Vol 65, No 7 (2025)

Sympathetic phenomena on the Sun are events that occur at short time intervals in active regions located at large distances from each other. The presence of such events indicates that even very distant active regions may be connected physically to each other. In this paper, we present the results of analysis of several sympathetic bursts identified using the archive of observations on the Nobeyama Radioheliograph. Bursts in active regions spaced by 400 000 to 1 200 000 km occurred with a delay of 2 to 20 minutes. The estimated propagation speed of the disturbing agent is 1000–5000 km/sec.

Knowledge of the past solar activity is important for predicting the future solar activity. One of the key quantities characterizing the solar activity is the solar modulation parameter (SMP). It parameterizes solar activity by the use of equation that describes the propagation of cosmic rays in the solar system. SMP for the last few decades is determined using neutron monitors. Cosmogenic isotopes are commonly used to obtain information on SMP beyond the instrumental period. We used data on the ¹⁰Be production rate for the last 9.5 thousand years. According to Kovaltsov and Usoskin [2010], there is an unambiguous relationship between the ¹⁰Be production rate, the geomagnetic field strength, and SMP. We used this relationship to determine the solar modulation parameter for the Holocene. It is shown that the time dependence of SMP is non-stationary. For further analysis, the empirical mode decomposition method was applied [Huang et al., 2003]. Analysis of the modes obtained showed that among the younger modes, there are cycles with periods of 710 and 208 years. The latter mode is a manifestation of the De Vries cycle known in the analysis of cosmogenic isotopes. The existence of a cycle with a period of 710 years cannot be explained within the framework of standard concepts of cosmogenic isotopes. We associate the existence of the 710-year cycle with fluctuations in the tilt of the Earth’s magnetic dipole. It is shown that, taking into account the influence of the dipole tilt fluctuations on the formation rate of cosmogenic isotopes, the De Vries cycle in the Holocene was the dominant low-frequency cycle with a period of about a hundred years. The wavelet analysis showed that its amplitude remained virtually unchanged for 9.5 thousand years. The aim of the work is to study the cyclicity of solar activity taking into account the existence of fluctuations in the tilt of the Earth’s magnetic dipole.

It is known that during solar flares, electrons are accelerated to high energies and electromagnetic radiation is generated in a wide range of frequencies. Fast electrons generate hard X-rays in solar plasma and can excite plasma waves. The latter generate electromagnetic waves recorded by radio telescopes on the Earth. It is known also that electron beams injected into plasma generate a reverse current, which consists of thermal electrons. The paper examines the effect of the reverse current electric field on the generation of plasma waves. It is shown that the reverse current of the electric field can cause a decrease in the intensity of the Langmuir waves excited in plasma and, consequently, the intensity of radio emission generated by plasma waves.

In this work, we studied variations in the atmospheric characteristics at high latitudes of the Northern Hemisphere associated with a powerful burst of solar activity in the period of January 13–23, 2005, which caused a series of solar proton events, strong magnetic storms, and a deep Forbush decrease of galactic cosmic rays. It is shown that this burst was accompanied by a significant disturbance of the middle and lower atmosphere at high latitudes. The most pronounced changes in the stratospheric circulation (a sharply intensified stratospheric polar vortex) occurred on January 15–19. It coincided with a considerably increased ionization rate in the mesosphere and upper stratosphere, as well as with an increase of the North Atlantic Oscillation index and a weakening of the planetary wave activity. In the lower atmosphere, an intensive regeneration of cyclones was observed near the south-eastern coast of Greenland. Intensification of the polar vortex was accompanied by a noticeable decrease of temperature (by ~10 K) in the stratosphere at latitudes >70°N. A further sharp weakening of the vortex in late January contributed to the onset of a process close to a sudden stratospheric warming. The results of the study suggest that the development of observed atmospheric disturbances was possibly influenced by phenomena associated with a sharp increase in the flare activity on the Sun during January 13–23, 2005, including a series of powerful solar proton events that considerably increased the ionization rate in the middle atmosphere.

According to the results of paleoclimatic studies, the modern stage in the Earth's climate history covers the shortest Quaternary geological period lasting about 3 million years. The question arises about future climate changes after the currently observed warming. There is still no consensus among scientists regarding the explanation of the processes that currently occur in the Earth's climate. The article analyzes climate changes since the spread of complex life forms, i.e. the developed plant and animal life, which started on our planet about 542 million years ago (Phanerozoic eon). Reconstructions of the Phanerozoic temperature based on geological and isotopic data of sedimentology and paleoecology are considered. A comprehensive and quantitative assessment of how global temperatures have changed over the past 540 million years is given. Long-term trends in the climate characteristics over hundreds and tens of millions and thousands of years are considered to understand the climate change after the end of the modern Holocene interglacial period. Some possible approaches to the problem of climate change are discussed to demonstrate the need for an interdisciplinary view.

The estimate of the longitudinal magnetic field obtained from the Hinode spectropolarimeter data will be different if it is determined in different ways. In particular, the values obtained by the Centers Of Gravity (COG) method for the Fe I λ 6301 and 6302 Å lines do not coincide. Some of the differences are due to the different inaccuracies of the COG method for each of the two lines. However, some of the differences can be explained by the fact that the response functions of these lines to changes in the magnetic field are formed at different heights. This should be accompanied by a certain morphological picture of magnetic fields. It consists in the fact that most of the magnetic configurations of the quiet photosphere are similar to each other. To a rough approximation, their structure can be compared with the structure of a sunspot — there is a central region with the strongest field, close to vertical, and slopes — an analog of penumbra, where the field weakens and / or turns to horizontal. This turn occurs at the heights of the greatest response of the Fe I λ 6301 and 6302 Å lines to changes in the magnetic field with a reversal length of about tens of kilometers.

This study evaluates the possibility of efficient radio emission generation in the bow shock region of hot Jupiter–type exoplanets. As a source of energetic electrons, the shock drift acceleration mechanism at a quasi-perpendicular shock is proposed. Electrons reflected and accelerated by the shock propagate through the relatively dense stellar wind plasma and excite plasma waves; therefore, a plasma emission mechanism is considered as the source of the resulting radio waves. Using the bow shock of the hot Jupiter HD~189733b as a case study, the properties of the energetic electron beam, the excited plasma waves, and the resulting radio frequencies are estimated. An energy-based analysis is carried out to identify the range of stellar wind parameters for which radio emission from the bow shock of the exoplanet HD~189733b could be detectable by modern astronomical instruments.

Changes in the structure of the global magnetic field (GMF) in cycles 21–24 and at the beginning of cycle 25 are considered. It is shown that the GMF structure differs both in different cycles and at different phases of each cycle. Stable longitudinal structures formed in the epochs of maximum activity display rotation with the Carrington period (CR), which may indicate their connection with local magnetic fields. In each individual structure, two extended longitudinal intervals are distinguished with dominating fields of positive or negative polarity that occupy opposite longitudinal intervals and alternate in the even and odd cycles. An increase in the contribution of the sector structures simultaneously with the increasing chaos in the latter leads to a decrease in the mean magnetic field intensity over a CR in the weak cycles 23–25. It is assumed that the total contribution of changes in the magnetic fields of the polar dipole and the sum of the sector (n=m) and tesseral (n ≠ m ≠ 0) harmonics with even n and odd m are decisive in the formation and cyclic changes in the observed GMF sector structure.