| Abstract : | Solar atmosphere provides a conducive environment for the
generation, propagation, mode-conversion, and dissipation of various
MHD waves. The 5-min oscillations appearing on the solar photosphere
are due to the acoustic waves which are generated in the convection
zone of the Sun, via turbulent convection and are trapped in the
acoustic cavities formed inside the Sun. These acoustic oscillations
are suppressed in the strong magnetic regions due to the inhibition of
convection. However, solar flares are known to excite these
oscillations in the sunspots. During the solar flares, abrupt changes
in Lorentz force can also induce seismic emission in the sunspots.
Moreover, the trapped low-frequency acoustic waves beneath the solar
photosphere are considered to leak along the inclined magnetic fields
due to reduction in cut-off frequency. The slow-magnetoacoustic waves
are known to propagate along the magnetic field with increasing
amplitude, while fast magnetoacoustic waves are refracted above β = 1
layer, and downward propagating waves are known to cause
high-frequency acoustic halos surrounding strong magnetic
concentrations. The internal or atmospheric gravity waves in the Sun
are generated by the buoyancy force and are also recognized as an
important contributor to the dynamics and energetics of the lower
solar atmosphere. While propagating energy upwards, their
characteristics negative phase shift over height is a well-recognized
observational signature. However, the propagation of these waves in
the magnetized structures shows that these waves are
scattered/suppressed and refracted, suggesting that the propagation of
gravity waves is hampered in the presence of magnetic fields.
In this thesis, we have investigated the evolution of velocity and
magnetic fields in the solar atmosphere with an emphasis to understand
the propagation of waves in the lower solar atmosphere, utilizing data
obtained from various space-based (SDO, RHESSI, and GOES) and ground-based
solar observing facilities (MAST, IBIS/DST, and GONG). |
