24th Solar Activity Cycle Research Articles

MODELING OF SPATIAL-TEMPORAL VARIATIONS OF PHYSICAL PROCESS PARAMETERS IN THE IONOSPHERIC PLASMA OVER UKRAINE DURING THE MAXIMUM PHASE OF THE 24-TH SOLAR ACTIVITY CYCLE (2012—2015)

The object of research is physical processes occurring in the ionospheric plasma. The subject of research: spatial-temporal variations of the main parameters of the ionospheric plasma, which were obtained using incoherent scatter radar. Research methods include the ground-based radiophysical method of incoherent scatter of radio waves, statistical analysis of observation results, and semi-empirical modeling of parameters of dynamic and thermal processes. Modeling and analysis of spatial-temporal variations of the dynamic and thermal processes parameters in the ionosphere during the maximum phase of the 24th solar activity cycle (2012—2015) have been performed using experimental data obtained by the Kharkiv incoherent scatter radar. For the periods of the equinoxes and solstices, diurnal dependences of process parameters in the ionospheric plasma at altitudes from 210 to 450 km were constructed. The values of plasma transfer velocity due to ambipolar diffusion, the density of the full plasma flux, and the flux of charged particles due to ambipolar diffusion were determined. The values of the energy supplied to the electron gas, the density of the heat flux transferred by electrons from the plasmasphere to the ionosphere, as well as the velocity of the equivalent neutral wind and the meridional component of the neutral wind velocity, were calculated. It was established that for the considered periods, the effects of space weather variations and geomagnetic activity were significantly manifested in variations of the plasma flux density due to ambipolar diffusion, the density of the full plasma flux, as well as the energy supplied to electrons per unit time. Quantitative and qualitative characteristics of these parameters were typical but changed significantly (by 2…3 times) in some cases, even with a slight increase in geomagnetic activity.

MODELING OF SPATIAL-TEMPORAL VARIATIONS OF DYNAMIC AND THERMAL PROCESS PARAMETERS IN GEOSPACE OVER UKRAINE DURING THE MINIMUM OF 24-TH CYCLE OF SOLAR ACTIVITY (2009, 2019)

We have performed the modelling of spatiotemporal variations of parameters of dynamic and thermal processes in ionospheric plasma at the phases of the minimum of the 24-th cycle of solar activity according to the Kharkiv radar of incoherent scattering. The diurnal dependences of parameters of the processes in the ionospheric plasma at altitudes from 210 to 450 km are constructed for typical geophysical periods (vernal and autumn equinoxes, summer and winter solstices). In the paper, the analysis of spatial and temporal variations of parameters of dynamic and thermal processes in the ionosphere is presented. We determined the value of the plasma transfer velocity due to ambipolar diffusion, the density of the full plasma flux, and the flux of charged particles due to ambipolar diffusion, the value of the energy supplied to the electron gas, the density of the heat flux transferred by electrons from the plasmasphere to the ionosphere, as well as the velocity of the equivalent neutral wind, and the meridional component of the neutral wind velocity. We found that weak variations in space weather do not lead to significant changes in spatiotemporal variations of the parameters of dynamic and thermal processes in the ionosphere for most of the studied periods. Quantitative and qualitative characteristics of most of these parameters and their diurnal variations were typical for the considered seasons. On the contrary, the velocity of the equivalent neutral wind changed significantly (up to 2—2.5 times) even with a weak increase in geomagnetic activity. The reasons for such changes may be the strengthening of horizontal thermospheric winds and the penetration of zonal magnetospheric electric fields into midlatitudes during the equinoxes. The obtained results of calculations can be used in basic studies of solar-terrestrial relations and geospace, for the solution of applied problems related to the ability to predict the state of space weather, as well as for further development of the regional ionosphere model CERIM IION. The object of research: physical processes in the ionospheric plasma. The subject of research: spatiotemporal dependences of the main parameters of ionospheric plasma, which were obtained using incoherent scattering radar. Research methods — terrestrial radiophysical method of incoherent scatter of radio waves, statistical analysis of observation results, semi-empirical modelling of parameters of dynamic and thermal processes.

Long‐Term Relationship Between foF2 From China Ionospheric Stations and Solar Activity During the 24th Solar Activity Cycle

AbstractThis paper employs the complete data of six ionospheric observation stations in China in the 24th solar activity cycle and researches the variation of frequency of the F2 layer (foF2) and the relationship with the solar activity indices. We discover that the dependence of foF2 on the sunspot number (R) and the solar radio flux of 10.7 cm wavelength (F10.7) is strongest in mid‐solar years, and weakest in high solar years. At the same time, the long‐term variation trends of foF2, R and F10.7 in the complete 24th solar activity cycle are analyzed using the mutual information method in information theory. We utilize the linear and nonlinear methods to compare the effects of long term change relationship between foF2 and R during the rising and falling phases of solar activity. The findings reveal that the sunspot number is more suitable to depict the long‐term trend of foF2 in China, and the relationship between them is better described by nonlinear quasi‐polynomial. This result has important implications for improving foF2 forecasts and the prediction accuracy of some ionospheric models.

September 2017 Solar Flares Effect on the Middle Atmosphere

This paper examines the response of the upper atmosphere to increased radiation following exceptional solar activity in September 2017. The active region of the Sun AR2673 has caused intense solar-terrestrial disturbance. This active region has generated several powerful X-class solar flares. The strongest outburst of the 24th solar activity cycle X9.3 occurred on 6 September 2017. The second powerful solar flare X8.2 occurred on 10 September 2017. Both flares caused an increase of the solar irradiance in extreme ultraviolet and soft X-ray spectral regions, and Ly-α line. The empirical FISM2 model was used to obtain data on the radiation fluxes from solar flares. The HAMMONIA chemistry–climate model was used to analyze the effect of radiation on the neutral atmosphere. This work presents the results of the effect of solar flares on the chemical composition and ozone of the upper and middle atmosphere.

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.

Statistical analysis of the orbital motion of selected Earth’s artificial satellites during the 24th cycle of solar activity

Statistical analysis of the orbital motion of selected Earth’s artificial satellites during the 24th cycle of solar activity

Statistical characteristics of geomagnetic storms in the 24th cycle of solar activity

Statistical characteristics of geomagnetic storms in the 24th cycle of solar activity

Statistical Characteristics of Geomagnetic Storms in the 24th Cycle of Solar Activity

Statistical Characteristics of Geomagnetic Storms in the 24th Cycle of Solar Activity

Use of the DBM Model to the Predict of Arrival of Coronal Mass Ejections to the Earth

This paper analyzes the results of modeling coronal mass ejection (CME) propagation in 2010–2011 obtained using input data from different sources: CME catalogs SEEDS and CACTus, and predictions of the velocity of quasi-stationary solar wind fluxes, as an environment, through which CMEs propagate. As the model of quasi-stationary solar wind fluxes, the model for predicting the velocity of the solar wind of the Space Weather Forecast Center of the Skobeltsyn Institute of Nuclear Physics of Moscow State University, operating online, is used. The CME prediction is carried out using the Simple Drag-Based Model. A comparison was performed between the ICME arrival time and their velocities obtained when modeling with data from the open ICME catalogs: the Richardson and Cane ICME catalog and the GMU CME List. Based on the comparison, it was concluded that a more accurate prediction for the growth phase of the 24th solar activity cycle was obtained using data on CME parameters from the CACTus database. The obtained errors in predicting the ICME parameters are comparable with the errors of other existing models.

Зависимость солнечного ультрафиолетового излучения в диапазоне 280—400 нм от изменений общего магнитного поля Солнца

The study presents the results of the correlation analysis for the average seasonal values of intensity of solar UV radiation (297–330 nm), as well as for the energy of the lines of solar spectral irradiance with total solar irradiance and total magnetic field of the Sun for the period of 2008–2018 (the 24th cycle of solar activity). The analysis is carried out using the spectral observations of solar UV radiation at Novolazarevskaya station (Antarctica), the SORCE spacecraft and WSO (Wilcox Solar Observatory) data. The dependence of the UVB-UVA radiation of 280–315 nm (UV-B) and 315–400 nm (UV-A) on changes in the total magnetic field of the Sun is revealed.

24th Cycle of Solar Activity: Geoefficiency of Flares

Various aspects of the of geoefficiency of solar-activity phenomena, such as flares and coronal mass ejections (CMEs), are considered. The number of geoefficient events was about two times lower in the 24th cycle than in the 23rd cycle. Statistical data on major flares and the Dst index in different phases of the 24th cycle is compared. Large flares (X-ray class > M5) were analyzed based on data from GOES-15 satellite observations in the 24th solar activity cycle. The three main geomagnetic indices, Ap, Kp, and Dst, were analyzed in comparison with the F10.7 index and the sunspot number (SSN).

The Current 24th Cycle of Solar Activity in the Minimum Phase: Preliminary Results and Features of Development

The characteristics and course of development of the current 24th solar activity (SA) cycle allow it to be considered a cycles in an epoch of lowered SA. Comparison of evolutionary changes in the cycles of different epochs in the phases of the minimum made it possible to distinguish two groups by the rate of decline. The first group with a relatively fast decline (~15 months) includes all cycles of epochs of increased SA, transition periods, and cycle 16 from the epoch of lowered SA. The second, with a slow decline (~40 months), contains the rest of the cycles of epochs of lowered SA, including the current 24th one, the minimum of which can be expected in the first half of 2020.

Possibility of Diagnostics of the Beginning of Solar Cycle 25 Based on Its Precursors at Mid-Heliolatitudes

The potential to diagnose the beginning of the solar cycle based on the detection of small-scale magnetic formations, the magnetic nodes of ephemeral active regions in the zone of mid-heliolatitudes from 40° to 60°, has been studied. Magnetic nodes were detected at the stage of their emergence by the multifractal segmentation method, which was previously used to fix new magnetic fluxes of active regions in the zone of low heliolatitudes. Statistical estimates of the number of magnetic nodes recorded by this method were performed based on magnetograph data from the Synoptic Optical Long-term Investigations of the Sun of the National Solar Observatory (SOLIS NSO) for the 24th solar activity cycle, as well as for the beginning of the 25th activity cycle. A precursor of solar cycle 24 has been found in the form of a burst in the number of magnetic nodes in 2007–2008 that significantly exceeds the background value characteristic of the period 2011–2015. Two years later, the first active regions began to appear at latitudes of 30° ± 10°. A similar sequence of phases in the beginning of the cycle was found for cycle 25. Unlike the situation with solar cycle 24, the mass appearance of high-latitude active regions of cycle 25 occurred about 2.5 years after the burst in the number of nodes of ephemeral active regions.

Behavior of F2-layer parameters and solar activity indices in the 24th cycle

The analysis of the behavior of the critical frequency foF2 during the 24th solar activity cycle (Danilov and Konstantinova, 2020a, c) is prolonged for two more months and the nighttime hours. In addition to the Rz and Ly-α indices used in the aforementioned papers for correction of the F10.7 index during the 24th cycle, the commonly used Mg II index is added. The results confirm the previous conclusions on the existence of the “vague” period with chaotic behavior of foF2 and the recovery of the negative trend in foF2 after 2008–2010. A comparison of the F10.7 index with three other SA indices (Ly-α, Rz, and Mg II) for the 22nd, 23rd, and 24th SA cycles is performed. It is shown that the relationship between F10.7 and other indices is close in the 22nd and 23rd cycles but differs from that in the 24th cycle. The corrected values of F10.7 in the 24th cycle are proposed for analysis of ionospheric trends during that cycle.

Trends in Parameters of the F2 Layer and the 24th Solar-Activity Cycle

Trends in foF2 are analyzed according to the data of Juliusruh and Boulder ionospheric stations to 2018. It is shown that the use of the traditional solar-activity index, F10.7, leads to an unexplainable foF2 trend if the data for the 24th solar-activity cycle are included in the analysis. It is suggested that the F10.7 index does not correctly describe the solar ultraviolet-radiation variation in that cycle. Correction of that index with the Rz (sunspot number) and Ly-α (intensity of the Lyman-alpha line in the solar spectrum) indices is performed. It is shown that reasonable values of the foF2 trends are then obtained. A similar analysis for hmF2 trends leads to the same results.

Physical Conditions in Coronal Holes

The physical conditions in the chromosphere of polar and equatorial coronal holes in the decay phase of the 24-th solar activity cycle are studied. Models of the chromosphere are constructed based on the intensities of the HeI 10830 A and Hα lines and using a non-LTE program. The calculations showed that the temperature in equatorial coronal holes is similar to that of polar coronal holes. The temperature in coronal holes is lower than that of the unperturbed chromosphere and increases depending on height in the chromosphere. The difference between the atmospheres of coronal holes and the quiet Sun begins at the level of the upper photosphere- lower chromosphere.

Dynamics of Electric Current’s Parameters in Active Regions on the Sun and Their Relation to the Flare Index

Data from the Helioseismic and Magnetic Imager (HMI) on board the Solar Dynamics Observatory (SDO) on the components of the magnetic field vector in the photosphere for 39 active regions (AR) of the 24th solar activity cycle are used to calculate the parameters of the electric current. The time variations in the electric current parameters in the AR over the time the region is within ±35° of the central meridian are studied. An attempt is made to relate the parameters of the current in the photosphere and their dynamics to the level of flare activity of the region. These studies have yielded the following results: (1) The change in the total unsigned current in an AR is synchronous or quasi-synchronous with changes in the magnetic flux; (2) A relation between the total unsigned current and the flare index (FI) exists, but is weak (correlation k = 0.48); (3) The imbalance of the vertical electric currents for all 39 of the AR studied here was low and did not exceed a few percent, which indicates closure of the current structures on all scales within an AR; (4) The highest correlation (k = 0.72) with the flare index is observed for a time averaged absolute value of the density of the vertical electric current; (5) Statistical studies yield a critical level of equal to 2.7 mA/m2: when this level is exceeded in an AR, flares with higher x-ray classes (M and X) are observed and when the current density falls below the threshold value, there is a reduction in the flare productivity of the region; (6) For the example of two regions with an emerging magnetic flux it is shown that pumping magnetic energy into the corona requires some time; the time interval between the jump in and the onset of the development of the first powerful flares in x-ray classes M and X is at least 12-20 hours; (7) The character of the relation between the time variations in the average value of the density of the horizontal current and the imbalance in the vertical current ρjz with the level of flare activity of an AR is more complicated and requires separate, more detailed studies.

Minor Ground Level Enhancements in the Solar Cosmic Rays in the 24th Solar Activity Cycle

The first (preliminary) results of a systematic search for minor ground level enhancement (GLEs) in solar cosmic rays (SCRs) in the 24th solar activity cycle are presented. The search was conducted based on the data of the global network of neutron monitors with allowance for the results of direct satellite measurements. The initial assumption is that such increases point to the possible acceleration of solar particles in shock waves, which are generated by coronal mass ejections. The shape of the integral spectrum of the accelerated particles according to observations of neutron monitors and measurements from near-Earth space vehicles could serve as a determinant for checking that hypothesis. Studying the spectra manifests an informativity of our approach to a better understanding of SCR source properties.

Trends in hmF2 and the 24th solar activity cycle

The measurements of the F2-layer height, hmF2, at Juliusruh station during 1958–2018 are analyzed by the method developed by the authors earlier and used to determine long-term trends in parameters of the F2 layer. It is found that, in the same way as for the behavior of the critical frequency described by the authors in the previous publication, peculiarities in the hmF2 behavior are observed after 2002–2003. If the solar activity index F10.7 is used, an increase in the ΔhmF2 value is observed and provides a positive trend in hmF2 that contradicts to the available ideas on the continuing process of cooling and contraction of the upper atmosphere. If the F10.7 index corrected by other SA indices (the sunspot number Rz or the Lyman-alpha line intensity) is used, as it has been done for the foF2 trends in the previous publications by the authors, the picture of changes in the hmF2 trends is obtained similarly to the changes in the foF2 trends. A well pronounced negative trend in hmF2 is observed to 2002–2003, and then it is substituted by a chaotic change in ΔhmF2 during the “vague” period, whereas during the last analyzed years it becomes negative again. Analysis of the slope s of the foF2(hmF2) dependence shows that there is a systematic decrease in s with time. That confirms the conclusion of the authors on a decrease in the oxygen amount in the thermosphere.

Coronal Holes during the Period of Maximum Asymmetry in the 24th Solar Activity Cycle

The current 24th solar activity cycle differs substantially from previous cycles in a number of parameters, especially in terms of a large asymmetry in the number of sunspots (Sp) during the second peak of its maximum. From March 2013 through December 2015. a significant predominance was observed in the number of sunspots in the southern hemisphere. The main purpose of this paper is to clarify the behavior of coronal holes (CH) during this period. This study is based on an analysis of data recorded by the 19.3 nm channel of the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamic Observatory (SDO). Two methods of detecting CH (simplified visual and the Spatial Possibilistic Clustering Algorithm (SPoCA)) are used to obtain time series of daily total CH areas for the Sun’s northern and southern hemispheres. The two methods agree on the estimated areas of the CH. A comparison of the observed variations in the areas of the CH with the numbers and areas of sunspots showed that in this period, activity predominates in the S-hemisphere both in terms of sunspots and in terms of the total CH area. Here a rise in the area of the CH follows a rise in sunspot activity by roughly half a year. It is suggested that the CH and spots are associated elements of the overall magnetic activity of the Sun, in qualitative agreement with studies of activity complexes. A dipole poloidal field in the form of open CH fields and a toroidal field in the form of active regions are related on time scales substantially shorter than the solar cycle.