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The spatial damping of magnetohydrodynamic waves in a flowing partially ionised prominence plasma  

J. L. Ballester   Submitted: 2010-01-27 08:06

Solar prominences are partially ionised plasmas displaying flows and oscillations. These oscillations show time and spatial damping and, commonly, have been explained in terms of magnetohydrodynamic (MHD) waves. We study the spatial damping of linear non-adiabatic MHD waves in a flowing partially ionised plasma, having prominence-like physical properties. We consider single fluid equations for a partially ionised hydrogen plasma including in the energy equation optically thin radiation, thermal conduction by electrons and neutrals, and heating. Keeping the frequency real and fixed, we have solved the obtained dispersion relations for the complex wavenumber, k, and have analysed the behaviour of the damping length, wavelength and the ratio of the damping length to the wavelength, versus period, for Alfvén, fast, slow and thermal waves.

Authors: M. Carbonell, P. Forteza, R. Oliver, J. L. Ballester
Projects: None

Publication Status: A&A (submitted)
Last Modified: 2010-01-27 14:03
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J. L. Ballester   Submitted: 2007-09-11 08:48

Many studies about the North-South asymmetry of solar activity and its features have been performed by different authors. However, most of these studies do not care whether or not the asymmetry of the time series under consideration is statistically significant. Of course, in the case the asymmetry is statistically insignificant, any study about its behavior is meaningless. The main aim of this study is to point out the difficulties found when trying to assess the statistical significance of the North-South asymmetry (hereafter SSNSA) of the most usually considered time series of solar activity. First of all, we distinguish between solar activity time series composed by integer or non-integer and dimensionless data, or composed by non-integer and dimensional data. For each of these cases, we discuss the most suitable statistical tests which can be applied and highlight the difficulties to obtain valid information about the statistical significance of solar activity time series. Our results suggest that, apart from the need to apply the suitable statistical tests, other effects such as the data binning, the considered units and the need, in some tests, to consider groups of data, affect substantially the determination of the statistical significance of the asymmetry. Our main conclusion is that the assessment of the statistical significance of the N-S asymmetry of solar activity is a difficult matter and that an absolute answer cannot be given, since many different effects influence the results given by the statistical tests. In summary, the quantitative results about the statistical significance of the N-S asymmetry of solar activity provided by different authors, as well as the studies about its behaviour, must be considered with care because they depend from the chosen values of different parameters or from the considered units.

Authors: M. Carbonell. J. Terradas, R. Oliver, J. L. Ballester
Projects: None

Publication Status: Accepted Astronomy and Astrophysics
Last Modified: 2007-09-12 06:36
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The spatial damping of magnetohydrodynamic waves in a flowing partially ionised prominence plasma
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