Kinematics and Physics of Celestial Bodies最新文献

Direct magnetic field measurements in sunspots by many spectral lines are important for elucidating the true magnitude and structure of the magnetic field at different levels of the solar atmosphere. Currently, magnetographic measurements are the most widespread, but such measurements mainly represent the longitudinal component of the magnetic field. In the sunspot umbra, such measurements give unreliable information and do not allow for determining the actual value of the module (absolute value) of the magnetic field. Such data can be obtained from spectral-polarization observations, thanks to which the magnetic field can be determined directly from Zeeman splitting, rather than as calibrated polarization in line profiles. The presented work presents the results of the study into the magnetic field in the sunspot on July 17, 2023, which was observed on the Echelle spectrograph of the horizontal solar telescope of the Astronomical Observatory of Taras Shevchenko National University of Kyiv. The I ± V profiles of ten photospheric lines of Fe I, Fe II, Ti I, and Ti II were analyzed in detail. The strongest magnetic field measured by the Fe I lines reaches 2600 G, and the difference in the measured intensities by these lines is sometimes at the level of 50–80%. The umbral lines of Ti I show, in general, the same magnetic fields as Fe I lines, while the lines of Fe II and Ti II show significantly weaker fields. Although the lateral field profile in the spot by most of the Fe I lines is smooth, quasi-Gaussian, one of the lines, namely Fe I λ 629.10 nm, shows a “dip” at 400–600 G in the sunspot umbra, which, most likely, is real. The obtained data probably indicate a combination of at least two effects: the dependence of measurements on the height of line formation in the solar atmosphere and the manifestation of Zeeman “saturation” in lines with different Lande factors. It also turned out that the umbral line of Ti I λ 630.38 nm shows somewhat stronger magnetic fields compared to non-umbral lines. The obtained data are planned to be used to clarify the general picture of the magnetic field in the spot by means of simulation.

Magnetic storm, ionospheric storm, atmospheric storm, and electrical storm are the components of a geospace storm resulting from a solar storm. In the literature, the main attention is paid to the analysis of severe and extreme geospace storms. It is these storms that have the greatest impact on the Earth–atmosphere–ionosphere–magnetosphere system. They are most dangerous for space-based and ground-based technological systems. Such storms have a significant impact on human well-being and health. Minor and moderate storms are much less studied than severe and extreme ones. There are good reasons to believe that such storms can have some impact on the systems and people. It is important that the frequency of occurrence of moderate storms is much greater than the frequency of occurrence of severe storms. All this determined the relevance of this work, which consists in the study of magnetic disturbances that arise during moderate geospace storms, which receive undeservedly little attention. The purpose of this paper is to analyze on a global scale the temporal variations of geomagnetic field components during moderate magnetic storms on April 28–29 and May 1–2, 2023. The latitudinal dependence of the geomagnetic field components temporal variations during two moderate magnetic storms in April–May 2023 and on reference days was analyzed on a global scale using the data of the global network of Intermagnet stations. The limits of fluctuations in the level of the geomagnetic field under quiet conditions and during moderate storms were estimated. The range of variations in the geomagnetic field level under quiet conditions decreased from 200–260 to 30–50 nT with decreasing geographic latitude. During the storms, these limits increased 1.3–2.1 times. The variations in the level of components at stations equidistant from the equator were close. This is true for both the Western and Eastern Hemispheres. The fluctuations of the geomagnetic field level at the stations operating approximately at the same latitude but in different hemispheres were also close.

Based on observations conducted at the Ernest Gurtovenko Horizontal Solar Telescope, the height of the polar chromosphere of the Sun was determined for the period 2012–2023. The measurement was calculated as the difference between the positions of the maximum radial brightness gradients in the continuum and at the core of the H_α line. The results indicate that the height of the polar chromosphere is lower near the maximum of the solar cycle (approximately 4500 km, or 6.3″) and higher near the minimum of the cycle (approximately 5000 km, or 6.9″). The chromosphere’s height at the southern pole in 2012–2013 and, particularly, 2016–2017 was higher than at the northern pole. This north–south asymmetry is likely related to differences in the dynamics and magnitude of the polar magnetic fields during Solar Cycle 24. The findings demonstrate that the time changes in the chromosphere’s height closely correlate with sunspot numbers, the strength of the polar magnetic field, and chromospheric indices of solar activity. The correlation coefficient between the average annual height of the chromosphere and the smoothed relative sunspot number is –0.64 for the northern hemisphere and –0.75 for the southern hemisphere. The correlation coefficient between the average annual height of the chromosphere and the smoothed values of the polar magnetic field strength (based on data from the Wilcox Solar Observatory) is 0.86 for the northern hemisphere and 0.53 for the southern hemisphere (the latter value increases to 0.77). The correlation coefficient between the average annual height of the chromosphere and the chromospheric index I_K2 reaches the highest values, 0.91, for the northern pole and 0.80 for the southern pole.

Wave disturbances from the solar terminator in the morning and evening hours were investigated using a ground-based network of very low frequency (VLF) radio stations. The data of measurements of the amplitudes of VLF radio signals on the GQD–A118 radio path with a transmitter in Great Britain (GQD, f = 22.1 kHz) and a receiving point in France (A118) were used. Amplitudes of radio signals change as a result of the propagation of atmospheric waves at the altitudes of localization of the upper wall of the Earth-ionosphere VLF waveguide. This makes it possible to use a network of VLF radio stations to monitor wave activity in the mesosphere (lower ionosphere). Based on the analysis of experimental data, it was established that pronounced periodic fluctuations in the amplitudes of radio signals are observed in the evening and in the morning for several hours after the passage of the solar terminator. Histograms of the distribution of these fluctuation periods for several months were constructed. The predominance of periods of radio signal fluctuations of 20–25 min was revealed both in the evening and in the morning hours. For the evening terminator, this result is consistent with our previous studies. The predominance of approximately the same wave periods in the morning was established for the first time. It is assumed that the observed fluctuations are caused by the propagation of acoustic-gravity waves (AGWs) from the solar terminator. The existence of a dominant period probably indicates that these perturbations represent a fundamental wave mode moving synchronously with the solar terminator.

The study of MHD waves in coronal structures is of great importance in coronal seismology. The study of these waves makes it possible to reveal the physical structure and heating mechanism of the solar corona. It is of great interest to calculate the line profile in the emission spectrum of a magneto-sonic wave for various physical parameters, calculate the energy flux and compare them with observations. In this paper, the profiles of the FeIX λ171Å line in the emission spectrum of slow magneto-acoustic waves propagating in coronal loops are calculated for cases of an optically thin layer and the change in density. The line profiles were calculated for the following parameter values: wave velocity amplitude ({{upsilon }_{0}}) = 10 km/s, coronal loop width 2000 and 5000 km, wavelength Λ = 20 000 and 50 000 km, Doppler width Δλ_d = 0.01 Å, and at values of the angle of the line of sight and at different phases of the wave. The energy flux density is 622.5 erg/(cm² s). The calculated values of the energy flux density strongly depend on the angle of the line of sight and on the phase of the wave and range from zero at large values of θ to ~4 × 10³ erg/(cm² s), the values of Doppler velocities ({{upsilon }_{{text{d}}}}) and velocities of non-thermal movements ({{upsilon }_{{{text{nt}}}}}) at small values of θ have a maximum value of ~13 km/s and decrease almost to zero at large values of θ. At different values of the angle of the line of sight, the asymmetry is almost not noticeable. An interesting result is that the values of the calculated (observed) energy flux can be both much less and much more than the true value: from almost zero at small values of θ. These values depend not only on the angle of the line of sight, but also on the width of the coronal loop and the wavelength.

Nonlinear equations called the Stenflo equations are usually used for the analytical description of the propagation of internal gravity waves in the Earth’s upper atmosphere. Solutions in the form of dipole vortices, tripole vortices, and vortex chains are previously obtained by these equations. The Stenflo equations also describe rogue waves, breathers, and dark solitons. If disturbances cease to be small, then their profiles are usually deformed, and, presumably, they cannot be considered plane waves. This study shows that this is not always the case for internal gravity waves and that these waves can propagate as plane waves even with large amplitudes. An exact solution of the system of nonlinear Stenflo equations for internal gravity waves that contain nonlinear terms in the form of Poisson brackets is given. The solution is obtained in the form of plane waves with arbitrary amplitude. To find a solution, the original system of equations is transformed. It is split into equations for the stream and vorticity functions as well as equations for the perturbed density. To solve the obtained equations, the procedure of the successive zeroing of Poisson brackets is applied. As a result, linear equations that allow one to find the accurate analytical solutions for internal gravity waves in the form of plane waves with arbitrary amplitude are obtained. By solving these linear equations in two different ways, we have analytically found expressions for the perturbed quantities and the dispersion equation. The nonlinear equations obtained for the current, vorticity, and perturbed density functions can be used to find other nonlinear solutions. The given solutions in the form of plane waves with arbitrary amplitude may be of interest for the analysis of the propagation of internal gravity waves in the Earth’s atmosphere and the interpretation of experimental data.

A structural analysis of the time series of pole coordinate changes (version C01 IERS) for the period of 1975.0–2011.0 has been performed based on the nonlinear least squares method. Average estimates of the parameters of the main components of the pole movement—namely, Chandler, annual, and semiannual wobbles—are obtained for this period. The obtained values of periods T and amplitudes A of the main components are as follows: T = 433.49 ± 0.22 days and A = 160 ± 3 mas for the Chandler oscillations; T = 365.19 ± 0.37 days and A = 93 ± 5 mas for the annual oscillations; and T = 183.03 ± 0.34 days and A = 4 ± 2 mas for the semiannual oscillations. Changes in the pole coordinates are examined in the time series when focusing on the manifestation of Chandler oscillations. The dynamics of oscillation parameters (including amplitude, period, phase, and Q factor) is studied. Changes in the Chandler oscillation parameters show their interdependence. The correlation coefficient between phase and period variations is +0.94, and a similar relationship is observed between phase and amplitude variations with a correlation coefficient of +0.88. It is shown that the phase change precedes the changes in the amplitude and in the period. This behavior of the parameters of the Chandler wobble suggests that changes in the period and in the amplitude should be considered a consequence of the phase changes. It is revealed that an increase in the amplitude of Chandler oscillations correlates with a decrease in the attenuation decrement with a correlation coefficient of –0.98. These findings align with the statistical patterns articulated by Melchior, which are indicative of (a) inconstancy of the period of Chandler oscillations over time and (b) proportional changes between the period and the amplitude of oscillations. Thus, preference should be given to the one-component complicated model of the Chandler pole movement with a variable period for the studied period of time.

The cumulative solution for GPS weeks 935–1933 (December 7, 1997–January 28, 2017) was obtained in the GNSS Data Analysis Centre of the Main Astronomical Observatory of the National Academy of Sciences of Ukraine after adjustment of 6993 daily normal equation files received as a result of the regular processing and the second reprocessing campaign of archival observations. The ADDNEQ2 program of the Bernese GNSS Software ver. 5.2 was used. Before the adjustment, the times series of station coordinates received from the mentioned processing were analyzed to find outliers and determine sets of coordinates and velocities. For foreign EPN stations, the files prepared by the EUREF Permanent GNSS Network were used (EPN_outliers.lst and EPN_discontinuities.snx respectively). For 233 permanent GNSS stations, the 356 sets of coordinates and 256 sets of velocities that correspond them were established. According to the duration of observations, the coordinate sets were divided into three groups: (1) less than 1 year (94 sets), (2) 1–3 years (92 sets), (3) more than 3 years (166 sets). Four coordinate sets were excluded from further analysis. The IGb08 reference frame was realized by applying No-Net-Translation conditions on the coordinates of the IGS Reference Frame stations. The velocities of these stations were heavily constrained (10^–9 m/year for each components) that, in term of adjustment means, a fixing of velocities values. As result, the coordinates and velocities of the Ukrainian and the Eastern European stations in the IGb08 reference frame at epoch 2005.0 were estimated with high precision. The mean repeatabilities for components of station coordinates are 1.69, 1.40, and 3.63 mm for the north, east, and height components respectively.

The processes that lead to formation of spatial distribution of polarization parameters in the Earth’s atmosphere are studied. Among the modern development of devices for atmospheric polarimetric measurements, the prospects for creating equipment for on-ground measurements are highlighted. A method is described for determining polarization parameters at the celestial hemisphere with use of data on the on-ground polarimetric measurements. A spatial diagram of the mutual location of the main components in the light-scattering process is provided. Formulas for calculating the angle (AoLP) and degree (DoLP) of the celestial linear polarization in the case of light scattering by a purely gaseous component of the atmosphere are given. The effect of changes in the characteristics of the atmospheric aerosol on the specified celestial polarization parameters is considered. The key idea of the proposed method for controlling the reliability of on-ground polarimetric measurements consists in using the stability of the spatial distribution of the AoLP parameter in the celestial hemisphere. The algorithm for such control is described and recommendations for its practical application are provided. The use of the DoLP parameter is indicated as an opportunity only for qualitative evaluation of the data of on-ground polarimetric measurements. Examples of visualization of the spatial distribution of celestial polarization parameters in the model environment for a selected position, date, and time of observation are given.