Sunspot Number Research Articles

Deciphering solar magnetic activity: The (solar) hale cycle terminator of 2021

We previously identified an event in the solar timeline that appeared to play a role in how sunspot Cycle 23 (SC23) transitioned into sunspot Cycle 24 (SC24). The timeframe for this transition was rapid, taking place over a very short time and perhaps in a time as short as a single solar rotation. Further, we inferred that the transition observed was a critical moment for the Sun’s global-scale magnetic field as it was being manifest in the spatially and temporally overlapping magnetic systems belonging to the Sun’s 22-year (Hale) magnetic cycle. These events have been dubbed as Hale Cycle terminations, or ‘terminators’ for short. Subsequent exploration of the sunspot record revealed a relationship between terminator separation (as a measure of overlap in the Hale Cycles) and the upcoming sunspot cycle amplitude using a Hilbert transform. Finally, we extrapolated the contemporary sunspots data’s Hilbert phase function to project the occurrence of the SC24 terminator in Mid-2020 and inferred that this would result in a large sunspot Cycle 25 (SC25) amplitude. This paper presents observational evidence that the end of SC24 and the initial growth of SC25 followed a terminator that occurred in mid-December 2021 (approximately 12/13/2021). Using this December 2021 terminator identification we can finalize our earlier preliminary forecast of SC25 amplitude - anticipating a peak total monthly sunspot number of 184±17 with 68% confidence, and 184±63 with 95% confidence. Finally, we use other terminator-related superposed epoch analyses developed in parallel work we project the timing of SC25 sunspot maximum to occur between late 2023 to mid 2024.

The Solar Chromosphere as Induction Disk and The Inverse Joule-Thomson Effect

The connection between nuclear fusion in the Sun’s core and solar irradiance is obscured among other things by uncertainty over the mechanism of coronal heating. Data for solar wind density and velocity, sunspot number, and EUV flux suggest that electromagnetic energy from the Sun’s convection zone is converted by induction through the chromosphere into thermal energy. The helium and hydrogen mixture exhaled by the Sun is then heated by the inverse Joule-Thomson effect when it expands via the corona into space. The almost complete shutdown of the solar wind on 10-11 May 1999 demonstrated that its velocity is a more faithful indicator of solar activity than are sunspots as it reflects short-term variations in coronal heating rather than quasicyclical fluctuations in the Sun’s magnetism. Its reconstruction from the cosmic ray flux using isotopes spanning over 800,000 yr should therefore benefit the analysis and long-term forecasting of Earth and space weather

The possible impact of solar activity on the summer temperature distribution over Eurasia

The effect of solar activity on the regional temperature in winter has been widely discussed. However, whether the summer temperature of land in the northern hemisphere is sensitive to solar activity remains to be further investigated. In this study, the empirical orthogonal function (EOF) analysis, spectrum analysis, and correlation analysis are employed to reveal the possible link between the summer temperature distribution over Eurasian land (0–180°E and 20°N−80°N) and solar activity. The results show that the corresponding time series of the second pattern significantly exhibits an 11-year solar periodicity. Its tripolar temperature distribution is similar to the correlation maps between the temperature and sunspot number (SSN). Particularly, Central Asia (50°E−90°E and 30°N−60°N) is the key response region over Eurasia. The temperature of Central Asia shows a weak but significant negative correlation with SSN. Further analysis of atmospheric circulation indicates that the solar-induced cyclonic and negative geopotential height anomalies in Central Asia weaken the high-pressure ridge on the southwest side and strengthen northwesterly winds. At the same time, with the increase in the cloud cover and the decrease of shortwave radiation, the temperature is lowered. Due to the impact of solar activity, the upper atmosphere over Eurasia forms a wave train-like structure, resulting in a tripolar temperature distribution pattern. On the other hand, the 21-year sliding correlation results suggest that the connection between solar activity and the temperature in Central Asia was strong and decadal stable until 1980. Whereas the temperature and atmospheric circulations in high latitudes become more sensitive to solar activity after 1980. Anyway, solar activity still can be considered a non-negligible factor in the prediction of the summer temperature in Eurasia.

Influence of the solar activity on the background of a high-resolution gamma-ray spectrometer

The count rate in the peak of a gamma-ray spectrum at 2223 keV was measured over a period of 25 years. The peak is produced by neutron capture on hydrogen, a constituent of the spectrometer's shield. Since the neutrons are produced by cosmic rays, the count rate in the peak is correlated with the solar activity via the interaction between the solar wind and the cosmic rays. The correlation between the total daily number of sunspots, as a measure of the solar activity, and the count rate in the peak was investigated as a function of the time shift between the time dependence of the count rate in the peak and the time dependence of the total daily number of sunspots. Variations of the correlation coefficient as a function of the shift are discussed in terms of phenomena occurring on the surface of the Sun. The variations indicate a long-term correlation, corresponding to the 11-year solar cycle, and a short-term correlation, corresponding to the sunspots.

Lagged response of summer precipitation to solar activity in the mid-lower reaches of the Yangtze River

In the context of more frequent extreme precipitation worldwide, the Sun’s influence on global or regional rainfall patterns has attracted much attention. Due to its vital importance to Chinese industrial and agricultural production, the precipitation property in the mid-lower reaches of the Yangtze River (MLRYR) remains a hot issue. Although previous works have implied the plausible influence of solar activity on precipitation in the mid-lower reaches of the Yangtze River, the time-lagged effect is still an open question. In this paper, we adopt the China-Z index (CZI) to represent the original precipitation data, which is proposed to monitor moisture conditions over China and is more sensitive to solar activity. We explore the lagged correlations between summer precipitation in the mid-lower reaches of the Yangtze River and solar activity. The China-Z index in June-July is negatively correlated with the sunspot number in July of the preceding year, giving a time lag of 11 months. Based on the composite analysis, we suggest that solar activity possibly modulates the precipitation by influencing the local moisture and its vertical movement through the sea-land thermal contrast and the associated East Asian summer monsoon on a much larger scale.

Introducing a design procedure for Archimedes Screw Turbine based on optimization algorithm

Archimedes screw turbines have gained popularity in generating power from flowing water. One aspect that hasn't been considered yet is optimizing those parameters that are considered assumptions in the prediction models. In this research, a simple procedure was introduced to design an appropriate Archimedes screw turbine for a given site using a prediction model and an optimization model. First, the mathematical efficiency prediction model of Archimedes screw turbines was developed and validated with experimental and real-world Archimedes screw turbine data. Then, the grey wolves optimization algorithm was developed to be used as an actual engineering application, sensitively analyzed, and coupled with the prediction model. The prediction models were evaluated. The model convergence was investigated, and then, the optimization parameters were found to get maximum efficiency. The results revealed that the optimum number of iterations and grey wolves are 200 and five, respectively. Also, the best values for the inner diameter to the outer diameter ratio, the pitch to the outer diameter ratio, tilt angle, and blade number were found in ranges: 0.43–0.56, 1–1.2, 20–22.5, and 2–4, respectively.

Rediscovering the observations of solar prominences from 1906 to 1957 recorded at the Madrid Astronomical Observatory

The Madrid Astronomical Observatory implemented a solar observation program from 1876 to 1986. In addition to sunspots, the observers at this observatory recorded other solar features such as prominences. In this work, we have consulted the documentary sources of the Madrid Astronomical Observatory (the information is not digitally available), digitized the records of the observers on the annual number of prominences, and constructed a homogeneous series of the total and hemispheric annual number of prominences with heights of 25″ and more for the period 1906–1957. To evaluate the quality of the data and assess their potential, we have compared the Madrid prominence series with the number of prominences recorded by the Astronomical Observatory of the University of Coimbra and other time series such as the sunspot number index, solar radio flux at 10.7 cm, and sunspot areas. We have also analyzed the hemispheric prominence numbers and the asymmetry index. We obtained the strongest correlation between Madrid and Coimbra prominence series (r = 0.7), whereas the correlations between the Madrid prominence series and the other solar activity time series are similar (r ≈ 0.6). In addition, we found that the correlation coefficient between the Madrid prominence series and the sunspot number is lower than that from the Coimbra prominence series and the sunspot number. We suggest that these differences are a consequence of the way prominences were counted in the Madrid Astronomical Observatory.

Exploring the Temporal Variation of the Solar Quadrupole Moment J 2

Recently, Rozelot & Eren pointed out that the first solar gravitational moment (J 2) might exhibit a temporal variation. The suggested explanation is through the temporal variation of the solar rotation with latitude. This issue is deeper developed due to an accurate knowledge of the long-term variations in solar differential rotation regarding solar activity. Here we analyze solar cycles 12–24, investigating the long-term temporal variations in solar differential rotation. It is shown that J 2 exhibits a net modulation over the 13 studied cycles of ≈(89.6 ± 0.1) yr, with a peak-to-peak amplitude of ≈0.1 × 10−7 for a reference value of 2.07 × 10−7). Moreover, J 2 exhibits a positive linear trend in the period of minima solar activity (sunspot number up to around 40) and a marked declining trend in the period of maxima (sunspot number above 50). In absolute magnitude, the mean value of J 2 is more significant during periods of minimum than in periods of maximum. These findings are based on observational results that are not free of errors and can be refined further by considering torsional oscillations for example. They are comforted by identifying a periodic variation of the J 2 term evidenced through the analysis of the perihelion precession of planetary orbits either deduced from ephemerides or computed in the solar equatorial coordinate system instead of the ecliptic coordinate one usually used.

Occurrences of different types of Solar Flares with Sunspot number during solar cycle 23-25

Occurrences of different types of Solar Flares with Sunspot number during solar cycle 23-25

Forecasting solar energetic proton integral fluxes with bi-directional long short-term memory neural networks

Solar energetic particles are mainly protons and originate from the Sun during solar flares or coronal shock waves. Forecasting the Solar Energetic Protons (SEP) flux is critical for several operational sectors, such as communication and navigation systems, space exploration missions, and aviation flights, as the hazardous radiation may endanger astronauts’, aviation crew, and passengers’ health, the delicate electronic components of satellites, space stations, and ground power stations. Therefore, the prediction of the SEP flux is of high importance to our lives and may help mitigate the negative impacts of one of the serious space weather transient phenomena on the near-Earth space environment. Numerous SEP prediction models are being developed with a variety of approaches, such as empirical models, probabilistic models, physics-based models, and AI-based models. In this work, we use the bidirectional long short-term memory (BiLSTM) neural network model architecture to train SEP forecasting models for three standard integral GOES channels (>10 MeV, >30 MeV, >60 MeV) with three forecast windows (1-day, 2-day, and 3-day ahead) based on daily data obtained from the OMNIWeb database from 1976 to 2019. As the SEP variability is modulated by the solar cycle, we select input parameters that capture the short-term, typically within a span of a few hours, and long-term, typically spanning several days, fluctuations in solar activity. We take the F10.7 index, the sunspot number, the time series of the logarithm of the X-ray flux, the solar wind speed, and the average strength of the interplanetary magnetic field as input parameters to our model. The results are validated with an out-of-sample testing set and benchmarked with other types of models.

Karl von Lindener’s sunspot observations during 1800–1827: Another long-term dataset for the Dalton Minimum

On a centennial timescale, solar activity oscillates quasi-periodically and also tends to occasionally get into a low-activity period. The Dalton Minimum (circa 1790s–1820s) was one of such low-activity periods that had been captured in telescopic sunspot observations. However, it has been challenging to analyse the Dalton Minimum, as contemporary source records remained mostly unpublished and almost inaccessible to the scientific community. Recent studies have established reliable datasets for sunspot group number, sunspot number, and sunspot positions. This study further analyzes independent Silesian sunspot observations from 1800 to 1827 in a manuscript from the Library of Wrocław University (Ms AKC.1985/15) and complements it with the metadata for the observer: Karl Christian Reinhold von Lindener. We identified 547 days of sunspot observations in these records and derived the sunspot group number, individual sunspot number, and sunspot positions between 1800 and 1827. The results of this study have significantly revised von Lindener’s sunspot group number, which was previously known for only 517 days in scientific databases, and removed contamination from general descriptions. Using our results, we extended investigations into individual sunspot counts and derived their positions. In our analysis, we locate von Lindener’s sunspot positions in both solar hemispheres and contrast the Dalton Minimum with the Maunder Minimum, adding further independent credits to the previous results for Derfflinger’s and Prantner’s datasets. Sunspot positions are also slightly biased towards the northern solar hemisphere in early Solar Cycle 6 (1812–1813). The high-latitude sunspot positions indicate the onset of Solar Cycle 7 as early as June 1822.

Development of methods for analysing telemetry of small spacecraft using machine learning methods

This article explores the influence of some averaged planetary geomagnetic indices, as well as solar activity indexes (Dst, Kp, Ap and Wolf numbers) on small spacecraft systems. The global experience in the field of research is described, and various directions in which leading specialists work are analysed. Methods of data analysis using Python are also provided. The procedure of correlation between space weather data and telemetry data of small spacecraft at a single moment in time is carried out. At the end of the experiment, a conclusion is drawn on which specific indicators should be focused on. Suggestions for further research on this topic are also provided.

НЕЗВИЧАЙНА СОНЯЧНА АКТИВНА ОБЛАСТЬ NOAA 13088/13102

Background. Under certain conditions, deep fluctuating magnetic fields lead to violations of Hale’s and Joy’s laws of observed magnetism on the surface of the Sun. These magnetic fluctuations can be excited by two qualitatively different mechanisms of a small-scale dynamo. The first mechanism is a macroscopic MHD dynamo, while the second mechanism is a classical MHD diffusion dynamo. An important difference between the two mechanisms is the percentage of observed anti-Hale sunspot groups (relative to the total number of sunspots) in solar cycle minima. In the case of the first mechanism, the percentage of anti-Hale groups does not depend on the phase of the cycle, while the specified percentage associated with the second mechanism should reach its maximum value in solar minima. To separate the minor contributions of the two named sources of magnetic fluctuations, the researchers proposed a theoretical test based on statistical analysis of observational data over long periods of time (Sokoloff, & Khlystova, 2010). According to the proposed test, the percentage of anti-Hale groups of spots increases during the minima of the cycles, which indicates the favor of the diffusion dynamo. In order to confirm the dominant contribution of the diffusion dynamo to the surface magnetism, this work investigates a specific anomalous active region near the solar minimum. Methods. Macroscopic and classical MHD, which study the behavior of electromagnetic and hydrodynamic fields in turbulent plasma. Analysis of data from observations of the surface magnetism of the Sun. Results. We investigated the evolution of the NOAA 13088/13102 active region observed on August 24, 2022, shortly after the cycle 25 minimum. For the analysis, data from observations using instruments installed on board space observatories were used. A feature was revealed, which consists in the deviation of the surface magnetic configuration of this active region from Hale’s law of the magnetic polarity of groups of spots and Joy’s law of the inclination of the axes of bipolar groups to the latitudinal direction. In addition, it was established that the active region of NOAA 13088/13102 is characterized by rather high flare activity. Conclusions. We believe that the magnetic anomalies of the active region of NOAA 13088/13102 that we found were caused by the influence of magnetic fluctuations excited by the mechanism of the deep small-scale diffusion dynamo, since it is this source that gives the most noticeable contribution to the surface magnetism near the cycle minima. The detection and study of unusual anti-Hale’s AOs with increased eruptive activity, similar to NOAA 13088/13102, may find application in predicting periods of dangerous manifestations of space weather and in forecasting the dynamics of solar cycles.

Probing Climate Change in Greece with a 2m dish radio telescope

We study the effect of solar activity on the climate in Greece. We search for correlations between solar and terrestrial indicators. The solar proxies which are representative of the activity of our star include the number of sunspots, the intensity of solar radiation, the radio flux at 10.7cm and the galactic cosmic rays. Earth’s weather indicators include six parameters, temperature, relative air humidity, wind direction and intensity, atmospheric pressure and precipitation. The solar data span several years starting from 1975 to 2005, including decades-long variations. The meteorological data come from 12 stations located in various parts of Greece. The main part of the research is the unique experiment in Greece which aims to continuously monitor and record the solar radio flux at 10.7 cm using a 2m paraboloid radio telescope (the pilot project of the THERMOpYlae Hellenic radio telescope).

Periodicities in Solar Activity, Solar Radiation and Their Links with Terrestrial Environment

Solar magnetic activity is expressed via variations of sunspots and active regions varying on different timescales. The most accepted is an 11-year period supposedly induced by the electromagnetic solar dynamo mechanism. There are also some shorter or longer timescales detected: the biennial cycle (2 - 2.7 years), Gleisberg cycle (80 - 100 years), and Hallstatt’s cycle (2100 - 2300 years). Recently, using Principal Component Analysis (PCA) of the observed solar background magnetic field (SBMF), another period of 330 - 380 years, or Grand Solar Cycle (GSC), was derived from the summary curve of two eigenvectors of SBMF. In this paper, a spectral analysis of the averaged sunspot numbers, solar irradiance, and the summary curve of eigenvectors of SBMF was carried out using Morlet wavelet and Fourier transforms. We detect a 10.7-year cycle from the sunspots and modulus summary curve of eigenvectors as well a 22-year-cycle and the grand solar cycle of 342 - 350-years from the summary curve of eigenvectors. The Gleissberg centennial cycle is only detected on the full set of averaged sunspot numbers for 400 years or by adding a quadruple component to the summary curve of eigenvectors. Another period of 2200 - 2300 years is detected in the Holocene data of solar irradiance measured from the abundance of 14C isotope. This period was also confirmed with the period of about 2000 - 2100 years derived from a baseline of the solar background magnetic field, supposedly, caused by the solar inertial motion (SIM) induced by the gravitation of large planets. The implication of these findings for different deposition of solar radiation into the northern and southern hemispheres of the Earth caused by the combined effects of the solar activity and solar inertial motion on the terrestrial atmosphere is also discussed.

Prediction of even and odd sunspot cycles

Here we study the prediction of even and odd numbered sunspot cycles separately, thereby taking into account the Hale cyclicity of solar magnetism. We first show that the temporal evolution and shape of all sunspot cycles are extremely well-described by a simple parameterized mathematical expression. We find that the parameters describing even sunspot cycles can be predicted quite accurately using the sunspot number 41 months prior to sunspot minimum as a precursor. We find that the parameters of the odd cycles can be best predicted with maximum geomagnetic aa index close to the fall equinox within a 3-year window preceding the sunspot minimum. We use the found precursors to predict all previous sunspot cycles and evaluate the performance with a cross-validation methodology, which indicates that each past cycle is very accurately predicted. For the coming sunspot cycle 25 we predict an amplitude of 171 ± 23 and the end of the cycle in September 2029 ± 1.9 years. We are also able to make a rough prediction for cycle 26 based on the predicted cycle 25. While the uncertainty for the cycle amplitude is large we estimate that the cycle 26 will most likely be stronger than cycle 25. These results suggest an increasing trend in solar activity for the next decades.

Is there a link between the length of the solar cycle and Earth’s temperature?

The Sun provides most of external energy to Earth’s system and thus has the potential of influencing it. Various studies reported a correlation between the solar cycle length and the northern hemisphere temperatures on Earth. Here, we reassess the cycle length record by incorporating the newly revised and updated sunspot number series as well as plage area composite, before comparing it to Earth temperature records. We find that cycle length series constructed from sunspot and plage data exhibit the same behaviour, both showing a downward trend after 1940. Our results suggest that the agreement between solar cycle lengths and temperatures found earlier is an artefact of (1) some arbitrary choices made by those studies when constructing the cycle length series as well as (2) a rather short time interval, to which the analyses were restricted. When considering the entire period of reliable sunspot and temperature data, these records diverge before about 1870 and after 1960. We also find a poor agreement between Earth temperatures and cycle length when using plage areas instead of sunspot data to derive cycle lengths. Our result of the divergence between cycle length series and Earth’s temperature after 1960 implies that the cycle length cannot be used to support a solar origin for the warming on Earth over the last 5 decades.

Sunspot observations at Kawaguchi Science Museum: 1972 – 2013

AbstractIndividual sunspot observations have formed a ground basis of international sunspot number, a unique reference for long‐term solar variability in the centennial timescale. The original datasets were subjected to exploitations and analyses upon the recalibrations of the sunspot number series. In this context, this study reviewed and analysed original sunspot records and their databases in the Kawaguchi Science Museum (KSM) in Japan. KSM hosts sunspot drawings and logbooks from 1972 to 2013. This dataset has a longer chronological coverage than what was known to the scientific community (1981–2010). These records have been digitized and publicized in a museum database, which allows users to access individual sunspot drawings and numerical data in KSM logbooks. These records are highly homogeneous as a single observer's dataset (Hitoshi Takuma), who used a 15‐cm refractor at the Kawaguchi Juvenile Museum in 1972–2003 and a 20‐cm refractor at KSM in 2003–2013. We also reviewed the Takuma data series, his monthly observation days (21.3 days/month), sunspot number in the whole disk and each hemisphere, and sunspot positions in a butterfly diagram. We also assessed Takuma's data stability in comparison with the international sunspot number and reference datasets of the SILSO. Takuma's data appear stable until 2003, when he changed the observation site and instrument. His data stability was quantitatively compared with the SILSO reference datasets, confirming the substantial long‐term stability of the data and establishing its reliability as an alternative reference for sunspot number recalibration.

Sunspot activity influences tree growth: Molecular evidence and ecological implications.

Solar activity has a significant influence on Earth's climate and may drive many biological processes. Here, we measured growth in 11 tree species distributed along an ≈600-km latitudinal gradient in South-Central Chile, recording the width of their growth-rings among periods of maximum (highest number of sunspots) and minimum (lowest number of sunspots) solar activity. In one of these species, Quillaja saponaria, we experimentally assessed three ecophysiological traits (CO2 fixation through photosynthesis [Amax], growth and leaf production) as well as the expression of five genes related to cell wall elongation and expansion following exposure to high and low levels of UV-B radiation, simulating scenarios of maximum and minimum solar activity, respectively. We found lower tree growth during the periods of maximum solar activity, with this trend being more evident at lower latitudes, where UV-B radiation is higher. Exposure of Q.saponaria to higher levels of UV-B affected the ecophysiological parameters, revealing a decrease in Amax, growth and leaf production. In addition, higher levels of UV-B led to repression in four of the five genes studied. Our results may help foresee environmental scenarios for different plant species associated with solar activity.

Drought evolution in the Haihe River basin during 1960–2020 and the correlation with global warming, sunspots, and atmospheric circulation indices

Abstract The Haihe River basin is the main grain production base and the highland of economic strategic development in China. Based on daily meteorological data during 1960–2020, the characteristics of drought evolution in the Haihe River basin were analyzed by the standardized precipitation evapotranspiration index (SPEI). Pearson correlation method and cross-wavelet analysis were used to explore the correlation between the SPEI and climate factors (global warming, sunspots, and atmospheric circulation indices). Global warming has led to a trend of increasing drought in the basin, and there is an obvious zonality in the change of the trend, with the strongest impact on the central region of the basin (112°E–120°E, 38°N–41°N). The SPEI was negatively correlated with the number of sunspots. The more sunspots there were, the more severe the drought in the basin. The drought was most susceptible to the El Niño-Southern Oscillation (ENSO) and the Atlantic Multidecadal Oscillation (AMO), followed by the Arctic Oscillation (AO) and the Pacific Decadal Oscillation (PDO). The North Atlantic Oscillation (NAO), the Pacific North America index (PNA), and the Western Pacific index (WP) were the least associated with the drought in the basin.