Kinematics and Physics of Celestial Bodies最新文献

The features of the spatial distribution of atmospheric gravity waves (AGW) in the polar thermosphere of the Earth are investigated. The research is based on data from direct satellite measurements of the parameters of the neutral atmosphere. According to satellite data, the amplitudes of AGWs that are systematically observed in the polar regions of both hemispheres are usually several times higher than the amplitudes of these waves in the middle and low latitudes. At the same time, the polar AGWs of large amplitudes are recorded against the background of high-speed spatially inhomogeneous wind flows, which indicates their possible amplification caused by interaction with the wind. Based on the analysis of measurement data on the Dynamics Explorer 2 satellite, the relationship between the spatial distribution of the atmospheric gravitational waves and the auroral oval has been revealed. On a large volume of experimental data, seasonal patterns of the distribution of the wave field over the Antarctic and the Arctic have been established. A comparative analysis of the features of the AGWs in the polar thermosphere of both hemispheres for the conditions of the polar day and polar night has been carried out. Some differences in the distribution of the AGWs were noted depending on the Kp-index. It has been suggested that the observed seasonal features of the AGW distribution and its dependence on the level of geomagnetic activity are associated with the restructuring of the polar wind circulation when the conditions of solar illumination and geomagnetic conditions change.

An analysis is presented of the scientific research accomplished by Ukrainian astronomer Mykola Evdokymov, a specialist in the field of astrometry. The astronomer’s main works, carried out using a Repsold meridian circle, are dedicated to determining stellar parallaxes, the positions of zodiacal and faint circumpolar stars, and the positions of large planets. At Kharkiv Astronomical Observatory, Evdokymov conducted systematic observations of the following objects and phenomena: solar and lunar eclipses, including as a member of the observatory’s expeditions during the total solar eclipses of 1914 and 1936; comets (Halley, Delavan, Stearns, Pons–Winnecke); and meteor showers. He participated in determining the positions of reference stars for the asteroid (433) Eros. He conducted systematic studies of the meridian circle, developed new astronomical instruments, organized the functioning of a time service at the observatory, and carried out the determination of star declinations by measuring the sums and differences of the zenith distances of star pairs by the Sanders–Raymond method (using a meridian circle and a transit instrument).

The data acquired at ten geomagnetic observatories (Paratunka, Magadan, Yakutsk, and Khabarovsk (the Russian Federation); Memambetsu, Kanoya, and Kakioka (Japan); Cheongyang (Republic of Korea); Shumagin and College (USA)) during the Kamchatka meteoroid event of December 18, 2018, and on the reference days of December 17 and 19, 2018, have been used to analyze temporal variations in the geomagnetic field components. The distance r from the observatories to the site of explosive energy release by the meteoroid varied from 1.001 to 4.247 Mm. The passage of the Kamchatka meteoroid through the magnetosphere and atmosphere was accompanied by variations mainly in the H geomagnetic field component. The magnetic effect from the magnetosphere was observed to occur twice, 51 and 28 min prior to the meteoroid explosion; the amplitude of the disturbances in the geomagnetic field did not exceed 0.2–1 nT, and the durations were observed to be approximately 20 and 10 min, respectively. Alternating peaks in the level of the H component were observed to lag behind the meteoroid explosion by 8 to 13 min for r from 1.001 to 4.247 Mm. The amplitude of the oscillations varied with increasing r from ~0.5 to ~0.1 nT, while the duration of the magnetic effect from the ionosphere varied in the 16–25-min range for all distances. The apparent speed of propagation in this group of disturbances that were of MHD nature was observed to be approximately 10 km/s. In the second group of disturbances, the time lag increased with increasing distance within the distance range mentioned above from 56 to 218 min. The duration of the disturbance was approximately 16–65 min, the apparent speed was 336 m/s, and the period was 5–10 min. This disturbance in the magnetic field was caused by an atmospheric gravity wave propagating from the meteoroid explosion. The theoretical models for the magnetic effects observed are presented and theoretical estimates are performed. The observations are in agreement with the estimates.

The results of spectropolarimetric and filter observations of the facular region in the lines Fe I 1564.3, Fe I 1565.8 nm, Ba II 455.4 nm, and Ca II H 396.8 nm obtained near the center of the solar disk at the German Vacuum Tower Telescope (Tenerife, Spain) are discussed. It is shown that the facular contrast at the center of the Ca II H line increases more slowly as the magnetic field strength increases and, then it begins to decrease if the field increases further. It is concluded that the reason for such behavior is the nonlinear height dependence of the line source function due to the deviation from the local thermodynamic equilibrium. It is found that waves propagating both upward and downward can be observed in any area of the facula, regardless of its brightness. In bright areas with a strong magnetic field, upward waves predominate, while downward waves are more often observed in less bright areas with a weak field. It is shown that the facular contrast measured at the center of the Ca II H line correlates with the power of wave velocity oscillations. In bright areas, it increases with the power regardless of the direction in which the waves propagate. In facular regions with decreased brightness, the opposite dependence is observed for both types of waves. In turn, the power of wave velocity oscillations is sensitive to the field strength magnitude. In the magnetic elements of the facula with increased brightness, the stronger the field, the higher the power of oscillations of both upward and downward waves. In areas with decreased brightness, the inverse dependence is observed. It is concluded that the contrast increase with the increase in the power of wave velocity oscillations observed in bright areas of the facula can be considered as evidence that these areas look bright not only because of the Wilson depression but also because of the heating of the solar plasma by the waves.

A solar eclipse (SE) pertains to rare high-energy natural phenomena. For instance, a change in the internal (thermal) energy of the air in a layer only 100 m in height attains 10¹⁸ J while the power of the process is on the order of terawatts. The energy of the processes produced by the SE in the upper atmosphere and geospace is significant. For instance, the thermal energy of the ionospheric plasma in a volume of ~10¹⁹ m³ decreases by 10¹¹ J. The magnetic field in a volume of ~10²¹ m³ decreases by 50 nT, and its energy by 10¹⁵ J. SEs are accompanied by disturbances in all subsystems of the Earth–atmosphere–ionosphere–magnetosphere system. Disturbances in the upper atmospheric and ionospheric parameters act to inevitably produce geomagnetic field variations. At present, geophysicists have no consensus on how SE manifests itself in the geomagnetic field. The available data are inconsistent. Most of the researchers believe that the geomagnetic effect of SE exists. In some cases, the temporal variations in the geomagnetic field, as a whole, repeat the changes in the illumination of the Earth’s surface; in other cases, they may be ahead or delayed by ~1 hour in relation to the changes in illumination. Most often, the geomagnetic effect is studied in the region of the total SE where it should be the most pronounced. The further the observatory is located from the umbra, the more difficult it is to relate the magnetic variations to the SE. Finding the response of the geomagnetic field to the SE is a complicated task. A possible response is “masked” by variations of another nature. Moreover, the magnitude and sign of the geomagnetic field disturbance significantly depend on the state of space weather, season, local time, location of the magnetic observatory, and, of course, the magnitude of the eclipse. Therefore, the study of the effect of SEs on the geomagnetic field remains an important task. The purpose of this study is to present the results of analysis of temporal variations in the geomagnetic field observed by the International Real-Time Magnetic Observatory Network (INTERMAGNET) during the SE of June 10, 2021. The main feature of this eclipse was that the SE was annular (maximum magnitude M_max ≈ 0.943). The annular SE occurred on June 10, 2021 with a commencement time 08:12:20 UT over Canada. The Moon’s shadow moved across the Atlantic Ocean, Greenland, the Arctic Ocean, the North Pole, and the northern parts of Europe and Asia. A partial SE occurred in Mongolia and China, and it ceased at 11:33:43 UT. The annularity was observed from 10:33:16 to 10:36:56 UT over Greenland. The analysis of the geomagnetic effect was based on the INTERMAGNET database. The data were processed with 1-min temporal resolution and 0.1-nT level resolution, and temporal variations in the X, Y, and Z components recorded at 15 magnetic observatories were studied

Magnetic field pulsations in the magnetosphere and the time of their detection and location on the Earth’s surface are analyzed. Measurements of magnetic field fluctuations from fluxgate magnetometers of the Cluster II satellites and measurements from ground-based magnetometers in the auroral oval region are used. The substorms on August 13, 2019, are examined. In particular, two substorms and flapping motions of the magnetotail current sheet are analyzed. The measurements from ground-based observatories are selected using the 3DView software, a tool for the visualization of spacecraft position with associated geomagnetic tail field lines. A continuous wavelet transform is used to identify geomagnetic pulsations, and an integrated representation in two frequency bands, 45–150 s (Pc4/Pi2) and 150–600 s (Pc5/Pi3), is considered to determine the pulsation type and estimate the observed shifts between the pulsations recorded in the Earth’s magnetotail and in the auroral oval region. Correlated Pi2 and Pc5 pulsations in the auroral region and in the magnetotail are detected. The magnitude of detected pulsations depends on the relative position of ground-based magnetometers and the projection of the field line on which the spacecraft are located. Based on the time delay between the maxima of geomagnetic pulsations at the Earth’s surface in relation to disturbances in the magnetosphere, the velocity of disturbance propagation along the magnetic field line is estimated.

A method of identification of acoustic-gravity waves (AGWs) in the atmosphere according to the satellite measurement data has been proposed. It has been shown that the polarization relations between fluctuations of the wave parameters (velocity, density, temperature, and pressure) for freely propagating waves and evanescent wave modes are considerably different, which makes it possible to identify different types of atmospheric waves in the experimental data. A diagnostic chart was plotted that can be used for determining a wave type and its direction of the vertical motion based on the phase shifts of the observed parameters. Using phase shifts between the velocity fluctuations and thermodynamic parameters of the atmosphere, not only the wave type but also its spectral characteristics can be determined. Verification of the proposed method was performed for identifying polar wave perturbations based on the measurements from the Dynamics Explorer 2 low-orbit satellite. Verification showed that the polarization relations of AGWs in the thermosphere preferably correspond to the gravitational branch of acoustic-gravity waves, which freely propagate in the direction of bottom up. This conclusion agrees with other results of the observations of AGWs in the atmosphere and the ionosphere using the ground and satellite methods. The evanescent waves were not observed at the considered orbits of the satellite.

Profiles of the Fe IX line at a wavelength of λ = 17.1 nm in the radiation spectrum of slow magneto-acoustic waves, propagating in coronal loops, are calculated under conditions of an optically thin layer and a constant density. The parameter values used in calculations of the line profiles are as follows: the amplitude of the velocity of particles’ displacements in a wave v₀ = 10 km/s, the width of the coronal loop is 2000 and 5000 km, the wavelength Λ = 20 000 km and 50 000 km, and the value of the Doppler width Δλ_d = 1 pm; the values for the angle of view and the wave phases were varied. The true value of the energy flux density is 622 erg/cm²s. The values of the energy flux density obtained in calculations strongly depend on the angle of view θ and the wave phase: they range from 0 and, when the values of θ are large, to 2000 erg/cm²s. The values of the Doppler velocities v_d and the velocities of nonthermal motions v_nt take maximal values of ~12 km/s at small angles θ and almost vanish at large angles θ. When the angle of view is small (θ < 30°), a weak blue asymmetry is noticeable. When the angle of view is large (θ > 30°), the asymmetry is almost invisible.

The solar eclipse (SE) on June 10, 2021, was annular and a member of Saros 147. The first contact occurred at 08:12:20 UT on June 10, 2021, and the fourth contact occurred at 13:11:19 UT. The maximal SE magnitude was observed from 09:49:50 to 11:33:43 UT. The annularity took place from 10:33:16 to 10:36:56 UT. The solar eclipse began over the territory of Canada. The shadow moved across Greenland (where the annularity took place), the Arctic Ocean, the North Pole, New Siberia Island, and the Russian Federation. The partial eclipse was observed in Mongolia, in a major part of China, in the northeast of the United States, in North Alaska, all over the Arctic Ocean, and in the North Atlantic, as well as over a major part of Ukraine, except for the Odessa, Nikolaev, and Kherson regions and Crimea. In this work, the observations of the thermal (temperature) effect of the SE of June 10, 2021, in the surface air layer in the city of Kharkiv are described; the thermal effects of eight SEs that occurred in the same region in 1999–2021 are compared. The observations of the effects in the surface air layer were made at Karazin National University Radiophysics Observatory, in the vicinity of Kharkiv. The air temperature, atmospheric pressure and humidity, and the wind speed and direction were measured with standard instrumentation. The temperature measurement accuracy was 0.1°C. The solar eclipse energy balance is estimated. The internal energy of gas in the surface atmosphere has been shown to decrease by ~5.3 × 10¹⁸ J due to the SE, which corresponds to an average power of 1.2 PW. The specific energy and power were 6.5 kJ/m³ and 1.4 W/m³. The variations in the air temperature of the surface atmosphere were observed during the day of the solar eclipse and on the reference days. They were analyzed along with the tropospheric weather for those days. The weather was not favorable for observations of the thermal effect of the eclipse. The atmospheric cooling occurring during the eclipse magnitude maximum is estimated; the decrease in the temperature amounted to approximately 1°C. The differences in the thermal effects during the eight SEs compared are explained by different seasons, local time, cloud structure, state of the Earth’s surface, and atmospheric convection.