Vol 32, No 2 (2016)

Results of the analysis of spectral observations of two Ellerman bombs in the Hα line are presented. These bombs (EB-1 and EB-2) appeared and evolved in the active region NOAA 11024 in the emerging magnetic flux area. The spectral data of a high temporal and spatial resolution were obtained with the French–Italian solar telescope THEMIS (Tenerife Island, Spain; THEMIS stands for Télescope Héliographique pour l’Etude du Magnétisme et des Instabilités Solaires) on July 4, 2009. The Hα-line profiles obtained for different periods of the Ellerman bombs (EBs) evolution were asymmetrical, demonstrating the emission excess in the long-wavelength wing. The intensity variations in the line wings indicate both the gradual and pulsed release of energy in the course of EBs. Temporal variations in the line-of-sight velocities V_los of the chromospheric material at a level of the Hα-core formation showed two periods in the velocity enhancement, containing several individual peaks. The maximum line-of-sight velocity of the material was–9 and 8 km/s toward and from the observer, respectively. Rapid upward and downward plasma streams (where V_los reaches–80 and 50 km/s, respectively) were sometimes observed. The Ellerman bombs were accompanied by small chromospheric ejections (surges) lasting for 0.5–1.5 min. A fine structure of EBs was found in the H_α-line spectra obtained during 4 min, when the intensity in the line wings sharply increased. The peculiarities of variations in the intensity of the H_α-line wings and the line-of-sight velocity of the chromospheric material suggest that two investigated EBs appeared and evolved as a physically connected pair. Our results support the model wherein the magnetic reconnection in the lower atmospheric layers is considered as a triggering mechanism for the EB formation.

Data on the value and sign of the circumpolar magnetic field of the Sun at a maximum of its activity in cycle 24 have been analyzed. The data were obtained from observations at the Wilcox Solar Observatory and from synoptic maps of the magnetic field built in the SOLIS project (SOLIS stands for Synoptic Optical Long-term Investigations of the Sun) and with the Helioseismic and Magnetic Imager (HMI). We studied the dynamics of the total magnetic fields in the circumpolar latitudinal zones of different extension in the northern and southern hemispheres. The epochs of the sign reversal of the polar magnetic field were determined. It was found that, in cycle 24, the magnetic field polarity changed three times in the northern hemisphere and only once in the southern one. In the northern hemisphere, the reversal of the polar magnetic field finished approximately a year earlier than that in the southern one. The obtained results are compared to the data on the sign reversal of the polar magnetic field of the Sun reported for the previous solar cycles.

One of the mechanisms of Alfven turbulence generation in the foreshock region is investigated by the example of the Earth bow shock. The effect of the temperature of high-velocity beams on characteristics of generated disturbances is examined. It is shown that the beam temperature has a significant impact on transverse scales of disturbances. The higher the temperature, the greater the limitations on transverse wavelengths. The development of instability in the propagation of reflected, intermediate, and diffusion proton beams in the foreshock region of the Earth bow shock is considered. Perturbation motion dynamics in foreshock region is analyzed.

The aim of this article is to draw attention to the priority of the well-known astronomer and geophysicist, member of the Academy of Sciences of Ukraine A.Ya. Orlov (1880–1954) in the determination of the following parameters describing the secular motion of the earth’s poles: speed (4 mas/year) and direction (69° west). These results (1954) are based on the astronomical observations from 1900 to 1950 with zenith telescopes at international latitude stations. Orlov is well known in the world astronomical community as the founder of the Poltava Gravimetric Observatory, the Main Astronomical Observatory, and the national research school of global geodynamics. However, his pioneering work on secular polar motion is little known worldwide. At present, Orlov’s estimates for secular polar motion have been verified by century-long observations (1900–2012) obtained with different telescopes at many observatories worldwide and by different, both astronomical and space-based, methods (LLS, VLBI, GNSS, etc.).