Geomagnetism and Aeronomy最新文献

An algorithm for automatic approximation of the time dependence x(t) is built for the observed coordinate of the coronal mass ejection (CME) front from the admissible starting point to the first appearance in the field of view of the LASCO coronagraph and further, up to a heliocentric distance of ~25 solar radii (R_S). In the region from the starting point to the first appearance of the CME, two sections are assumed, with uniform (impulsive) acceleration and with uniform motion; then, the motion is approximated by observations. At the beginning of the approximation, either the CME start time is found through the appearance of certain frequencies of radio emissions (RSTN data) and type II and IV radio emissions (sequence characteristics are determined by machine learning), or the start time is determined by averaging over the allowable takeoff area; then the polynomial-ballistic model is optimized. The first and second derivatives x(t) determine the speed and acceleration of the CME at any point of its trajectory. Such an algorithm is necessary to obtain the most accurate kinematic characteristics of CMEs, which can allow one to study the physical, spatial, and temporal relationships between flares and CMEs in all their diversity. Widely used approximation techniques simplify the real CME trajectories x(t), thereby possibly discarding important features of the CME kinematics and flare development in the posteruptive phase. The algorithm was trained and tested on 17 solar flares and associated CMEs, which are known for their powerful proton events with proton energies greater than 300 MeV. The rate of the first occurrence of CMEs turned out to be different from the average rate given in the LASCO catalog, which is important for estimating the energy of flares and CMEs. In 7 out of 17 events, there was acceleration only in the impulsive phase (and then deceleration), while acceleration in the impulsive and posteruptive phases occurred in 10 events. In 4 out of 17 events, CME velocities greater than 2000 km/s were reached at a distance of 20R_S. The accuracy of determining the kinematic characteristics of CMEs can be improved by using additional observations, for example, SDO AIA in the September 10, 2017 event.

The purpose of this work is to supplement the “Stars with solar-type activity” catalog with information about confirmed exoplanets and exoplanet candidates. To do this, cross-identification of the catalog stars with data from the NASA exoplanet archive was carried out. This article presents the distribution of the number of suspected stars with exoplanets by brightness, spectral type, amplitude of variability, as well as other statistical analysis data. Particular attention has been paid to the comparison of the periods of rotation of stars and the orbital periods of revolution of exoplanets around them. Analysis of the data suggests the need to change the previously determined types of variability in some stars.

The solar dynamo generates a toroidal magnetic field that, forms active regions (ARs) on the surface of the Sun. The toroidal magnetic field lines rise through the turbulent convection zone, where distortions, deformation of already formed regular toroidal magnetic flux bundles and the formation of irregular, complex magnetic structures are possible. At the minimum of solar activity, the toroidal magnetic field of the old cycle disappears and the magnetic field of the new cycle is still very weak. During this period, it is possible to assess the role of the turbulence in the formation of an AR. In this paper, we analyzed ARs of two solar activity minima (between cycles 23–24 and between cycles 24–25). We analyzed ARs located within 60° from central meridian and exhibiting magnetic flux at the maximum development of at least 10²¹ Mx. Bipolar and multipolar ARs were divided into regular ones (consistent with the mean-field dynamo theory) and irregular ones, the formation of which was influenced by the turbulence of the convection zone (unipolar spots were considered separately). It was found that regular ARs significantly predominate during solar minima, their magnetic flux is a half or more of the total magnetic flux (0.6 for the first period, 0.5 for the second period). Irregular ARs are fewer in number than regular ones, and in terms of magnetic flux they make up about one-third of the total magnetic flux (0.3 and 0.2 in the first and second periods, respectively). Irregular ARs are predominantly represented by bipolar structures of improper orientation, while very complex multipolar ARs are extremely rare. It is concluded that the generation of ARs with the magnetic flux exceeding 10²¹ Mx occurs due to the global dynamo action, while the turbulence of the convection zone causes deformation of the magnetic flux bundles without significant magnetic flux generation.

The synchronicity between the extreme values of summer insolation in the northern hemisphere and the global climatic events of the Holocene is found. The transition from the cold Pleistocene to the warm Holocene epoch is synchronized with the summer irradiation maximum. The Little Ice Age is synchronized with the minimum of summer irradiation in the northern hemisphere. For the Holocene and Late Pleistocene, the leading role of climatic precession in changes in the global climate of the Earth has been determined. Accounting for variations in solar activity made it possible to detail the structure of the minimum irradiation of the northern hemisphere during the Little Ice Age. The necessity and possibility of simultaneously taking variations in incoming radiation of different physical nature associated with changes in the Earth’s orbital motion and changes in the activity of the Sun into account are shown in the reconstruction and forecasting of global climatic events.

The Antarctic is a highly connected system with nonlinear interactions between the atmosphere, ocean, ice, and biota, as well as complex connections to the rest of the Earth system. Antarctica and the Southern Ocean make up the most important part of the Earth system. Antarctica is the coldest, driest, and most remote continent and is undergoing a variety of environmental changes in response to climate change, in particular modern warming, which is the subject of intense scientific debate. Almost all of Antarctica is located south of the Antarctic Circle (66°33′ S). The question remains as to whether the recent and accelerating warming trend is part of natural climate variability or the result of anthropogenic activities. We may not get an unambiguous answer if we do not decipher how climate processes changed in the distant past. Long-term trends (ups and downs) in continental ice deposits in the Antarctic region and in carbon dioxide content can be distinguished over the interval of approximately the last 500 Ma. Nearly 60–50 million years ago there was a long trend of decreasing carbon dioxide concentration, average temperature and lowering of the ocean level. Over the last million and hundreds of thousands of years, the history of the Earth has been characterized by alternating cycles of cold (glacial) and warm (interglacial) climatic fluctuations, which led to a number of large-scale environmental and atmospheric changes, in particular, the formation and melting of huge ice sheets, dramatic changes in global sea level, etc. This article examines long-term trends in climate change in various regions of Antarctica in the past, climate change since the end of the last ice age, and current climate change, and the relationship of these changes with the causes that give rise to them. The main attention is drawn to the changes in climatic characteristics during the Holocene and the features of changes in recent decades. The results we obtained are important for understanding past and future climate variability.

The longitudinal distribution and characteristic features of sunspot groups during the end of the descending branch of Solar Cycle 24 are analyzed. The main activity turned out to be concentrated in the 60° longitude band, whose position coincided in the northern and southern hemispheres. We obtained a synodic rotation period of the activity zone of 26.6 days, which is shorter than during the corresponding phase of the previous cycles and is probably related to the variation not only in latitude but also in the depth of the active longitude source localization. The groups of sunspots observed in the active longitude zone are characterized by a more compact latitudinal distribution and an increased number of not only large sunspots but also small ones with areas smaller than 50 Msh. Furthermore, the lifetime of small sunspots in this area is longer in contrast to similar sunspots found elsewhere on the solar surface. This indicates a common source of sunspot generation in the active longitude zone. The analysis of the rotation rate of individual sunspot groups with areas larger than 150 Msh in the active longitude zone by the solar disk showed that only a portion of them rotate at a rate close to that of the active longitude zone itself, while another portion rotate at the Carrington rate characteristic of sunspot groups outside the active longitude zone. We assume that this can be due to the different depths of the bases of the different sunspot groups and to the difference in the localization of the sunspot bases and the active longitude source. As a result, only a portion of the groups can consistently receive magnetic flux from a faster rotating source, which leads to an acceleration of their rotation.

Properties of the solar radio spectrum, as well as the temporal profiles of flare emission, indicate the thermal nature of the sub-terahertz (sub-THz) component observed as the growth of radio emission in the frequency range of 100–1000 GHz. The sub-THz flare onset can be ahead of the impulsive phase for several minutes. However, the origin of the pre-impulsive and impulsive sub-THz emission remains unclear. The present work is devoted to a detailed analysis of the M4.0 X-class solar flare observed on March 28, 2022 with the Bauman Moscow State Technical University Radio Telescope RT-7.5 at 93 GHz. We supply these data with multiwavelength solar observations in the X-ray (GOES, GBM/Fermi), extreme ultraviolet (AIA/SDO), and microwave ranges. The differential emission measure (DEM) responsible for EUV emission is determined by solving the inverse problem based on the AIA/SDO data. Using the DEM and assuming a thermal free-free emission mechanism in pre-impulsive and impulsive phases, we calculated the millimeter emission flux of coronal plasma of the flare source, which turned out to be much smaller than the observed values. We concluded that electrons accelerated in the corona and heat fluxes from the coronal loop top cannot be responsible for heating the sub-THz emission source located in the transition region and upper chromosphere. A possible origin of chromospheric heating in the pre-impulsive phase of the solar flare is discussed.

The depth profiles of cosmogenic isotopes in the lunar regolith depend on the flux and spectrum of Galactic and solar cosmic rays (GCRs and SCRs) and, therefore, depend on solar activity on a time scale comparable to the lifetime of these isotopes. In this work, we analyzed the content of various radionuclides (¹⁴C, ²⁶Al, ¹⁰Be, and ⁵³Mn) in samples obtained by the Apollo 15 mission. Comparing the results of modeling performed for the average GCR flow using the GEANT4.10 package with experimental data, we obtained a correction factor for the calculated formation rates of Y₀ ~ 0.6 for all the considered radionuclides. We attribute this result to the overestimated value of the flux of secondary particles in the lunar soil in the calculation using the GEANT4.10 package. This conclusion is supported by independent laboratory experiments. The estimated ¹⁰Be depth profile can be consistent with the experimental data only if the additional (apart from the GCR) contribution of protons accelerated on the shock wave from a nearby supernova ~2.5 million years ago is taken into account. We also calculated the ⁵³Mn depth profile (with the longest half-life of those we considered), which can also be described taking the contribution of the supernova into account. We note that three long-lived isotopes, ²⁶Al, ¹⁰Be, and ⁵³Mn, with different half-lives were modeled with the same average modulation potential. This allowed us to conclude that solar activity did not undergo noticeable changes on a time scale of about 10 million years.

In this paper, we show that inside the magnetic force tube formed by the open field of the coronal hole (CH), the magnetic field (MF) decreases with the distance from the Sun according to the inverse square law. In the study, we select such time periods when there were no active formations on the solar disk, with the exception of CHs (period 2006–2009, the minimum phase of the 23rd activity cycle). The main result of the study, the inverse square law, was obtained by comparing the duration of the CH passage through the central meridian with the duration of the increase in the SW velocity caused by these CHs in the Earth’s orbit. The ratio of the two indicated time intervals turns out to be very close to unity. The data from SOHO (Solar and Heliospheric Observatory), GGS WIND (Global Geospace Science Program WIND), and ACE (Advanced Composition Explorer) spacecraft were used. A special computer program was used to digitize the CH coordinates on daily EIT images at the λ195 Å (SOHO) line and calculate the CH areas in the sector affecting the SW parameters (ellipse 0.6R_o by 0.3R_o). Based on the inverse square law, MF (~2 G) and the particle flux density (~1.2 × 10¹³ particles/s cm²) on the solar surface at the base of 15 studied CHs were calculated using the SW parameters near the Earth’s orbit.

The paper presents the results of studying light curves of the star HD 168443 obtained from the ground-based and space photometric observations within the ASAS, KWS surveys, and the Hipparcos mission from 1990 to 2020. During 30 years of observations, the average annual brightness of the star remained constant within the measurement errors, the mean V-value was 6^m.96. Using the dense data series in 2007–2009, the photometric period of 34.7 days was found, and the low-amplitude brightness variability was studied with this period. We determined epochs and amplitude of rotational modulation produced by the development of active regions. These parameters do not change during 2–5 rotations of the star. The amplitude of the rotational modulation increases in 2007 before the epoch of maximum brightness. The star was the brightest in 2009, its V-magnitude was 6^m.92. The location of starspots on the surface of the star during these epochs is also considered.