Geomagnetism and Aeronomy最新文献

Alfvén waves with periods of a few seconds excited in solar coronal magnetic loops during flare energy release can lead to effective heating of the plasma in the lower atmosphere of the Sun, which is responsible for continuous optical radiation. Meanwhile, the question of the propagation time of these modes from the corona to the photosphere has not yet been considered in detail. Based on solar atmospheric model by Avrett and Loeser (2008), for different values of background magnetic fields, taking into account their height dependence, the estimates of the propagation time of Alfvén waves from the corona to the photosphere were obtained. The characteristic values exceeding several minutes and impose certain restrictions on wave heating of the lower atmosphere of the Sun. The implications of the results are discussed.

The presence of groups of cycles with larger/smaller amplitudes and alternation of these groups suggests the existence of a long-period solar activity (SA) cycle with epochs of increased/decreased activity. Since SA and its changes significantly influence climate and humans across the near-Earth space, it is reasonable to have a portrait (template) that reflects the main characteristics of these groups, making it possible to qualitatively and semiquantitatively assesses of SA epochs in the past and future. In the study, the properties of epochs SA of maximum/minimum are determined by the characteristics of reliable cycles 10–23 (14 cycles, a total period of 153 years, and the relationship between the amplitude of the cycles and their duration is taken into account). The formation of the pattern is based on the “envelope” of the maxima of these cycles. The possibility of correcting the Dalton minimum is discussed and a long-term forecast of SA is constructed.

El Niño (ENSO), a consequence of changes in ocean circulation patterns, has a significant impact on the global climate and associated economic activity. According to our hypothesis, in addition to internal climatic factors, the ocean circulation regime can be controlled by small changes in total solar irradiation (TSI) occurring in the 11-year solar activity cycle. In this case, positive feedback with a gain of about 10 is possible in near-equatorial regions. In this paper, we attempt to predict monthly averages of an index describing ENSO using TSI as an additional predictor. For prediction, we train a recurrent neural network with a long- and short-term memory (LSTM) unit on ENSO alone and with the addition of TSI. As a result, we find that the ENSO training error is reduced when TSI is added as a predictor. Our result indicates the possibility of using TSI as one of the predictors in constructing modern nonlinear predictive global climate models.

We propose a model of a light bridge as a current-carrying magnetic flux tube formed by convection. It is shown that convection in the sunspot penumbra provides the electric current necessary to heat the flux rope plasma and forms structures of a light bridge type. The steady-state heating mode of the light bridge is considered, since the light bridge life time (days) is much longer than the typical heating time (minutes). Radiation losses determine the current value I > 10¹¹A required to heat the light bridge to a temperature up to 6800 K. The parameters of the light bridge plasma are presented, and the observed double structure of the light bridge emission is explained.

Based on a large volume of observational data of magnetic fields obtained at both ground-based and space observatories, cyclical variations of the meridional flows of the solar magnetic fields in 21–25 cycles of solar activity are considered. It is shown that magnetic fields of medium strength of different polarities form oppositely directed magnetic fluxes moving from one pole to the opposite, with a period of about 22 years. Flows of high-strength magnetic fields migrate from high to low latitudes symmetrically in both hemispheres with a period of about 11 years. The interaction of multidirectional magnetic fluxes of medium and strong magnetic fields leads to sharp changes in the structure of the global magnetic field, latitudinal redistribution of magnetic fields of positive and negative polarity, the formation of a sector structure of the global magnetic field at the maximum and a zonal structure at the minimum of solar activity, and a change in sign of the magnetic field at the poles of the Sun.

This paper presents another model of a flare filament with a force-free magnetic field structure. The distribution of the magnetic field and currents within the volume of the rope is defined by the so-called flux function. To obtain a force-free solution, the Laplacian of this function must strictly depend only on the function itself. However, there are a large number of such functions, which raises the question: how does the choice of a particular flux function affect the physical properties of the magnetic flux rope constructed based on it? In previous studies, the author generally used an exponential dependence of the flux function on the coordinates, but in this article, a power function was used, and it turned out that the physical parameters of the flare ropes almost coincide. All force-free magnetic flux ropes have one common physical property: as the rope loop apex extends into the corona, the external pressure that prevents its lateral expansion steadily decreases, and upon reaching a certain critical reduction, the longitudinal magnetic field of the rope turns to zero at the current inversion surface (CIS). At this point, the force-free parameter and the azimuthal electric current experience a discontinuity at this surface, causing their values in the vicinity of the CIS to grow indefinitely (in magnitude). The electron drift velocity here inevitably exceeds the ion acoustic velocity, leading to the excitation of plasma ion-acoustic instability, a sharp drop in plasma conductivity within the rope, and the generation of a super-Dreicer electric field. Parker’s effect (alignment, with some delay, of the torque along the rope axis due to the transfer of azimuthal field to the energy release region) leads to quasi-periodic pulsations of hard flare radiation and ultimately ensures the flare release of a significant portion of the free magnetic energy stored in the long loop of the magnetic flux rope.

In analogy with the acceleration mechanism implemented in the Jupiter–Io system, the electron acceleration mechanism is discussed with the example of the plasmasphere of exoplanet HD 189733b. Under conditions when the oncoming stellar wind flow with the stellar magnetic field included in it reaches a region of the atmosphere with a sufficient number of neutral particles, the different frequencies of collisions of stellar electrons and ions with neutrals ensure charge separation and the emergence of an electric field of charge separation. In this process, an important role is played by the anisotropy of the conductivity of the exoplanet’s plasmasphere, which ultimately leads to a powerful electric field, that has a projection on the direction of the magnetic field and causes electron acceleration. The characteristic energies and fluxes of accelerated electrons for exoplanet HD 189733b are estimated. The possibilities of this acceleration mechanism are discussed from the viewpoint of the occurrence of plasma instability in the atmosphere of the exoplanet and generation of a radio emission flux necessary for recording on Earth. A conclusion is drawn about the energy sufficiency of the proposed acceleration mechanism for observing the radio emission of this exoplanet. The possibilities of implementing the electron acceleration mechanism described above for the other two most studied hot Jupiter-type exoplanets—WASP 12 b and HD 209458 b—are also discussed.

The problem of the end of the modern interglacial is discussed. Following theoretical predictions, cooling should soon begin after the end of the modern interglacial and Quaternary climate period. However, as climatologists note, now weather anomalies have begun to occur more often: high and low temperatures, heavy rainfall, thunderstorms, hurricanes, and floods are breaking long-term records. Unfortunately, the scientific community has not reached a consensus regarding the causes of climate change during this period. Global numerical models of Earth’s climate system have discrepancies with observed climate changes. Supporters of anthropogenic global warming, in spite of everything, ignore the natural factors of climate change, such as tectonic waves, glacial destruction, and the ocean, which actively participates in the exchange of gases with the atmosphere, volcanic activity, earthquakes, etc. Data on changes in the global temperature of Earth’s surface on a time scale of the last 700 million years and ~70 million years are analyzed and periods of warming and cooling were identified. The cyclicality of climate changes in the Quaternary (the last approximately 2.5 million years) is analyzed as one of the most important features of the climate system, used to assess both changes in individual environmental components in the past and to predict climate change in the future.

The characteristics of solar cycles important for the development of dynamo theory can manifest themselves differently when different activity indices are used. To study the features of the north–south (N–S) asymmetry of solar activity, a comparison was made of the time profiles of active regions (ARs) of the 23rd and 24th cycles based on data on their number (the most accessible and frequently used) and magnetic flux (allowing a more complete assessment about the generative function of the dynamo process). We used data on 3047 ARs that appeared on the disk from June 1996 to December 2020 according to the MMC ARs CrAO (magneto-morphological classification of ARs of the Crimean Astrophysical Observatory) catalog (http://sun.crao.ru/databases/catalog-mmc-ars). The attribution of AR to the classes of the regular and irregular sunspot groups was taken into account in accordance with the MMC ARs CrAO. Analysis of the results showed the following. Variations of ARs of both MMC classes are associated with a cycle, which confirms their relationship with the action of the global dynamo. Due to the overlap of multipeak ARs profiles of different classes, a classic double-peak cycle structure is formed in the two hemispheres. Variations in the relative position of profiles for the number and magnetic flux of ARs (for groups of each class in each hemisphere) during the cycle can be associated with changes in the sizes of ARs. This makes it possible to suggest the multicomponent nature of the dynamo process, which consists in joint manifestation of global (responsible for the production of ARs) and turbulent (associated with the fragmentation of magnetic structures due to turbulence in the convection zone) components of the dynamo. The strongest magnetic fluxes observed for the irregular groups in the maximum of the cycle may also indicate action of the turbulent component of the dynamo distorting the regular flux tube. The pronounced N–S asymmetry of these fluxes agrees with the hypothesis on the possibility of weakening of the toroidal field in one of the hemispheres due to the interaction of the dipole and quadrupole components.

The paper studies the dynamics of high-temperature structures (with a temperature of T ≥ 10 MK) in the corona above active regions (ARs) in quiet temporal intervals, before solar flares of high X-ray classes and during and after individual flare events, and determines the role of electric currents in heating the coronal plasma. In the study, we used data from the Solar Dynamics Observatory (SDO) spacecraft: magnetograms obtained by the Helioseismic and Magnetic Imager (HMI) instrument (used to detect and calculate the magnitude of large-scale electric current) and photoheliograms of the solar corona in ultraviolet radiation 94, 131, 171, 193, 211, and 335 Å channels of the Atmospheric Imaging Assembly (AIA/SDO) instrument (used to construct maps of temperature distribution in the corona above the AR, detect high-temperature structures, and study their evolution). The objects of the study were ARs NOAA 12 192 (October 2014) and 12 371 (June 2015) of the 24th solar activity cycle, which have high absolute values of large-scale electric current. The following results were obtained: (1) The discovered high-temperature structures represent a channel of large-scale electric current at coronal heights. (2) High-temperature structures in the corona above the studied ARs exist over a long (several days) time interval, which indicates the presence of a constant source of plasma heating; the temperature of the structures, the area they occupy, and their spatial orientation change over time. (3) High-temperature structures in the corona consist of individual elements with a cross section of ~10⁸ cm. (4) Several hours before the X-ray flares of classes M and X datected in the studied ARs during their monitoring time, a significant decrease in the area occupied by high-temperature structures was observed, and in some cases, a decrease in temperature to 3–5 MK, which indicates a change in the physical conditions in the corona before powerful flares.