Sunspot Activity Research Articles

Analysis of pre-telescopic sunspots and auroras from 8th to 16th century

In this paper, we use non-parametric kernel approach to estimate the probability density function (pdf) of auroral-night and naked-eye-sunspot series over multi-century timescale. We selected the events observed in medieval epoch, and auroral records from low geographical latitude (<45°). These astronomical phenomena are recorded mainly in the Oriental historical sources and much less in Occidental sources. The collected events are published in many recent catalogues. The density function are calculated using the Gaussian kernel, including 95% CI obtained by bootstrapping.Results confirm the existence of strong connection between auroras and sunspot activity, especially from 11th to 16th century. Indeed, a high correlation degree r = 0.72 is obtained for the period AD 800–1500 between the two pdf of sunspots (pdfS) and auroras (pdfA) for bandwidth h = 10 years, and exceed 0.8 for h > 43 years. However, we notice a time-shift between the two density functions. To calculate it, we use the cross-correlation technique, and we find τ = −5.9 years, that is strangely close to the half of solar cycle period. It is very important to note that our results revealed that the high frequency of low latitude auroras occurs before the maximum of naked-eye sunspots activity, and not afterward, on contrary to what is expected.The pdf curves show multiple peaks occurring at quasi-periodic times and show clearly the three grand minima of solar activity: Oort, Wolf and Spörer. In auroral-night data, the mean period at 95% CI obtained is:T‾=61±7years. Using power spectrum analysis, we observe clearly a strong signal of 60 years period that is a new evidence of the existence of such cycle. More importantly, we identified a cycle of 262 years period in the sunspot data, and a new oscillation of 310 years in auroral-night data. These two cycles appear clearly in the pdf curves using optimized bandwidth obtained by the direct plug-in approach of Sheather and Jones.

Can the long-term hemispheric asymmetry of solar activity result from fluctuations in dynamo parameters?

Context. The hemispheric asymmetry of sunspot activity observed possesses a regular component varying on a timescale of several solar cycles whose origin and properties are currently debated. Aims This paper addresses the question of whether the long-term hemispheric asymmetry can result from random variations of solar dynamo parameters in time and latitude. Methods. Scatter in the observed tilt angles of sunspot groups was estimated to infer constraints on fluctuations in the dynamo mechanism for poloidal field regeneration. A dynamo model with fluctuations in the Babcock-Leighton type α-effect was designed in accordance with these constraints and then used to compute a large number of magnetic cycles for statistical analyses of their hemispheric asymmetry. Results Hemispheric asymmetry in the simulated dynamo results from the presence of an equator-symmetric part in the oscillating magnetic field. The sub-dominant quadrupolar oscillations are stochastically forced by dominant dipolar oscillations via the equator-symmetric part of the fluctuating α-effect. The amplitude and sense of the asymmetry of individual cycles varies on a timescale of the order of four dynamo-cycle periods. The variations are irregular and not periodic. The model suggests that asymmetry in the polar magnetic fields in the solar minima can be used as a precursor for asymmetry of sunspot activity in the following solar cycle.

Aspects of the Influence of the Global Heliospheric Current Sheet on GCR Propagation

The influence of the global heliospheric current sheet on the heliospheric characteristics important for GCR propagation is considered, particularly the strong dependence of the solar wind velocity on the distance from the current sheet. A simple model of the solar wind velocity is proposed that, after estimating the parameters from observations, can be used for theoretical studies of GCR modulation. The choice of the GCR propagation model to be used for periods of low and medium sunspot activity is discussed.

North–South Asymmetry in Solar Activity and Solar Cycle Prediction, IV: Prediction for Lengths of Upcoming Solar Cycles

We analyzed the daily sunspot-group data reported by the Greenwich Photoheliographic Results (GPR) during the period 1874 – 1976 and Debrecen Photoheliographic Data (DPD) during the period 1977 – 2017 and studied North–South asymmetry in the maxima and minima of the Solar Cycles 12 – 24. We derived the time series of the 13-month smoothed monthly mean corrected whole-spot areas of the sunspot groups in the Sun’s whole sphere (WSGA), northern hemisphere (NSGA), and southern hemisphere (SSGA). From these smoothed time series we obtained the values of the maxima and minima, and the corresponding epochs, of the WSGA, NSGA, and SSGA Cycles 12 – 24. We find that there exists a 44 – 66 years periodicity in the North–South asymmetry of the minimum. A long periodicity (130 – 140 years) may exist in the asymmetry of the maximum. A statistically significant correlation exists between the maximum of SSGA Cycle $n$ and the rise time of WSGA Cycle $n+2$ . A reasonably significant correlation also exists between the maximum of WSGA Cycle $n$ and the decline time of WSGA Cycle $n+2$ . These relations suggest that the solar dynamo carries memory over at least three solar cycles. Using these relations we obtained the values $11.7\pm 0.15~\text{years}$ , $11.2\pm 0.2~\text{years}$ , and $11.45\pm 0.3~\text{years}$ for the lengths of WSGA Cycles 24, 25, and 26, respectively, and hence, July 2020, October 2031, and March 2043 for the minimum epochs (start dates) of WSGA Cycles 25, 26, and 27, respectively. We also obtained May 2025 and March 2036 for the maximum epochs of WSGA Cycles 25 and 26, respectively. It seems during the late Maunder Minimum sunspot activity was absent around the epochs of the maxima of the NSGA-cycles and the minima of the SSGA-cycles, and some activity was present at the epochs of the maxima of some SSGA-cycles and the minima of some NSGA-cycles.

Assessing GRACE-based terrestrial water storage anomalies dynamics at multi-timescales and their correlations with teleconnection factors in Yunnan Province, China

Changes in terrestrial water storage anomalies (TWSA) are not only influenced by local climate conditions but also by teleconnection factors. To date, how teleconnection factors including sunspot activities could affect TWSA has been under-examined. In this study, we investigate the TWSA dynamics in the Yunnan Province (YP), China, and assess their relationships with teleconnection factors at multiple timescales. Results show that: (1) GRACE data is able to reflect TWSA dynamics in the study region, as demonstrated by its high correlations with soil moisture, precipitation, and groundwater anomalies; (2) GRACE-based TWSA shows a downward trend of varying degrees at the monthly, seasonal, annual and multi-year scales, with obvious periodic changes of 11 and around 60 months; (3) precipitation magnitude and its distribution characteristics in humid areas are the main driving factors of TWSA, and teleconnection factors have stronger association with precipitation-concentration degree (PCD) than precipitation magnitude; (4) the 2009 extreme drought has caused a sharp decrease in TWSA, and the correlations between TWSA with Arctic Oscillation (AO) and El-Niño Southern Oscillation (ENSO) were 0.88 (a = 0.01) and −0.58 (a = 0.01). This study sheds new insights into how teleconnection factors could TWSA dynamics in a changing environment.

Mid- to late Holocene cooling events in the Korean Peninsula and their possible impact on ancient societies

AbstractWe present a multiproxy record using pollen, magnetic susceptibility, carbon isotopic composition, carbon/nitrogen ratio, and particle size of mid- to late Holocene environmental changes based on a sediment core from the Pomaeho lagoon on the east coast of Korea. The records indicate that climate deteriorations around 6400 cal yr BP and 4000 cal yr BP caused rapid vegetation changes in the study area, which were presumably attributable to low sunspot activity and strong El Niño–like conditions, respectively. These two cooling events were likely modulated by different climate mechanisms, as El Niño–Southern Oscillation activity began to strengthen around 5000 cal yr BP. These events may have had a substantial impact on ancient societies in the study area. Combining our results with archaeological findings indicated that climate deterioration led to drastic declines in local populations around 6400 cal yr BP, 4400 cal yr BP, and 4000 cal yr BP. Because of its high population, coastal East Asia (e.g., eastern China, Japan, and Korea) is particularly vulnerable to potential cooling events in the future. Therefore, there is a strong need for detailed paleoclimate information in this region.

Harmonic analysis and distribution-free inference for spherical distributions

Fourier analysis, and representation of circular distributions in terms of their Fourier coefficients, is quite commonly discussed and used for model-free inference such as testing uniformity and symmetry, in dealing with 2-dimensional directions. However, a similar discussion for spherical distributions, which are used to model 3-dimensional directional data, is not readily available in the literature in terms of their harmonics. This paper, in what we believe is the first such attempt, looks at probability distributions on a unit sphere through the perspective of spherical harmonics, analogous to the Fourier analysis for distributions on a unit circle. Representation of any continuous spherical density in terms of spherical harmonics is given, and such series expansions provided for some commonly used spherical distributions, as well as for two new spherical distributions that are introduced. Through the prism of harmonic analysis, one can look at the mean direction, dispersion, and various forms of symmetry for these models in a nonparametric setting. Aspects of distribution-free inference such as estimation and large-sample tests for various symmetries, are provided, each type of symmetry being characterized through its harmonics. The paper concludes with a real-data example analyzing the longitudinal sunspot activity.

On Contribution of Poloidal Branch of Solar Activity to Heliosphere and GCR Modulation

The point of view is substantiated that during periods of low sunspot activity many heliospheric characteristics (the solar wind velocity, the form of the heliospheric current sheet, the strength of the heliospheric magnetic field) can be considered as the manifestations in the heliosphere of the poloidal branch of solar activity. As these characteristics strongly influence the process of the GCR transport through the heliosphere the contribution of the poloidal branch of solar activity to the GCR solar modulation should also be substantial. This conclusion is at odds with the wide-spread belief that the modulated GCR intensity is mainly determined by the sunspot cycle.

Cycle Analysis Method of Tree Ring and Solar Activity Based on Variational Mode Decomposition and Hilbert Transform

According to the correlation of tree ring and solar activity, the cycle analysis method based on variational mode decomposition (VMD) and Hilbert transform is proposed. Firstly, the tree ring width of cypress during 1700 to 1955 beside the Huangdi Tomb and the long-term sunspot number during 1700 to 1955, respectively, are decomposed by VMD into a series of intrinsic mode functions (IMFs). Secondly, Hilbert transformation on the decomposed IMF component is performed. Then, the marginal spectra are given and analyzed. Finally, their quasiperiodic properties are obtained as follows: the tree ring width has the quasiperiodicity of 2 to 7a, 10.8a, and 25a; the sunspot number has the quasiperiodicity of 8.3a, 9.9a, 11.1a, 52.2a, and 101.2a. The result obtained by analyzing that quasiperiodicity shows that the main periods of tree ring width and the sunspot number in the same period are basically consistent, and tree ring width has other cycles. This shows that sunspot activity is an important factor affecting tree ring growth, and tree ring width is influenced by other external environments.

Hypothesis Testing for Nonlinear Phenomena in the Geosciences Using Synthetic, Surrogate Data

Studying nonlinear and potentially chaotic phenomena in geophysics from measured signals is problematic when system noise interferes with the dynamic processes that one is trying to infer. In such circumstances, a framework for statistical hypothesis testing is necessary but the nonlinear nature of the phenomena studied makes the formulation of standard hypothesis tests, such as analysis of variance, problematic as they are based on underlying linear, Gaussian assumptions. One approach to this problem is the method of surrogate data, which is the technique explained in this paper. In particular, we focus on (i) hypothesis testing for nonlinearity by generating linearized surrogates as a null hypothesis, (ii) a variant of this that is perhaps more appropriate for image data where structural nonlinearities are common and should be retained in the surrogates, and (iii) gradual reconstruction where we systematically constrain the surrogates until there is no significant difference between data and surrogates and use this to understand geophysical processes. In addition to time series of sunspot activity, solutions to the Lorenz equations, and spatial maps of enstrophy in a turbulent channel flow, two examples are considered in detail. The first concerns gradual wavelet reconstruction testing of the significance of a specific vortical flow structure from turbulence time series acquired at a point. In the second, the degree of nonlinearity in the spatial profiles of river curvature is shown to be affected by the occurrence of meander cutoff processes but in a more complex fashion than previously envisaged.

War of the Waves: Radio and Resistance During World War II

What is the role of the media in coordinating and mobilizing insurgency against a foreign military occupation? We analyze this question in the context of the Nazi-fascist occupation of Italy during WWII. We study the effect of BBC radio counter-propaganda (Radio Londra) on the intensity of internal resistance to the Nazi-fascist regime. Using variation in monthly sunspot activities affecting the sky-wave propagation of BBC broadcasting towards Italy, we show that BBC radio had a strong impact on political violence. We provide further evidence to prove that BBC radio played an important role in coordinating resistance activities, but had no lasting role in motivating the population against the fascist regime.

Shape of the 11-Year Cycle of Solar Activity and the Evolution of Latitude Characteristics of the Sunspot Distribution

The solar activity index and parameters of the spatial distribution of sunspots are known to be related. Using these relationships, we propose interrelated approximations for the sunspot number (SN) and the two key latitude characteristics of their distribution in the cycle: the mean latitude of sunspots and the standard deviation of their latitudes. The two parameters of these approximations are the cycle amplitude SNmax and the drift of its downward branch relative to the cycle beginning t0. These approximations specifically take into account the relationship between amplitudinal and spatial properties of the 11-year solar cycle, as well as the universality of the behavior of the activity and mean latitude of sunspots in the declining phase of the cycle. We demonstrate that the pair of parameters SNmax and t0 allows approximation of both the shape of the cyclic curve and the latitude–time diagram for sunspots of this cycle (“Maunder’s butterfly”).

The 1855 to 1859 locust plague in China

Historical disaster studies tend to be addressed from various perspectives, and case studies (i.e., event reconstruction) are an important aspect of such research. Using records extracted from historical documents and focusing on locust plague events, this study investigated disasters that occurred from 1855 to 1859. The objective was to reconstruct the temporal dynamics and spatial patterns of a major locust plague event to explore the social impact and reveal the underlying climate trends. The results suggested that: (1) the locust plagues followed an approximately 5-year duration from 1855 to 1859. Over this period, the frequency of individual plagues varied greatly and 1857 was the peak year. Locust plagues showed clear distribution patterns on a spatial scale during this period, with the mean center located in Henan Province. Locust plagues tended to be localized at the beginning and then spread out from the original locations, presenting a general spatial pattern of “radiating after clustering.” (2) Locust plagues were closely related to drought and showed a correlation with the overall drainage pattern of major bodies of water in the regions studied. The main reason for the locust plagues was probably drought events, climate and other geographic factors. The droughts were likely related to teleconnection between the increasing El Nino, frequency of sunspot activity and declining SSTs. (3) Locust plagues impacted society and damaged agricultural yields, as indicated by higher rice prices and increased wars. A hysteresis transfer effect was observed between locust plagues and the corresponding social responses; rice prices increased about half to 1 year after locust plagues occurred, while the frequency of wars increased after a clear delay of about 1–2 years. This showed locust plagues caused the rice price and refugee increasing and then caused social unrest.

Global warming and the Anthropocene

By burning fossil fuels, humans have changed the carbon cycle, loading the atmosphere with extra carbon dioxide (CO2). Before the current Ice Age, high atmospheric CO2 levels generated warm climates. The Ice Age developed as the volcanic supply of CO2 lessened, and rock weathering increased. The CO2 lost from the atmosphere by chemical weathering was transferred to the ocean and trapped in carbonate sediments. Humans now replicate what volcanic activity did in the distant past, our CO2 emissions driving global warming. Earth's present climate should be cool, based on the present configuration of the Earth's orbit and the tilt of its axis, and on the decline in sunspot activity since 1990. Warming will grow further with rising emissions, further raising sea level. If business continues as usual we will end with an Eocene‐like ‘greenhouse climate’ and drowned coastal cities.

Reconstructing solar magnetic fields from historical observations

Aims. Sunspot activity is often hemispherically asymmetric, and during the Maunder minimum, activity was almost completely limited to one hemisphere. In this work, we use surface flux simulation to study how magnetic activity limited only to the southern hemisphere affects the long-term evolution of the photospheric magnetic field in both hemispheres. The key question is whether sunspot activity in one hemisphere is enough to reverse the polarity of polar fields in both hemispheres. Methods. We simulated the evolution of the photospheric magnetic field from 1978 to 2016 using the observed active regions of the southern hemisphere as input. We studied the flow of magnetic flux across the equator and its subsequent motion towards the northern pole. We also tested how the simulated magnetic field is changed when the activity of the southern hemisphere is reduced. Results. We find that activity in the southern hemisphere is enough to reverse the polarity of polar fields in both hemispheres by the cross-equatorial transport of magnetic flux. About 1% of the flux emerging in the southern hemisphere is transported across the equator, but only 0.1%–0.2% reaches high latitudes to reverse and regenerate a weak polar field in the northern hemisphere. The polarity reversals in the northern hemisphere are delayed compared to the southern hemisphere, leading to a quadrupole Sun lasting for several years.

Decadal variability in the Northern Hemisphere winter circulation: Effects of different solar and terrestrial drivers

Northern Hemisphere winter circulation is affected by both solar and terrestrial forcings. El-Niño events and volcanic eruptions have been shown to produce a negative and a positive North Atlantic Oscillation (NAO) signature, respectively. Recent studies show a positive NAO signature related to both geomagnetic activity (proxy for solar wind driven particle precipitation) and sunspot activity (proxy for solar irradiance). Here the relative role of these four different drivers on the Northern Hemisphere wintertime circulation is studied using a statistical analysis of observational and reanalysis data during 1868–2014. The phase of the Quasi-Biennial Oscillation (QBO) is used to study driver signals in different stratospheric conditions. Moreover, the effects are separated for early/mid- and late winter. Our findings suggest a stratospheric mediation of the ENSO signal to the Atlantic side, which is delayed and modulated by the QBO unlike the signal in the Pacific side. The positive NAO by volcanic activity is preferentially obtained in the westerly QBO. We also find a substantial QBO modulation for geomagnetic activity and late winter sunspot activity, which favours a stratospheric pathway and the top-down mechanisms. However, signal in the North Pacific produced by early/mid-winter sunspot activity remain rather similar in different QBO phases and supports a direct forcing from the troposphere by the bottom-up sunspot mechanism.

Extreme phenophase delays and their relationship with natural forcings in Beijing over the past 260years.

By merging reconstructed phenological series from published articles and observations of China Phenology Observation Network (CPON), the first blooming date of Amygdalus davidiana (FBA) in Beijing between 1741 and 2000 is reconstructed. The Butterworth method is used to remove the multi-year variations for generating the phenological series of annual variations in the first blooming date of A. davidiana. The extreme delay years in the phenological series are identified using the percentage threshold method. The characteristics of the extreme delays and the correspondence of these events with natural forcings are analysed. The main results are as follows. In annual phenological series, the extreme delays appeared in single year as main feature, only A.D.1800-1801, 1816-1817 and 1983-1984 were the events of two consecutively extreme years. Approximately 85% of the extreme delays occurred during 1-2years after the large volcanic eruptions (VEI ≥ 4) in the eastern rim or the western rim of the Pacific Ocean, as the same proportion of the extreme delays followed El Niño events. About 73% years of the extreme delays fall in the valleys of sunspot cycles or the Dalton minimum period in the year or the previous year. According to the certainty factor (CF), the large eruptions have the greatest influence to the extreme delays; sunspot activity is the second, and ENSO is the last one. The extreme phenological delayed year is most likely to occur after a large eruption, which particularly occurs during El Niño year and its previous several years were in the descending portion or valley of sunspot phase.

Equatorial Magnetohydrodynamic Shallow Water Waves in the Solar Tachocline

Abstract The influence of a toroidal magnetic field on the dynamics of shallow water waves in the solar tachocline is studied. A sub-adiabatic temperature gradient in the upper overshoot layer of the tachocline causes significant reduction of surface gravity speed, which leads to trapping of the waves near the equator and to an increase of the Rossby wave period up to the timescale of solar cycles. Dispersion relations of all equatorial magnetohydrodynamic (MHD) shallow water waves are obtained in the upper tachocline conditions and solved analytically and numerically. It is found that the toroidal magnetic field splits equatorial Rossby and Rossby-gravity waves into fast and slow modes. For a reasonable value of reduced gravity, global equatorial fast magneto-Rossby waves (with the spatial scale of equatorial extent) have a periodicity of 11 years, matching the timescale of activity cycles. The solutions are confined around the equator between latitudes ±20°–40°, coinciding with sunspot activity belts. Equatorial slow magneto-Rossby waves have a periodicity of 90–100 yr, resembling the observed long-term modulation of cycle strength, i.e., the Gleissberg cycle. Equatorial magneto-Kelvin and slow magneto-Rossby-gravity waves have the periodicity of 1–2 years and may correspond to observed annual and quasi-biennial oscillations. Equatorial fast magneto-Rossby-gravity and magneto-inertia-gravity waves have periods of hundreds of days and might be responsible for observed Rieger-type periodicity. Consequently, the equatorial MHD shallow water waves in the upper overshoot tachocline may capture all timescales of observed variations in solar activity, but detailed analytical and numerical studies are necessary to make a firm conclusion toward the connection of the waves to the solar dynamo.

War of the Waves: Radio and Resistance during World War II

We analyze the role of the media in coordinating and mobilizing insurgency against an authoritarian regime, in the context of the Nazi-fascist occupation of Italy during WWII. We study the effect of BBC radio on the intensity of internal resistance. By exploiting variations in monthly sunspot activity that affect the sky-wave propagation of BBC broadcasting toward Italy, we show that BBC radio had a strong impact on political violence. We provide further evidence to document that BBC radio played an important role in coordinating resistance activities but had no lasting role in motivating the population against the Nazi-fascist regime. (JEL D74, L82, N44)

Анализ динамики радиальногоприроста в 445-летнейдревесно-кольцевой хронологиисосны из Прибайкальскогонационального парка

Исследован методический аспект обработки дендрохронологической информации, связанной с выделением долговременной и кратковременной компонент изменчивости из временного ряда радиального прироста, полученного по трем кернам из старовозрастной сосны с острова Ольхон. Проанализированы различные варианты индексации хронологии и рассчитан коэффициент корреляции между хронологиями разного типа. По результатам исследования определен лучший вариант индексации. Для долговременной компоненты установлена связь с числами Вольфа, при этом она демонстрирует цикличность колебаний, соответствующую истинному Солнечному циклу. The most part of known in present time long tree-ring chronologies were build with use of timber cores from wooden buildings and archeological timber samples, wchich were dated with use cores from living trees by cross-date method. Thus, they consist of dendrochronological information from several organisms. At the same time, the investigation of features of tree-rings forming by one genotype for maximally possible long time interval has the independent value for progress of our knowledge about biological base of radial growth variability and the wood stock forming. The goal of investigation wath the analisys of radial growth variability in uncial ald-age tree of Scots pine (Pinus sylvestris L.) The length of investigated chronology was 445 years. The investigated tree is situated on Baycal island Olchon in forest on sandy soils near Saraysk bay. Three cores were taken by Pressler borer and was delivered to the laboratory where specially prepared for future research. Rings width were measured and analysed with use of special equipment Lintab and computer program TSAP. By results of measuring of each core was made three individual chronology, and on the base of them was calculated the average chronology. The correlation between absolutely value of radial growth chronologies and chchronologies calculated by indexation with use of different variants of growth norm; the features of long-term component of the radial growth calculated by method of of 11-year moving average; features of correlation between sunspot activity and long-term and short-term components of radial growth were investigated. It was established, that for investigation of short-term variability of radial growth and effect of climate changes on radial growth the best variant of indexation is on the base of 5-year average norm of ring width. Also it was established, that impact of solar activity on radial growth has nonstationary function and probably modified by impact of other astrophysical factors.