Solar Activity Cycle Research Articles

A comparative study of ionospheric TEC diurnal variations at two stations near cusp latitudes in the Southern Hemisphere

Based on ionospheric total electron content (TEC) data for Zhongshan station (ZHS) and Scott Base station (SBA) in Antarctica, acquired during 2010–2020, high-latitude ionospheric TEC diurnal variations of two near cusp latitude stations were studied. The magnetic latitude and longitude differences between the two stations were approximately 5° and 135°, respectively. It was found that during the 11-year solar activity cycle, the maximum diurnal variation of the ionospheric TEC at ZHS occurred mainly between local noon and magnetic noon. Statistically, the TEC peaks occurred closer to local (magnetic) noon under low (high) solar activity conditions. The maximum diurnal variation of ionospheric TEC at SBA occurred mainly around local noon under low solar activity conditions but before magnetic midnight under high solar activity conditions. The effects of solar radiation, particle precipitation, and polar ionospheric convection pattern on the diurnal variation of TEC were investigated. At both stations, photoionization caused by solar radiation was the main reason for the maximum diurnal variation of ionospheric TEC around local noon. During high solar activity with high concentration plasma in the dayside polar ionosphere, the convection pattern was the dominant influence on the maximum diurnal variation of TEC before magnetic midnight (noon) at SBA (ZHS).

Self-organization of water molecules over 11-year solar cycle

The variations of solar activity and distribution of solar energy due to the rotation of the Earth around its axis and around the Sun exert a strong influence on the self-organization of water molecules. As a result, the rate of hydrolytic processes with the participation of water clusters displays diurnal, very large annual variations, and is also modulated by the 11-year cycles of solar activity. It also depends on the geographic latitude and can be different at the same time in the Northern and Southern Hemispheres. This phenomenon is important for all forms of life on the Earth. It may be well accounted for by the influence of muons which are constantly generated in the upper atmosphere by the solar wind. Muons reach the surface of the Earth and can penetrate to some depth underground. Buildings also absorb muons. For this reason, the rates of hydrolysis outside and inside buildings, as well as underground, can differ significantly from each other.

A New 3D Solar Wind Speed and Density Model Based on Interplanetary Scintillation

Abstract The solar wind (SW) is an outflow of the solar coronal plasma, which expands supersonically throughout the heliosphere. SW particles interact by charge exchange with interstellar neutral atoms; on the one hand, they modify the distribution of this gas in interplanetary space, and, on the other hand, they are the seed populations for heliospheric pickup ions and energetic neutral atoms (ENAs). The heliolatitudinal profiles of the SW’s speed and density evolve during the solar activity cycle. A model of the evolution of the SW’s speed and density is needed to interpret observations of ENAs, pickup ions, the heliospheric backscatter glow, etc. We derive the Warsaw Heliospheric Ionization Model 3DSW—WawHelIon 3DSW—based on interplanetary scintillation (IPS) tomography maps of the SW speed. We use the IPS tomography data from 1985 to 2020, compiled by Tokumaru et al. We derive a novel statistical method of filtering these data against outliers; we present a flexible analytic formula for the latitudinal profiles of the SW speed, based on Legendre polynomials of varying order with additional restraining conditions at the poles; fit this formula to the yearly filtered data; and calculate yearly SW density profiles using the latitudinally invariant SW energy flux observed in the ecliptic plane. Despite the application of a refined IPS data set, a more sophisticated data filtering method, and a more flexible analytic model, the present results mostly agree with those obtained previously, demonstrating the robustness of IPS studies of the SW’s structure.

Solar activity and space weather

After providing an overview of solar activity as measured by the sunspot number (SSN) and space weather events during solar cycles (SCs) 21-24, we focus on the weak solar activity in SC 24. The weak solar activity reduces the number of energetic eruptions from the Sun and hence the number of space weather events. The speeds of coronal mass ejections (CMEs), interplanetary (IP) shocks, and the background solar wind all declined in SC 24. One of the main heliospheric consequences of weak solar activity is the reduced total (magnetic + gas) pressure, magnetic field strength, and Alfvén speed. There are three groups of phenomena that decline to different degrees in SC 24 relative to the corresponding ones in SC 23: (i) those that decline more than SSN does, (ii) those that decline like SSN, and (iii) those that decline less than SSN does. The decrease in the number of severe space weather events such as high-energy solar energetic particle (SEP) events and intense geomagnetic storms is deeper than the decline in SSN. The reduction in the number of severe space weather events can be explained by the backreaction of the weak heliosphere on CMEs. CMEs expand anomalously and hence their magnetic content is diluted resulting in weaker geomagnetic storms. The reduction in the number of intense geomagnetic storms caused by corotating interaction regions is also drastic. The diminished heliospheric magnetic field in SC 24 reduces the efficiency of particle acceleration, resulting in fewer high-energy SEP events. The numbers of IP type II radio bursts, IP socks, and high-intensity energetic storm particle events closely follow the number of fast and wide CMEs (and approximately SSN) because all these phenomena are closely related to CME-driven shocks. The number of halo CMEs in SC 24 declines less than SSN does, mainly due to the weak heliospheric state. Phenomena such as IP CMEs and magnetic clouds related to frontside halos also do not decline significantly. The mild space weather is likely to continue in SC 25, whose strength has been predicted to be not too different from that of SC 24.

Helium Fluxes Measured by the PAMELA Experiment from the Minimum to the Maximum Solar Activity for Solar Cycle 24

Abstract Time-dependent energy spectra of galactic cosmic rays (GCRs) carry fundamental information regarding their origin and propagation. When observed at the Earth, these spectra are significantly affected by the solar wind and the embedded solar magnetic field that permeates the heliosphere, changing significantly over an 11 yr solar cycle. Energy spectra of GCRs measured during different epochs of solar activity provide crucial information for a thorough understanding of solar and heliospheric phenomena. The PAMELA experiment collected data for almost 10 years (2006 June 15–2016 January 23), including the minimum phase of solar cycle 23 and the maximum phase of solar cycle 24. In this paper, we present new spectra for helium nuclei measured by the PAMELA instrument from 2010 January to 2014 September over a three-Carrington-rotation time basis. These data are compared to the PAMELA spectra measured during the previous solar minimum, providing a picture of the time dependence of the helium-nuclei fluxes over a nearly full solar cycle. Time and rigidity dependencies are observed in the proton-to-helium flux ratios. The force-field approximation of the solar modulation was used to relate these dependencies to the shapes of the local interstellar proton and helium-nuclei spectra.

Dependence of X-ray emission from Europa on solar activity cycle

The atmosphere of the Jovian Europa being tenuous, the interaction of the energetic solar photons is a probable source of excitation for the emission of X-rays from the surface of the satellite. Solar photons in the X-region of the electromagnetic spectrum have energies greater than the binding energy of the elemental constituents of the surface, cause excitation of electrons, and on de-excitation cause emission of X-rays through X-ray fluorescence. We developed models for the computation of the solar X-ray flux during the representative phases of a solar activity cycle (1-100 Å), and using these fluxes, we computed the photon-induced X-ray fluorescent and Rayleigh scattering emission flux from the regolith of the Europa by taking into account its predominant H2O ice composition. This work observed that during the extreme case of the quiet Sun condition and an X2-class flare, the X-ray energy flux at the Europa distance of 4.96 AU vary from 1.08 × 10-7 to 5.23 × 10-4 ergs-cm-2s-1. This flux from the H2O ice composition can generate a total X-ray energy flux, inclusive of the X-ray fluorescent and Rayleigh scattering events, varying as 1.40 × 10-23 to 6.21 × 10-20 ergs-cm-2s-1. These computed numbers of the X-ray energy fluxes at the telescope of the Chandra X-ray Observatory are of lesser magnitude in comparison to its observed numbers (3.0 × 10-16). This deduction reveals the influence of a stronger excitation source than the photon-induced mechanisms of the generation of X-rays from the surface of the Europa.

Agricultural Production in the United States and its Synchronism with the Cycles of Solar Activity

Agricultural Production in the United States and its Synchronism with the Cycles of Solar Activity

Spectral Properties of Low-order Dynamo Systems

The solar 11-year activity cycle is a famous manifestation of magnetic activity of celestial bodies. The physical nature of the solar cycle is believed to be large-scale magnetic field excitation in the form of a wave of a quasi-stationary magnetic field propagating from middle solar latitudes to the solar equator. The power spectrum of solar magnetic activity recorded in sunspot data and underlying solar dynamo action contains quite a stable oscillation known as the 11-year cycle as well as the continuous component and some additional weak peaks. We consider a low-order model for the solar dynamo. We show that in some range of governing parameters this model can reproduce spectra with pronounced dominating frequency and wide spectral peaks in the low-frequency region. The spectra obtained are qualitatively similar to the observed solar activity spectrum.

11-year dynamics of coronal hole and sunspot areas

Abstract The paper presents study the 11-year dynamics of solar activity on the basis of new observational material on coronal holes (CHs) and sunspots in the period from May 13, 2010 to May 13, 2021. We used the Heliophysics Event Knowledgebase (HEK) to obtain information on CHs areas. For 11 years of observations, we processed about 18000 CHs. Slightly more than 8000 are polar, the rest are nonpolar CHs. The statistical volume of the presented material is quite extensive and gives grounds for the study of the dynamics of different types of CHs during the cycle. Our research has shown: in the 24th solar activity cycle, the South led for polar CHs and the North led for nonpolar ones. We established a relationship between the number and area of CHs and the phase of the solar cycle. The number and daily total area of polar CHs increases at the minima of solar activity and decreases at the maximum of the cycle. This is consistent with the general concept of polar CHs as the main source of the solar dipole magnetic field. An asymmetry in both the number and areas of polar coronal holes in the northern and southern hemispheres is observed. It is shown that the areas of nonpolar CHs change quasi-synchronously with sunspot activity, which suggests a physical connection between these two phenomena.

On Long-Term Variations in Solar Wind and Solar Activity Parameters with Possible Application to the Global Climate Problem

Comparison is carried out of the long term variation of the year averaged solar wind speed and interplanetary scintillation index with the variations of Wolf's numbers and A_P indexes of geomagnetic activity for the data of 20-24 solar activity cycles. It is shown that the slow non-monotonous trend in the scintillation parameters at middle and high heliolatitudes exists with the typical scale of order of century cycle. Correlation between the variations of Wolf's numbers and anomalies of the air temperature is analyzed for long data series from 1610 up to the present time. Possible application of the results to the global climate problem is discussed.

Applicability of NeQuick G ionospheric model for single-frequency GNSS users over India

<abstract> <p>The major source of error in the positioning of GNSS is from the region of Ionosphere. The single-frequency GNSS receiver cannot eliminate the ionospheric error due to dispersive medium and frequency-dependent. The low-cost GNSS receivers are highly dependent on single-frequency approaches of Ionosphere region popularly known as Klobuchar, NeQuick G, and BDS2 methods to estimate the data of position, velocity and time. The regional satellite navigation system of India, known as Navigation with Indian Constellation (NavIC) adopted ionospheric models based on single-frequency namely, Klobuchar and grid-based correction models. The Klobuchar modelos accuracy is less for predicting ionospheric delays in low latitude regions like India under Equatorial Ionization Anomaly (EIA) conditions. In this paper, the NeQuick G modelos applicability for NavIC users over the Indian region is investigated. NeQuick G modelos performance is validated with dense GPS TEC network data of 26 stations spread across India and IRI-2016 model, during 2014, 2015 and 2016. The predicted TEC results indicate that EIA structures are well captured by NeQuick G and IRI-2016 models. The results indicate that both NeQuick G and IRI-2016 models well predict season asymmetry and decrease of TEC intensity due to descending phase solar cycle activity. It is found that NeQuick G is one of the contenders of single frequency ionospheric models for GNSS/NavIC users in India.</p> </abstract>

Contribution of the International Reference Ionosphere-2016 Model in the Evidence of the Winter Anomaly

This study is a contribution to the estimation of the winter anomaly in the F2 layer of the ionosphere at low latitudes. The aim is to study the variability of the virtual height (hmF2) of the F2 region of the ionosphere through the predictions of the latest International Reference Ionosphere model (IRI-2016). The present work allows analyzing the temporal evolution of hmF2 according to the different phases of three (3) solar cycles during the quiet geomagnetic activity to estimate the seasonal anomaly at the Ouagadougou station. The analysis of the seasonal profiles shows that the variability of hmF2 is: 1) strongly linked to the solar cycle activity, 2) dependent on the season and 3) variable from one cycle to the next for the same phase. It appears that hmF2 increases during the ascending phase to reach its maximum value at the phase maximum. During the descending phase, it decreases until the phase minimum where it finds its minimum value. The difference between winter and summer on the hmF2 values for each phase of the cycle is obtained at the phase minimum and is estimated to be at least 16 km. In low latitudes, solar irradiation is greater in summer than in winter. From this study, hmF2 values are larger in winter compared to summer indicating an anomaly in the virtual height of the F2 layer of the ionosphere through the predictions of IRI-2016 at the Ouagadougou station.

Свойства короткопериодной возмущенности полного электронного содержания на средних и высоких широтах

The study presents the results of comparative analysis of features of a short-period (with periods of internal gravity waves) variability of total electron content (TEC) in the ionosphere at middle (Novosibirsk) and high (Norilsk) latitudes over a long period of time (2003–2020). The period analyzed makes it possible to estimate not only diurnal and seasonal variations in the variability, but also its changes within the solar activity cycle. The level of TEC variability is shown to experience pronounced seasonal variations with maxima in winter months. The difference between the level of variability in winter and summer is about two times for Novosibirsk and up to seven times for Norilsk. The variability features a distinct diurnal variation; however, the diurnal dependence at the mid- and high-latitude stations differs significantly. At high latitudes, the level of variability in the winter period strictly depends on solar activity. For the mid-latitude station, there is no clear dependence of variability level on solar activity; in the years of solar maximum, on the contrary, a slight decrease in the variability is observed. In summer, the level of variability at both middle and high latitudes remains practically unchanged and does not depend on solar activity. The main features in the dynamics of variability are shown to be similar at stations located at other longitudes, except for the East American sector. The result obtained suggests that the short-period TEC variability at high latitudes is primarily related to changes in solar activity, but regular variations in the variability at midlatitudes are probably not associated with heliophysical activity. The observed increase in the level of short-period variability in the winter mid-latitude ionosphere is assumed to be related to an increase in wave activity in the stratosphere.

Features of short-period variability of total electron content at high and middle latitudes

The study presents the results of comparative analysis of features of a short-period (with periods of internal gravity waves) variability of total electron content (TEC) in the ionosphere at middle (Novosibirsk) and high (Norilsk) latitudes over a long period of time (2003–2020). The period analyzed makes it possible to estimate not only diurnal and seasonal variations in the variability, but also its changes within the solar activity cycle. The level of TEC variability is shown to experience pronounced seasonal variations with maxima in winter months. The difference between the level of variability in winter and summer is about two times for Novosibirsk and up to seven times for Norilsk. The variability features a distinct diurnal variation; however, the diurnal dependence at the mid- and high-latitude stations differs significantly. At high latitudes, the level of variability in the winter period strictly depends on solar activity. For the mid-latitude station, there is no clear dependence of variability level on solar activity; in the years of solar maximum, on the contrary, a slight decrease in the variability is observed. In summer, the level of variability at both middle and high latitudes remains practically unchanged and does not depend on solar activity. The main features in the dynamics of variability are shown to be similar at stations located at other longitudes, except for the East American sector. The result obtained suggests that the short-period TEC variability at high latitudes is primarily related to changes in solar activity, but regular variations in the variability at midlatitudes are probably not associated with heliophysical activity. The observed increase in the level of short-period variability in the winter mid-latitude ionosphere is assumed to be related to an increase in wave activity in the stratosphere.

Relationship between geomagnetic storm development and the solar wind parameter ß

We have analyzed the dynamics of solar wind and interplanetary magnetic field (IMF) parameters during the development of 933 isolated geomagnetic storms, observed over the period from 1964 to 2010. The analysis was carried out using the epoch superposition method at intervals of 48 hrs before and 168 hrs after the moment of Dst minimum. The geomagnetic storms were selected by the type of storm commencement (sudden or gradual) and by intensity (weak, moderate, and strong). The dynamics of the solar wind and IMF parameters was compared with that of the Dst index, which is an indicator of the development of geomagnetic storms. The largest number of storms in the solar activity cycle is shown to occur in the years of minimum average values (close in magnitude to 1) of the solar wind parameter β (β is the ratio of plasma pressure to magnetic pressure). We have revealed that the dynamics of the Dst index is similar to that of the β parameter. The duration of the storm recovery phase follows the characteristic recovery time of the β parameter. We have found out that during the storm main phase the β parameter is close to 1, which reflects the maximum turbulence of solar wind plasma fluctuations. In the recovery phase, β returns to background values β~2‒3.5. We assume that the solar wind plasma turbulence, characterized by the β parameter, can play a significant role in the development of geomagnetic storms.

Связь развития геомагнитных бурь с параметром ß солнечного ветра

We have analyzed the dynamics of solar wind and interplanetary magnetic field (IMF) parameters during the development of 933 isolated geomagnetic storms, observed over the period from 1964 to 2010. The analysis was carried out using the epoch superposition method at intervals of 48 hrs before and 168 hrs after the moment of Dst minimum. The geomagnetic storms were selected by the type of storm commencement (sudden or gradual) and by intensity (weak, moderate, and strong). The dynamics of the solar wind and IMF parameters was compared with that of the Dst index, which is an indicator of the development of geomagnetic storms. The largest number of storms in the solar activity cycle is shown to occur in the years of minimum average values (close in magnitude to 1) of the solar wind parameter β (β is the ratio of plasma pressure to magnetic pressure). We have revealed that the dynamics of the Dst index is similar to that of the β parameter. The duration of the storm recovery phase follows the characteristic recovery time of the β parameter. We have found out that during the storm main phase the β parameter is close to 1, which reflects the maximum turbulence of solar wind plasma fluctuations. In the recovery phase, β returns to background values β~2‒3.5. We assume that the solar wind plasma turbulence, characterized by the β parameter, can play a significant role in the development of geomagnetic storms.

A Multiscale Approach to Geomagnetic Storm Morphology Analysis Based on DMA Activity Measures

The article is focused on the approach based on the discrete mathematical analysis conception and continues a series of studies related to the application of the previously developed methodology to geophysical data analysis. The main idea of the study is the modification of earlier conceptions regarding the interpreter’s logic that allows introducing a multiscale approach and performing the time series analysis using the activity measure plots, implying the vertical scale. This approach was used to study the morphology of several intense geomagnetic storms at the final stages of the 23rd and 24th solar activity cycles. Geomagnetic observatory data and interplanetary magnetic field parameters as well as the solar wind flux speed and proton density were analyzed for each of the studied storms using the activity measures. The developed methods, applied to geomagnetic storm morphological analysis, displayed good results in revealing the decreases and increases in various durations and intensities during storms, detecting low-amplitude disturbances, and storm sudden commencement recognition. The results provide an opportunity to analyze any physical data using a unified scale and, in particular, to implement this approach to geomagnetic activity studies.

Frequency Modulation as a Cause of Additional Branches of the Gleissberg Cycle in Solar Activity

Frequency Modulation as a Cause of Additional Branches of the Gleissberg Cycle in Solar Activity

Two Links between Parameters of 11-year Cycle of Solar Activity

Two Links between Parameters of 11-year Cycle of Solar Activity

First light observations of the solar wind in the outer corona with the Metis coronagraph

In this work, we present an investigation of the wind in the solar corona that has been initiated by observations of the resonantly scattered ultraviolet emission of the coronal plasma obtained with UVCS-SOHO, designed to measure the wind outflow speed by applying Doppler dimming diagnostics. Metis on Solar Orbiter complements the UVCS spectroscopic observations that were performed during solar activity cycle 23 by simultaneously imaging the polarized visible light and the H I Lyman-α corona in order to obtain high spatial and temporal resolution maps of the outward velocity of the continuously expanding solar atmosphere. The Metis observations, taken on May 15, 2020, provide the first H I Lyman-α images of the extended corona and the first instantaneous map of the speed of the coronal plasma outflows during the minimum of solar activity and allow us to identify the layer where the slow wind flow is observed. The polarized visible light (580–640 nm) and the ultraviolet H I Lyα (121.6 nm) coronal emissions, obtained with the two Metis channels, were combined in order to measure the dimming of the UV emission relative to a static corona. This effect is caused by the outward motion of the coronal plasma along the direction of incidence of the chromospheric photons on the coronal neutral hydrogen. The plasma outflow velocity was then derived as a function of the measured Doppler dimming. The static corona UV emission was simulated on the basis of the plasma electron density inferred from the polarized visible light. This study leads to the identification, in the velocity maps of the solar corona, of the high-density layer about ±10° wide, centered on the extension of a quiet equatorial streamer present at the east limb – the coronal origin of the heliospheric current sheet – where the slowest wind flows at about 160 ± 18 km s−1 from 4 R⊙ to 6 R⊙. Beyond the boundaries of the high-density layer, the wind velocity rapidly increases, marking the transition between slow and fast wind in the corona.