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Changes in the umbra brightness and in the magnetic field over time should occur on long-period sunspot oscillations in accordance with Birman's idea of inhibition of circulation (overturning) convection by a strong vertical magnetic field in antiphase mode.When the sunspot as a whole shifts upward, its power flux tube expands with a fixed magnetic flux, the magnetic field decreases, and the umbra brightness should increase. Vice versa, when the magnetic flux tube of the sunspot is lowered, it is compressed, the field grows, and the umbra brightness should decrease. Until now, this oscillatory process, which is described by the theoretical model of a shallow sunspot, has remained unexplored. This paper attempts to prove the Birman effect (Biermann, 1941) on the example of long-period oscillations of the sunspot 2010/12/07-13 (NOAA 11 133), for which there are available data from both the Solar and Heliospheric Observatory (SOHO) and Solar Dynamics Observatory (SDO). [ABSTRACT FROM AUTHOR]

Two main features define a sunspot as an object: a strong magnetic field and a low umbra temperature. The same can be said about a facular knot, in the center of which there is a dark micropore, and the magnetic field is several hundred Gauss (which noticeably exceeds the level of equipartition of about 200–250 G), sometimes reaching 1000 or 1200 G. The temperature decrease in these activity elements is explained by the suppression of circulation (overturning) convection by a strong vertical magnetic field. The first to express this idea was Biermann (1941). Within the framework of this conception, a saturation effect should be expected: when the magnetic field completely suppresses convection, its further growth should not lead to a decrease in temperature. There is still no clear answer to the question of the saturation effect. We will try to answer it in the first part of the work according to the Solar Dynamics Observatory. We show that saturation occurs at B = 2300–2400 G. A further increase in the magnetic field of the spot no longer leads to a decrease in the brightness of its umbra. The relationship of the magnetic field and intensity is also manifested in long-period oscillations of the magnetic field of spots. In this case, the brightness of the spot umbra changes in antiphase with its magnetic field (Efremov et al., 2020) in accordance with the theoretical model of a shallow sun spot (Solov'ev and Kirichek, 2014, 2016). A similar effect was established by us in the second part of this work for facular knots: during slow facular oscillations with periods of more than 1 h, its brightness changes in antiphase with a magnetic field. The obtained results convincingly confirm the Birman hypothesis. [ABSTRACT FROM AUTHOR]

A distinctive feature of chromospheric magnetic fields in the facular regions on the Sun is their very fine spatial structure. In accordance with the observations performed in Ca II K and H line (the level of the lower chromosphere, about 0.5–1 Mm over the photosphere), numerous "slender fibrils mapping the magnetic field" were recorded. It is noted that "...the loops are organized in canopy-like arches" (Jafarzadeh et al., 2017). In this paper we perform some modification of the facular model presented by Solov'ev and Kirichek (2019) as a steady magnetic "fountain" with many thin trickles of plasma flows. The radial-azimuthal temperature profiles of the facula are calculated. It is shown that the difference in the vertical and horizontal scales of the system does not improve the correspondence between the model parameters of the faculae and their observed characteristics. [ABSTRACT FROM AUTHOR]

The paper considers a special class of artifacts that appears in the useful signal when the source moves along a discrete matrix of the receiver. A parasitic component forms in the signal due to the displacement of the extreme value of the distributed field of the physical quantity from pixel to pixel (p2p effect). It is shown that a stepwise discretization of Δt < T (p2p) is a necessary but not sufficient condition for the formation of the p2p-artifact. For small field gradients (in particular, with good spatial resolution), the parasitic signal in the time series of the studied variable is either weakened or does not form at all. This assumption has been qualitatively verified by comparative analysis of sunspot data obtained with SOHO/MDI and SDO/HMI. In addition, the Y-p2p effect, which is associated with sunspot displacement along the meridian and influences the process of long-period sunspot oscillations, is considered in detail based on SDO/HMI data. It was found that there is an inverse relationship between changes in the umbral area of a spot and variations of its magnetic field strength. This property of long-period sunspot oscillations as a single magnetic structure indicates the magnetic flux in the sunspot umbra is preserved, and it plays an extremely important role for our understanding of the physical nature of these oscillations. [ABSTRACT FROM AUTHOR]

Abstract: Long-period oscillations in the brightness of the Sun as a star have been analyzed on the basis of measurements of the solar light reflected by planets when they come into the field of view of the Large Angle and Spectrometric Coronagraph (LASCO C3) onboard the Solar and Heliospheric Observatory (SOHO). We took sequences of FITS intensitygrams from the archive of the SOHO/LASCO C3 space observatory for the observational data; they were 1024 × 1024 pixels in size, and they were acquired with the 12-min interval. In 5-day continuous time series of the brightness of Mars and Jupiter, coinciding modes of 8-10 and 36-38 h were found. This coincidence apparently indicates their solar origin. In addition, for Mars, we obtained 25-day series of time variations of the reflected solar radiation, in which a mode with even a lower frequency of 8-10 days was detected. [ABSTRACT FROM AUTHOR]

The properties of the 12-h artifact in the data of the SDO/HMI instrument (Helioseismic and Magnetic Imager) caused by the nonzero radial velocity of the station relative to the Sun are investigated. The study has been carried out with respect to long-period oscillations of the magnetic field of sunspots for different station positions in the Earth’s orbit by the alternative spectral method of singular decomposition of the signal CaterPillarSSA. Features of artifact filtering, both in special positions of the station (at the points of aphelion and perihelion) and at arbitrarily selected orbital points, are considered. It is shown that the 12-h artifact mode can be completely filtered from the time series of the observed variable, not only at these two orbital points (because of the symmetry of the station’s radial velocity with respect to the zero mean here) but also at any others. It is shown that only a 12-h mode is physically justified, while the 24-h harmonic appears only as an artifact in the Fourier decomposition of the amplitude-modulated signal. It is emphasized that the values of the magnetic field measured with SDO/HMI are sensitive only to the station’s radial velocity absolute values with respect to the Sun and do not depend on its direction. It has been noted that the periods of sunspot oscillation as a whole obtained from SDO/HMI data after orbital artifact filtration fit well into the dependence diagram of the period of sunspot oscillations on the value of its magnetic field strength constructed earlier by SOHO/MDIdata. [ABSTRACT FROM AUTHOR]

A solar faculae having an appearance of quite long-lived magnetic nodes can perform (as well as sunspots, chromospheric filaments, coronal loops) free oscillations, i.e., they can oscillate about the stable equilibrium position as a single whole, changing quasi-periodically magnetic field averaged over the section with periods from 1 to 4 hours. Kolotkov et al. (2017) described the case in which the average magnetic field strength of the facula node considerably decreased during observations of SDO magnetograms (13 hours), and, at the same time, its oscillations acquired a specific character: the fundamental mode of free oscillations of the facula considerably increased in amplitude (by approximately two times), while the period of oscillations increased by three times. At the end of the process, the system dissipated. In this work, we present the exact solution of the equation of small-amplitude oscillations of the system with a time-variable rigidity, describing the oscillation behavior at which the elasticity of the system decreases with time, while the period and amplitude of oscillations grow. [ABSTRACT FROM AUTHOR]

For the first time, the ultra-low oscillation mode of the sunspot magnetic field strength has been detected with a high degree of confidence by ground-based observations of sunspots with the Global Oscillation Network Group (GONG) network of telescopes. Synchronous series of magnetograms derived from the GONG and Solar and Heliospheric Observatory/Michelson Doppler Imager (SOHO/MDI) have been processed. They were obtained on September 27-30, 2010, for the active region NOAA 11109 with a total duration of 80 h. The periods of magnetic field oscillations found by space data coincide with the periods defined with GONG. This confirms the physical reality of the oscillatory process. The power spectrum contains harmonics with periods of 26 h, 8-10 h, and 3-4 h. [ABSTRACT FROM AUTHOR]

The geometric parameters and relationships of the horizontal and vertical velocities in a giant convective cylindrical cell were analyzed based on a continuity equation with the given vertical distribution of unperturbed gas density in the convective zone of the Sun. It has been found that the lower edge of such a convective cell must be positioned at a depth of 20 Mm in the secondary helium ionization zone. In addition, under the assumption that the plasma conductivity in the convective zone is caused by small-scale turbulence, a new stationary solution was obtained for the problem of magnetic field diffusion in the pattern of slow conductive plasma flows in scales of a convective cell. [ABSTRACT FROM AUTHOR]

It is shown that long-period (T = 10-20 h) oscillations of the magnetic field in sunspots, combined in bipolar groups, are excited synchronously in the main and tail spots of a group. At the same time, there is no correlation between long-period oscillations of the field of sunspots which are in different active regions, i.e., spaced sunspots oscillate independently. This fact eliminates the question about the apparatus nature of the oscillations of interest (if there is an artifact, oscillations of all sunspots on the visible solar hemisphere would be synchronous!). High-resolution (0.5 angular seconds per pixel) MDI(SOHO) data show a high correlation between long-period oscillations of the magnetic field at isolated points of the sunspot shadow. This points to the fact that the sunspot shadow participates in long-period oscillations as a quite integral physical formation. [ABSTRACT FROM AUTHOR]

As a result of processing long (up to 144 h) series of sunspot magnetograms obtained on the SOHO (Solar and Heliospheric Observatory) spacecraft with the MDI (Michelson Doppler Imager) instrument it is shown that the mode with a period of 800-1300 min is a limiting low-frequency oscillation mode of the magnetic field of a sunspot as a whole. Its period is essentially and nonlinearly depends on the sunspot magnetic field strength. In addition to this mode, higher harmonics are also revealed in the sunspot oscillation spectra in the bands 40-45, 60-80, 135-170, 220-250, and 480-520 min. The oscillation power in these bands monotonically and rapidly decreases with increasing frequency, which is characteristic for overtones arising due to the nonlinear nature of oscillations. The limiting oscillation mode stably exists in sunspots for 1.5-2 days, which coincides with the average lifetime of a supergranular cell. The mode with the period of 35-48 h observed in the power spectrum is not an eigen mode of sunspots, because its period is independent of its magnetic field strength. Probably, it occurs as a quasiperiod of an external exciting force caused by disturbances from supergranular cells surrounding the sunspot. [ABSTRACT FROM AUTHOR]

When a magnetic instability collapses, a wave separating the stable and unstable state propagates along the superconductor. An induction method is used to determine the configuration of the interface of these states. For a 0.16 mm in diameter Nb–Ti wire the moving boundary is 1.7–2.4 mm long, depending on the magnetic field. [ABSTRACT FROM AUTHOR]

Examines the effect of magnetic field on the detonation initiation by spark discharge in hydrogen-air mixture. Intensity of shock wave arising in the detonation combustion chamber; Effect of magnetic field on the plasma region formed by the electric discharge; Influence of magnetic induction on the velocity of primary shock wave.

A specific type of artifacts (named as “p2p”), that originate due to displacement of the image of a moving object along the digital (pixel) matrix of receiver are analyzed in detail. The criteria of appearance and the influence of these artifacts on the study of long-term oscillations of sunspots are deduced. The obtained criteria suggest us methods for reduction or even elimination of these artifacts. It is shown that the use of integral parameters can be very effective against the “p2p” artifact distortions. The simultaneous observations of sunspot magnetic field and ultraviolet intensity of the umbra have given the same periods for the long-term oscillations. In this way the real physical nature of the oscillatory process, which is independent of the artifacts have been confirmed again. A number of examples considered here confirm the dependence between the periods of main mode of the sunspot magnetic field long-term oscillations and its strength. The dependence was derived earlier from both the observations and the theoretical model of the shallow sunspot. The anti-phase behavior of time variations of sunspot umbra area and magnetic field of the sunspot demonstrates that the umbra of sunspot moves in long-term oscillations as a whole: all its points oscillate with the same phase. [ABSTRACT FROM AUTHOR]