Sunspot Area Research Articles

The impact of asymmetrical distribution of solar activity on geomagnetic indices throughout five solar activity cycles

The irregularity of the solar activities based on sunspot numbers (SSNs) and areas (SSAs) over the solar disk has been considered. More activities phenomena occurred in one of the solar hemispheres than the other at the same time, which they are referred to as the North-South (N-S) asymmetry of solar activity. Daily averages of geomagnetic indices aa, Ap, Kp, and Dst over the period 1967–2016 have been examined according to the asymmetrical distribution of both solar hemispheric activities. The possible connection between the geomagnetic activity disturbances and the sign of non-uniformity of solar activity, i.e. the N-S asymmetry for each geomagnetic index has been confirmed. The dependence of the sign of geomagnetic disturbances on the solar activity cycle, has been examined. We have classified the considered data into two groups according to the activity of northern (N) or southern (S) solar hemisphere. The solar cycles 20 and 24 have northern hemisphere dominance. These activities shifted from northern to southern hemisphere in solar cycles 21, 22, and 23. The geomagnetic disturbances exhibited significant asymmetrical states at different periods. The most significant northern and southern peaks occurred at/near the minimum of the solar cycle or in periods of descending phase of the solar cycle. The geomagnetic activity has southern dominance during solar cycle 22 and it favoured the northern activity during solar cycle 23. The dependence of the geomagnetic activity disturbance of aa, Ap, Kp, and Dst indices over the solar activity cycle is confirmed and the sign of the asymmetry changes from one solar cycle to another.

Revisiting the Question: The Cause of the Solar Cycle Variation of Total Solar Irradiance

The Mg II index and sunspot area are usually used to represent the intensification contribution by solar bright structures to total solar irradiance (TSI) and sunspot darkening, respectively. In order to understand the cause of the solar cycle variation of TSI, we use extension of wavelet transform, wavelet coherence (WTC), and partial wavelet coherence (PWC), to revisit this issue. The WTC of TSI with sunspot area shows that the two time series are very coherent on timescales of one solar cycle, but the PWC of TSI with sunspot area, which can find the results of WTC after eliminating the effect of the Mg II index, indicates that the solar cycle variation of TSI is not related to sunspots on the solar surface. The coherence of two time series at these timescales should be due to a particular phase relation between sunspots and TSI. The WTC and PWC of TSI with Mg II index show that the solar cycle variation of TSI is highly related to Mg II index, which reflects the relation of TSI with the long-term part of Mg II index that shows the intensification contribution by the small magnetic features to TSI. Consequently, the solar cycle variation of TSI is dominated by the small magnetic features on the solar full disk. Additionally, we also show the combined effects of the sunspot darkening and the intensification contribution represented by Mg II index to TSI on timescales of a few days to several months and indicate that the faculae increase TSI and contribute to its variation at these timescales.

The Present Special Solar Cycle 24: Casting a Shadow over Periodicity of the North–South Hemispherical Asymmetry

The N-S asymmetry (the north-south hemispheric asymmetry) of sunspot areas for each of the cycles 7-24 have been investigated, and a trend of a long-term characteristic timescale of about eight cycles is inferred, which is confirmed again by studying the fitted lines of the yearly values of the N-S asymmetry of sunspot numbers and sunspot group numbers at solar cycle 24. Then, a periodic behavior of about 12 solar cycles is found in the cumulative counts of yearly sunspot areas for each of the cycles 7-24. Nevertheless, the cumulative counts of sunspot numbers and sunspot group numbers for cycle 24 have different behaviors. Moreover, the dominant hemispheres for cycles 7-23 show a trend of a long-term characteristic timescale of about 12 cycles. However, we cannot determine the dominant hemisphere of cycle 24, as these three parameters give different results for the dominant hemisphere. Cycle 24 is a particular solar activity cycle, as sunspot areas suggest a long characteristic timescale of about 12-cycle length, while sunspot numbers and sunspot group numbers support an eight-cycle period of the N-S asymmetry.

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

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

Spectral energy of multisource and multielement of solar energetic particles during the spotless days on solar cycle 24

We characterized solar energetic particle power-law spectra from selected two sunspotless events with more than 30 consecutive day’s length on July 21 to August 20, 2008 (31 days) and July 31 to August 31, 2009 (32 days) in the solar cycle 24. Their spectral of energetic interplanetary multielements of seven charge particles (H, He, C, O, Ne, Si, and Fe) from 15 keV to 0.5 GeV per nucleon have been compiled from onboard instruments of several satellites with different distances from the Sun (GOES, ACE, STEREO, and Voyager). Their spotless spectral energetic particles were also compared with appearances of AR12192, owing very large sunspot area (>2000 millionth of solar hemisphere) without foreshortening effect, on October 19-27, 2014. Our results from six charge elements show that there were intrinsic differences among those events on aspects of flux particles enhancement by double power-law or V-shape. Flux enhancements occurred after 10 MeV for sunspotless days and 20-30 MeV for AR 12192 passage. The effects of very strong magnetic field in AR 12192 influences two mechanisms, flux enrichment of charge particles in lower energy and on the contrary to inhibit streaming of particles in higher energy. It is suggested that interactions of multielements of solar energetic particles with interplanetary magnetic fields and plasma speed play an important role, as seen from the variations of rollover power-law of spectral energy.

Filling Factors of Sunspots in SODISM Images

The calculated filling factors (FFs) for a feature reflect the fraction of the solar disc covered by that feature, and the assignment of reference synthetic spectra. In this paper, the FFs, specified as a function of radial position on the solar disc,are computed for each image in a tabular form. The filling factor (FF) is an important parameter and is defined as the fraction of area in a pixel covered with the magnetic field, whereas the rest of the area in the pixel is field-free. However, this does not provide extensive information about the experiments conducted on tens or hundreds of such images. This is the first time that filling factors for SODISM images have been catalogued in tabular formation. This paper presents a new method that provides the means to detect sunspots on full-disk solar images recorded by the Solar Diameter Imager and Surface Mapper (SODISM) on the PICARD satellite. The method is a totally automated detection process that achieves a sunspot recognition rate of 97.6%. The number of sunspots detected by this method strongly agrees with the NOAA catalogue. The sunspot areas calculated by this method have a 99% correlation with SOHO over the same period, and thus help to calculate the filling factor for wavelength (W.L.) 607nm.

The Association of Filaments, Polarity Inversion Lines, and Coronal Hole Properties with the Sunspot Cycle: An Analysis of the McIntosh Database

Abstract Filaments and coronal holes, two principal features observed in the solar corona, are sources of space weather variations. Filament formation is closely associated with polarity inversion lines (PILs) on the solar photosphere which separate positive and negative polarities of the surface magnetic field. The origin of coronal holes is governed by large-scale unipolar magnetic patches on the photosphere from where open magnetic field lines extend to the heliosphere. We study the properties of filaments, PILs, and coronal holes in solar cycles 20, 21, 22, and 23 utilizing the McIntosh archive. We detect a prominent cyclic behavior of filament length, PIL length, and coronal hole area with significant correspondence with the solar magnetic cycle. The spatio-temporal evolution of the geometric centers of filaments shows a butterfly-like structure and distinguishable poleward migration of long filaments during cycle maxima. We identify this rush to the poles of filaments to be co-temporal with the initiation of polar field reversal as gleaned from Mount Wilson and Wilcox Solar Observatory polar field observations, and quantitatively establish their temporal correspondence. We analyze the filament tilt angle distribution to constrain their possible origins. The majority of the filaments exhibit negative and positive tilt angles in the northern and the southern hemispheres, respectively, strongly suggesting that their formation is governed by the overall large-scale magnetic field distribution on the solar photosphere and not by the small-scale intra-active region magnetic field configurations. We also investigate the hemispheric asymmetry in filaments, PILs, and coronal holes. We find that the hemispheric asymmetry in filaments and PILs is positively correlated with sunspot area asymmetry, whereas coronal hole asymmetry is uncorrelated.

Sunspot Positions and Areas from Observations by Pierre Gassendi

Solar activity behaviour on the eve of the Maunder minimum may provide important information on the period of further suppression of sunspot population. We analyse sunspot positions and areas in the 1630s extracted from rare drawings published by Pierre Gassendi in Opera Omnia. This work was published in two different editions, the first in Lyon and the second almost 70 years later in Florence. The drawings published in Lyon are found to be slightly different from those published in Florence, which produces a discrepancy in the position of spots of a few degrees, while sunspot group areas may differ by a factor of two. We reveal that the orientation of the drawings in the book is not always the same as might be seen in the telescope. We conjecture that the time of Gassendi’s observations covers the beginning of a new Schwabe cycle in the southern hemisphere. The differential rotation rate in the 1630s is also assessed and discussed.

Sunspot Catalogue of the Observatory of the University of Coimbra (1929 – 1941)

A sunspot catalogue was published by the Coimbra Astronomical Observatory (Portugal), now named Geophysical and Astronomical Observatory of the University of Coimbra, for the period 1929-1941. We digitalized data included in that catalogue and provide a machine-readable version. We show the reconstructions for the (total and hemispheric) sunspot number index and sunspot area according to this catalogue, comparing it with the sunspot number index (version 2) and Balmaceda sunspot area series (Balmaceda et al., J. Geophys. Res. 114, A07104, 2009). Moreover, we also compared the Coimbra catalogue with records made at the Royal Greenwich Observatory. The results demonstrate that the historical catalogue compiled by the Coimbra Astronomical Observatory contain reliable sunspot data and therefore can be considered for studies about solar activity.

Reanalysis of Solar Observing Optical Network Sunspot Areas

We address recent concerns that the sunspot-area measurements performed by the United States Air Force (USAF) Solar Observing Optical Network (SOON) have been underestimating sunspot areas. We examine briefly the history of SOON, and we perform an analysis of a three-decade time series of SOON measurements. By remeasuring USAF sunspot areas, we find that sunspot areas are being underestimated by between 8% and 17% due to the measuring techniques employed by SOON analysts. In particular, the SOON practice of rounding down limb-area correction factors results in some individual regions having areas reported by up to 50% less than their true values. This does not, however, account for the full discrepancy in sunspot areas between SOON and other observatories, which, in recent years, may be as high as a 50% discrepancy.

Stable Sunspot Area Level of Debrecen Photoheliographic Data and Multivariate Correction Factor of SOON Data

We investigate the spatial and temporal variation of sunspot group areas reported by the Greenwich Photoheliographic Results (GPR), the Solar Optical Observing Network (SOON), the Kislovodsk Mountain Astronomical Station (KMAS), and the Debrecen Photoheliographic Data (DPD) databases. We identify improved correction factors for reconciling these individual records to a common scale. Our results show that the DPD sunspot group areas are stable over the studied interval (1974 – 2014). We find an improved fit between GPR and DPD sunspot group areas when using a correction factor such that $\mathrm{GPR} = 0.975(\pm 0.006) \times \mathrm{DPD}$ , independent of the position of the sunspot group on the solar disk. We also find that the scale of KMAS sunspot group areas fits that of DPD well, but has a small position-dependent trend near the limb. However, in order to set SOON sunspot group area records onto the scale of DPD, we find that there is a need for a multivariate correction factor. This multivariate correction factor has a value ranging between 1.1 and 1.9 and is dependent upon the time of the SOON observation, the distance of the group from disk center, and the observatory within the SOON network. Finally, we provide further context to the systematic bias in SOON sunspot group area observations toward lower values relative to those recorded in the GPR and DPD databases that has previously been reported in the literature. We have identified the two main contributors to the SOON area deficit; some penumbral parts are unobserved, and the spot areas are underestimated. Our analysis is vital for studies that require stable, long-term solar activity records such as solar irradiance models that estimate irradiance reduction from records of sunspot group numbers, areas, and locations.

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.

Do Solar Cycles Share Spectral Properties with Tropical Cyclones that Occur in the Western North Pacific Ocean?

Understanding solar influences on extreme weather is important. Insight into the causes of extreme weather events, including the solar-terrestrial connection, would allow better preparation for these events and help minimize the damage caused by disasters that threaten the human population. In this study, we examined category three, four, and five tropical cyclones that occurred in the western North Pacific Ocean from 1977 to 2016. We compared long-term trends in the positions of tropical cyclone occurrence and development with variations of the observed sunspot area, the solar North-South asymmetry, and the southern oscillation index (SOI). We found that tropical cyclones formed, had their maximum intensity, and terminated more northward in latitude and more westward in longitude over the period analyzed; they also became stronger during that period. It was found that tropical cyclones cannot be correlated or anti-correlated with the solar cycle. No evidence showing that properties (including positions of occurrence/development and other characteristics) of tropical cyclones are modulated by solar activity was found, at least not in terms of a spectral analysis using the wavelet transform method.

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.

Sunspot Observations Made by Hallaschka During the Dalton Minimum

We present and analyse the sunspot observations performed by Franz I. C. Hallaschka in 1814 and 1816. These solar observations were carried out during the so-called Dalton minimum, around the maximum phase of the Solar Cycle 6. These records are very valuable because they allow us to complete observational gaps in the collection of sunspot group numbers, improving its coverage for this epoch. We have analysed and compared the observations made by Hallaschka with the records made by other contemporary observers. Unfortunately, the analysis of the sunspot areas and positions showed that they are too inaccurate for scientific use. But, we conclude that sunspot counts made by Hallaschka are similar to those made by other astronomers of that time. The observations by Hallaschka confirm a low level of the solar activity during the Dalton minimum.

Solar activity simulation and forecast with a flux-transport dynamo

We present the assessment of a diffusion-dominated mean field axisymmetric dynamo model in reproducing historical solar activity and forecast for solar cycle 25. Previous studies point to the Sun's polar magnetic field as an important proxy for solar activity prediction. Extended research using this proxy has been impeded by reduced observational data record only available from 1976. However, there is a recognised need for a solar dynamo model with ample verification over various activity scenarios to improve theoretical standards. The present study aims to explore the use of helioseismology data and reconstructed solar polar magnetic field, to foster the development of robust solar activity forecasts. The research is based on observationally inferred differential rotation morphology, as well as observed and reconstructed polar field using artificial neural network methods via the hemispheric sunspot areas record. Results show consistent reproduction of historical solar activity trends with enhanced results by introducing a precursor rise time coefficient. A weak solar cycle 25, with slow rise time and maximum activity $-14.4 \%$ ($\pm 19.5\%$) with respect to the current cycle 24 is predicted.

A Numerical Simulation Approach for Sunspot Area Calculation

A Numerical Simulation Approach for Sunspot Area Calculation

A Numerical Simulation Approach for Sunspot Area Calculation

The aim of this paper is the numerical simulation of the sunspot area (SSA) and its location on the walls and on the floor of a room with a single window facing south. The input parameters of the calculation code are the geometry of the cell located in the site of Ksar Challala (35.1 N, 2.19 E, 800 m) in Algeria for the 21st of March, June and December. The SSA is a function of the window’s area, the date and time, the orientation of the room, the altitude and the azimuth of the sun. The obtained results show that the western wall is affected by the sun in the morning, the eastern wall in the afternoon, the floor and the north wall in the middle of the day. By increasing the window area from 1 m2 to 2 m2 we found that the SSA increases considerably.

Periodic behaviour of coronal mass ejections, eruptive events, and solar activity proxies during solar cycles 23 and 24

We report on the parallel analysis of the periodic behaviour of coronal mass ejections (CMEs) based on 21 years [1996–2016] of observations with the SOHO/LASCO–C2 coronagraph, solar flares, prominences, and several proxies of solar activity. We consider values of the rates globally and whenever possible, distinguish solar hemispheres and solar cycles 23 and 24. Periodicities are investigated using both frequency (periodogram) and time-frequency (wavelet) analysis. We find that these different processes, in addition to following the ≈11-year Solar Cycle, exhibit diverse statistically significant oscillations with properties common to all solar, coronal, and heliospheric processes: variable periodicity, intermittence, asymmetric development in the northern and southern solar hemispheres, and largest amplitudes during the maximum phase of solar cycles, being more pronounced during solar cycle 23 than the weaker cycle 24. However, our analysis reveals an extremely complex and diverse situation. For instance, there exists very limited commonality for periods of less than one year. The few exceptions are the periods of 3.1–3.2 months found in the global occurrence rates of CMEs and in the sunspot area (SSA) and those of 5.9–6.1 months found in the northern hemisphere. Mid-range periods of ≈1 and ≈2 years are more wide spread among the studied processes, but exhibit a very distinct behaviour with the first one being present only in the northern hemisphere and the second one only in the southern hemisphere. These periodic behaviours likely results from the complexity of the underlying physical processes, prominently the emergence of magnetic flux.

Dependence of the Spring-Autumnal asymmetry in geomagnetic activity on the solar main dipole magnetic field polarity over last 140 years

Spring-Autumnal asymmetry (SA asymmetry) from years 1873–2010 in the geomagnetic activity is investigated based on the geomagnetic indices (aa, Ap and Kp). Results have shown that in general the SA asymmetry of the geomagnetic activity appears to be alternation, except for the interval during which the change of dominant solar dipole magnetic field polarity occurs. Our study implies that both the polarity of the main solar dipole field and the north-south asymmetry of the sunspot area in the two solar hemispheres control the strength of the south component (Bs) of the interplanetary magnetic field (IMF) near the Earth and the resulting SA asymmetry of the geomagnetic activity in the corresponding seasons. A simple sector structure model is devised to establish the relationship between the polarity of solar main dipole magnetic field, the IMF Bs component and the corresponding SA asymmetry in the geomagnetic activity. This is confirmed by examining the solar wind parameters from the spacecraft observations during the recent decades.