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Complex Dynamical Phenomena in Solar Plasmas

Final Activity Report Summary - CODPHESP (Complex Dynamical Phenomena in Solar Plasmas)

This project has been devoted to the study of complex dynamical phenomena in solar plasmas. The main emphasis has been on the study of the dynamics of solar oscillatory and convective motions, as observed in the solar photosphere, and on the dynamical processes occurring in the regions of high magnetic activity of the solar atmosphere. From the methodological point of view, the project aimed to give a contribution to this field of research trying to promote the application of some recent techniques, used so far in the study of turbulence and complex systems, in the analysis of dynamical processes observed in solar plasmas.

The most important scientific achievement of our project concerns the study of solar oscillatory and convective motions. The spatio-temporal dynamics of the solar photosphere has been studied by analysing line of sight velocity fields (computed from high resolution data coming from the MDI/SOHO instrument) through the Proper Orthogonal Decomposition (POD) technique. This method provides an optimal modal decomposition of turbulent phenomena, showing a complex space-time behaviour characterised by the presence of coherent structures. The results of our work have shown that POD is able to capture the main energetic and spatial features of the solar photosphere. In particular, the dynamical processes of interest, related to oscillatory and small scale convective phenomena, are automatically separated from the most energetic but less interesting modes which capture the contribution of solar rotation and large scale convection.

We have found a clear association between low-frequency oscillations and small spatial scales, close to the solar granulation, and this is the most interesting and most surprising result provided by our analysis. This suggests the presence of a strong coupling between low-frequency modes and the turbulent convection. Such coupling could be related to the dishomogeneities and small scale structures arising from the highly nonlinear dynamics of the convective layers, a point which needs to be investigated in future theoretical studies.

The complex dynamics of magnetic activity regions of the solar atmosphere has been investigated with the aid of both observations and theoretical models. An analysis of spectropolarimetric observations performed by the THEMIS/MTR instrument has been carried out. These data provides the possibility to calculate the magnetic field vector maps, which can be analysed, among other, with advanced techniques such as the cancellation analysis which leads to the characterisation of the topological evolution of turbulent vector fields. Through this study, which is in progress, it is possible to characterize the magnetic topology evolution of different active regions and to investigate the relation of these evolutions with the other properties of the active regions, and in particular the occurrence of solar flares. A dynamical model has also been built up to describe the intermittent behaviour, both in space and time, of the energy dissipation rate in fully turbulent, magnetohydrodynamic flows, like those occurring in active region loops observed in the solar corona.

The numerical simulations performed show that this model is able to reproduce the statistical properties of intermittent energy dissipation in magnetohydrodynamic turbulent flows. These results open the way to the applications of the proposed model to describe the injection, storage, and dissipation of magnetohydrodynamic turbulence in coronal loops.