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Tesi etd-10112006-083057

Thesis type
Tesi di dottorato di ricerca
Rappazzo, Antonio Franco
email address
Nonlinear Processes in Coronal Heating and Slow Solar Wind Acceleration
Settore scientifico disciplinare
Corso di studi
Relatore Einaudi, Giorgio
Relatore Prof. Shore, Steven Neil
Parole chiave
  • Turbulence
  • Sun
  • Slow Solar Wind
  • MHD
  • Coronal Heating
Data inizio appello
Riassunto analitico
The present work consists of two parts: the first devoted to the study of the heating of the magnetically confined Solar Corona, and the second to the acceleration of the Slow Solar Wind.

I have developed a parallel code using MPI. With this I have performed direct 3D reduced MHD simulations, modeling the heating of coronal loops in the solar atmosphere via the tangling of coronal field lines by photospheric footpoints motions within the framework of the “Parker scenario”. I carried out long-time simulations with the highest resolutions and longest extent to date. This has allowed me to derive scaling properties with loop length, and ratio of photospheric velocity to coronal Alfvén speeds. The development of a turbulent dynamics makes the dissipation rate independent of the Reynolds number. The dynamics in physical space is desribed by weak turbulence, which develops when an MHD system is embedded in a strong axial magnetic field.

The slow wind originates in and around the coronal streamer belt. Recently the LASCO instrument onboard the SOHO spacecraft has observed plasma density enhancements forming beyond the cusp of a helmet streamer. I refine a previous theoretical model for the formation and initial motion of these density enhancements, including few spherical geometry effects in a Cartesian model. Namely the average expansion suffered by a parcel of plasma propagating outward, and the diamagnetic force due to the overall magnetic field radial gradients (melon-seed force). It is found that the magnetized wake configuration is resistively unstable, that an outward accelerating magnetic island develops at the center of the streamer, and that density enhancements occur within the magnetic islands. The values of the acceleration and density contrasts can be in good agreement with LASCO observations, provided the spherical divergence of the magnetic lines starts beyond a critical distance from the Sun. This result provides a constraint on the topology of the magnetic field.