Geomagnetism and Aeronomy最新文献

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.

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.