Stability and mode analysis using irreversible energy principles

COSTA, A.

PHYSICA SCRIPTA

Año: 2007

0281-1847

Low coronal  highly anisotropic structures as loops and prominences are relatively stable configurations with densities about hundreds times higher and temperatures about hundreds times lower than their surrounding corona. MHD open systems, generally driven by coupled mechanical and thermal perturbations, can go beyond linear state configurations into new stationary states known as nonlinear equilibria. Thus, a crucialrequirement for any theoretical model that intends to describe these far-from-equilibrium statesis to give account of the stability and evolution of the numerous nonlinear thermodynamic stationary states that can arrive.Observations obtained with high spatial and time resolution instruments of the new spacecraft generation describe  a wide spectrum of configurations which sustain fast and slow magnetoacoustic oscillations or propagating MHD waves that are ducted by the magnetic fields of the low $eta$-corona media. Measurements of characteristic periods, speeds and damping times as well as different theoretical models that intend to describe non-dissipative damping mechanisms and leakage processes of systems with high Reynolds number  provide with new diagnostic tools to reveal unknown or more accurate solar physics parameters. We summarize some theoretical and observational results that give account of  the coronal seismology state of art. We present a thermodynamic  stability criterion to describe modes and stability  of coronal structures. We give some results of its application to coronal seismology.  This allows us to discuss the feasibility of wave-based and flow-based models for solar loops and to offer a different explanation to the presence of frequencies associated to heliosismological p--modes at the altitude of the corona.