component of the magnetic field itself, in a particular spot, changes significantly along the defined contour which reflects the fibrous structure…
We present simultaneous photospheric and chromospheric observations of the trailing sunspot in NOAA 10904, obtained with the Swedish Solar Telescope (SST) La Palma, Canary Islands. Time series of high resolution \ion{Ca}{ii}\,$H$ images show transient jet-like structures in sunspot umbrae are elongated, which we call umbral microjets. These jets are directed roughly parallel to nearby penumbral microjets, suggesting that they are aligned with the background magnetic field. In general, first a bright dot-like structure appears, from which a jet later emerges, although some jets appear without a…
We analyse sunspot oscillations using Interface Region Imaging Spectrograph (IRIS) slit-jaw and spectral data and narrow-band chromospheric images from the New Solar Telescope (NST) for the main sunspot in NOAA AR 11836. We report that the difference between the shock arrival times as measured the Mg II k 2796.35Å and Si IV 1393.76Å line formation levels changes during the observed period and peak-to-peak delays may range from 40~s to zero. The intensity of chromospheric shocks also displays a long term (about 20~min) variations. NST's high spatial resolution \ha\ data allowed us to conclude t…
Sunspots are the longest-known manifestation of solar activity, and their magnetic nature has been known for more than a century. Despite this, the boundary between umbrae and penumbrae, the two fundamental sunspot regions, has hitherto been solely defined by an intensity threshold. Here, we aim at studying the magnetic nature of umbra-penumbra boundaries in sunspots of different sizes, morphologies, evolutionary stages, and phases of the solar cycle. We used a sample of 88 scans of the Hinode/SOT spectropolarimeter to infer the magnetic field properties in at the umbral boundaries. We defined…
The subsurface structure of a solar sunspot is important in the stability of the sunspots and the energy transport therein. Two subsurface structure models have been proposed, the monolithic and cluster models, but no clear observational evidence supporting a particular model has been found so far. To obtain clues about the subsurface structure of sunspots, we analyzed umbral flashes in merging sunspots registered by IRIS Mg II 2796 Angstrom slit-jaw images (SJIs). Umbral flashes are regarded as an observational manifestation of magnetohydrodynamic (MHD) shock waves originating from convection…
In this study, we investigate magnetic properties of umbra of magneto-conjugate leading and following sunspots, i.e. connected through magnetic field lines. We established dependences between individual sunspot umbra field characteristics, and between these characteristics on the umbra area ($S$) separately for sunspot pairs, for which the minimal angle between the umbra magnetic field line of the leading ($L$) sunspot and the positive normal line to the Sun surface is smaller, than that in the following ($F$) sunspot ($α_{min-L}<α_{min-F}$; such sunspot pairs are the bulk) and, on the contrar…
A typical sunspot, as seen in white-light intensity images, has a two part structure: a dark umbra and a lighter penumbra. Such distinction primarily arises due to the different orientations of magnetic fields in these two regions. In this study, we use the Kodaikanal white-light digitized data archive to analyze the long-term evolution of umbral and penumbal area. We developed an 'automated algorithm' to uniquely identify the sunspot umbra (including the calculation of penumbra to umbra ratio) from these digitized intensity images. Our analysis reveals that the ratio increases slightly with t…
Data analysis of sunspot oscillation based on 6-hr SDO run of observation showed that low frequency (0.2 < ! < 1 mHz) oscillations are local similar to three and five minute oscillations. The oscillations in the sunspot are concentrated in cells of a few arcsec, each of which has its own oscillation spectrum. The analysis of two scenario for sunspot oscillations leads to conclusion that local sunspot oscillations occur due to subphotospheric resonator for slow mhd waves. Empirical models of sunspot atmosphere and the theory of slow waves in thin magnetic flux tubes is applied to the modeling o…
We analyze spectropolarimetric sunspot umbra observations taken in the near-infrared Si i 1082.7 nm line taking NLTE effects into account. The data were obtained with the GRIS instrument installed at the German GREGOR telescope. A point spread function (PSF) was constructed using prior Mercury observations with GRIS and the information provided by the adaptive optics system of the GREGOR telescope. The data were then deconvolved from the PSF using a principal component analysis deconvolution method and were analyzed via the NICOLE inversion code. The Si i 1082.7 nm line seems to be in emission…
Realistic 3D radiative MHD simulations reveal the magneto-convective processes underlying the formation of the photospheric fine structure of sunspots, including penumbral filaments and umbral dots. Here we provide results from a statistical analysis of simulated umbral dots and compare them with reports from high-resolution observations. A multi-level segmentation and tracking algorithm has been used to isolate the bright structures in synthetic bolometric and continuum brightness images. Areas, brightness, and lifetimes of the resulting set of umbral dots are found to be correlated: larger u…
Three-minute oscillations over sunspot's umbra in AR 11131 were observed simultaneously in UV/EUV emission by SDO/AIA and in radio emission by Nobeyama Radioheliograph (NoRH). We use 24-hours series of SDO and 8-hours series of NoRH observations to study spectral, spatial and temporal variations of pulsations in the 5-9 mHz frequency range at different layers of the solar atmosphere. High spatial and temporal resolution of SDO/AIA in combination with long-duration observations allowed us to trace the variations of the cut-off frequency and spectrum of oscillations across the umbra. We found th…
Umbral flashes (UFs) are emissions in the core of chromospheric lines caused by upward propagating waves steepening into shocks. UFs are followed by an expanding blue shifted umbral wave (UW) and red-shifted plasma returning to the initial state. Here we use 5 s cadence images acquired at $\pm$0.04~nm off the Halpha line center by the Visible Imaging Spectrometer (VIS) installed on the Goode Solar Telescope (GST) to detect the origin of UFs and UWs in a sunspot with a uniform umbra free of LBs and clusters of umbral dots. The data showed that UFs do not randomly originate over the umbra. Inste…
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…
The images of sunspots in sixteen active regions taken at the UCCI Observatory in Grand Cayman during June - November 2015, were used to determine their fractal dimensions using the perimeter-area method for the umbral and the penumbral region. Scale free fractal dimensions of 2.09 $\pm$ 0.42 and 1.72 $\pm$ 0.4 were found respectively. This value was higher than the value determined by Chumak and Chumak (1996) who used a similar method but for the penumbral region only for their sample set. There is a positive correlation r = 0.58 between umbral and the penumbral fractal dimensions for the spe…
Context. It is unclear why there is a rather sharp boundary in sunspots between the umbra and the penumbra. Both regions exhibit magnetoconvection, manifesting in penumbral filaments in the penumbra and in umbral dots in the umbra. Aims. Here we compare the physical properties of umbral dots and penumbral filaments. Our goal is to understand how the properties of these convective features change across the boundary between the umbra and the penumbra and how this is related to the rapid increase in brightness at the umbra-penumbra boundary. Methods. We derived ensemble averages of the physical …
Recent observations of sunspot's umbra suggested that it may be finely structured at a sub-arcsecond scale representing a mix of hot and cool plasma elements. In this study we report the first detailed observations of the umbral spikes, which are cool jet-like structures seen in the chromosphere of an umbra. The spikes are cone-shaped features with a typical height of 0.5-1.0 Mm and a width of about 0.1 Mm. Their life time ranges from 2 to 3 min and they tend to re-appear at the same location. The spikes are not associated with photospheric umbral dots and they rather tend to occur above darke…
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 $μ$hem to 2000 $μ$hem. Interestingly, our analysis also reveals that this ratio for smaller sunspots (area $<$ 100 $μ$hem) does not have any long-term systematic trend w…
Umbral flashes are sudden brightenings commonly visible in the core of chromospheric lines. Theoretical and numerical modeling suggest that they are produced by the propagation of shock waves. According to these models and early observations, umbral flashes are associated with upflows. However, recent studies have reported umbral flashes in downflowing atmospheres. We aim to understand the origin of downflowing umbral flashes. We explore how the existence of standing waves in the umbral chromosphere impacts the generation of flashed profiles. We performed numerical simulations of wave propagat…
Sunspots are prominent manifestations of the solar cycle and provide key constraints for understanding its operation. Also, knowing internal structure of sunspots allows us to gain insights on the energy transport in strong magnetic fields and, thus, on the processes inside the convection zone, where solar magnetic fields are generated and amplified before emerging at the surface on various scales, even during solar minima. In this paper, we present results of a spectropolarimetric analysis of a sunspot observed during the declining phase of the solar cycle 23. By inversion of full Stokes spec…
In the present work, we introduce and explain a method of solution of the radiative transfer equation based on a thin cloud model. The efficiency of this method to retrieve dynamical chromospheric parameters from Stokes I profiles of Ca II 854.2 nm line showing spectral emission is investigated. The analyzed data were recorded with the Crisp Imaging Spectro-Polarimeter (CRISP) at Swedish 1-m Solar Telescope on La Palma on 2012 May 5 between 8:11 - 9:00 UT. The target was a large decaying sunspot (NOAA 11471) at heliocentric position W 15 deg S 19 deg. This sunspot has a large umbra divided int…
High resolution spectropolarimetric observations of 3 sunspots taken with Hinode demonstrate the existence of supersonic downflows at or close to the umbra-penumbra boundary which have not been reported before. These downflows are confined to large patches, usually encompassing bright penumbral filaments, and have lifetimes of more than 14 hr. The presence of strong downflows in the center-side penumbra near the umbra rules out an association with the Evershed flow. Chromospheric filtergrams acquired close to the time of the spectropolarimetric measurements show large, strong, and long-lived b…
To deepen the analysis of the photometric properties of the umbra of a sunspot, we study proper motions of small features such as umbral dots (UDs) inside a single sunspot observed by the Solar Optical Telescope of Hinode close to the disk center. We consider horizontal flows with high precision and details to study the transient motion behavior of UDs in short time intervals. Blue continuum images were first deconvolved with the point-spread function, such that the stray light is precisely removed and the original resolution is improved. Several images were co-added to improve the signal-to-n…
The umbral regions of sunspots and pores in the solar photosphere are generally dominated by $3$~mHz oscillations, which are due to $p$-modes penetrating the magnetic region. In these locations, wave power is also significantly reduced with respect to the quiet Sun. However, here we study a pore where the power of the oscillations in the umbra is not only comparable, or even larger than that of the quiet Sun, but the main dominant frequency is not $3$~mHz as expected, but instead $5$~mHz. By combining Doppler velocities and spectropolarimetry and analysing the relationship between magnetic fie…
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…
Sunspot atmospheres are highly inhomogeneous hosting both quasi-stable and transient features, such as `umbral micro-jets' and dark fibril-like events. We seek to understand the morphological properties and formation mechanisms of small-scale umbral brightenings (SSUBs; analogous to umbral micro-jets) and to understand whether links between these events and short dynamic fibrils, umbral flashes, and umbral dots can be established. An SST filtergram time-series sampling the Ca II H line and a CRISP full-Stokes 15-point Ca II 8542 A line scan dataset were used. The average lifetime and lengths o…
We present the results of high resolution co-temporal and co-spatial photospheric and chromospheric observations of sunspot penumbral intrusions. The data was taken with the Swedish Solar Telescope (SST) on the Canary Islands. Time series of Ca\,II H images show a series of transient jets extending roughly 3000 km above a penumbral intrusion into the umbra. For most of the time series jets were seen along the whole length of the intruding bright filament. Some of these jets develop a clear $λ$-shaped structure, with a small loop appearing at their footpoint and lasting for around a minute. In …
High resolution spectropolarimetric observations by Hinode reveal the existence of supersonic downflows at the umbra-penumbra boundary of 3 sunspots that was recently reported by Louis et al. (2010). These downflows are observed to be co-spatial with bright penumbral filaments and occupy an area greater than 1.6 arcsec$^2$. They are located at the center-side penumbra and have the same polarity as the sunspot which suggests that they are not associated with the Evershed Flow. In this paper we describe the supersonic velocities observed in NOAA AR 10923 and discuss the photospheric as well as c…
The acoustic resonator is an important model for explaining the three-minute oscillations in the chromosphere above sunspot umbrae. The steep temperature gradients at the photosphere and transition region provide the cavity for the acoustic resonator, which allows waves to be both partially transmitted and partially reflected. In this paper, a new method of estimating the size and temperature profile of the chromospheric cavity above a sunspot umbra is developed. The magnetic field above umbrae is modelled numerically in 1.5D with slow magnetoacoustic wave trains travelling along magnetic fiel…
High spatial and temporal resolution images of a sunspot, obtained simultaneously in multiple optical and UV wavelengths, are employed to study the propagation and damping characteristics of slow magnetoacoustic waves up to transition region heights. Power spectra are generated from intensity oscillations in sunspot umbra, across multiple atmospheric heights, for frequencies up to a few hundred mHz. It is observed that the power spectra display a power-law dependence over the entire frequency range, with a significant enhancement around 5.5 mHz found for the chromospheric channels. The phase-d…
The Maunder Minimum (MM) was a prolonged period of low solar activity that occurred between 1645 and 1715. The true level of solar activity corresponding to this epoch is still a matter of debate. In order to compare solar activity during the MM with that of other epochs, we have evaluated the umbra-penumbra area ratio (U/P hereafter) during the MM. Thus, we have analyzed 196 sunspot drawings including 48 different sunspots observed during the period 1660-1709. The mode value of the ratio obtained from the occurrence frequency distribution lies between 0.15 and 0.25. Furthermore, the median an…
We present results from the investigation of 5-min umbral oscillations in a single-polarity sunspot of active region NOAA 12132. The spectra of TiO, H$α$, and 304 Å are used for corresponding atmospheric heights from the photosphere to lower corona. Power spectrum analysis at the formation height of H$α$ - 0.6 Å to H$α$ center resulted in the detection of 5-min oscillation signals in intensity interpreted as running waves outside the umbral center, mostly with vertical magnetic field inclination $>15°$. A phase-speed filter is used to extract the running wave signals with speed $v_{ph}> 4$ km …
We report spectropolarimetric observations of a supersonic downflow impacting the lower atmosphere within a large sunspot umbra. This work is an extension of Schad et al. 2016 using observations acquired in the He I 10830 Angstrom triplet by the Facility Infrared Spectropolarimeter. Downflowing material accelerating along a cooled coronal loop reaches peak speeds near 200 km s$^{-1}$ and exhibits both high speed emission and absorption within the umbra, which we determine to be a consequence of the strong height dependence of the radiatively-controlled source function above the sunspot umbra. …
Rotation of the leading sunspot of active region NOAA 10421 was investigated using magnetograms and Dopplergrams from the MDI instrument of the Solar and Heliospheric Observatory (SOHO), and white-light images from the Transition Region and Coronal Explorer (TRACE). The vertical, radial, and azimuthal axisymmetrical components of both magnetic and velocity field vectors were reconstructed for the sunspot umbra and penumbra. All three components of both vectors in the umbra and penumbra show torsional oscillations with the same rotational period of about 3.8 days. The TRACE white-light data als…
The comparative analysis for 1324 measurements of the corresponding sunspot magnetic fields with B > 2.5 kG (according to Crimean data) obtained at Crimean and Mt. Wilson observatories from 2010 to 2017 has been carried out. It has been shown that the difference between measurements can exceed 1 kG in some cases. The averaged values of the magnetic field are equal to 2759 G (Crimea) and 2196 G (Mt. Wilson). The maximum sunspot magnetic field measured at Mt. Wilson does not reach 2.7 kG while according to Crimean data it can exceed 4.0 kG. The correlation coefficient between measurements of mag…
Solar Optical Telescope onboard Hinode observed a sunspot (AR 11836) with two light bridges (LBs) on 31 Aug 2013. We analysed a 2-hour \ion{Ca}{2} H emission intensity data set and detected strong 5-min oscillation power on both LBs and in the inner penumbra. The time-distance plot reveals that 5-min oscillation phase does not vary significantly along the thin bridge, indicating that the oscillations are likely to originate from the underneath. The slit taken along the central axis of the wide light bridge exhibits a standing wave feature. However, at the centre of the wide bridge, the 5-min o…
In the solar atmosphere, the acoustic cutoff frequency is a local quantity which depends on the atmospheric height. It separates the low-frequency evanescent waves from the high-frequency propagating waves. We measure the cutoff frequency of slow magnetoacoustic waves at various heights of a sunspot umbra and compare the results with the estimations from several analytical formulae. We analyzed the oscillations in the umbra of a sunspot belonging to active region NOAA 12662 observed in the 10830 Å spectral region with the GREGOR Infrared Spectrograph and in the Fe I 5435 Å line with the GREGOR…
We report the discovery of a brightness enhancement in the center of a large sunspot umbra at a wavelength of 3 mm using the Atacama Large Millimeter/sub-millimeter Array (ALMA). Sunspots are amongst the most prominent features on the solar surface, but many of their aspects are surprisingly poorly understood. We analyzed a λ=3 mm (100 GHz) mosaic image obtained by ALMA, which includes a large sunspot within the active region AR12470 on December 16, 2015. The 3 mm map has a field-of-view and spatial resolution, which is the highest spatial-resolution map of an entire sunspot in this frequency …
The presence of fine structures in the sunspot vector magnetic fields has been confirmed from Hinode as well as other earlier observations. We studied 43 sunspots based on the data sets taken from ASP/DLSP, Hinode (SOT/SP) and SVM (USO). In this \emph{Letter}, (i) We introduce the concept of signed shear angle (SSA) for sunspots and establish its importance for non force-free fields. (ii) We find that the sign of global $α$ (force-free parameter) is well correlated with the global SSA and the photospheric chirality of sunspots. (iii) Local $α$ patches of opposite signs are present in the umbra…
Sunspots are the most notable structure on the solar surface with strong magnetic fields. The field is generally strongest in a dark area (umbra), but sometimes stronger fields are found in non-dark regions such as a penumbra and a light bridge. The formation mechanism of such strong fields outside umbrae is still puzzling. Here we report clear evidence of the magnetic field of 6,250 G, which is the strongest field among Stokes I profiles with clear Zeeman splitting ever observed on the Sun. The field was almost parallel to the solar surface and located in a bright region sandwiched by two opp…
We use high spatial and temporal resolution observations, simultaneously obtained with the New Vacuum Solar Telescope and Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory, to investigate the high-frequency oscillations above a sunspot umbra. A novel time--frequency analysis method, namely the synchrosqueezing transform (SST), is employed to represent their power spectra and to reconstruct the high-frequency signals at different solar atmospheric layers. A validation study with synthetic signals demonstrates that SST is capable to resolving weak signals even when their…
Extreme UV (EUV) and X-ray loops in the solar corona connect regions of enhanced magnetic activity, but they are not usually rooted in the dark umbrae of sunspots because the strong magnetic field found there suppresses convection. This means that the Poynting flux of magnetic energy into the upper atmosphere is not significant within the umbra as long as there are no light bridges or umbral dots. Here we report a rare observation of a coronal loop rooted in the dark umbra of a sunspot without any traces of light bridges or umbral dots. We used the slit-jaw images and spectroscopic data from I…
We study chromospheric oscillations including umbral flashes and running penumbral waves in a sunspot of active region (AR) using scanning spectroscopy in H-alpha and Ca II 8542A, with the Fast Imaging Solar Spectrograph (FISS) at the 1.6 meter New Solar Telescope at Big Bear Solar Observatory. A bisector method is applied to spectral observations to construct chromospheric Doppler velocity maps. Temporal sequence analysis of these shows enhanced high-frequency oscillations inside the sunspot umbra in both lines. Their peak frequency gradually decreases outward from the umbra. The oscillation …
Spectropolarimetric temporal series from Fe I $λ$ 6301.5 Å and Ca II infrared triplet lines are obtained by applying the Stokes synthesis code NICOLE to a numerical simulation of wave propagation in a sunspot umbra from MANCHA code. The analysis of the phase difference between Doppler velocity and intensity core oscillations of the Fe I $λ$ 6301.5 Å line reveals that variations in the intensity are produced by opacity fluctuations rather than intrinsic temperature oscillations, except for frequencies between 5 and 6.5 mHz. On the other hand, the photospheric magnetic field retrieved from the w…
Solar active regions show a wide variety of oscillatory phenomena. The presence of the magnetic field leads to the appearance of several wave modes, whose behavior is determined by the sunspot thermal and magnetic structure. We aim to study the relation between the umbral and penumbral waves observed at the high photosphere and the magnetic field topology of the sunspot. Observations of the sunspot in active region NOAA 12662 obtained with the GREGOR telescope (Observatorio del Teide, Spain) were acquired on 2017 June 17. The data set includes a temporal series in the Fe I 5435 Å line obtained…
Recent observations of the solar photosphere revealed the presence of elongated filamentary bright structures inside sunspot umbrae, called umbral filaments (UFs). These features differ in morphology, magnetic configuration, and evolution from light bridges that are usually observed to intrude in sunspots. To characterize an UF observed in the umbra of the giant leading sunspot of active region NOAA 12529, we analyze high-resolution observations taken in the photosphere with the spectropolarimeter aboard the Hinode satellite and in the upper chromosphere and transition region with the IRIS tel…
It was empirically determined that the umbra-penumbra boundaries of stable sunspots are characterized by a constant value of the vertical magnetic field. We analyzed the evolution of the photospheric magnetic field properties of a decaying sunspot belonging to NOAA 11277 between August 28 - September 3, 2011. The observations were acquired with the spectropolarimeter on-board of the Hinode satellite. We aim to proof the validity of the constant vertical magnetic-field boundary between the umbra and penumbra in decaying sunspots. A spectral-line inversion technique was used to infer the magneti…
We present a study of wave processes in the sunspot region NOAA 12670 on 2017 August 10 observed by the Goode Solar Telescope in the TiO 7057 A and Ha 6563 A spectral lines. To study the distribution of power oscillations and their dynamics, we applied the pixelized wavelet filtering (PWF) technique. For the first time, the spatial structure of oscillation sources as a footpoints of fine magnetic tubes, anchored in the sunspot umbra was obtained. We found that at the chromosphere level, emission variation is a combination of numerous independent oscillations located in the sources with small a…
We analyse the chromospheric Doppler velocity oscillations in a sunspot using the high resolution spectral observations obtained from the Fast Imaging Solar Spectrograph(FISS) of the New Solar Telescope at the Big Bear Solar Observatory. The Doppler velocity maps are constructed from the bisectors of the spectral observations. The time series analysis of Doppler velocity maps show enhanced power in the sunspot umbra at higher frequencies and in the penumbra at lower frequencies. We find that the peak power frequency decreases gradually from the umbra to outward.
We investigate a small-scale ($\approx$ 1.5 Mm along the slit), supersonic downflow of about 90 km s$^{-1}$ in the transition region above the light-bridged sunspot umbra in AR 11836. The observations were obtained with the Interface Region Spectrograph (IRIS) on 2013 September 2, from 16:40 to 17:59 UT. The downflow shows up as red-shifted "satellite" lines of the Si IV and O IV transition region lines and is remarkably steady over the observing period of nearly 80 min. The downflow is not visible in the chromospheric lines, which only show an intensity enhancement at the location of the down…
The umbral oscillations of velocity are commonly observed in the chromosphere of a sunspot. Their sources are considered to be either the external p-mode driving or the internal excitation by magnetoconvection. Even though the possibility of the p-mode driving has been often considered, the internal excitation has been rarely investigated. We report the identification of the oscillation patterns that may be closely related to the events of internal excitation from the observations of velocity oscillations in the temperature minimum region of two sunspots. The velocities were determined from th…
We investigate bipolar sunspot regions and how tilt angle and footpoint separation vary during emergence and decay. The Helioseismic and Magnetic Imager on board the Solar Dynamic Observatory collects data at a higher cadence than historical records and allows for a detailed analysis of regions over their lifetimes. We sample the umbral tilt angle, footpoint separation, and umbral area of 235 bipolar sunspot regions in Helioseismic and Magnetic Imager - Debrecen Data (HMIDD) with an hourly cadence. We use the time when the umbral area peaks as time zero to distinguish between the emergence and…
