Polar and Low-Latitude Faculae in Activity Cycles 23–24

Geomagnetism and Aeronomy - Polar and low-latitude faculae were identified in daily images based on white-light observations from the MDI (1996–2011) and SOHO (2010–2019) space...     

Results of Spectral Corona Observations in Solar Activity Cycles 17–24

The results of the work of the global observation network are considered, and a comparative analysis of the data of various coronal observatories is performed. The coronal activity index has been reconstructed for the period 1939–2016 based on the data of various observatories in Kislovodsk system. For this purpose, the corona daily intensity maps from the Sacramento Peak and Lomnický ?tít observatories according to the Solar-Geophysical Data journal have been digitized; they supplement the data of other observatories. The homogeneity and continuity of the corona observations at the Kislovodsk station, including activity cycle 24, is confirmed. Unfortunately, the only observatory at present that continues observation of the spectral corona in Fe XIV 5303 Å and Fe XIV 6374 Å lines is the Kislovodsk astronomical station Mountain Astronomical Station (MAS) of the Central Astronomical Observatory, Russian Academy of Sciences (Pulkovo). The data on the combined corona in 5303 Å line are analyzed. It is shown that there is a high correlation of the intensity index of green corona with solar radiation measurements in the vacuum UV region. Data on the beginning of the new 25th activity cycle in the corona at high latitudes are presented.     

Polar Activity of the Sun and Latitudinal Activity Drifts in Cycles 15–24

Geomagnetism and Aeronomy - The solar activity at different latitudes is analyzed based on daily observations at Kodaikanal, Mount Wilson, Sacramento Peak, and Meudon observatories in the CaIIK...     

Positive and Negative Photospheric Fields in Solar Cycles 21–24

Geomagnetism and Aeronomy - The distribution of positive and negative photospheric fields is considered based on the synoptic maps of the photospheric magnetic field from the National Solar...     

Asymmetry of Sunspot Distribution in Solar Cycles 12–24 and the Gnevyshev–Ohl Rule

Geomagnetism and Aeronomy - The nonaxisymmetric component of the sunspot distribution (longitudinal asymmetry) is considered based on the Greenwich–USAF/NOAA data for 1874–2016. Vector...     

Study of Distribution and Asymmetry in Soft X-ray Flares over Solar Cycles 21–24

Geomagnetism and Aeronomy - This paper investigates the North–South (N–S) as well as East–West (E–W) distribution and asymmetry in Soft X-ray flares (SXR) activity during...     

Rotation of the Solar Corona from Observations of Radio and X-Ray Solar Emission for Solar Activity Cycles 22–24

Geomagnetism and Aeronomy - The values of the radio and X-ray solar flux over the last three cycles of solar activity were studied for the presence of quasi-periodic oscillations via the...     

Characteristic Features of Solar Cosmic Rays in the 21st–24th Solar-Activity Cycles According to Data from Catalogs of Solar Proton Events

Geomagnetism and Aeronomy - Homogeneous series of solar cosmic-ray events for four solar-activity cycles against the background of decreased activity in cycles 23 and 24 are considered. The number...     

Latitudinal Profiles of the Photospheric Magnetic Field in Solar Cycles 19–21

For various groups of photospheric magnetic fields differing in strength, averaged synoptic maps have been obtained from the data of the Kitt Peak National Solar Observatory (1976–2003). The latitudinal profiles of magnetic field fluxes are considered individually for each 5-G field strength interval. Changes in the maxima of the latitude profiles and their localization in the latitude are studied. The results are evidence that the latitudinal distribution of the magnetic fields changes significantly at field strengths of 5, 15, and 50 G. The magnetic flux for groups of fields differing in strength decreases monotonically as the strength increases, starting from B > 5 G; the fluxes of the southern hemisphere exceed those of the northern hemisphere. A very special group is formed by the weakest fields with B < 5 G, which are opposite in phase to stronger fields in terms of localization and time changes.     

Time Series Forecasting of Hourly Relativistic Electrons at Geostationary Orbit during Solar Cycles 23–24

Geomagnetism and Aeronomy - Forecasting of the dynamically relativistic electrons is crucial to alert of the flux enhancements that pose a significant threat to satellite operation at geostationary...     

Coronal Holes as Tracers of the Sun’s Global Magnetic Field in Cycles 21–23 of Solar Activity

The dependences of the number and parameters of non-polar coronal holes (CHs) on characteristics of the Sun’s global magnetic field (GMF) are investigated in cycles 21–23 of solar activity (1976–2012) based on data from the CH catalog of the Mountain Astronomical Station of the Main (Pulkovo) Astronomical Observatory of the Russian Academy of Sciences. The influence of variations in the GMF structural arrangement on the CH number and parameters is considered. It is shown that the more stable and steadystate the GMF topology is in the cycle, the higher are the GMF values. The majority of CHs form over periods of stable GMF structure. With a growth in the rate of structural GMF changes, the CH number and the values of all CH parameters decrease. The correlation between the area, extension in latitude and longitude, and magnetic flux of CHs and the intensity of both the calculated coronal field and the observed large-scale photospheric magnetic field is higher in cycles with larger magnetic-field values and with a more stable GMF structure. Non-polar CHs are divided into three groups depending on the GMF value and a rate of the structural GMF rearrangement.     

Large Flares (M1–X7) in Solar Activity Cycle 24

Geomagnetism and Aeronomy - The large (X-ray class &gt; M1) and very large (X-ray class &gt; X1) flares (according to the observations of GOES-15 and Preliminary data from Current Catalog...     

Latitude-Longitude Characteristics of the North–South Asymmetry of Solar Activity

Geomagnetism and Aeronomy - The characteristics of the latitude-longitude distribution of the north–south (NS) asymmetry of the number of sunspots for the period of 1874–2013 are...     

On The Question of North–South Asymmetry of Solar Activity

Geomagnetism and Aeronomy - The paper studies the dynamics of the distribution of the index of the north–south asymmetry of the sunspot number for the phase of the 11-year cycle, from cycle...     

Possible Solar Modulation of Average Temperature in the Contiguous United States during 1895–2018

Geomagnetism and Aeronomy - With monthly average temperature series in the contiguous United States during the period from January 1895 to July 2018, the author uses wavelet analysis to investigate...     

Manifestation of the Lunar–Solar Tide and Free Oscillations of the Earth in the Variations of the Magnetic Field

The results of processing and analyzing the instrumental observations of the Earth’s magnetic field at the Geophysical Observatory Mikhnevo of the Institute of Geosphere Dynamics of the Russian Academy of Sciences (IGD RAS) for 2010–2015 are presented. Quasi-harmonic components with the periods close to the lunar–solar tidal waves are revealed in the spectra of geomagnetic variations over a period of 0.4 to 30 days. The elliptical S₁ tidal wave which is detected in the geomagnetic variations has modulations with periods of 1/3, 1/2, and 1 year. The spectra of the geomagnetic variations contain peaks corresponding to the free oscillations of the Earth. The analysis of the time series of the magnetic field for the period of the strong earthquakes in the absence of geomagnetic disturbances revealed the fine structure of the Earth’s fundamental spheroidal mode ₀S₂, which splits into five singlets. The established features of the spectrum of geomagnetic variations are helping the development of the new method for studying the deep structure of the Earth and the properties of the inner geospheres for estimating the viscosity of the Earth’s outer core and dynamics of the current systems in the outer (liquid) core, as well as for exploring, with the use of empirical data, the general regularities governing the regimes of energy exchange processes in the geospheres.     

Solar cycle variations in the ionospheric Alfven resonator 1985–1995

Based on long-term observations of the resonance structure in the electromagnetic background noise spectrum (resonance spectrum structure, RSS), recorded in the frequency range 0.1–10 Hz over one complete solar cycle (11 years, from 1985 to 1995), it was found that the resonance conditions for Alfven waves in the ionosphere (ionospheric Alfven resonator) are determined at midlatitudes by the level of solar activity. RSS are regularly observed in years of minimum solar activity, and are practically absent in years of maximum solar activity. It is shown that consideration of the ionospheric Alfven resonator explains the dependence of the RSS on solar activity.     

Effects of Energetic Solar Emissions on the Earth–Ionosphere Cavity of Schumann Resonances

Schumann resonances (SR) are the electromagnetic oscillations of the spherical cavity bounded by the electrically conductive Earth and the conductive but dissipative lower ionosphere (Schumann in Z Naturforsch A 7:6627–6628, 1952). Energetic emissions from the Sun can exert a varied influence on the various parameters of the Earth’s SR: modal frequencies, amplitudes and dissipation parameters. The SR response at multiple receiving stations is considered for two extraordinary solar events from Solar Cycle 23: the Bastille Day event (July 14, 2000) and the Halloween event (October/November 2003). Distinct differences are noted in the ionospheric depths of penetration for X-radiation and solar protons with correspondingly distinct signs of the frequency response. The preferential impact of the protons in the magnetically unshielded polar regions leads to a marked anisotropic frequency response in the two magnetic field components. The general immunity of SR amplitudes to these extreme external perturbations serves to remind us that the amplitude parameter is largely controlled by lightning activity within the Earth–ionosphere cavity.     

Solar sources of interplanetary shocks on November 7–11, 2004

In a methodically independent manner compared to earlier works, an adjustment is performed to a series of solar sources, including six interplanetary shocks observed on November 7–11, 2004, during a very large solar-terrestrial storm. The results of different researchers are compared with one another and with this publication.     

Dynamics of Ionospheric Alfvén Resonances from the End of Cycle 21 through Cycle 24 of Solar Activity

Geomagnetism and Aeronomy - The results of the study of the dynamics of ionospheric Alfvén resonances (IARs) in a range of 0–10 Hz based on data from magnetic field observations at the...