Vol 11, No 3 (2025)
Articles
PROCESSES OF ACCELERATION AND TRANSFER OF ELECTRONS IN A PULSE CIRCULAR RIBBON FLARE
Abstract
We discuss acceleration and transport of electrons in the circular flare SOL2024-03-25T06:37:00 of the M4.4 X-ray class, characterized by a record-short duration of hard X-ray emission pulse. We have used radio data in the 0.1–40 GHz range, including images of the flare region in the Siberian Radio Heliograph frequency range. Microwave and hard X-ray emissions are generated in the vicinity of the magnetic domain by the interaction of ropes visible at 1600 Å. The impulsive stage ended with a short peak <5 s long, recorded simultaneously at 35 GHz and in the 100–300 keV range. After the peak under ropes, a long loop in the ultraviolet (UV) rises and a broad plasma ejection appears which is directed along the outer spine observed before the flare. Large loops connect the spine and the remote source. There is a broadband microwave source at the remote footpoint at 215 arc. sec., with the delay of its maximum from the peak in the flare core being ~5 s, and the electron propagation velocity along the large loops estimated at one-third of the velocity of light. A distinctive feature of the radiation of the remote source was high degree of its circular polarization. The meter flare emission indicates that tops of large loops are filled with non-thermal electrons with large pitch angles. The set of spatial, spectral, and polarization characteristics of microwave sources obtained for the first time is discussed in the context of the known results on the nature of circular ribbon flares.
Solar-Terrestrial Physics. 2025;11(3):3-12
3-12
FEATURES OF TURBULENT CASCADE DEVELOPMENT IN THE MAGNETOSHEATH DURING ICME
Abstract
Large-scale disturbances in the interplanetary medium are the main cause of the global perturbations inside Earth’s magnetosphere. Transition region called magnetosheath is known to be located in front of the magnetosphere in which plasma and magnetic field properties, as well as their variations differ significantly from those in the solar wind. Particularly, plasma passage through the magnetosheath has been demonstrated to modify substantially features of the cascade of turbulent fluctuations of the solar wind, with the pattern of the modification being different for quiet and disturbed conditions in the interplanetary medium. In this study, we examine features of turbulent cascade formation in the magnetosheath during interplanetary manifestation of coronal mass ejection (ICME), by analyzing several cases of ICME interactions with the magnetosphere. The analysis is conducted by comparing magnetic field variations measured simultaneously in the solar wind and in the dayside magnetosheath by Wind, Cluster, THEMIS, and MMS spacecraft in 2016–2017. Interaction of ICME with the magnetosphere is shown to cause the least change in the fluctuation power if there is a compression region in front of it; on the opposite, when there is no compression region, the fluctuation power increases considerably. ICMEs that caused significant changes in the Dst index were determined to be accompanied by the least changes in the turbulent cascade in the magnetosheath, whereas the most significant modification of the turbulence features were observed during ICMEs which did not trigger substantial geomagnetic disturbances
Solar-Terrestrial Physics. 2025;11(3):13-21
13-21
EFFECT OF SOLAR ACTIVITY AND SOLAR WIND PARAMETERS ON PLASMA TEMPERATURE AND DENSITY IN EARTH’S PLASMASPHERE
Abstract
Measurements from the Interball-1 and Magion-5 satellites of the Interball mission in 1995–2001 have been used to analyze the dependence of the equatorial plasmasphere characteristics on magnetic local time, as well as on solar activity, dynamic pressure, and solar wind density. The proton density at solar minimum is on average higher than at solar maximum, which is probably due to changes in plasma mass composition in the plasmasphere at solar maximum. The daytime and nighttime proton temperatures increase with increasing solar extreme ultraviolet flux, at least in the years of solar maximum. The plasmaspheric plasma density and thermal pressure rise with increasing dynamic pressure and/or density of the undisturbed solar wind, which might be associated with restructuring of the convective electric field in the magnetosphere.
Solar-Terrestrial Physics. 2025;11(3):22-30
22-30
INFLUENCE OF INTERPLANETARY PARAMETERS ON THE DEGREE OF SYMMETRY OF THE RING CURRENT
Abstract
The paper studies the influence of interplanetary factors on the degree of symmetry of the magnetospheric ring current. The geomagnetic indices SYM-H, ASY-H, and interplanetary parameters for the period 1981–2015 are considered. The indicator of the degree of symmetry of the ring current is the ratio SYM-H/ASY-H. Analysis is based on annual averages of geomagnetic and interplanetary parameters. This approach allows us to identify large-scale patterns. The relationships are examined of the degree of symmetry of the ring current and the indices SYM-H and ASY-H with the value B of the interplanetary magnetic field (IMF), the IMF north-south component Bn, and the solar wind velocity V. It is concluded that properties of magnetospheric ring currents are described by these indices more adequately when offsets in their values are taken into account than without regard for them. It is found that when offsets in ASY-H are considered the symmetric ring current prevails approximately twice over the asymmetric one for average conditions in the solar wind: V<550 km/s, B<10 nT, ǀBnǀ<2 nT. Under quiet solar wind conditions (V<450 km/s, B<5.5 nT, ǀBnǀ<0.7 nT), the degree of symmetry of the ring current increases. It is established that with intensification of interplanetary parameters (V, B, ǀBnǀ) the symmetric ring current index SYM-H grows more strongly than the asymmetric ring current index ASY-H.
Solar-Terrestrial Physics. 2025;11(3):31-36
31-36
GEOMAGNETIC CUTOFF OF COSMIC RAYS DURING THE MARCH 23–24, 2023 MAGNETIC STORM: RELATIONSHIP WITH SOLAR WIND PARAMETERS AND GEOMAGNETIC ACTIVITY TAKING INTO ACCOUNT LATITUDINAL EFFECTS
Abstract
In this paper, we calculate geomagnetic cutoff rigidities during the strong magnetic storm of March 23–24, 2023, using 1) the spectrographic global survey method based on observational data from cosmic ray recording by the global network of stations (Rsgs); 2) numerical trajectory calculations in a model magnetic field of the magnetosphere (Reff). The geomagnetic cutoff rigidity has been determined for nine cosmic ray stations at different latitudes. We calculated the correlations of the variations in the geomagnetic cutoff rigidity ΔRsgs and ΔReff with magnetic and dynamic solar wind parameters and the geomagnetic activity indices Dst and Kp. It has been found that the geomagnetic cutoff rigidity calculated by both methods correlate most strongly with Dst and the electromagnetic parameters of the solar wind. No significant correlation with the dynamic parameters was observed. The analysis has shown that the response of ΔRsgs to the controlling magnetic parameters and Dst changes with latitude of the observation station: the correlation reaches its highest values at midlatitudes and drops significantly toward the equator. The correlations of ΔReff calculated by the model do not reveal a latitudinal dependence.
Solar-Terrestrial Physics. 2025;11(3):37-43
37-43
STUDYING DYNAMICS OF ENERGY SPECTRUM OF SOLAR DIURNAL VARIATIONS IN COSMIC RAYS DURING SOLAR ACTIVITY CYCLES 20–25, USING METHOD OF CROSSED MUON TELESCOPES
Abstract
The cosmic ray (CR) intensity recorded by ground-based detectors experiences solar diurnal variations (SDVs) associated with the existence of anisotropic angular distribution of CRs in near-Earth space. Long-term observations show that SDVs exhibit a dependence on the solar activity cycle, experiencing periodic 11- and 22-year variations. Such behavior of SDVs is linked to a change in the nature of galactic CR propagation in the heliosphere when it changes during a solar activity cycle. On the other hand, this phenomenon can be partially due to a change in the magnitude of CR drift by the geomagnetic field associated with changes in the SDV energy spectrum.
In this work, we determine the dynamics of the SDV energy spectrum in solar activity cycles. The solution to this problem presents certain difficulties associated with peculiarities of ground-based CR recording and with the sensitivity of CR detectors to changes in the state of environment. Therefore, we employ an approach using crossed muon telescopes to estimate it, which allows us to bypass the above difficulties. We analyze data from Yakutsk, Nagoya, Sao Martinho, and Hobart muon telescopes for 1972–2022. It is shown that at solar minima during periods of positive polarity of the Sun's general magnetic field, a significant softening of the spectrum is observed. The results are discussed.
Solar-Terrestrial Physics. 2025;11(3):44-49
44-49
MHD WAVES IN THE PRE-FRONT REGION OF THE INTERPLANETARY SHOCK ON MAY 10, 2024
Abstract
The article reports on the study of the dynamics of the IMF turbulent component from the quiet period on May 7, 2024 to the arrival of an interplanetary shock wave in the second half of May 10, 2024. To achieve the stated goal, 1-minute direct measurements of interplanetary medium parameters on the ACE, DSCOVR, and WIND spacecraft are involved in the analysis. Spectral analysis methods are used to study the evolution of power spectra of fluctuations in IMF modulus and MHD waves in the inertial portion of the SW turbulence spectrum at frequencies ~2.5∙10–4–8.3∙10–3 Hz. The contribution of Alfvén, fast, and slow magnetosonic waves to the observed power spectrum of the IMF modulus measured by each of the three spacecraft is determined, and power spectra of MHD waves of these types are identified. It is shown that the power of the spectra of fluctuations in the IMF modulus and MHD waves increases by more than an order of magnitude as the shock wave approaches the point of its recording on the spacecraft. It is concluded that this is due to the generation of MHD waves by fluxes of energetic storm particles (ESP) — cosmic rays with energies ~1 MeV, observed in the region ahead of the interplanetary shock wave front. Analysis of all measurement data allows for the assumption that a significant increase in low-energy CR fluxes (~1 MeV) and SW turbulence levels may lead to a change in the IMF direction in the region adjacent to the IPS front.
Solar-Terrestrial Physics. 2025;11(3):50-58
50-58
FEATURES OF PROPAGATION OF COMPRESSIONAL LONG-PERIOD OSCILLATIONS PENETRATING FROM THE INTERPLANETARY MEDIUM IN THE MAGNETOSPHERE—IONOSPHERE SYSTEM
Abstract
We have studied properties of Pi3 pulsations with a period of ~30 min in the magnetosphere—ionosphere system, using satellite and ground-based observations. According to the data from ground-based magnetic stations in the pre-noon sector of the magnetosphere, propagation of pulsations was revealed in azimuth from the day side to the night side at a velocity 3–9 km/s in the band of corrected geomagnetic latitudes Φʹ=76–79°. Along the meridian, the signal propagated poleward at a velocity 0.5–5 km/s. Analysis of signal spectra at stations located along different meridians shows three maxima: one latitude-independent maximum at a frequency of 0.55 mHz, and two latitude-dependent maxima at frequencies of 0.82 and 0.96 mHz respectively, at higher and lower latitudes. The first maximum corresponds to ULF waves penetrating from the solar wind; the other two, to magnetospheric field line resonances. The equivalent current system (ECS) during the pulsation recording was obtained by two methods: the method of spherical elementary current systems and the magnetogram inversion technique. Analysis of ECS derived by both methods has demonstrated that they match each other. The ECS during pulsations in the pre-noon sector is a large vortex consisting of smaller vortices that propagate in the ionosphere along the “sea-land” boundary line, i.e. meridional poleward propagation at velocities close to the average pulsation propagation velocities prevailed. According to the map of field-aligned current distribution in the ionosphere, the width of the maximum of the westward electrojet lies at the latitude of the ECS maximum (in the south of the large vortex) on the boundary between the regions of inflowing and outflowing field-aligned currents (regions 1 and 2), where field line resonances are observed. The obtained ECS corresponded to the DP2 current system with a predominant westward electrojet in the pre-noon and night sectors. Satellite data analysis has shown the following. In the solar wind, ULF waves in the Pi3 pulsation range propagated at a velocity of 186.4 km/s, which is significantly lower than the velocity of the average being as high as 550 km/s. This velocity is explained by the fact that the waves propagate toward the Sun and are carried by the solar wind to Earth. In the magnetosphere, pulsations with a predominant compression component propagated from the night side to the day side at a velocity 90–110 km/s; from the delays in the onset of maxima of energetic electron differential fluxes, velocities 20–40 km/s were identified.
Pulsations in this event were caused by both external (oscillations in the solar wind) and internal sources (magnetospheric resonator, which could be excited, among other things, by a substorm). The dynamics of the “fine structure” of a large vortex - small vortices, in the magnetosphere as a whole coincides in propagation velocity and direction with geomagnetic pulsations.
Solar-Terrestrial Physics. 2025;11(3):59-69
59-69
PREDICTION OF ELECTRON FLUXES IN A CIRCULAR POLAR ORBIT: SELECTION OF PREDICTORS
Abstract
We have investigated the relationship of variations in >0.7 and >2 MeV electron fluxes of Earth's outer radiation belt in a circular polar orbit with solar wind and interplanetary magnetic field parameters, as well as with geomagnetic indices and the logarithmic electron flux in the geostationary orbit in order to explore the possibility of predicting them. We have selected the optimal input features for predicting electron fluxes in low polar orbits, which is important for ensuring the radiation safety of future space missions.
We have examined integral and maximum electron fluxes of these energies over the span of a day. We have obtained forecasts with a horizon of 1 and 2 days for an interval of 2 months in 2020 for daily maximum and integral fluxes based on linear regression.
Solar-Terrestrial Physics. 2025;11(3):70-79
70-79
IONOSPHERE RESPONSE TO THE IMPACT OF AN EXTRAORDINARY RADIO WAVE WHEN LOCATED AT A FREQUENCY CLOSE TO THE HEATING FREQUENCY
Abstract
The paper presents the results of experiments on the impact of powerful high-frequency radio emission from the SURA mid-latitude heating facility (56.1° N, 46.1° E) on Earth's ionosphere. The disturbance in the ionosphere was created by a radio wave of extraordinary polarization under conditions when the ordinary component of the powerful wave was not reflected by the ionosphere. The sounding of the disturbed region was carried out with a probe radio wave of the same polarization at a frequency higher than the heating frequency by 228–400 kHz. During the impact on the ionosphere, a weak scattered signal with an amplitude 40–60 dB lower than the amplitude of the specular reflection signal from the F-region was received from the height of reflection of the powerful radio wave. This means that the artificial disturbance of the plasma density occurred in the region of reflection of the powerful radio wave of extraordinary polarization. Possible causes of the disturbance are discussed.
Solar-Terrestrial Physics. 2025;11(3):80-90
80-90
METEOROLOGICAL RESPONSE TO CHANGES IN IONOSPHERIC ELECTRIC POTENTIAL CAUSED BY DISTURBED SOLAR WIND
Abstract
The ionospheric electric potential (EP) is utilized as a characteristic of the solar forcing to determine the tropospheric response during strong disturbances. We compare EP calculations carried out using the 2001 and 2005 versions of the Weimer model. Differences in the spatial distribution of EP during geomagnetic superstorms have been revealed for the models considered. The behavior of EP anomalies and contrast averaged over high latitudes is shown. The EP contrast is the difference between EP anomalies averaged over regions of the same sign. It has been found that changes in EP anomalies differ in different versions of the model, whereas EP contrast variations, calculated by both versions, behave synchronously during disturbances. Correlation analysis of variations in the averaged EP contrast with variations in the PC geomagnetic index has shown that both can be used as indicators of solar activity to study individual geomagnetic superstorms. An increase in the EP contrast is accompanied by an increase in the contrast of the meteorological parameters, in particular in the contrast of high clouds during disturbances.
Solar-Terrestrial Physics. 2025;11(3):91-97
91-97
CHINESE-RUSSIAN JOINT RESEARCH CENTER ON SPACE WEATHER: RESULTS AND PROSPECTS
Abstract
We present an overview of the history, the main scientific results and prospects of the Chinese-Russian Joint Research Center on Space Weather. The Chinese-Russian Joint Research Center was established by the Institute of Solar-Terrestrial Physics SB RAS (ISTP SB RAS) and National Space Science Center CAS (NSSC CAS) in 2000. The center deals with fundamental issues in modern solar-terrestrial physics, such as quantitative description of the processes in complex interconnected system Sun — interplanetary medium — magnetosphere — ionosphere — atmosphere, assessment of capabilities of predicting interactions within this system, development of effective models for forecasting the state of the atmosphere and near-Earth space. Over the 24-year period, the Joint Research Center has united more than 10 scientific institutes in Russia and China; about 60 scientific projects have been implemented, and more than 400 joint scientific articles have been published. Joint efforts of Russian and Chinese researchers allowed obtaining important results in study of physical processes in near-Earth space. The Chinese-Russian Joint Research Center has proven its usefulness and continues studying the Sun, solar-terrestrial relations, and near-Earth space.
The future work of the Joint Research Center will be closely linked to the implementation of major unique projects in China and Russia: the International Meridian Circle Program (IMCP) led by NSSC CAS, and the National Heliogeophysical Complex of the Russian Academy of Sciences (NHC RAS) led by ISTP SB RAS. We describe these projects in this paper
Solar-Terrestrial Physics. 2025;11(3):98-113
98-113
THE RAYLEIGH—TAYLOR INSTABILITY AS A TRIGGER OF SOLAR FLARES
Abstract
The review of authors’ papers is devoted to the essential role of the Rayleigh—Taylor instability (RTI) as a trigger of flare energy release. We have analyzed two cases of RTI: near coronal loop footpoints and at the loop top. RTI near loop footpoints requires pre-heating of chromospheric plasma. This pre-heating can be realized due to Joule dissipation in partially ionized plasma under condition of the Cowling resistivity. RTI at the loop top arises in current-carrying coronal loop loaded by prominence. We have determined the conditions of RTI as a flare trigger in both cases. It is shown that RTI generates super-Dreicer electric field in the chromospheric parts of a loop. This is the promising solution of longstanding “number problem” of particle acceleration. RTI can be also a cause of prompt (~10 s) hot onset precursor events (HOPE).
Solar-Terrestrial Physics. 2025;11(3):114-119
114-119
OBSERVATIONS OF LARGE-SCALE SOLAR MAGNETIC FIELDS WITH A NEW CHINESE TELESCOPE CONSTRUCTED FOR THE INTERNATIONAL MERIDIAN CIRCLE PROGRAM (IMCP)
Abstract
One of the very important international events in space science that has happened recently is the launch of the International Meridian Circle Program (IMCP). A key element of IMCP is a quite new instrument — the Solar Full-disk Multi-layer Magnetograph (SFMM) installed at Gan Yu Solar Station (GYSS) of the Purple Mountain Observatory (Jiangsu Province). The main objective of this telescope is to provide data on distribution of magnetic fields across the solar surface, which is necessary for prediction of some space weather (SW) parameters since this information is actually the low boundary condition for corresponding numerical simulations.
There are plans to construct a network of such telescopes (similar to GONG or to ngGONG), so it is very important to test how reliable the measurements of weak large-scale magnetic fields (LSMF) are with these instruments. It is just LSMF, not strong magnetic fields in active regions (which are relatively easy to measure), that determines the structure of the heliosphere. To do this, using first observations with SFMM at GYSS, is the main purpose of this study.
After a brief description of the instrument and some methodical issues, we present the results of comparison of SFMM observations with the Wilcox Solar Observatory (WSO) data. WSO measurements of LSMF are the most reliable in the world, and the results of such comparison are extremely important. We have found out that the correlation coefficient is high enough (≈0.70) if we consider the whole range of measured strengths, but it is lower (≈0.57) if the consideration is rerstricted only to relatively weak (|B|≤10.0 G) fields. Note that there is a significant difference between regression coefficients (R) for these two cases: R≈5.1 in first case and only R≈1.8 in the second one. The reason of this is still unclear and will be the subject of future investigations.
Solar-Terrestrial Physics. 2025;11(3):120-124
120-124
MONITORING OF SPACE WEATHER EFFECTS WITH SOZVEZDIE-270 NANOSATELLITE CONSTELLATION OF MOSCOW UNIVERSITY
Abstract
The space project Sozvezdie-270 of Moscow University is in progress now. It involves the deployment of a CubeSat nanosatellites constellation. To the present, 20 satellites have been launched, 9 of them continue to function in near-Earth orbit; one more will be launched in the near future. Instruments were developed specifically for the experiments on board small spacecraft of the CubeSat format, which provide measurements of fluxes and spectrum of charged particles, primarily electrons of relativistic and sub-relativistic energies, as well as gamma quanta. Along with the space constellation, a network of ground receiving stations is also being created. A multi-satellite constellation gives a number of advantages in studying dynamic processes in near-Earth space. In particular, it makes it possible to carry out simultaneous measurements of charged particle fluxes with instruments of the same type at different points in near-Earth space. Such measurements provide unique information about the flux of sub-relativistic electrons, including variations due to precipitation of electrons, which is of great importance for understanding the mechanisms of acceleration and losses of trapped and quasi-trapped electrons in Earth’s radiation belts (ERB).
We discuss various recent space weather manifestations associated with increased solar flare activity. Among such effects is the filling of the polar caps with particles of solar cosmic rays, dynamic processes in outer ERB during magnetic storms, rapid variations in electron fluxes due to precipitation.
We discuss various recent space weather manifestations associated with increased solar flare activity. Among such effects is the filling of the polar caps with particles of solar cosmic rays, dynamic processes in outer ERB during magnetic storms, rapid variations in electron fluxes due to precipitation.
Solar-Terrestrial Physics. 2025;11(3):125-134
125-134
SPACE WEATHER RESEARCH IN YAKUTIA
Abstract
The article reports on the studies of various manifestations of space weather (SW) on Earth, conducted by SHICRA SB RAS at the network of geophysical stations located in Yakutia. It is noted that the Institute researchers study various phenomena occurring in the solar wind and Earth’s magnetosphere such as magnetic clouds, Forbush effects, magnetic storms, substorms and associated subauroral glow, as well as high-latitude impulses in the dayside magnetosphere and sudden phase anomalies in the lower ionosphere. In addition to the data from the network of stations in Yakutia, data from other domestic and foreign stations, as well as direct measurements of the parameters of the interplanetary medium and magnetosphere, carried out on various spacecraft, are used to study these phenomena. The paper also describes physical models of magnetic clouds in the solar wind, high-latitude disturbed ionosphere, and methods for short-term forecasting of SW based on cosmic ray (CR) measurements developed at SHICRA SB RAS.
Solar-Terrestrial Physics. 2025;11(3):135-145
135-145