Umbral Area Research Articles

Statistical Comparison between Pores and Sunspots during the Time Interval 2010–2023

To reveal the physical properties of pores and sunspots varying with solar cycle, we carried out a statistical comparison among pores, transitional sunspots, and mature sunspots using Solar Dynamics Observatory/Helioseismic and Magnetic Imager from 2010 April to 2023 July. The OTSU method and region-growing algorithm were combined to detect umbrae of 11,876 sunspots covering solar cycles 24 and 25. The relationships between umbral area, continuum intensity (I), line-of-sight (LOS) magnetic field strength (B los), and line-of-sight velocity (V los) of umbrae were investigated in detail. The main conclusions are as follows. (1) The steepness between the total magnetic flux and total area of transitional sunspots appears to be flattened in each phase of the observed solar cycles, and does not have a significant variation over the solar cycle. (2) For three groups of sunspots, the umbral physical parameters’ means and their correlations show only minor variations with the solar cycle, which are in error ranges. (3) As the mean umbral LOS magnetic field strength increases, the correlation of the umbral I–B los increases. The flattening of transitional sunspots in total area–total magnetic flux scatter is related to the evolution of sunspots itself, and may not correspond to the solar cycle. The umbral physical parameters and their correlations do not exhibit a discernible regularity over the solar cycle. Our analysis results contribute to a more comprehensive understanding of the dynamic processes of sunspot magnetic fields and give a new perspective on revealing the physical features of vertical magnetic flux tubes.

Magnetic properties of the umbral boundary during sunspot decay

Context. In recent years, the magnetic properties of the umbra-penumbra boundary of sunspots and the boundary of pores at various evolutionary stages have been characterised using datasets from different instruments. Aims. We aim to study the intrinsic differences between the intensity and vector magnetic field properties derived from Hinode/SP and SDO/HMI observations of a decaying sunspot. Methods. We analysed the sunspot embedded in active region NOAA 12797 during six days in 30 SP/Hinode scans and 704 HMI/SDO for both regular maps and maps corrected for scattered light, HMIdcon. We studied the correlation of the magnetic properties and continuum intensity in the datasets within the spot, and we investigated the differences at the umbra-penumbra boundary. We examined the decaying process in detail using the full temporal resolution of the HMIdcon maps. Results. We find a good one-to-one correspondence between the magnetic properties in the SP and HMIdcon maps, but the continuum intensity of the spots in the SP maps is found to be 0.04 IQS brighter than in the HMIdcon maps. The considerable influence of scattered light in the HMI maps makes it the least ideal dataset for studying the boundary of spots without a penumbra. The properties at the umbra-penumbra boundary evolve slowly during the sunspot decay stage, while the penumbra still provides some stability. In contrast, they respond more abruptly to areal changes in the naked-spot stage. During the sunspot decay, we find linear decay in the area and in the magnetic flux. Moreover, the umbra shows two characteristic decaying processes: a slow decay during the first three days, and a sudden fast decay during the final dissipation of the penumbra. We find indications of a 3.5 h lag between the dissipation of the vertical fields in the umbral region and the photometric decay of the umbral area. Conclusions. The differences found in the continuum intensity and in the vertical component of the magnetic field, Bver, between the analysed datasets explain the discrepancies among the Bver values found at the boundaries of umbrae in previous studies.

Commissioning of Elekta Infinity™ 6 MV flattening filter-free using Monte Carlo simulation

Commissioning a simulation model of the linear accelerator (Linac) in radiotherapy needs to be done to validate the dose distribution accuracy. For this purpose, the Monte Carlo simulation method is commonly employed, and it involves using the EGSnrc software. This software consists of BEAMnrc for modeling Linac and DOSXYZnrc for calculating dose distribution in a water phantom. This study used Monte Carlo simulation to commission the Linac Flattening Filter-Free (FFF) Elekta Infinity™ 6 MV photon mode. The commissioning results show that the simulated dose distribution satisfied the acceptance criteria of simulation results using initial electron energy of 6.9 MeV at 5 × 5, 10 × 10, and 20 × 20 cm2 field sizes with average local difference of percent depth dose (PDD) of about 2.99%. The dose and dmax increasedwith higher initial electron energy increased, while percentage depth dose (PDD) decreased at smaller field sizes. At larger field sizes, the dose profile widened and the PDD Linac FFF decreased more significantly than PDD Linac Flattening Filter (FF). Additionally, both exhibited differences in the uniformity of dose values in the umbra area. The surface dose for a 10 × 10 cm2 field size was 25.2% and 34.4% for both 6 MV-FF and 6 MV-FFF, respectively.

Temporal and Latitudinal Variation in Penumbra-Umbra Ratios of the Sunspots: Analyses of RGO, Kodaikanal and Debrecen Databases

We study the latitudinal distribution and temporal evolution of the sunspot penumbra-umbra ratio (q) for the even and odd Solar Cycles 12 – 24 of RGO sunspot groups, SC21 – SC24 of Debrecen sunspot groups and Kodaikanal sunspot dataset for SC16 – SC24. We find that RGO even (odd) Cycles have q-values 5.20 (4.75), Kodaikanal even (odd) cycles have q-values 5.27 (5.43), and Debrecen cycles have q-value 5.74 on the average.We also show that q is at its lowest around the Equator of the Sun and increases towards higher latitudes having maximum values at about 10 – 25 degrees. This is understandable because smaller sunspots and groups locate nearer to the Equator and have smaller q-values than larger sunspots and groups, which maximize at about 10 – 20 degrees at both hemispheres. The error limits are very wide, and, thus, the confidence in this result is somewhat vague.For the Debrecen dataset, we find a deep valley in the temporal q-values before the middle of the cycle. We show that this exists simultaneously with the Gnevyshev gap (GG) in the graph of the total and umbral areas of the large sunspot groups. Other databases do not show GG in their q-graphs, although GG exists in their temporal total area and umbral area.

Atmospheric Density Inversion Based on Swarm-C Satellite Accelerometer

We used the Swarm-C accelerometer data to invert the orbital atmospheric density in this study. First, the Swarm-C satellite mission data were obtained from the ESA’s public data platform, and preliminary data error correction was performed. This paper refers to the calibration method of GRACE-A satellite accelerometer data. It adds linear temperature correction on the original basis. Moreover, this study’s accelerometer data correction results were compared with the data correction results published by the ESA. In order to explore the influence of light radiation on the accelerometer, we established a geometric model of Swarm-C to simulate the physical shape of the satellite surface. The light radiation pressure model and the shadow area judgment model were established, the change in the light radiation acceleration during the transition process of the satellite from the umbra area to the penumbra area and then to the shadowless area was studied, and the state transition during the transition process was analyzed. Finally, the atmospheric drag coefficient was calculated based on the Sentman model. Atmospheric density inversion calculations were performed using the above data. We show the spatial distribution of atmospheric density at a fixed latitude, testing our results during geomagnetic storms. We compared the density results with existing research data, demonstrating the effectiveness of our approach.

Sunspot extraction and hemispheric statistics of YNAO sunspot drawings using deep learning

Sunspot drawings around the globe provide long historical records for understanding the long-term trends in the solar activity cycle. Yunnan Astronomical Observatory (YNAO) in China contributes to the relatively continuous sunspot drawings from 1957 to 2015. This paper proposes a new deep learning method named SPR-mask to extract pores, spots, umbrae and penumbrae in the YNAO sunspot drawings. SPR-mask consists of three parts: backbone, shared head and mask branch. It especially adopts a scale-aware attention network (SAAN) and a PointRend module in the mask branch to improve the accuracy of target edge segmentation. Besides that, each sunspot belonging to the northern or southern (N-S) hemisphere is determined by transforming its cartesian coordinates to spherical coordinates after extracting $P$ , $B_{0}$ and $L_{0}$ handwritten in sunspot drawings using a revised Lenet-5 deep learning method. The precision, recall and $AP$ of SPR-mask are 0.92, 0.93, and 0.92, respectively. The test results show the SPR-mask method has a good performance. The numbers and areas of pores, spots, umbrae and penumbrae for the N-S hemisphere are presented and analyzed separately. The YNAO data are also compared with Royal Greenwich Observatory (RGO), Kanzelhöhe Observatory (KSO) and Purple Mountain Astronomical Observatory (PMO) data. The results show similar trends, high correlations, and N-S asymmetries. All data of YNAO are publicly shared at https://github.com/yzs64/YNAO_sd/ , which are abundant and complementary to the other sunspot catalogs in the world.

Penumbra–Umbra Area Ratio of Sunspots during Cycle-3 and Cycle Magnitude

Penumbra–Umbra Area Ratio of Sunspots during Cycle-3 and Cycle Magnitude

Chinese Sunspot Drawings and Their Digitization—(VII) Sunspot Penumbra to Umbra Area Ratio Using the Hand-Drawing Records from Yunnan Observatories

The ratio of penumbral to umbra area of sunspots plays a crucial role in the solar physics fields, especially for understanding the origin and evolution of the solar activity cycle. By analyzing the recently digitized sunspot drawings observed from Yunnan Observatories (1957–2021), we investigate the long-term variation of the penumbral to umbra area ratio of sunspots. An automatic extraction method, based on the maximum between-class variance and the morphological discrimination, is used to accurately extract penumbra and umbra and to calculate the ratio over six solar cycles (cycle 19–24). The expected value of the ratio of penumbra to umbra area is found to be 6.63 ± 0.98, and it does not exhibit any systematic variation with sunspot latitudes and phases. The average ratio fluctuates from 5 to 7.5 per year and the overall trend has decreased after 1999 compared to the previous one. The ratio of sunspot penumbra to umbra area satisfies the log-normal distribution, implying that its variation is related to the evolution of the photospheric magnetic field. Our results are consistent with previous works.

Variations of the Internal Asymmetries of Sunspot Groups during Their Decay

Abstract The aim of the present study is to show the varying asymmetries during the decay of sunspot groups. The source of input data is the SOHO/MDI-Debrecen Database sunspot catalog that contains the magnetic polarity data for time interval 1996–2010. Several types of asymmetries were examined on the selected sample of 142 sunspot groups. The leading–following asymmetry increases in three phases during the decay and exhibits anticorrelation with size. It is also related to a hemispheric asymmetry: during the decay, the area asymmetry index has higher values in the southern hemisphere, which may be due to the higher activity level in the southern hemisphere in cycle 23. The total umbral area is inversely proportional to the umbra/penumbra ratio, but it is directly proportional to the umbral decay rate. During the decay, the umbra/penumbra (U/P) ratio decreases unambiguously in the trailing parts but in most cases in the leading parts as well. The U/P variation is a consequence of the different depths of umbral and penumbral fields.

Sunspots Extraction in PMO Sunspot Drawings Based on Deep Learning

Sunspot numbers and sunspot areas are the most fundamental indices of long-term solar activity levels and the solar magnetic dynamo. This paper presents a deep-learning method for segmenting the components of sunspots in the Purple Mountain Astronomical Observatory (PMO) historical hand drawings spanning from 1954 to 2011. A total of 44568 samples were labeled as the following four types to build the training set and the test set at a ratio of 9:1. They are (1) pores without penumbrae, (2) spots with penumbrae, (3) umbrae within spots, and (4) holes within spots. A Hybrid Task Cascade Region-based Convolutional Neural Networks (HTC RCNN) is adopted; it is designed as three cascade stages adapted to increasingly higher Intersection over Unions to obtain increasing detector quality. The features of sunspots are extracted and fused by a backbone combining residual network 50 and a feature pyramid network. After training the network using the training set, the method is tested by the test set. The precision, recall, and mean Average Precision are 0.90, 0.90, and 0.89, respectively, indicating that the method has a satisfying performance. The components of each sunspot are extracted separately, yielding the numbers and areas of pores, spots, umbrae and penumbrae. Detailed data of the PMO drawings from 1954 to 2011 are shared in public (http://61.166.157.71/HTCSD.html). It is another piece of the puzzle of long-term solar activity cycles and solar magnetic dynamo research.

Study of the Decay Rates of the Umbral Area of Sunspot Groups Using a High-resolution Database

Abstract The emergence and decay of the sunspot groups are important components of the solar dynamo models. There are two different types of studies on the evolution of active regions. One of them is based on fewer data with higher spatial resolution, the other one uses more data with lower spatial resolution. The input data of the present study allow the investigation with high resolution both spatially and temporally. The temporal resolution of the Solar and Heliospheric Observatory Debrecen sunspot database is one and a half hours, and it also makes it possible to identify all individual sunspots with the position, area, and magnetic polarity. More than 200 sunspot groups have been selected, which have clear maxima on the solar disk, and the decrease of their umbral area is observable during at least four days. The decay rates were calculated by using two data: the umbral area and the number of contained sunspots—these decay rates were computed for the total umbral area of sunspot groups and their leading and following parts. The decay rate has a linear area dependency, and it is higher for the following part than for the leading one.

Comparative Study of a Sunspot at Two Different Instances of Time

We investigate the evolutionary effects on the brightness of a sunspot as well as on the properties of its fine-structures using two sets of time series of G-band images of a single sunspot in NOAA 10944 recorded at two symmetric locations on the solar disc by Hinode/SOT (Solar Optical Telescope). The second time series (phase W) was recorded 2.5 d after recording the first time series (phase E). Both time series of images were corrected for instrumental stray light; then the p-mode oscillations were removed. Our analysis demonstrates that the spatially and temporally averaged intensities of the umbra as well as the penumbra in both phases are practically the same. Nevertheless, considering only intensities smaller than 1.0$\mbox{I}_{\mathrm{ph}}$ the penumbra in the phase W is brighter with a contrast of 2 per cent. However, the ratio of the peak intensities of penumbral grains to their background intensities decreases, on average, from 2.9 to 2.6 from phase E to phase W. The penumbra is on average, 6.9 times brighter than the umbra in both phases. The umbra gets smaller in size with a ratio of 0.90 and its magnetic field strength decreases about 200 G after the 2.5 d evolution. Although the central umbral dots (UDs) with lifetimes longer than 2 min are by the factor of 1.6 more frequent in phase E, the most of the physical and kinematic properties of UDs do not show considerable changes after the sunspot evolution at this 2.5 d time interval. The registered UDs have intensities smaller than 0.84$\mbox{I}_{\mathrm{ph}}$ with a mean intensity of about 0.29$\mbox{I}_{\mathrm{ph}}$. The equivalent diameters of the individual UDs have a symmetric distribution around 180 km with a standard deviation about 35 km. The brightest UDs show a constant median diameter. The UDs registered in both phases have a mean lifetime of 7.4 min. Our results suggest that UDs with a certain lifetime have an admissible lower limit for their mean size which grows with lifetime. The proper motions of UDs show velocities less than $1.0~\mbox{km}\,\mbox{s}^{-1}$ with a maximum population around $0.2~\mbox{km}\,\mbox{s}^{-1}$. The UDs formed in the phase W are faster when the umbral area is smaller and the magnetic field is weaker.

SDO Data Artifacts and Anticorrelation of Oscillations in the Sunspot Magnetic Field and Umbral Area

The paper considers a special class of artifacts that appears in the useful signal when the source moves along a discrete matrix of the receiver. A parasitic component forms in the signal due to the displacement of the extreme value of the distributed field of the physical quantity from pixel to pixel (p2p effect). It is shown that a stepwise discretization of Δt < T (p2p) is a necessary but not sufficient condition for the formation of the p2p-artifact. For small field gradients (in particular, with good spatial resolution), the parasitic signal in the time series of the studied variable is either weakened or does not form at all. This assumption has been qualitatively verified by comparative analysis of sunspot data obtained with SOHO/MDI and SDO/HMI. In addition, the Y-p2p effect, which is associated with sunspot displacement along the meridian and influences the process of long-period sunspot oscillations, is considered in detail based on SDO/HMI data. It was found that there is an inverse relationship between changes in the umbral area of a spot and variations of its magnetic field strength. This property of long-period sunspot oscillations as a single magnetic structure indicates the magnetic flux in the sunspot umbra is preserved, and it plays an extremely important role for our understanding of the physical nature of these oscillations.

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.

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.

A Curious History of Sunspot Penumbrae: An Update

The ratio of penumbral to umbral area of sunspots is an important topic for solar and geophysical studies. Hathaway (Solar Physics, 286, 347, 2013) found a curious behaviour in this parameter for small sunspot groups (areas smaller than 100 millionths of solar hemisphere, msh) using records from Royal Greenwich Observatory (RGO). Hathaway showed that penumbra-umbra ratio decreased smoothly from more than 7 in 1905 to lower than 3 by 1930 and then increased to almost 8 in 1961. Thus, Hathaway proposed the existence of a secular variation in the penumbra-umbra area ratio. In order to confirm that secular variation, we employ data of the sunspot catalogue published by the Coimbra Astronomical Observatory (COI) for the period 1929-1941. Our results disagree with the penumbra-umbra ratio found by Hathaway for that period. However, the behaviour of this ratio for large (areas greater or equal than 100 msh) and small groups registered in COI during 1929-1941 is similar to data available from RGO for the periods 1874-1914 and 1950-1976. Nevertheless, while the average values and time evolution of the ratio in large groups is similar to the ratio for small groups according to Coimbra data (1929-1941) it is not analogous for RGO data for the same period. We also found that the behaviour of the penumbra-umbra area ratio for smaller groups in both observatories is significantly different. The main difference between the area measurements made in Coimbra and RGO is associated with the umbra measurements. We would like to stress that the two observatories used different methods of observation and while in COI both methodology and instruments did not change during the study period, some changes were carried out in RGO that could have affected measurements of umbra and penumbra. These facts illustrate the importance of the careful recovery of past solar data.

Variations and Regularities in the Hemispheric Distributions in Sunspot Groups of Various Classes

The present study investigates the variations and regularities in the distributions in sunspot groups (SGs) of various classes in the northern and southern hemispheres from Solar Cycles (SCs) 12 to 23. Here, we use the separation scheme that was introduced by Gao, Li, and Li (Solar Phys.292, 124, 2017), which is based on $A/U$ (A is the corrected area of the SG, and U is the corrected umbral area of the SG), in order to separate SGs into simple SGs ($A/U \leq 4.5$) and complex SGs ($A/U > 6.2$). The time series of Greenwich photoheliographic results from 1875 to 1976 (corresponding to complete SCs 12 – 20) and Debrecen photoheliographic data during the period 1974 – 2015 (corresponding to complete SCs 21 – 23) are used to show the distributions of simple and complex SGs in the northern and southern hemispheres. The main results we obtain are reported as follows: i) the larger of the maximum annual simple SG numbers in the two hemispheres and the larger of the maximum annual complex SG numbers in the two hemispheres occur in different hemispheres during SCs 12, 14, 18, and 19; ii) the relative changing trends of two curves – cumulative SG numbers in the northern and southern hemispheres – for simple SGs are different from those for complex SGs during SCs 12, 14, 18, and 21; and iii) there are discrepancies between the dominant hemispheres of simple and complex SGs for SCs 12, 14, 18, and 21.

Long-term oscillations of sunspots and a special class of artifacts in SOHO/MDI and SDO/HMI data

A specific type of artifacts, that originate due to displacement of the image of a moving object along the digital (pixel) matrix of receiver are analyzed in detail. The criteria of appearance and the influence of these artifacts on the study of long-term oscillations of sunspots are deduced. The obtained criteria suggest us methods for reduction or even elimination of these artifacts. It is shown that the use of integral parameters can be very effective against the artifact distortions. The simultaneous observations of sunspot magnetic field and ultraviolet intensity of the umbra have given the same periods for the long-term oscillations. In this way the real physical nature of the oscillatory process, which is independent of the artifacts have been confirmed again. A number of examples considered here confirm the dependence between the periods of main mode of the sunspot magnetic field long-term oscillations and its strength. The dependence was derived earlier from both the observations and the theoretical model of the shallow sunspot. The anti-phase behavior of time variations of sunspot umbra area and magnetic field of the sunspot demonstrates that the umbra of sunspot moves in long-term oscillations as a whole: all its points oscillate with the same phase.

Century long study of sunspot activity using the Kodaikanal white-light data

AbstractSunspots are the most obvious and high contrast observable feature of solar magnetic activity in the photosphere. The morphological and kinematic behavior of sunspots on the solar surface need to be studied over a long time period to understand solar magnetic activity. For this, it is important to understand the long term emergence patterns, and developments, decay of the sunspots on the solar surface over many cycles. The long time sequence of the Kodaikanal white-light images provide a consistent data set for this study. The digitized images were calibrated for relative plate density and aligned in such a way that the solar north is in upward direction. A sunspot detection technique was used to identify the sunspots on the digitized images. In addition to describing the calibration procedure and availability of the data, we here present results on the sunspot, umbral and penumbral area measurements and their variation with time.

Possible Explanation of the Different Temporal Behaviors of Various Classes of Sunspot Groups

In order to investigate the periodicity and long-term trends of various classes of sunspot groups (SGs), we separated SGs into two categories: simple SGs ( $A/U \leq 4.5$ , where $A$ represents the total corrected whole spot area of the group in millionths of the solar hemisphere (msh), and $U$ represents the total corrected umbral area of the group in msh); and complex SGs ( $A/U > 6.2$ ). Based on the revised version of the Greenwich Photoheliographic Results sunspot catalogue, we investigated the periodic behaviors and long-term trends of simple and complex SGs from 1875 to 1976 using the Hilbert-Huang Transform method, and we confirm that the temporal behaviors of simple and complex SGs are quite different. Our main findings are as follows. i) For simple and complex SGs, the values of the Schwabe cycle wax and wane, following the solar activity cycle. ii) There are significant phase differences (almost antiphase) between the periodicity of $53.50 \pm 3.79$ years extracted from yearly simple SG numbers and the periodicity of $56.21 \pm 2.92$ years extracted from yearly complex SG numbers. iii) The adaptive trends of yearly simple and complex SG numbers are also quite different: for simple SGs, the values of the adaptive trend gradually increase during the time period of 1875 – 1949, then they decrease gradually from 1949 to 1976, similar to the rise and the maximum phase of a sine curve; for complex SGs, the values of the adaptive trend first slowly increase and then quickly increase, similar to the minimum and rise phase of a sine curve.