Prezentacja na temat: "Krzysztof Murawski. Obserwacje sejsmiczne - Ziemia."— Zapis prezentacji:
Obserwacje sejsmiczne - Ziemia
Schemat budowy Słońca
Solar corona: Main physical facts about the corona: almost fully ionised plasma, temperature is over 1 MK, magnetically-dominated, plasma- (ratio of gas and magnetic pressures) is low ( ), The plasma is “cold”! the origin of the solar wind space weather, a natural plasma laboratory controlled fusion. The uppermost part of the solar atmosphere
Structures in the solar corona:
SOHO – SOlar and Heliospheric Observatory Launched in 1995 by ESA and NASA
TRACE – Transition Region And Coronal Explorer NASA, 1998
Do we see MHD waves? Moreton waves Seen in H in the chromosphere at K (Moreton ’60) Propagation speeds km/s, away from a flare site Propagate almost isotropically; confined to an arc rarely exceeding 120º Have been identified as the intersection of coronal shock waves (due to a flare) with the chromosphere (Uchida ‘68; ‘74) Are not seen to decelerate The generation mechanism has not been made clear yet
Do we see MHD waves? - Moreton waves
Do we see MHD waves? – Coronal Moreton waves
E.g., important for interpretation of the “EIT wave”: Perspectives of Global Coronal Seismology?
Fale jak na powierzchni wody?
Do we see MHD waves? New: Coronal Moreton waves Thompson et al. (1999) with SOHO/EIT have investigated a global coronal wave generated by the coronal mass ejection or a flare and occupying a significant part of the solar disk. This wave has been called a coronal Moreton wave. Properties accumulated from observations of more than 50 events: (see or Ballai et al for details) The waves prefer to propagate radially from the epicentre, stopping at neutral lines and coronal hole boundaries, and distorted by active regions. Speeds range is from km/sec. Active regions distort the waves locally, bending them possibly toward the lower Alfvén speed regions. The waves can cause "visible deflection" of coronal magnetic field lines and probably are associated with filament oscillations.
Observational evidence for coronal waves is abundant: Periods from 1 s to several min. (Quasi) Periodicity: Resonance (characteristic spatial scales) Dispersion Nonlinearity / self-organisation Characteristic scales: 1 Mm-100 Mm, Alfvén speed 1 Mm/s, sound speed 0.3 Mm/s → periods 1 s – several min - magnetohydrodynamic (MHD) waves
Simulations require computers...
Symulacje numeryczne – model Mędrek, Murawski, Nakariakov (1998)
Impuls w koronie Słońca Mędrek, Murawski, Nakariakov (1998)
Impuls w fotosferze Mędrek, Murawski, Nakariakov (1998)
TRACE versus CDS : What is perceived as a coronal loop in SoHO/CDS (with an effective resolution of ~10”) consists of about ~10 loop strands that can be resolved with TRACE (~1”).
: : What is the spatial size of the finest loop strands ?
Parówki w pętli?
Żmijki w pętli?
Mimo trzęsień nadal istnieje… Solanki (2003)
Słońca a Ziemia
Conclusions There are MHD waves in the Sun, in STP MHD waves are natural for plasma heating/acceleration MHD waves are sensitive to flows Must take into account effects of inhomogeneity/structuring. The structuring plays a crucial role in the wave dissipation and transformation. The waves are an efficient tool for MHD seismology of the solar atmosphere, which allows us to determine values of the mean parameters of the corona, such as the magnetic field strength, density, pressure, and transport coefficients. Some of these values: the magnetic field strength, viscosity, resistivity and thermal conductivity, are not open to measurement by any other means. We can do this by measuring the properties of MHD waves and oscillations (periods, wavelengths, amplitudes, temporal and spatial signatures), combined with theoretical modelling of the wave phenomena.