Subjects -> ASTRONOMY (Total: 94 journals)
 Showing 1 - 46 of 46 Journals sorted alphabetically Advances in Astronomy       (Followers: 51) Annual Review of Astronomy and Astrophysics       (Followers: 39) Annual Review of Earth and Planetary Sciences       (Followers: 63) Artificial Satellites       (Followers: 23) Astrobiology       (Followers: 14) Astronomical & Astrophysical Transactions: The Journal of the Eurasian Astronomical Society       (Followers: 6) Astronomical Journal       (Followers: 8) Astronomical Review       (Followers: 4) Astronomische Nachrichten       (Followers: 4) Astronomy & Geophysics       (Followers: 48) Astronomy and Astrophysics       (Followers: 60) Astronomy and Astrophysics       (Followers: 32) Astronomy and Computing       (Followers: 2) Astronomy Letters       (Followers: 22) Astronomy Reports       (Followers: 15) Astronomy Studies Development       (Followers: 12) Astroparticle Physics       (Followers: 8) Astrophysical Bulletin       (Followers: 3) Astrophysical Journal       (Followers: 19) Astrophysical Journal Letters       (Followers: 14) Astrophysical Journal Supplement Series       (Followers: 14) Astrophysics       (Followers: 29) Astrophysics and Space Science       (Followers: 46) Astrophysics and Space Sciences Transactions (ASTRA)       (Followers: 56) Astropolitics: The International Journal of Space Politics & Policy       (Followers: 12) Celestial Mechanics and Dynamical Astronomy       (Followers: 11) Chinese Astronomy and Astrophysics       (Followers: 24) Colloid Journal       (Followers: 3) Comptes Rendus Physique       (Followers: 2) Computational Astrophysics and Cosmology       (Followers: 3) COSPAR Colloquia Series       (Followers: 11) Earth, Moon, and Planets       (Followers: 55) Earth, Planets and Space       (Followers: 74) EAS Publications Series       (Followers: 8) EPL Europhysics Letters       (Followers: 8) Experimental Astronomy       (Followers: 39) Expert Opinion on Astronomy and Astrophysics       (Followers: 7) Extreme Life, Biospeology & Astrobiology - International Journal of the Bioflux Society       (Followers: 6) Few-Body Systems       (Followers: 1) Foundations of Physics       (Followers: 41) Frontiers in Astronomy and Space Sciences       (Followers: 12) Galaxies       (Followers: 6) Globe, The       (Followers: 4) Gravitation and Cosmology       (Followers: 4) Icarus       (Followers: 75) International Journal of Advanced Astronomy       (Followers: 28) International Journal of Astrobiology       (Followers: 4) International Journal of Astronomy       (Followers: 19) International Journal of Astronomy and Astrophysics       (Followers: 29) International Journal of Satellite Communications Policy and Management       (Followers: 13) International Letters of Chemistry, Physics and Astronomy       (Followers: 12) ISRN Astronomy and Astrophysics       (Followers: 7) Journal for the History of Astronomy       (Followers: 19) Journal of Astrobiology & Outreach       (Followers: 3) Journal of Astronomical Instrumentation       (Followers: 3) Journal of Astronomical Telescopes, Instruments, and Systems       (Followers: 5) Journal of Astrophysics       (Followers: 26) Journal of Astrophysics and Astronomy       (Followers: 52) Journal of Atmospheric and Solar-Terrestrial Physics       (Followers: 199) Journal of Cosmology and Astroparticle Physics       (Followers: 38) Journal of Geophysical Research : Planets       (Followers: 178) Journal of Geophysical Research : Space Physics       (Followers: 178) Journal of High Energy Astrophysics       (Followers: 22) Kinematics and Physics of Celestial Bodies       (Followers: 10) KronoScope       (Followers: 1) Macalester Journal of Physics and Astronomy       (Followers: 4) MNASSA : Monthly Notes of the Astronomical Society of South Africa       (Followers: 1) Molecular Astrophysics       (Followers: 1) Monthly Notices of the Royal Astronomical Society       (Followers: 14) Monthly Notices of the Royal Astronomical Society : Letters Nature Astronomy       (Followers: 8) New Astronomy       (Followers: 27) New Astronomy Reviews       (Followers: 17) Nonlinear Dynamics       (Followers: 19) NRIAG Journal of Astronomy and Geophysics       (Followers: 5) Open Astronomy       (Followers: 2) Physics of the Dark Universe       (Followers: 4) Planetary and Space Science       (Followers: 101) Planetary Science       (Followers: 52) Proceedings of the International Astronomical Union       (Followers: 2) Publications of the Astronomical Society of Australia       (Followers: 2) Publications of the Astronomical Society of Japan       (Followers: 3) Publications of the Astronomical Society of the Pacific       (Followers: 4) Research & Reviews : Journal of Space Science & Technology       (Followers: 17) Research in Astronomy and Astrophysics       (Followers: 29) Revista Mexicana de Astronomía y Astrofísica       (Followers: 2) Science China Physics, Mechanics & Astronomy       (Followers: 4) Solar Physics       (Followers: 34) Solar System Research       (Followers: 14) Space Science International       (Followers: 192) Space Science Reviews       (Followers: 97) Space Weather       (Followers: 24) Transport and Aerospace Engineering       (Followers: 13) Universe       (Followers: 5)
Similar Journals
 Kinematics and Physics of Celestial BodiesJournal Prestige (SJR): 0.328 Citation Impact (citeScore): 1Number of Followers: 10      Hybrid journal (It can contain Open Access articles) ISSN (Print) 1934-8401 - ISSN (Online) 0884-5913 Published by Springer-Verlag  [2626 journals]
• Influence of Vertical Heterogeneity of Atmospheric Temperature on the
Propagation of Acoustic-Gravity Waves
• Abstract: — A new approach to the study of acoustic-gravity waves in the Earth’s atmosphere in the presence of vertical temperature inhomogeneity is proposed. Using this approach, the local AGW dispersion equation was obtained for the atmosphere with a small vertical temperature gradient. The modification of the acoustic and gravitational regions of freely propagating AGWs on the spectral plane $$\left( {\omega ,{{k}_{x}}} \right)$$ depending on the temperature gradient was investigated. It is shown that the acoustic and gravitational regions approach each other with a positive temperature gradient, while the distance between them increases with a negative gradient. On the spectral plane, the indicators of the location of the acoustic and gravitational regions of freely propagating AGWs are the dispersion curves of the non-divergent and inelastic horizontal wave modes. The possibility of overlapping the acoustic and gravitational regions of AGWs in a nonisothermal atmosphere was investigated.
PubDate: 2020-11-01

• Two-Frequency Acoustic-Gravitational Waves and Simulation of Satellite
Measurements
• Abstract: — The theory of acoustic gravity waves (AGW) considers free disturbances of the atmosphere within the framework of a single-frequency approach. In this case, the theory implies the existence of two separate types of waves with different natural frequencies: acoustic and gravitational. In the single-frequency approach, wave fluctuations of density, temperature, and velocity are related to each other through the spectral characteristics of the wave, and these relationships are unchanged. However, satellite observations of AGW parameters cannot always be explained within the framework of a single-frequency approach. This paper presents a two-frequency approach to studying AGWs using the model of two coupled oscillators. It is shown that the perturbed movements of the elementary volume of the medium occur simultaneously at two natural frequencies. In this case, the connections between the wave fluctuations of the parameters are determined by the initial conditions, which can be arbitrary. Solutions in real functions for an isothermal atmosphere are obtained. The conditions under which single-frequency AGWs are obtained from the general two-frequency solution are investigated. The AGW waveforms measured from the satellite for velocities and displacements in single-frequency and dual-frequency modes are numerically simulated. The results of simulating two-frequency AGWs agree with the data of satellite measurements. Two-frequency AGWs are not always implemented at two different frequencies. It is shown that, when the frequencies approach each other, the beat effect occurs and two closely related modes become indistinguishable. At the same wavelength, they have one center frequency and one phase velocity. The main feature of the two-frequency approach to the study of AGW is the expansion of the relationships between the wave parameters of the medium. This makes it possible to achieve satisfactory agreement of the model waveforms with the data of satellite measurements. Thus, the use of a two-frequency AGW treatment opens up new possibilities in the interpretation of experimental data.
PubDate: 2020-11-01

• Asymmetry of Lines in the Spectra of the Sun and Solar-Type Stars
• Abstract: The asymmetry of the Fe I and Fe II lines in the solar flux spectra has been analyzed using three FTS atlases and the HARPS atlas; it was also analyzed in the spectra of 13 stars using observations on the HARPS spectrograph. Individual line bisectors of each star have been averaged to reduce observation noise. The obtained average bisectors in the stellar spectra are more or less similar to the C-shape well known for the Sun. In stars with rotation velocities greater than 5 km/s, the shape of the bisectors is closer to the slash symbol (/). The curvature and span of the bisectors increase with the temperature of the star. Our results confirm the known facts about the strong influence of rotation velocity on the span and shape of bisectors. The average convective velocity was determined based on the span of the average bisector, which shows the largest difference between the velocity of cold falling and hot rising convective flows of matter. It is equal to –420 m/s for the Sun as a star. In solar-type stars, it grows from –150 to –700 m/s with an effective temperature of 4800 to 6200 K, respectively. For the stars with greater surface gravity and greater metallicity, the average convective velocity decreases. It also decreases with star age and correlates with the velocity of micro- and macroturbulent movements. The results of the solar flux analysis showed that absolute wavelength scales in the FTS atlases coincide to approximately –10 m/s, except for the atlas of Hinkle et al., the scale of which is shifted and depends on the wavelength. In the range from 450 to 650 nm, the scale shift of this atlas varies from –100 to –330 m/s, respectively, and it equals –240 m/s on average. The resulting average star bisectors contain information about the fields of convective velocities and may be useful for hydrodynamic modeling of stellar atmospheres in order to study the characteristic features of surface convection.
PubDate: 2020-11-01

• Ionospheric Effects of the August 11, 2018, Solar Eclipse over the
People’s Republic of China
• Abstract: — The purpose of the work is to describe ionospheric effects of the August 11, 2018, partial solar eclipse (SE) that occurred over the People’s Republic of China as observed via GPS technology. Solar eclipses are rare phenomena of nature. During 2–3 h, the rearrangement of processes acting at the Earth’s surface, in the atmosphere, geospace, i.e., in the Earth–atmosphere–ionosphere–magnetosphere system (EAIMS), occurs. The response of this system depends on the solar activity, season, time of day, and on the state of atmospheric and space weather. Therefore, the investigation of the EAIMS response to SEs remains an urgent problem. The response is accompanied by controllable dynamic processes, the study of which improves our understanding of the near-Earth environment. Studying the EAIMS response to SEs is of fundamental importance to science. Its practical applications include the following. Solar eclipses cause significant disturbances in EAIMS, which affect the propagation of radio waves in almost all frequency ranges and, as a result, deteriorate the performance of radars, radio astronomy and radio navigation systems, and tools for remote environment sensing. SE effects have been studied for over 100 years. Thus far, the following regular effects have been studied quite well: reductions in the electron density, electron and ion temperatures, variations in ion composition, and plasma vertical movements. The irregular effects have been studied to a much less extent, and they can vary from one solar eclipse to another. The main feature of the SE over the PRC has been the fact that it was observed during the time before local time sunset period. The maximum magnitude of the eclipse within the PRC area varied from 0.07 to 0.52, while the Sun’s surface area shadowed by the Moon was observed to be 0.02–0.42. The onset of the eclipse over the PRC has been observed to occur in the period ∼09:54–10:05 UT, and the ending time varied from 10:07 UT to 11:10 UT. The SE duration varied from a few minutes to approximately 67 min. The insignificant duration of the eclipse and the dusk terminator affected the SE effects. The state of space weather during the solar eclipse was favorable for observing SE effects occurring in the ionosphere. The global navigation satellite system data have been processed to reveal the ionospheric response to the August 11, 2018, SE. The ionospheric time delay and, respectively, the vertical total electron content (TEC), have been calculated combining the pseudo-range and integrated-phase data at two frequencies. Regardless of the dusk terminator influence, we have managed to confidently detect the ionospheric SE effects, which proved to be sufficiently small due to a small SE phase. Over the People’s Republic of China area, a funnel-shaped decrease in TEC has been observed to occur approximately 1300 km in latitude and 2000 km in longitude. The TEC reduction has been found to be 7%. The solar eclipse was accompanied by the generation of aperiodic TEC disturbances at a rate of 0.4–0.8 TEC unit/h and 105-min in duration. Wave disturbances caused by the SE have not been observed confidently, which is due to a small SE phase and insignificant disturbances in the electron density.
PubDate: 2020-11-01

• Verification of Einstein’s Formula for Gravitational Deflection of Light
Using Observations of Galactic Microlensing
• Abstract: General relativity (GR) has a solid experimental base. However, the emergence of new experimental capabilities and independent observational information stimulates continuing tests of general relativity. The purpose of this work is to evaluate the potential of gravitational microlensing of distant sources on the stars of our Galaxy and to verify Einstein’s formula of gravitational refraction. This effect has been repeatedly tested in the Solar System in high-accuracy experiments with the propagation of radio waves, when the measurements are most effective for the distances from the signal trajectory to the Sun on the order of several solar radii. In the case of galactic microlensing, a quite different type of observational data and other characteristic distances are used that are determined in the high magnification events by the Einstein ring radii, which is typically of the order of 1 AU. Although the gravitational deflections of light by stars are very small and currently practically inaccessible by direct measurements, nonetheless, due to the large distances to the microlenses, the radiation flux from the source in strong microlensing events can increase several times. To verify Einstein’s formula, a more general dependence of the beam deflection angle $$\alpha \propto 1/{{p}^{{1 + \varepsilon }}}$$ on its impact distance p relative to the deflector is considered and, accordingly, the equations of gravitational lensing are modified. The challenge is to limit ε based on observational data. The Early Warning System data obtained in 2018 within the Optical Gravitational Lensing Experiment (OGLE) (http://ogle.astrouw.edu.pl/ogle4/ ews/2019/ews.html) was used. A sample of 100 light curves from the data obtained by the OGLE group in 2018 was formed. Each light curve was fitted as part of a modified model of gravitational lensing with parameter ε. As a result, 100 values of ε and estimates of their variances were obtained. It was found that the mean value of ε does not contradict GR within the limits of a one percent standard deviation. In the future, using a larger number of light curves will allow one to hope for a significant decrease in the error of ε due to statistical averaging.
PubDate: 2020-09-01

• Parameters of the Infrasonic Signal Generated by the Kamchatka Meteoroid
• Abstract: The subject of this study is the infrasonic signal generated by a high-speed (32 km/s), high-energy (173 kt TNT), and large-sized (9.4 m) celestial body, later called the Kamchatka meteoroid, which entered the terrestrial atmosphere and exploded on December 18, 2018. The focus of the study is the parameters of the infrasonic signal launched by the Kamchatka meteoroid. The study is based on the data on temporal dependences of pressure in the infrasonic wave collected by the I53US, I30JP, I59US, I46RU, I57US, and MAAG2 infrasonic stations included in the International Monitoring System (IMS) set up by the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO). The measurement data initially recorded on a relative scale were converted into absolute values. The temporal dependences of the infrasonic wave pressure were then filtered in the 1–40-s period range and were subsequently subjected to system spectral analysis that included the mutually complementary short-time Fourier transform, adaptive Fourier transform, and the wavelet transform with the Morlet wavelet as the basis function. As a result, it was found that the infrasonic signal amplitude exhibits quite a rapid decrease with distance between an infrasonic station and the meteoroid’s explosion site. The time delay of the infrasonic signal shows an increase with distance between the celestial body explosion and the site of signal detection. The signal celerity exhibits a dependence on the distance and the path orientation; it is estimated to be in the range of 269–308 m/s. The infrasonic signal duration shows virtually no dependence on the distance from the detonation point to an infrasonic station. The infrasonic signal spectra have a wide bandwidth with periods from ∼5 to ∼40 s. At the same time, the greatest energy falls within the isolated periods of 12–15 s and 28–33 s. The scatter diagrams and regressions for the infrasound main parameters were plotted. The celestial body’s kinetic energy (179 kt TNT) and acoustic efficiency (∼4%) were estimated from the prevailing infrasonic period.
PubDate: 2020-09-01

• Attenuation of Acoustic-Gravity Waves in an Isothermal Atmosphere:

• Abstract: — Within the model of a dissipative isothermal atmosphere, the attenuation of acoustic−gravity waves (AGWs) is studied on the basis of the modified Navier−Stokes and heat-transfer equations. Besides the usually considered velocity gradient, the modification of these equations takes into account the additional transfer of the momentum and energy induced by AGWs due to the density gradient. This results in that additional terms appear in the hydrodynamic equations of motion and heat transfer. Under these assumptions, the local dispersion equation for AGWs in an isothermal dissipative atmosphere, as well as an expression for the damping decrement, is obtained. In the limiting cases of high frequencies (sound waves) and low frequencies (gravitational waves), the nature of the attenuation allows a clear physical interpretation. Special aspects of the time-dependent attenuation for the evanescent acoustic−gravity modes of various types, including the Lamb waves and Brent−Väisälä oscillations, are also considered.
PubDate: 2020-09-01

• The Second Reprocessing Campaign of Historical Observations in the GNSS
Data Analysis Centre of MAO NAS of Ukraine
• Abstract: The second reprocessing campaign of historical observations of GNSS satellites at permanent stations located in Ukraine and in the Eastern Europe for GPS weeks 935–1708 (December 7, 1997 – October 6, 2012) was carried out in the GNSS Data Analysis Centre of the Main Astronomical Observatory NAS of Ukraine with using products updated in IGS repro2 and EPN-Repro2 campaigns – precise ephemerides of GPS and GLONASS satellites, coordinates and velocities of reference permanent GNSS stations, etc. The observations was analyzed with the Bernese GNSS Software ver. 5.2 according to the requirements of the EUREF Permanent GNSS Network (EPN), that were valid at that time. In total, observations on 72 GNSS stations, including 48 Ukrainian stations belonging to the following operators of GNSS networks: MAO NAS of Ukraine, Research Institute of Geodesy and Cartography, TNT TPI company (TNT TPI GNSS Network), PJSC System Solutions (System.NET), Lviv Polytechnic National University, UNAVCO, Inc. (USA), were processed. The IGb08 reference frame was realized by applying No-Net-Translation conditions on the coordinates of the IGS Reference Frame stations. As result, the stations’ coordinates in the IGb08 reference frame and the zenith tropospheric delays for all stations were estimated. The mean repeatabilities for components of stations’ coordinates for all weeks (the characteristics of the precision of the received daily and weekly solutions) are in the following ranges: for north and east components – from 0.6 mm to 1.6 mm (average values are 1.02 mm and 0.94 mm respectively), for height component – from 2.2 mm to 5.2 mm (average value is 3.36 mm) with the outlier of 5.79 mm for GPS week 943. The coordinates of the permanent GNSS stations for one weekly solution are presented.
PubDate: 2020-09-01

• Dynamics of Magnetic Structures during a Magnetospheric Substorm
• Abstract: The Earth’s magnetosphere and the ambient interplanetary environment can create favorable conditions for the nonlinear process of energy release in the form of changes in the topology of the magnetic field and current systems, particle acceleration, wave generation, and sharp gradients in the parameters inherent to a substorm phenomenon. Initially, early studies substantiated the role of variations in the solar wind parameters as a key factor responsible for the onset of a magnetospheric substorm; however, this factor was later shown not to be decisive. Over several decades, continuously improving methods for designing measurement tools and analyzing data helped to identify the processes that accompany the substorm phenomenon and describe them both qualitatively and quantitatively. However, there is no consensus in understanding the scenario of substorm development stepwise. The purpose of the research is to determine the propagation and orientation features of transients (fronts) in the current sheet of the Earth’s magnetotail during a substorm. To do this, the magnetic field measurements obtained by the four spacecraft of the Cluster II mission for July 20, 2013, are analyzed. During this event, spacecraft were located on the night side of the Earth’s magnetosphere and recorded changes in the geomagnetic field during the magnetospheric substorm. We used the single-spacecraft method for finding the minimum variance of the magnetic field and multispacecraft timing analysis involving cross-correlation of time series. The first method allows finding the direction of the normal to the structure under study; the second method makes it possible to find the direction and absolute value of its propagation velocity. The results of the study show that, with the development of substorms, the fronts that move towards the Earth exhibit a decrease in the propagation velocity and a significant degree of curvature. The first effect (a decrease in the propagation velocity of the fronts) indicates a decrease in the energy reserve of the current sheet for the generation of such transients, and the second effect (a significant degree of curvature) indicates the azimuthal localization of the front.
PubDate: 2020-09-01

• Helium Burning Duration for Stars of Populations I–III
• Abstract: Generalized fitting formulas have been obtained describing the dependence “helium burning time–mass of zero-age stars” for stars belonging to populations I–III and having the corresponding masses and elemental composition. The approximation has been performed for nonrotating and rotating stars. The regularities in the obtained dependences have been revealed on the content Z of heavy chemical elements (ranging from 0 to 0.1), which include characteristic values for stellar populations I–III in the presence or absence of axial rotation.
PubDate: 2020-07-01

• Statistical Analysis of Infrasonic Parameters Generated by the Chelyabinsk
Meteoroid
• Abstract: The passage of the Chelyabinsk meteoroid generated a wide variety of physical effects in all subsystems in the Earth–atmosphere–ionosphere–magnetosphere system. Earlier studies have been conducted in order to examine the Chelyabinsk meteoroid’s effects in the atmosphere, ionosphere, and the geomagnetic field. Particular attention has been given to the features of the infrasound signal generated by the Chelyabinsk meteoroid. At the same time, the results of the statistical analysis of infrasonic parameters are absent in the literature. The purpose of this paper is to construct scatter diagrams for basic infrasonic parameters of the signal propagating globally (such as signal-to-noise ratios, time lags, celerity, time durations, amplitudes, and periods per cycle) depending on either the distance between the infrasound source and the sensor or the source back-azimuth as well as to fit respective regression lines. The data have been retrieved from 15 infrasound stations of the International Monitoring System (IMS) set up by the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO). On individual occasions, these data have been complemented by the data acquired by the infrasound stations located at the Eurasian geophysical observatories. Scatter diagrams have been constructed for basic parameters of the infrasonic signal propagating globally. The estimated regression lines superimposed on the scatter diagrams of these parameters versus distance or back-azimuth are shown. Estimates of the infrasound signal celerity (approximately 280 m/s) and tropospheric and stratospheric wind speed (approximately 30 m/s) averaged over all propagation paths have been determined. The advantages and disadvantages of the proposed regression lines are discussed.
PubDate: 2020-07-01

• Characteristics of Infrasonic Signals Generated by the Lipetsk Meteoroid:
Statistical Analysis
• Abstract: The purpose of this paper is to construct basic correlation diagrams and plot the respective regression functions for the parameters of the infrasonic signals launched by the Lipetsk meteoroid. The celestial body that entered the Earth’s atmosphere at 01:16:20 UT on June 21, 2018, had the following initial parameters: 14.4 km/s speed, approximately 113 t mass, approximately 4 m size, and approximately 2.8 kt TNT kinetic energy. The infrasonic signals generated by the celestial body were observed on a global scale, and they were recorded by the International Monitoring System (IMS) set up by the Comprehensive Nuclear-Test-Ban Treaty Organization’s International Monitoring System (CTBTO). For data processing, techniques of mathematical statistics have been invoked. The basic results of the study are as follows. The infrasonic signal exhibits a linear dependence of the infrasonic signal time delay on the horizontal distance from the meteoroid explosion epicenter, and the signal celerity averaged over all propagation paths is estimated to be approximately 304–305 m/s. The infrasonic signal celerity first shows a rapid enough decrease with distance, but over the 4.5–8.66-Mm distance range exhibits fluctuations at approximately 302 m/s. The duration of the infrasonic signal shows a linear decrease with distance, and the signal duration dispersion is insignificant in the 5–8 Mm distance range. The mean periods of the infrasonic signal, independent of distance and averaged over various regression functions, are estimated to be 6.28 ± 0.98 s and 6.14 ± 0.76 s. The mean of the initial kinetic energy estimated using the oscillation period of the infrasonic signal is 2.26–2.43 kt TNT, which differs insignificantly from the NASA estimates (2.8 kt TNT). The approximation for the dependence of celerity versus sine of the back-azimuth angle of arrival shows that the corrected value of the celerity is approximately 300 m/s, and the mean of the troposphere-stratosphere wind is approximately 25–31 m/s. Analysis of the correlation diagrams has shown that a steady statistical link exists between the true and observed back-azimuth angles of infrasound sources. It is noted that the level of fluctuations in the azimuth tends to increase with distance.
PubDate: 2020-07-01

• Investigation and Analysis of Spatiotemporal Instability of the Earth’s
Atmosphere Based on Real-Time GNSS Data Processing
PubDate: 2020-07-01

• Solar Faculae: Microturbulence as an Indicator of Inclined Magnetic Fields
• Abstract: — The observations of the solar facula in the Ba II λ 455.403 Å line are used to construct a 3D model of the facula area by solving the inverse nonequilibrium radiative transfer problem and to investigate the fine structure of the field of unresolved velocities (microturbulence). New turbulent structures are formed in the layers of the upper photosphere. They are localized mainly between upward and downward flows with the formation of ring-shaped structures of increased turbulence around these flows. The mechanism of magnetic anisotropy of microturbulent velocity is proposed (small-scale eddy-type plasma motions mainly occur in the planes perpendicular to the magnetic field), which explains the height dependence of the field of unresolved velocities. Anisotropy of microturbulence begins to manifest itself in the lower photospheric layers outside the upward and downward flows, while it manifests itself in the higher layers inside these flows. The increase of microturbulence in the layers of the upper photosphere and the lower chromosphere in the areas between matter flows indicates the presence of inclined magnetic fields, which, along with the blurring of its spatial structure, indicates the existence of a magnetic canopy region. Microturbulence can be used as an additional tool for diagnostics of inclined magnetic fields.
PubDate: 2020-07-01

• Development of Firehose Instability of a Magnetosonic Type in the Presence
of High-Speed Proton Beams
• Abstract: — One of the varieties of firehose instability, whose cause is not the temperature anisotropy of plasma particles but the dynamic pressure of the beam, is considered. It is shown that such a generation mechanism can lead to an effective increase in low-frequency perturbations not only of the Alfven type but also of the magnetosonic type and also lead to instability not only in the finite and high-pressure plasma but also in a low-pressure plasma. The characteristics of magnetosonic waves that are generated during the development of instability are investigated. The growth rate, the maximum inclination angle of the wave vector, the propagation velocity of the perturbations, and the criterion for the development of instability are found. The influence of the beam temperature on the characteristics of the generated perturbations is studied. As an example of the development of such instability, the formation process of the turbulent region in front of the shock wave of the Earth, as well as before the shock wave from the supernova, is analyzed.
PubDate: 2020-05-01

• Morphology of the Flare-Productive Active Region NOAA 9087
• Abstract: — Evolution and morphological properties of the active region NOAA 9087 are analyzed based on space and ground observational data. Data on hard X-ray (HXR) and soft X-ray (SXR) were obtained from Yohkoh Telescopes (HXT and SXT) and the Geostationary Operational Environmental Satellite. Magnetograms and images in far ultraviolet were obtained from the Michelson Doppler Imager (MDI) and Extreme ultraviolet Imaging Telescope (EIT) of the Solar and Heliospheric Observatory (SOHO). White light images from the Big Bear Observatory (BBSO) and Hα-filtergrams from the Meudon Observatory were used. Data on the 2.69 GHz radio flux were taken from the World Data Center of the Learmonth Observatory (Australia). The investigated active region (AR) was observed on the solar disk from July 15 to 27, 2000, and showed a complex multipolar magnetic field configuration. A high flare activity and emissions were observed in this AR. According to Solar Geophysical Data (SGD), the 3N/M6.4 two-ribbon flare occurred on July 19, 2000, and lasted 2.5 h. The energy was released sequentially in different locations in the AR. All observational data indicate a continuous change in the structure and power of the flare at different wavelengths. HXR and type III radio bursts were observed at the initial phase of the flare. The HXR coronal source was above the line of magnetic polarity inversion of the AR. Observational evidence of magnetic reconnections during the main phase of the flare is obtained based on the analysis of sequential images of loops in the ultraviolet wavelength band. Postflare loops were observed in the 19.5 nm passband at the gradual phase, which is a manifestation of the EUV late phase. These extended loops connect the primary and secondary energy release sites of the flare. There was an additional energy transfer and heating mechanism during the main phase of the flare.
PubDate: 2020-05-01

• The Distribution Function of Cosmic Rays at the Initial Stage of a Solar
Proton Event
• Abstract: The propagation of solar cosmic rays in the interplanetary medium is considered on the basis of the kinetic equation describing the small-angle multiple scattering of charged particles. Energetic particles are assumed to be injected into the interplanetary medium by an instantaneous point-like source. The spatial-temporal distribution of the density and anisotropy of high-velocity particles during the anisotropic phase of a burst of solar cosmic rays is studied. An analytical expression for the distribution function of cosmic rays in the small-angle approximation is derived; the evolution of the angular distribution of energetic particles is investigated. It has been shown that, under weak scattering of charged energetic particles on fluctuations of the interplanetary magnetic field, the intensity of solar cosmic rays impulsively increases at the initial stage of their enhancement. The anisotropy in the angular distribution of solar cosmic rays monotonously decreases with time and exhibits the highest value at the moment of the first particles' arrival to a given point of space.
PubDate: 2020-05-01

• Extremely High Energy ( E &gt; 10 20 eV) Cosmic Rays: Potential
Sources
• Abstract: One of the unsolved problems of cosmic ray physics is determining the nature and sources of ultrahigh energy cosmic rays (UHECRs, E > 1018 eV). The high degree of isotropy of the observed UHECR intensity caused mainly by the deviations of the UHECR trajectories in extragalactic and Galactic magnetic fields, as well as the significant uncertainty in their chemical composition (atomic mass), preclude one from tracing the observed events to their sources and finding the mechanisms for their acceleration. There are two ways to reduce the influence of magnetic deflection: by considering events with extremely high energy (EHECR, E > 1020 eV) and taking into account modern models of the Galactic magnetic field to correct its influence on the EHECR trajectory. In this study, the observed arrival directions of EHECRs from the Pierre Auger Observatory (PAO) and Telescope Array (TA) detectors' data are adjusted for the influence of Galactic and random extragalactic magnetic fields. New celestial positions of EHECRs are compared to the samples of potential sources used by the PAO—17 active galactic nuclei (AGNs) with powerful gamma radiation (from the 2FHL catalog) and 23 starburst galaxies (radio-flux-selected)—as well as with samples of 42 radio-galaxies from the parameterized catalog of radio-galaxies and magnetars. Taking into account the energy loss length of the nuclear component (H, He, C, Si, Fe) of EHECRs in the extragalactic environment and the expected typical distances to potential sources (~100 Mpc for H and Si-Fe and ~50 Mpc for He and C), the astrophysical objects that could be sources of relevant events were distinguished in the above samples. The potential acceleration mechanisms in the selected objects are analyzed, and the contribution of possible Galactic sources to the observed EHECR flux is evaluated.
PubDate: 2020-05-01

• Variations in the Plasma Parameters of the Earth’s Magnetotail
during Substorm Initiation
• Abstract: A chain of events accompanying the occurrence of a substorm in the Earth’s ionosphere and magnetosphere is considered. Features of geomagnetic pulsations and mechanisms of their generation are indicated. Measurements of magnetic field fluctuations from fluxgate magnetometers, as well as the data on temperature, velocity, and concentration of electrons, and different types of ions from the PEACE and CIS-CODIF experiments of the Cluster-2 space mission, have been analyzed. It was found that a significant increase in temperature, velocity fluctuations, and concentration is observed during the initiation of a substorm that was accompanied by dipolarization (sharp change in the magnetic field configuration from the elongated tail-like force lines to a more dipole structure). A time delay in the heating of protons and oxygen ions, as well as in the concentration variations, was detected. The comparison of wave characteristics for different pressures was carried out using wavelet analysis. The magnetic field pressure, as well as dynamic and thermal pressure for different types of particles, was considered. Pc5 and strong Pc4 pulsations, as well as direct and inverse cascades, were observed in the fluctuations of the magnetic field pressure and thermal pressure of electrons and protons. The results point to a significant role of kinetic effects in the complex chain of processes in the Earth’s magnetosphere during the explosive phase of a substorm.
PubDate: 2020-03-01

• Generation of the Sun’s Radial Magnetic Field by Global Hydrodynamic
Flows
• Abstract: A theory on the emergence of global hydrodynamic flows of matter and the generation of global magnetic fields in the solar convective zone is proposed. The unstable profile of differential rotation plays a crucial role in it: all hydrodynamic flows on the Sun (poloidal circulation, torsion oscillations, and spatiotemporal variations of the poloidal flow) are generated due to the loss of stability of differential rotation. None of the models known to us, wherein torsion oscillations and variations of the meridional circulation are typically calculated separately and are thus considered to be independent flows, reproduce this result. The calculations within our model suggest, on the contrary, that the indicated flows are actually toroidal and poloidal components of a single, 3-dimensional global flow. The decisive role of torsion oscillations in the generation of the radial alternating magnetic field is highlighted in the present study. It is demonstrated by numerical simulation that the time-varying radial magnetic field on the surface of the Sun reaches its maximum at the poles, where it changes polarity with a period of ~22 years. This process may be identified with the observed effect of polarity reversal of the polar field within the Hale magnetic cycle. It is demonstrated that the lines of zero values (polarity reversal) of the surface radial magnetic field pass through the maxima of the velocity modulus of zonal flows (torsion oscillations). In addition, the lines of magnetic polarity reversal of the radial field and the maximum velocities of surface zonal flows drift from the poles to the equator. It is noted that the obtained results on the latitudinal evolution of surface zonal flows correlate with the behavior of deep zonal flows determined by processing helioseismological data.
PubDate: 2020-03-01

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