Complex Sunspot Groups Research Articles

The MODEST catalog of depth-dependent spatially coupled inversions of sunspots observed by Hinode/SOT-SP

We present a catalog that contains depth-dependent information about the atmospheric conditions inside sunspot groups of all types. The catalog, which we named MODEST, is currently composed of 944 observations of 117 individual active regions with sunspots and covers all types of features observed in the solar photosphere. We used the SPINOR-2D code to perform spatially coupled inversions of the Stokes profiles observed by Hinode/SOT-SP at high spatial resolution. SPINOR-2D accounts for the unavoidable degradation of the spatial information due to the point spread function of the telescope. The sunspot sample focuses on complex sunspot groups, but simple sunspots are also part of the catalog for completeness. Sunspots were observed from 2006 to 2019, covering parts of solar cycles 23 and 24. The catalog is a living resource, as with time, more sunspot groups will be included.

Sunspot Rotation in High- and Low-Flaring Active Regions

Sunspot rotations are closely linked with flaring activity. They are thought to contribute to the accumulation of helicity in magnetic flux tubes and to triggering magnetic reconnection in large solar flares. This link to solar flares has led to sunspot rotations being used as a parameter in solar flare prediction methods, but analysis for long-period observations of rotations in the literature is scarce. In this study, the rotation profiles of sunspots in a selection of six active regions are studied over time periods of 5 – 10 days to measure how sunspot rotation varies as active regions develop. The active regions are divided into two categories: high-flaring groups, which produced at least one X-class flare, and low-flaring regions that had little flaring activity. Comparison of the rotation profiles in these regions showed that young complex sunspot groups exhibit faster angular velocities and more frequent changes in rotation than older single-spot groups and, although the most rotating groups were also the most flare-productive, sudden changes in rotation were found to not definitively indicate an imminent eruption.

Cyclical Behavior of Magnetically Complex Sunspot Groups and Major Flares in Solar Cycles 22 – 24

Cyclical Behavior of Magnetically Complex Sunspot Groups and Major Flares in Solar Cycles 22 – 24

Curious Changes in Association of Complex Sunspot Groups with X-Ray Flares (≥M1) in Solar Cycles 22–24

Abstract We investigate the variations in the probabilities of complex sunspot groups (SGs)—large, asymmetric, or δ-type SGs—producing X-ray flares (≥M 1) in solar cycles (SCs) 22, 23, and 24 based on the SG data collected by the United States Air Force/Mount Wilson Observatory and the flare data recorded by Geostationary Operational Environmental Satellites. The following are the main findings. (1) For complex SGs in the whole disk as well as the northern and southern hemispheres during SC 22, their numbers and probabilities of producing flares change almost synchronously. (2) For complex SGs during SC 23, probabilities of producing flares during the early declining phase in the whole disk do not decrease with decreasing complex SG number; in the northern hemisphere, the probability of producing flares during the declining phase is significantly higher than that during the maximum phase; in the southern hemisphere, there is no definite variation trend in the probabilities of producing flares during the maximum and declining phases. (3) For complex SGs during SC 24, the probabilities of producing flares during the later rising and early declining phases are significantly higher than or comparable to those during the maximum phase no matter how their numbers change; in the northern hemisphere, the probability of producing flares during the rising phase is significantly higher than or at least comparable to that during the maximum phase; in the southern hemisphere, there is no definite variation trend in the probabilities of producing flares during the maximum and declining phases.

Deep Learning for Automatic Recognition of Magnetic Type in Sunspot Groups

Sunspots are darker areas on the Sun’s photosphere and most of solar eruptions occur in complex sunspot groups. The Mount Wilson classification scheme describes the spatial distribution of magnetic polarities in sunspot groups, which plays an important role in forecasting solar flares. With the rapid accumulation of solar observation data, automatic recognition of magnetic type in sunspot groups is imperative for prompt solar eruption forecast. We present in this study, based on the SDO/HMI SHARP data taken during the time interval 2010-2017, an automatic procedure for the recognition of the predefined magnetic types in sunspot groups utilizing a convolutional neural network (CNN) method. Three different models (A, B, and C) take magnetograms, continuum images, and the two-channel pictures as input, respectively. The results show that CNN has a productive performance in identification of the magnetic types in solar active regions (ARs). The best recognition result emerges when continuum images are used as input data solely, and the total accuracy exceeds 95%, for which the recognition accuracy of Alpha type reaches 98% while the accuracy for Beta type is slightly lower but maintains above 88%.

Automatic Detection of Magnetic δ $\delta$ in Sunspot Groups

Large and magnetically complex sunspot groups are known to be associated with flares. To date, the Mount Wilson scheme has been used to classify sunspot groups based on their morphological and magnetic properties. The most flare prolific class, the delta sunspot-group, is characterised by opposite polarity umbrae within a common penumbra, separated by less than 2 degrees. In this article, we present a new system, called the Solar Monitor Active Region Tracker - Delta Finder (SMART-DF), that can be used to automatically detect and classify magnetic deltas in near-realtime. Using continuum images and magnetograms from the Helioseismic and Magnetic Imager (HMI) onboard NASA's Solar Dynamics Observatory (SDO), we first estimate distances between opposite polarity umbrae. Opposite polarity pairs having distances of less that 2 degrees are then identified, and if these pairs are found to share a common penumbra, they are identified as a magnetic delta configuration. The algorithm was compared to manual delta detections reported by the Space Weather Prediction Center (SWPC), operated by the National Oceanic and Atmospheric Administration (NOAA). SMART-DF detected 21 out of 23 active regions (ARs) that were marked as delta spots by NOAA during 2011 - 2012 (within +/- 60 degrees longitude). SMART-DF in addition detected five ARs which were not announced as delta spots by NOAA. The near-relatime operation of SMART-DF resulted in many deltas being identified in advance of NOAA's daily notification. SMART-DF will be integrated with SolarMonitor (www.solarmonitor.org) and the near-realtime information will be available to the public.

TOWARD RELIABLE BENCHMARKING OF SOLAR FLARE FORECASTING METHODS

Solar flares occur in complex sunspot groups, but it remains unclear how the probability of producing a flare of a given magnitude relates to the characteristics of the sunspot group. Here, we use Geostationary Operational Environmental Satellite X-ray flares and McIntosh group classifications from solar cycles 21 and 22 to calculate average flare rates for each McIntosh class and use these to determine Poisson probabilities for different flare magnitudes. Forecast verification measures are studied to find optimum thresholds to convert Poisson flare probabilities into yes/no predictions of cycle 23 flares. A case is presented to adopt the true skill statistic (TSS) as a standard for forecast comparison over the commonly used Heidke skill score (HSS). In predicting flares over 24 hr, the maximum values of TSS achieved are 0.44 (C-class), 0.53 (M-class), 0.74 (X-class), 0.54 (>=M1.0), and 0.46 (>=C1.0). The maximum values of HSS are 0.38 (C-class), 0.27 (M-class), 0.14 (X-class), 0.28 (>=M1.0), and 0.41 (>=C1.0). These show that Poisson probabilities perform comparably to some more complex prediction systems, but the overall inaccuracy highlights the problem with using average values to represent flaring rate distributions.

An Analysis of the Sunspot Groups and Flares of Solar Cycle 23

Designing a statistical solar flare forecasting technique can benefit greatly from knowledge of the flare frequency of occurrence with respect to sunspot groups. This study analyzed sunspot groups and Hα and X-ray flares reported for the period 1997 – 2007. Annual catalogs were constructed, listing the days that numbered sunspot groups were observed (designated sunspot group-days, SSG-Ds) and for each day a record for each associated Hα flare of importance category one or greater and normal or bright brightness and for each X-ray flare of intensity C 5 or higher. The catalogs were then analyzed to produce frequency distributions of SSG-Ds by year, sunspot group class, likelihood of producing at least one flare overall and by sunspot group class, and frequency of occurrence of numbers of flares per day and flare intensity category. Only 3% of SSG-Ds produced a substantial Hα flare and 7% had a significant X-ray flare. We found that mature, complex sunspot groups were more likely than simple sunspot groups to produce a flare, but the latter were more prevalent than the former. More than half of the SSG-Ds with flares had a maximum intensity flare greater than the lowest category (C-class of intensity five and higher). The fact that certain sunspot group classes had flaring probabilities significantly higher than the combined probabilities of the intensity categories when all SSG-Ds were considered suggest that it might be best to first predict the flaring probability. For sunspot groups found likely to flare, a separate diagnosis of maximum flare intensity category appears feasible.

The solar dynamo in the light of the distribution of various sunspot magnetic classes over butterfly diagram

AbstractWe present the data concerning the distribution of various sunspot magnetic classes over the solar butterfly diagram and discuss how this data can inform solar dynamo models. We use the statistics of sunspots that violate the Hale polarity law to estimate the ratio of the fluctuating and mean components of the toroidal magnetic field inside the solar convective zone. An analysis of the spatial distribution of bipolar, unipolar and complex sunspot groups in the context of simple dynamo models results in the conclusion that the mean toroidal field is relatively simple and maintains its shape during the course of the solar cycle (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Periodical patterns in major flare occurrence and their relation to magnetically complex active regions

Abstract A periodical occurrence rate of major solar flares (observed in hard X-rays) of ∼24 days (synodic) was first reported by Bai (1987) [Bai, T. Distribution of flares on the sun – superactive regions and active zones of 1980–1985. ApJ 314, 795–807, 1987] for the years 1980–1985. Here, we report a significant relation between the appearance of the 24-day period in major Hα flares and magnetically complex sunspot groups (i.e., including a γ and/or δ configuration). From synoptic maps of magnetograms (NSO/KP) patterns in the magnetic flux evolution are traced which might be the cause of the 24-day period observed in flare activity.

The Influence of the Evolution of Sunspot Groups on the Determination of the Solar Velocity Field

Meridional motions and differential rotation of stable recurrent sunspot groups from the Greenwich data set are investigated. Simple and complex, as well as younger and older sunspot groups are treated separately. There is no difference in behavior of the meridional motions for the simple and complex sunspot groups, while complex groups rotate faster than the simple ones. If we attribute the differences of rotational velocities to the errors in position determination, it can be concluded that the rotational velocities determined by using sunspot groups as tracers are slightly overestimated. Both the meridional motions and differential rotation show the same dependence on the age, when simple and complex recurrent sunspot groups are considered.

On the 24-day period observed in solar flare occurrence

Time series of daily numbers of solar Hα flares from 1955 to 1997 are studied by means of wavelet power spectra with regard to predominant periods in the range of ∼ 24 days (synodic). A 24-day period was first reported by Bai (1987) for the occurrence rate of hard X-ray flares during 1980–1985. Considering the northern and southern hemisphere separately, we find that the 24-day period is not an isolated phenomenon but occurs in each of the four solar cycles investigated (No. 19–22). The 24-day period can be established also in the occurrence rate of subflares but occurs more prominently in major flares (importance classes ≥ 1). A comparative analysis of magnetically classified active regions subdivided into magnetically complex (i.e., including a γ and/or δ configuration) and non-complex (α, β) reveals a significant relation between the appearance of the 24-day period in Hα flares and magnetically complex sunspot groups, whereas it cannot be established for non-complex groups. It is suggested that the 24-day period in solar flare occurrence is related to a periodic emergence of new magnetic flux rather than to the surface rotation of sunspots.

On Novel Methods to Determine Areas of Sunspots from Photoheliograms

Two novel methods of measuring umbral and penumbral areas of sunspots and of complex sunspot groups are described. Both methods comprise the digitization of photoheliograms by a frame grabber and the computation of intensity histograms of selected areas of activity. The first method, called ‘cumulative histogram method’, in principle determines the intensity boundaries umbra–penumbra and penumbra–photosphere from the intersections of linear fits into the corresponding parts of the cumulative histograms of sunspots. The second method, called ‘maximum gradient method’, marks image pixels of a given intensity level ±2 units wide as a white isophote on a display. Interactive variation of this level makes it easy to visually select the contour line fitting the boundary penumbra–photosphere (or umbra–penumbra) best. At the same level usually the width of the contour line is smallest. In both cases the summation of the pixel numbers above the corresponding intensity levels yields the umbral and the total sunspot areas, respectively. Some limitations of the two methods are discussed.

Assessing the magnetic reconnection paradigm

The hypothesis of magnetic reconnection was originally proposed as an attempt to explain solar flares. Solar flares dissipate as much as 1029 erg/s in about 30 min, the total consumed energy being ∼1032 erg. Since there was no obvious phenomenon that could be identified as the power supply process, it was assumed that the necessary energy was stored prior to flare onset and was then released and dissipated very rapidly.Since solar flares tend to occur near complex sunspot groups, it was hypothesized that the necessary energy was stored as magnetic energy. The hypothesis of magnetic reconnection was introduced as the process that spontaneously converts the stored magnetic energy for flare processes. Thus it was hypothesized that to provide as much as 1029 erg/s, the process must also be explosive.

Narrow lanes of transverse magnetic field in sunspots

Solar flares are closely associated with magnetic activity on the surface of the Sun. They typically occur in complex sunspot groups, where the vertical magnetic fields reverse abruptly, and the horizontal (transverse) fields connecting the vertical poles are both sheared and strong. A single field inversion line may be the site of many flares. Here we report observations of a large, active sunspot group which reveal a series of oppositely directed vertical-field inversions separated by extremely narrow elongated channels of intense horizontal fields. In a minimum-energy configuration, lines of force connecting oppositely directed vertical fields simply arch across the inversion line; but when newly emerged sunspots move through older magnetic-field configurations, the poles are pushed together and the field lines turn sharply along the inversion line to reconnect with the vertical field some distance away. These multiple channels of horizontal field imply a large curl term (▿×B), and hence a substantial electric current. Our observations show that almost all of the larger flares in this region occur in these highly convoluted fields.

The white-light solar flare of March 27, 1991

A white-light-flare (WLF) was recorded on March 27, 1991 at Tashkent. The WLF occurred at the penumbra of a large, complex sunspot group. The energy released by the WLF per unit time was 2.4 × 1028 erg s-1.

Periodicities of solar irradiance and solar activity indices, I

Using a standard FFT time series analysis, our results show an 8–11 months periodicity in the solar total and UV irradiances, 10.7 cm radio flux, Ca-K plage index, and sunspot blocking function. The physical origin of this period is not known, but the evidence in the results exclude the possibility that the observed period is a harmonic due to the FFT transform or detrending. Periods at 150–157 and 51 days are found in those solar data which are related to strong magnetic fields. The 51-day period is the dominant period in the projected areas of developing complex sunspot groups, but it is missing from the old decaying sunspot areas. This evidence suggests that the 51-day period is related to the emergence of new magnetic fields. A strong 13.5-day period is found in the total irradiance and projected areas of developing complex groups. This confirms those results (e.g., Donnelly et al., 1983, 1984; Bai, 1987, 1989) which show that ‘active centers’ are located 180 deg apart from each other.

Effects of the March 1989 solar activity

On Monday, March 6, 1989, a very large and complex sunspot group, Region 5395, rotated into view around the east limb of the Sun and quickly gained attention when it produced an X15/3B flare (N35, E69). The event began a period of high solar activity that lasted two weeks and had many important consequences at Earth and in near‐Earth space.From March 6–19, Region 5395 produced 11 X‐class and 48 M‐class X ray flares. Prolonged proton events occurred that lasted several days and had an unusually high proportion of lower‐energy particles. The solar activity produced an historically “great” magnetic storm, long‐lasting Polar Cap Absorption events, and a major Forbush decrease, which is a decrease of the galactic cosmic ray flux observed at Earth. The ionosphere was greatly disturbed.

Solar irradiance variability

The solar “constant” varies over time scales from minutes to years and decades. For the influence on the atmospheric energy budget time scales longer than a few days become important, for climate research information over years to decades is needed. From direct measurements of the solar “constant” during the last 10 years, by e.g. the ACRIM experiment on the Solar Maximum Mission satellite (SMM), one indeed becomes aware of substantial changes on time scales longer than days. The most important influences seem to be related to solar activity. Results from a multi-variate spectral analysis to investigate the influence of sunspots and bright magnetic elements on the total solar irradiance during 1980 and in 1984/85 show that for periods up to about 100 days, most of the power in the spectrum of the ACRIM irradiance variance is explained by the effect of the complex sunspot groups showing new activity. The correlation with old sunspots is much lower. In 1984/85, near the solar minimum, around the 27 days rotational period of the sun the greatest part of the ACRIM irradiance power spectrum is related to the enhanced UV flux, which indicates that during the solar minimum, when only a few active regions are on the sun, the main contribution to the irradiance variation arises from the active network. After eliminating the effect of sunspots and bright magnetic elements from the irradiance power spectrum, there are still peaks around 9 and 27 days. This indicates that global effects not related to the solar activity produce irradiance variations, which may be modulated by the same mechanism as that producing solar activity. The same record of the total solar irradiance shows long-term variations over the last 8 years, which are related to the activity cycle and show a difference between the maximum in 1980 and the minimum in 1986 of 0.08% with the irradiance being higher during the solar maximum. Model calculations using these directly measured values as calibration and taking into account the influence of the excess radiation from bright magnetic elements and of the dark spots are used to extend the record back to 1954. The results are also compared with measurements in the late sixties, which were obviously of much less accuracy, but can be compared at least qualitatively with the model predictions. They show also how variable the influence of the activity on the irradiance is from the cycle to cycle.

An empirical basis for the ?alternative interpretation? of Sawyer et al

An analysis of the data of Achong and Stahl (1984) discloses discrete intervals which differ significantly in SID flare incidence and the proportion of complex sunspot groups present. This supports the alternative interpretation of Sawyer et al. (1985) in respect of the strong dependence of SID flare production on complex magnetic class.