Determination of the cross-field density structuring in coronal waveguides using the damping of transverse waves

Time and spatial damping of transverse magnetohydrodynamic (MHD) kink oscillations is a source of information on the cross-field variation of the plasma density in coronal waveguides. We show that a probabilistic approach to the problem of determining the density structuring from the observed damping of transverse oscillations enables us to obtain information on the two parameters that characterise the cross-field density profile. The inference is performed by computing the marginal posterior distributions for density contrast and transverse inhomo- geneity length-scale using Bayesian analysis and damping ratios for transverse oscillations under the assumption that damping is produced by resonant absorption. The obtained distributions show that, for damping times of a few oscillatory periods, low density contrasts and short inho- mogeneity length scales are more plausible in explaining observations. This means that valuable information on the cross-field density profile can be obtained even if the inversion problem, with two unknowns and one observable, is a mathematically ill-posed problem.Comment: 5 pages, 3 figures, accepte

Determination of Transverse Density Structuring from Propagating MHD Waves in the Solar Atmosphere

We present a Bayesian seismology inversion technique for propagating magnetohydrodynamic (MHD) transverse waves observed in coronal waveguides. The technique uses theoretical predictions for the spatial damping of propagating kink waves in transversely inhomogeneous coronal waveguides. It combines wave amplitude damping length scales along the waveguide with theoretical results for resonantly damped propagating kink waves to infer the plasma density variation across the oscillating structures. Provided the spatial dependence of the velocity amplitude along the propagation direction is measured and the existence of two different damping regimes is identified, the technique would enable us to fully constrain the transverse density structuring, providing estimates for the density contrast and its transverse inhomogeneity length scale

On the nature of transverse coronal waves revealed by wavefront dislocations

Coronal waves are an important aspect of the dynamics of the plasma in the corona. Wavefront dislocations are topological features of most waves in nature and also of magnetohydrodynamic waves. Are there dislocations in coronal waves? The finding and explanation of dislocations may shed light on the nature and characteristics of the propagating waves, their interaction in the corona and in general on the plasma dynamics. We positively identify dislocations in coronal waves observed by the Coronal Multi-channel Polarimeter (CoMP) as singularities in the Doppler shifts of emission coronal lines. We study the possible singularities that can be expected in coronal waves and try to reproduce the observed dislocations in terms of localization and frequency of appearance. The observed dislocations can only be explained by the interference of a kink and a sausage wave modes propagating with different frequencies along the coronal magnetic field. In the plane transverse to the propagation, the cross-section of the oscillating plasma must be smaller than the spatial resolution, and the two waves result in net longitudinal and transverse velocity components that are mixed through projection onto the line of sight. Alfv\'en waves can be responsible of the kink mode, but a magnetoacoustic sausage mode is necessary in all cases. Higher (flute) modes are excluded. The kink mode has a pressure amplitude that is smaller than the pressure amplitude of the sausage mode, though its observed velocity is larger. This concentrates dislocations on the top of the loop. To explain dislocations, any model of coronal waves must include the simultaneous propagation and interference of kink and sausage wave modes of comparable but different frequencies, with a sausage wave amplitude much smaller than the kink one.Comment: 11 pages. 5 figures. Accepted for publication in A&

Coronal cooling as a result of mixing by the nonlinear Kelvin–Helmholtz instability

This is the final version. Available from American Astronomical Society via the DOI in this recordRecent observations show cool, oscillating prominence threads fading when observed in cool spectral lines and appearing in warm spectral lines. A proposed mechanism to explain the observed temperature evolution is that the threads were heated by turbulence driven by the Kelvin–Helmholtz instability that developed as a result of wave-driven shear flows on the surface of the thread. As the Kelvin–Helmholtz instability is an instability that works to mix the two fluids either side of the velocity shear layer, in the solar corona it can be expected to work by mixing the cool prominence material with that of the hot corona to form a warm boundary layer. In this paper we develop a simple phenomenological model of nonlinear Kelvin–Helmholtz mixing, using it to determine the characteristic density and temperature of the mixing layer, which for the case under study with constant pressure across the two fluids are ρ_mixed=√ρ_1ρ_2 and T_mixed=√T_1T_2. One result from the model is that it provides an accurate, as determined by comparison with simulation results, determination of the kinetic energy in the mean velocity field. A consequence of this is that the magnitude of turbulence, and with it the energy that can be dissipated on fast time-scales, as driven by this instability can be determined. For the prominence-corona system, the mean temperature rise possible from turbulent heating is estimated to be less than 1% of the characteristic temperature (which is found to be T_mixed=10^5K). These results highlight that mixing, and not heating, are likely to be the cause of the observed transition between cool to warm material in Okamoto et al. (2015). One consequence of this result is that the mixing creates a region with higher radiative loss rates on average than either of the original fluids, meaning that this instability could contribute a net loss of thermal energy from the corona, i.e. coronal cooling.Science and Technology Facilities CouncilSpanish Ministerio de Ciencia, Innovacion y Universidade

Magnetohydrodynamic kink waves in two-dimensional non-uniform prominence threads

We analyse the oscillatory properties of resonantly damped transverse kink oscillations in two-dimensional prominence threads. The fine structures are modelled as cylindrically symmetric magnetic flux tubes with a dense central part with prominence plasma properties and an evacuated part, both surrounded by coronal plasma. The equilibrium density is allowed to vary non-uniformly in both the transverse and the longitudinal directions.We examine the influence of longitudinal density structuring on periods, damping times, and damping rates for transverse kink modes computed by numerically solving the linear resistive magnetohydrodynamic (MHD) equations. The relevant parameters are the length of the thread and the density in the evacuated part of the tube, two quantities that are difficult to directly estimate from observations. We find that both of them strongly influence the oscillatory periods and damping times, and to a lesser extent the damping ratios. The analysis of the spatial distribution of perturbations and of the energy flux into the resonances allows us to explain the obtained damping times. Implications for prominence seismology, the physics of resonantly damped kink modes in two-dimensional magnetic flux tubes, and the heating of prominence plasmas are discussed.Comment: 12 pages, 9 figures, A&A accepte

Legislació i normativa sobre gent gran: una aproximació

Partint de la Declaració Universal dels Drets Humans i passant per la Constitució Espanyola, arribarem a l’Estatut d’Autonomia de les Illes Balears. Enunciat a les normes fonamentals el nou repartiment competencial, una sèrie de reials decrets varen fer efectives les transferències de competències de l’Estat a l’Administració autonòmica. Al mateix temps, es va produint l’entrega de part d’aquestes mateixes competències als consells insulars. Paral·lelament es va promulgant la normativa autonòmica bàsica reguladora de l’acció social . Lleis i decrets n’estableixen el marc legislatiu, enllaçat amb l’estatal i complementant-lo. De la regulació de les condicions d’obertura dels centres de persones majors, a les ajudes específiques per a aquest col·lectiu. De les prestacions econòmiques als programes de vacances. I com a punt d’arribada, el Pla Estratègic de persones majors.Partiendo de la Declaración Universal de Derechos Humanos y pasando por la Constitución Española, llegaremos al Estatuto de Autonomía de las Islas Baleares. Enunciado en las normas fundamentales el nuevo reparto competencial, una serie de reales decretos harán efectivas las transferencias de competencias del Estado a la Administración Autonómica. A la vez, se va produciendo la entrega de parte de esas mismas competencias a los consejos insulares. Paralelamente, se promulga la normativa autonómica básica reguladora de la acción social. Leyes y decretos establecen el marco legislativo propio, engarzado con el estatal y complementándolo. De la regulación de las condiciones de apertura de los centros de personas mayores, a las ayudas específicas para dicho colectivo. De las prestaciones económicas a los programas vacacionales. Y como punto de llegada, el Plan Estratégico de personas mayores