Unit:
Τομέας Φυσικής Συμπυκνωμένης ΎληςLibrary of the School of Science
Author:
Κοντογιάννης Ιωάννης-Δημήτριος
Dissertation committee:
Ξενοφών Μουσάς Καθηγ.(Επιβλέπων), Παναγιώτα Πρέκα-Παπαδήμα Επικ. Καθηγ., Γεωργία Τσιροπούλα Ερευνήτρια Α, ΙΑΑΔΕΤ, ΕΑΑ
Original Title:
Μελέτη του ρόλου της λεπτής υφής της χρωμόσφαιρας στο σχηματισμό του μαγνητικού θόλου και στη διάδοση των κυμάτων
Summary:
The chromosphere is a very inhomogeneous and highly dynamic layer of the solar
atmosphere. High resolution observations have revealed that it consists mainly
of fine-scale structures, that are directly related to the magnetic field. In
this thesis we use multi-wavelength observations to study oscillatory phenomena
in the quiet Sun and their relation to the magnetic field and the chromospheric
fine-scale structures called mottles. The observations were obtained during a
coordinated campaign which included space-borne instruments (i.e. the
Transition Region and Coronal Explorer, the Michelson Doppler Imager onboard
SoHO, the Solar Optical Telescope Specropolarimeter onboard the Hinode
spacecraft) and a ground-based telescope (i.e. the Dutch Open Telescope). The
analysed data consist of time series of images of a solar network region
observed at different atmospheric layers from the photosphere to the upper
chromosphere, and of high resolution magnetograms. Using wavelet analysis we
investigate the oscillatory power distribution in the 2D field-of-view, as well
as its vertical distribution and its relation with the fine-scale chromospheric
mottles. The magnetic field of the chromosphere was calculated via the
extrapolation of the photospheric magnetic field, based on the electric
current-free assumption. Using a semi-empirical atmospheric model, we
calculated the height of the magnetic canopy. Wave propagation was investigated
through phase difference analysis. Our results show that the oscillatory power
has a fibrilar distribution which is highly correlated with the places where
chromospheric mottles are found. Around the magnetic network in the Hα line, we
found enhancement of the oscillatory power at the photosphere (power halo) and
suppression at the chromosphere (magnetic shadow). The magnetic shadow and the
power halo are attributed to the interaction between the acoustic oscillations
and mottles, which outline the inclined magnetic field of the chromosphere and
form the magnetic canopy. The magnetic canopy divides the solar atmosphere into
two components, a magnetized and a non-magnetized one and it is on this
critical surface that waves undergo mode conversion and reflection. We find
that the inclination of the magnetic field at the height of the magnetic canopy
defines the amount of waves that transmit to the chromosphere or reflect back
to the photosphere and form the magnetic shadow and power halo around the
network.
Keywords:
Chromosphere, Waves, Mottles, Magnetohydrodynamics, Sun
Number of references:
179
