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.

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.

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.

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 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.

Variations of weak photospheric magnetic fields with periods on the order of the solar magnetic cycle have been studied. We used synoptic maps of the photospheric magnetic field for the period 1978−2016 (NSO Kitt Peak). To isolate the contribution of weak magnetic fields, the saturation threshold for the synoptic maps was set at 5 G. A time–latitude diagram was constructed from the converted synoptic maps. For further analysis, 18 magnetic field profiles were selected from the diagram. It was found that a 22-year variation in weak magnetic fields is present not only at high, but also at low latitudes. We show that at all latitudes, with the exception of ~26° and ~33° in the Northern Hemisphere and ~−26° in the Southern Hemisphere, weak magnetic fields change cyclically with an average period of 22.3 years. At high latitudes, the magnetic fields of the two hemispheres change approximately out of phase. In contrast, equatorial latitudes are in phase with the high latitude fields of the Northern Hemisphere and out of phase with the Southern Hemisphere. Thus, at low latitudes, the dominant role of the Northern Hemisphere becomes noticeable: the equatorial fields are in phase with the fields of the Northern Hemisphere at high latitudes. The phase of the 22-year variation changes gradually with latitude, but when the 22-year variation is disrupted, phase jumps occur. Before and after the disruption period, the 22-year variation develops in antiphase.

We calculated variations in the cosmic ray geomagnetic cutoff rigidity ΔR_ef during a complex two-stage magnetic storm on November 9–10, 2004, using calculations of particle trajectories in the model magnetic field of the magnetosphere. The response of ΔR_ef to changes in solar wind and magnetosphere parameters reflects the nonsmooth two-stage evolution of this storm. It is found that the curve of changing values that ΔR_ef take as a function of the studied parameters during the main phases of each stage of the storm does not coincide with the curve during the recovery phases, which is a sign of hysteresis. As a result, two hysteresis loops are formed, one for each stage of the storm of November 9–10, 2004. The ambiguous dependence of ΔR_ef values on the studied parameters, which change cyclically during the development of magnetospheric current systems and their subsequent relaxation, is responsible for the formation of the loops. The configuration of two loops similar to those characteristic of dielectric hysteresis seems to be related to the abrupt change from Bz > 0 to Bz < 0, which delimits the stages of the studied storm.