Observational Evidence of Sausage-Pinch Instability in Solar Corona by SDO/AIA

We present the first observational evidence of the evolution of sausage-pinch instability in Active Region 11295 during a prominence eruption using data recorded on 12 September 2011 by the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO). We have identified a magnetic flux tube visible in AIA 304 \AA\ that shows curvatures on its surface with variable cross-sections as well as enhanced brightness. These curvatures evolved and thereafter smoothed out within a time-scale of a minute. The curved locations on the flux tube exhibit a radial outward enhancement of the surface of about 1-2 Mm (factor of 2 larger than the original thickness of the flux tube) from the equilibrium position. AIA 193 \AA\ snapshots also show the formation of bright knots and narrow regions inbetween at the four locations as that of 304 \AA\ along the flux tube where plasma emission is larger compared to the background. The formation of bright knots over an entire flux tube as well as the narrow regions in < 60 s may be the morphological signature of the sausage instability. We also find the flows of the confined plasma in these bright knots along the field lines, which indicates the dynamicity of the flux tube that probably causes the dominance of the longitudinal field component over short temporal scales. The observed longitudinal motion of the plasma frozen in the magnetic field lines further vanishes the formed curvatures and plasma confinements as well as growth of instability to stablize the flux tube.Comment: 12 pages, 5 figure

Політико-правові аспекти захисту прав національних меншин в Україні

The article deals with the research of basic categories of the rights of national minorities that reside on the territory of Ukraine. Moreover, political and legal principles as well as legislative sources for securing these rights at the state level in accordance with the international legal standards are analyzed. The peculiarities of Ukraine’s cooperation with international organisations and neighboring countries in the field of protection the rights of national minorities and regulation of interethnic relations are investigated. In Ukraine the guarantees and protection of the rights of national minorities at the legislative level comply with the world and European standards. The system of state administration bodies in the field of interethnic relations has been established but there are still some problems that need to be resolved on the Parliamentary level as well as on the level of executive agencies and local authorities. At the current stage it is necessary to adopt the law on «The Concept of National Ethnic Policy of Ukraine». Also, the political and legal status of indigenous peoples should be defined especially Crimean Tatars, deported ethnic minorities and some ethnographic groups of the Ukrainian ethnos. In addition, it is important to establish an effective mechanism for realization of the rights of national minorities in Ukraine and to ensure monitoring of the observance of these rights. Implementation of the appropriate measures would facilitate the prevention of confrontation in the Ukrainian society on the ethnic and political as well as language grounds. It would also promote the prevention of aggravation of interethnic relations and would ensure the formation of public tolerance to persons belonging to national minorities.Розглянуто основні категорії прав національних меншин, що проживають на території України. Проаналізовано політико-правові засади та законодавчі джерела забезпечення цих прав на рівні держави у відповідності з міжнародно-правовими стандартами. Розкрито особливості співробітництва України з міжнародними організаціями та державами-сусідами в сфері захисту прав національних меншин та регулювання міжетнічних відносин. В Україні гарантії та захист прав національних меншин на законодавчому рівні відповідають світовим і європейським стандартам, створена система органів державного управління у сфері міжетнічних відносин, проте існує низка проблем, які необхідно розв’язувати на рівні парламенту, органів виконавчої влади та місцевого самоврядування. На сучасному етапі необхідно прийняти Закон про «Концепцію державної етнонаціональної політики України», визначити політико-правовий статус корінних народів, зокрема кримськотатарського, депортованих національних меншин і етнографічних груп українського етносу, налагодити ефективний механізм реалізації прав національних меншин в Україні та здійснювати моніторинг за дотриманням цих прав. Застосування відповідних заходів сприятиме запобіганню проявам конфронтації в українському суспільстві на етнополітичному та мовному підґрунті, недопущенню загострення міжетнічних відносин, забезпечить формування у громадян толерантного ставлення до осіб, що належать до національних меншин.Розглянуто основні категорії прав національних меншин, що проживають на території України. Проаналізовано політико-правові засади та законодавчі джерела забезпечення цих прав на рівні держави у відповідності з міжнародно-правовими стандартами. Розкрито особливості співробітництва України з міжнародними організаціями та державами-сусідами в сфері захисту прав національних меншин та регулювання міжетнічних відносин. В Україні гарантії та захист прав національних меншин на законодавчому рівні відповідають світовим і європейським стандартам, створена система органів державного управління у сфері міжетнічних відносин, проте існує низка проблем, які необхідно розв’язувати на рівні парламенту, органів виконавчої влади та місцевого самоврядування. На сучасному етапі необхідно прийняти Закон про «Концепцію державної етнонаціональної політики України», визначити політико-правовий статус корінних народів, зокрема кримськотатарського, депортованих національних меншин і етнографічних груп українського етносу, налагодити ефективний механізм реалізації прав національних меншин в Україні та здійснювати моніторинг за дотриманням цих прав. Застосування відповідних заходів сприятиме запобіганню проявам конфронтації в українському суспільстві на етнополітичному та мовному підґрунті, недопущенню загострення міжетнічних відносин, забезпечить формування у громадян толерантного ставлення до осіб, що належать до національних меншин

Nonlinear Mirror and Weibel modes: peculiarities of quasi-linear dynamics

A theory for nonlinear evolution of the mirror modes near the instability threshold is developed. It is shown that during initial stage the major instability saturation is provided by the flattening of the velocity distribution function in the vicinity of small parallel ion velocities. The relaxation scenario in this case is accompanied by rapid attenuation of resonant particle interaction which is replaced by a weaker adiabatic interaction with mirror modes. The saturated plasma state can be considered as a magnetic counterpart to electrostatic BGK modes. After quasi-linear saturation a further nonlinear scenario is controlled by the mode coupling effects and nonlinear variation of the ion Larmor radius. Our analytical model is verified by relevant numerical simulations. Test particle and PIC simulations indeed show that it is a modification of distribution function at small parallel velocities that results in fading away of free energy driving the mirror mode. The similarity with resonant Weibel instability is discussed

The stationary concentrated vortex model

A new model of an axially-symmetric stationary concentrated vortex for an inviscid incompressible flow is presented as an exact solution of the Euler equations. In this new model, the vortex is exponentially localised, not only in the radial direction, but also in height. This new model of stationary concentrated vortex arises when the radial flow, which concentrates vorticity in a narrow column around the axis of symmetry, is balanced by vortex advection along the symmetry axis. Unlike previous models, vortex velocity, vorticity and pressure are characterised not only by a characteristic vortex radius, but also by a characteristic vortex height. The vortex structure in the radial direction has two distinct regions defined by the internal and external parts: in the inner part the vortex flow is directed upward, and in the outer part it is downward. The vortex structure in the vertical direction can be divided into the bottom and top regions. At the bottom of the vortex the flow is centripetal and at the top it is centrifugal. Furthermore, at the top of the vortex the previously ascending fluid starts to descend. It is shown that this new model of a vortex is in good agreement with the results of field observations of dust vortices in the Earth’s atmosphere

Ground-based acoustic parametric generator impact on the atmosphere and ionosphere in an active experiment

We develop theoretical basics of active experiments with two beams of acoustic waves, radiated by a ground-based sound generator. These beams are transformed into atmospheric acoustic gravity waves (AGWs), which have parameters that enable them to penetrate to the altitudes of the ionospheric E and F regions where they influence the electron concentration of the ionosphere. Acoustic waves are generated by the ground-based parametric sound generator (PSG) at the two close frequencies. The main idea of the experiment is to design the output parameters of the PSG to build a cascade scheme of nonlinear wave frequency downshift transformations to provide the necessary conditions for their vertical propagation and to enable penetration to ionospheric altitudes. The PSG generates sound waves (SWs) with frequencies f1 = 600 and f2 = 625 Hz and large amplitudes (100-420ms-1). Each of these waves is modulated with the frequency of 0.016 Hz. The novelty of the proposed analytical-numerical model is due to simultaneous accounting for nonlinearity, diffraction, losses, and dispersion and inclusion of the two-stage transformation (1) of the initial acoustic waves to the acoustic wave with the difference frequency Δf = f2 - f1 in the altitude ranges 0-0.1 km, in the strongly nonlinear regime, and (2) of the acoustic wave with the difference frequency to atmospheric acoustic gravity waves with the modulational frequency in the altitude ranges 0.1-20 km, which then reach the altitudes of the ionospheric E and F regions, in a practically linear regime. AGWs, nonlinearly transformed from the sound waves, launched by the two-frequency ground-based sound generator can increase the transparency of the ionosphere for the electromagnetic waves in HF (MHz) and VLF (kHz) ranges. The developed theoretical model can be used for interpreting an active experiment that includes the PSG impact on the atmosphere-ionosphere system, measurements of electromagnetic and acoustic fields, study of the variations in ionospheric transparency for the radio emissions from galactic radio sources, optical measurements, and the impact on atmospheric aerosols. The proposed approach can be useful for better understanding the mechanism of the acoustic channel of seismo-ionospheric coupling

Vortex Motions in the Solar Atmosphere: Definitions, Theory, Observations, and Modelling

Vortex flows, related to solar convective turbulent dynamics at granular scales and their interplay with magnetic fields within intergranular lanes, occur abundantly on the solar surface and in the atmosphere above. Their presence is revealed in high-resolution and high-cadence solar observations from the ground and from space and with state-of-the-art magnetoconvection simulations. Vortical flows exhibit complex characteristics and dynamics, excite a wide range of different waves, and couple different layers of the solar atmosphere, which facilitates the channeling and transfer of mass, momentum and energy from the solar surface up to the low corona. Here we provide a comprehensive review of documented research and new developments in theory, observations, and modelling of vortices over the past couple of decades after their observational discovery, including recent observations in Hα, innovative detection techniques, diverse hydrostatic modelling of waves and forefront magnetohydrodynamic simulations incorporating effects of a non-ideal plasma. It is the first systematic overview of solar vortex flows at granular scales, a field with a plethora of names for phenomena that exhibit similarities and differences and often interconnect and rely on the same physics. With the advent of the 4-m Daniel K. Inouye Solar Telescope and the forthcoming European Solar Telescope, the ongoing Solar Orbiter mission, and the development of cutting-edge simulations, this review timely addresses the state-of-the-art on vortex flows and outlines both theoretical and observational future research directions

Standing sausage waves in photospheric magnetic waveguides

By focusing on the oscillations of the cross-sectional area and the intensity of magnetic waveguides located in the lower solar atmosphere, we aim to detect and identify magnetohydrodynamic (MHD) sausage waves. Capturing several series of high-resolution images of pores and sunspots and employing wavelet analysis in conjunction with empirical mode decomposition (EMD) makes the MHD wave analysis possible. For this paper, two sunspots and one pore (with a light bridge) were chosen as representative examples of MHD waveguides in the lower solar atmosphere. The sunspots and pore display a range of periods from 4 to 65 minutes. The sunspots support longer periods than the pore - generally enabling a doubling or quadrupling of the maximum pore oscillatory period. All of these structures display area oscillations indicative of MHD sausage modes and in-phase behaviour between the area and intensity, presenting mounting evidence for the presence of the slow sausage mode within these waveguides. The presence of fast and slow MHD sausage waves has been detected in three different magnetic waveguides in the lower solar photosphere. Furthermore, these oscillations are potentially standing harmonics supported in the waveguides which are sandwiched vertically between the temperature minimum in the lower solar atmosphere and the transition region. Standing harmonic oscillations, by means of solar magneto-seismology, may allow insight into the sub-resolution structure of photospheric MHD waveguides

Incompressible magnetohydrodynamic modes in the thin magnetically twisted flux tube

Context. Observations have shown that twisted magnetic fields naturally occur, and indeed are omnipresent in the Sun’s atmosphere. It is therefore of great theoretical interest in solar atmospheric waves research to investigate the types of magnetohydrodynamic (MHD) wave modes that can propagate along twisted magnetic flux tubes. Aims. Within the framework of ideal MHD, the main aim of this work is to investigate small amplitude incompressible wave modes of twisted magnetic flux tubes with m ≥ 1. The axial magnetic field strength inside and outside the tube will be allowed to vary, to ensure the results will not be restricted to only cold plasma equilibria conditions. Methods. The dispersion equation for these incompressible linear MHD wave modes was derived analytically by implementing the long wavelength approximation. Results. It is shown, in the long wavelength limit, that both the frequency and radial velocity profile of the m = 1 kink mode are completely unaffected by the choice of internal background magnetic twist. However, fluting modes with m ≥ 2 are sensitive to the particular radial profile of magnetic twist chosen. Furthermore, due to background twist, a low frequency cut-off is introduced for fluting modes that is not present for kink modes. From an observational point of view, although magnetic twist does not affect the propagation of long wavelength kink modes, for fluting modes it will either work for or against the propagation, depending on the direction of wave travel relative to the sign of the background twist

An Inside Look at Sunspot Oscillations with Higher Azimuthal Wavenumbers

Solar chromospheric observations of sunspot umbrae offer an exceptional view of magneto-hydrodynamic wave phenomena. In recent years, a wealth of wave signatures related to propagating magneto-acoustic modes have been presented, which demonstrate complex spatial and temporal structuring of the wave components. Theoretical modelling has demonstrated how these ubiquitous waves are consistent with an m=0 slow magneto-acoustic mode, which are excited by trapped sub-photospheric acoustic (p-mode) waves. However, the spectrum of umbral waves is broad, suggesting that the observed signatures represent the superposition of numerous frequencies and/or modes. We apply Fourier filtering, in both spatial and temporal domains, to extract chromospheric umbral wave characteristics consistent with an m=1 slow magneto-acoustic mode. This identification has not been described before. Angular frequencies of 0.037 +/- 0.007 rad/s (2.1 +/- 0.4 deg/s), corresponding to a period approximately 170 s for the m=1 mode are uncovered for spatial wavenumbers in the range of 0.45<k<0.90 arcsec^-1 (5000-9000 km). Theoretical dispersion relations are solved, with corresponding eigenfunctions computed, which allows the density perturbations to be investigated and compared with our observations. Such magnetohydrodynamic modelling confirms our interpretation that the identified wave signatures are the first direct observations of an m=1 slow magneto-acoustic mode in the chromospheric umbra of a sunspot

Vortex motions in the solar atmosphere

Vortex flows, related to solar convective turbulent dynamics at granular scales and their interplay with magnetic fields within intergranular lanes, occur abundantly on the solar surface and in the atmosphere above. Their presence is revealed in high-resolution and high-cadence solar observations from the ground and from space and with state-of-the-art magnetoconvection simulations. Vortical flows exhibit complex characteristics and dynamics, excite a wide range of different waves, and couple different layers of the solar atmosphere, which facilitates the channeling and transfer of mass, momentum and energy from the solar surface up to the low corona. Here we provide a comprehensive review of documented research and new developments in theory, observations, and modelling of vortices over the past couple of decades after their observational discovery, including recent observations in Hα , innovative detection techniques, diverse hydrostatic modelling of waves and forefront magnetohydrodynamic simulations incorporating effects of a non-ideal plasma. It is the first systematic overview of solar vortex flows at granular scales, a field with a plethora of names for phenomena that exhibit similarities and differences and often interconnect and rely on the same physics. With the advent of the 4-m Daniel K. Inouye Solar Telescope and the forthcoming European Solar Telescope, the ongoing Solar Orbiter mission, and the development of cutting-edge simulations, this review timely addresses the state-of-the-art on vortex flows and outlines both theoretical and observational future research directions