Geomagnetism and Aeronomy最新文献

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.

Differences in geomagnetic and ionospheric activity are investigated for the maximum monthly–hourly values of the auroral electrojet AE index, measured on a network of magnetometers above 60° in the Northern hemisphere from 1995 to 2019. The selected extreme AE indices were compared with the time–matched 1-h Apo indices observed in the sub-auroral zone from 1995 to the present. A high correlation of 300 selected values of AE and Apo indices (cc = 0.69) was obtained for the period of their synchronous observations in 1995–2019. For a comparison, variations of the ionospheric zonal dispersion (Net Volume, NT) are considered designating the difference between the positive and negative deviations of TEC from the quiet state in the selected zone. The NT is produced from TEC-based W-index values at the grid in the auroral zones of the Northern and Southern hemispheres for the geomagnetic latitudes exceeding ±60°. The NT values were estimated from JPL maps of the total electron content, GIM–TEC, and the corresponding W-index maps converted from geographic to geomagnetic coordinates. We observed an asymmetry of the ionospheric variability in the Northern and Southern auroral zones with the dominance of the positive (negative) NT values in the local winter (summer). At the same time, the seasonal variation of the geomagnetic AE and Apo indices recorded mainly in the Northern Hemisphere shows changes similar to the ionospheric variations of NT in the Southern Hemisphere with a decrease in the amplitude by the winter solstice. The analytical dependences of NT indices on the day of year in the North and South auroral zones were derived suitable for estimating the ionospheric variability in the operational forecasting models of the ionosphere.

In this work, we studied the formation of a large-scale magnetic field. For this, we used the surface flux transport (SFT) model. We have studied the model’s accuracy and its sensitivity to uncertainties in its key parameters and input data. We also compared the simulated magnetic field with observations of the SDO/HMI and STOP/Kislovodsk magnetic fields. Overall there is good agreement between the simulations and observations. Although the model cannot reproduce fine details of the magnetic field, the long-term evolution of the polar field is very similar in simulations and observations. During even one activity cycle, large-scale field drift waves to high latitudes change polarity. Magnetic field drift waves, the sign of which corresponds to the magnetic polarity of the trailing parts of the active regions, often exist during the decline phase of activity. This does not quite correspond to the idea of mutual compensation of the leading fields of active regions across the equator. We also looked at the magnetic field flux across the equator. We confirmed that the flux across the equator does not show a clear predominance of leading sunspot polarity. The results are discussed to test dynamo models.

The article studies microstreams, increases in solar wind (SW) currents up to several tens of km/s, with a time scale of the order of a day. A comparative analysis of microstreams present in the polar and low-latitude SW at different heliocentric distances has been carried out. The comparison showed that the properties of microstreams in the near-Earth fast SW are qualitatively similar to the properties of microstreams present in the polar SW during periods close to solar activity minima, at heliocentric distances from 2 to 4.5 AU. At the same time, the quantitative parameters of microstreams (amplitudes of variations in radial and tangential velocity, as well as relative variations in temperature, density, and plasma pressure) show a monotonic decrease with increasing heliocentric distance, which can be interpreted as a consequence of the gradual evolution of microstreams with distance from the Sun. However, comparison with SW measurements in the low-latitude region of the heliosphere at distances of about 5 AU shows some significant differences, which indicate a more rapid evolution of microstreams in the inhomogeneous low-latitude SW.

In solar activity, in addition to the 11-year Schwabe cycle, there are also shorter-period oscillations in the range from 27 days to 11 years, which are called mid-term oscillations. In our study, we identify quasi-6-year oscillations in solar activity expressed by the sunspot number SN using wavelet analysis and investigate the characteristics of these variations during 1750–2020. The analysis shows that the ~6-year cycle in SN is a real independent oscillation. A similar quasi-6-year periodicity has been found in the monthly mean records of geomagnetic field components at the Sitka and Honolulu observatories during 1910–2020. It was found that the variations of the geomagnetic field in the range of 5–6-year periods can be caused by the effect of variations in solar activity in the same frequency range. In addition, in the SN series and geomagnetic field variations, a quasi-biennial cycle is well observed, the amplitude of which in some time intervals exceeds the amplitude of the cycle with a period of 5–6 years.

For the first time, several flare events are analyzed based on multifrequency observations using the Radio Solar Telescope Network. The purpose of the analysis is to identify signs of flare preparation. In all considered cases, preflare quasi-periodic fluctuations (QPFs) of radio emission were detected. The duration of preflare wavetrains is 6–20 min. Wavetrains consist of 3–5 pulses. QPFs at lower frequencies (200–600 MHz) begin later than those at high frequencies by 2–6 min. QPFs at frequencies of 2695–8800 MHz occur almost synchronously. The highest amplitude of QPFs is observed at a frequency of 4995 MHz. The observed QPFs can be explained by the force-free magnetic rope model (Solov’ev and Kirichek, 2023).

In this article we continue studying the influence of solar activity on the main trajectories of extratropical cyclones (storm tracks) in different parts of the North Atlantic during the cold half of the year (period of intense cyclogenesis). Long-term oscillations in the latitude of storm tracks in the areas located west and east of the Greenwich meridian are compared. It is shown that secular oscillations in latitudes of storm tracks (with periods of ∼80–100 years) are most distinctly pronounced in the western North Atlantic (longitudes 60°–40° W), weaken in the area of the Icelandic Low (30°−10° W), and completely disappear in the eastern part (0°−20° E), where multidecadal oscillations with periods of ∼50–60 years dominate. Bidecadal oscillations in cyclone trajectories (northward shift of trajectories during the declining phase and at the minima of even-numbered solar cycles) have the greatest amplitude in the region of the Icelandic Low and noticeably weaken east of Greenwich. It is shown that the shift of cyclone trajectories to the north in even cycles occurs under increased galactic cosmic ray (GCR) intensity compared to odd cycles. The data providing evidence for the influence of the stratospheric polar vortex on the position of North Atlantic cyclone trajectories are presented. It is suggested that possible reasons for oscillations in the vortex intensity are changes in the chemical composition and temperature regime of the middle polar stratosphere caused by variations in GCR fluxes and geomagnetic activity.

The study demonstrates the synchronicity of the positive and negative phases of summer irradiation of the Northern Hemisphere in the precession cycle with periods of global climate warming and cooling for the Late Pleistocene and Holocene. The cold phase 50–41.5 ka BP corresponds to the Shestikhinsky cooling in Eastern Europe and the development of glaciation in North America. The warm phase 41–30 ka BP accounts for climate warming in Europe (Bryansk interstadial, Paudorf, Gotwei warming) and in North America (Plum Point Interstadial). The period of maximum development of glaciation in Europe and North America is synchronized with the cold phase 29.5–17.5 ka BP. The warm phase 17–5.5 ka BP is associated with the transition from the cold Pleistocene to the relatively warm Holocene. The Little Ice Age falls on the cold phase 5 ka BP – 5000 CE. It is expected that warming of the climate with respect to the present will correspond to the Warm Epoch 5000–13 000 CE. Changes in solar radiation arriving in the first astronomical half of the year in 5° latitude zones were determined for all astronomical months of the tropical year for climatic precession extrema. This makes it possible to compare spatiotemporal changes in Earth’s solar climate during years of climate precession extrema.

In the recent work by Usoskin et al. (2021) a series of annual sunspot indices for the years 971 to 1899 was reconstructed. Using this series, we study behavior of the “length-amplidude rule” (LAR), according to which the mininum-to-minimum length of a given 11-year solar cycle anticorrelates with the amplitude of the next one. We show that approximately since the 14th century two regimes exist in the series: I) epochs of normal activity, when the LAR is observed; II) epochs of the Maunder, Spörer and Wolf grand minima, when there were no significant links between the amplitudes and lengths of the 11-year cycles. Before the 14th century the LAR and its relation to the level of global activity of the Sun is less pronounced, which, probably, is a consequence of inaccuracies of the 11-year cycle parameters determination in this epoch.