B028843 - PHYSICS OF THE SUN AND OF THE INTERPLANETARY MEDIUM

Italian or English

The Sun as a Star. Instrument for Sun’s observation, Line and continuum spectrum.
Radiative transport. Dynamical processes: dopplergrams, granulation, supergranulation.
Magnetic structures: magnetographs, magnetograms, sunspot, loops and prominences.
Explosives events: flares, CME, and space weather.
Heating of the chromosphere, of the corona, heating and acceleration of the solar wind.
The Heliosphere, in-situ data and turbulence.

Textbook: E. Landi Degl'Innocenti Fisica solare Ed. Springer

Articles and Review Articles provided during the lectures

Acquired Knowledge:
The Sun as a star and as an astrophysical laboratory. Physics underneath the processes that rule the Sun. Spectrum formation, dynamic Sun and role of magnetic fields.
The outer regions of the Sun.

Acquired Competences:
Line formation in a stellar atmosphere from equilibrium to non-equilibrium.
Role of magnetic field in the solar atmosphere.
The solar cycle, different aspects of the same phenomenon.

Acquired Skills (at the end of the course):
Solar observation interpretation (spectroscopy and photometry) from visible light to extreme ultraviolet.

Basic courses in physics and astrophysics.

Lectures

Contact: Office hours by appointment

Oral Exam on the topics of the lectures and on a research article chosen among a list provided at the end of the year

Historical and phenomenological introduction.

The Sun through observations.
- Ground-based observations: seeing, observing sites, solar telescopes with long and short focal length.
- Focal plane instrumentation: grating spectroscopy, Lyot filter, Fabry-Perot filter.
Spece instrumentation:
Coronagraph, EUV disk imager, in-situ measurements. New solar missions: Solar Orbiter and Parker Solar Probe.

The solar spectrum in photosphere.
- Radiative transport equation: introduction, formal solution.
- Stellar atmospheres: approximations, grey atmosphere, realistic models.
- Lorentz electron theory: Thompson scattering, Rayleigh scattering,resonance, quantistic correction.
- Line profiles: collisional, Doppler broadening.
- Line spectrum: introduction on non-LTE models.

Solar dynamics. Doppler effect. Cinematical effects on velocity measurements. Dopplergram. Granulation. Mesogranulation. Supergranulation.

Magnetic field: MHD equations, Alfven theorem. Flux tubes, sunspots, pores, active regions. Solar activity cycle.
- Zeeman effect: introduction, classical theoretical description. Basics of the quantum solution.

Outer layers of the solar atmosphere.
- The chromosphere: phenomena, physical and observative properties, magnetic field interactions.
- Transition region: phenomena, ionization balance in non-ETL.
- Prominences: phenomena, stability.
- Solar corona: phenomena, visible light corona, EUV and X corona, spectral line formation, and spectroscopic diagnostics.

The Sun’s Atmosphere: Corona and Coronal Heating:
- Phenomenology. Magnetic structure
- Energy conservation in a flux tube
- The coronal heating problem.
- Energy balance: quiet sun, active regions, coronal holes
- Source of energy: Poyinting vector at the photosphere
- Hydrostatic loop model: the law of Rosner-Tucker-Vaiana (RTN)
- Magnetic energy and X luminosity (Fisher-Pevtsov)
- Coronal heating: constraints from observations (RTN, thermal equilibrium, luminosity)
- Some mechanisms for coronal heating.

Flares:
- Classification,
- Observations in different bandpasses
- Neuper effect
- Energy balance
- The standard model
- A sort -f HR diagram for flares

Coronal Mass Ejections (CME):
- Pre-eruption phase (Filaments, prominences), Back reaction on the solar atmosphere (EIT and Moreton waves)
- Propagation in the heliosphere
- Impact on Earth
- Energy balance
- Morphology form remote sensing instruments
- Statistical properties
- Properties from in-situ detection
- Drag model for the CME propagation and space-weather

The Heliosphere and the solar wind:
- Historical introduction
- large-scale structure: fast and slow streams
- FIP effect, Freeze in temperature, ion heating
- In-situ detection: properties, mass flux, correlations with properties on the Sun.
- Magnetic and velocity spectra, Elsasser variable, spectral properties and evolution
- The Parker model for the solar wind
- Breezes and wind, stability and hysteresis cycle
- Energy balance,
- Derivation of some observed properties.

Hydrodynamic and Magnetohydrodynamic turbulence
- Historical introduction
- Kolmogorov Phenomenology
- An exact law for the cascade in incompressible turbulence
- Magnetic field and MHD turbulence
- Iroshnikov-Kraichnan Phenomenology
- Strong turbulence, critical balance, and dynamic alignement

Turbulence in the solar wind and kinetic properties
- Velocity and magnetic spectra
- Heating and measurements of the cascade rate
- Turbulence in fast streams: alfvenic fluctuations and spectral evolution
- Comparison of spectral slopes with phenomenologies
- Kinetic effect on heliospheric plasma: temperature and pressure anisotropy.
- Ion Velocity distribution functions
- Open questions