The Structure and Dynamic nature of the Solar Atmosphere

Abstract

This thesis presents an examination of a range of dynamic phenomena present throughout the
solar atmosphere, from the photosphere to the corona. Above the photosphere, where the
plasma fi is small, the emitting plasma structure and dynamics are tied intimately to the solar
magnetic field.

Firstly, a wavelet analysis is applied to multi-temperature spectroscopic data observing
network-internetwork regions across a coronal hole boundary region. The nature of quasiperiodic
variability is investigated through the different temperature lines across the observed
structures. Statistically significant periods are found within the range 100-900 seconds, along
with short period wavepackets with periods 50-100 seconds. These oscillations are discussed
in terms of possible wave mechanisms. An example of a time-dependent period is observed
above the network region on the coronal hole boundary and possible theoretical origins are
discussed.

Secondly, a detailed analysis is applied to an active region observed on the solar limb. A
dynamic transition region loop, and closely associated ejection event are observed within the
active region. These structures are characterised by their emission line profiles; the transition
region loop is found to have a flow geometry of -20---*40 km c 1 , and the ejection event is
found to have a velocity gradient up to -20—*50 km across its width, suggesting a rotating
transition region structure consistent with a macrospicule.

Thirdly, an upwardly propagating disturbance is observed along a coronal loop associated
with a plage region with a velocity 50-195 km s perpendicular to the line of sight, and period
of 5 minutes. A wavelet analysis reveals that the five minute period is present in co-spatial,
co-temporal chromospheric and transition region observations. This is interpreted as the first observation of a 5-mm p-mode propagating through the chromosphere, transition region and
into a coronal loop.

Fourthly, an observing campaign is designed and executed to probe the connectivity between
the chromosphere, transition region and corona within active regions. Oscillations within
the 3-min band are observed above the umbra of a sunspot active region. These oscillations
show two closely separated frequencies of 6.1 & 7.1 mHz in the chromosphere, 5.9 & 7.3 mHz
in the transition region and 5.9 & 7.3 mHz in the corona. These observations are interpreted as
acoustic/maneto-acoustic wave modes propagating upwards through the chromosphere, transition
region and into the corona. The frequencies are observed as oscillations in the chromosphere
and transition region, and propagations in the emerging coronal loops, due to the
combined effect of the temperature scale height in the different spectral lines and the diverging
magnetic flux geometry above the sunspot. The energy flux of acoustic waves is estimated in
the different temperature lines as 28.3 erg cm 2 in the chromosphere, 201.0 erg cm2 sin
the transition region and 225.6 erg cm 2 in the corona.

Finally, future work is discussed in terms of progressing the work completed, and exploiting
upcoming spaced based missions.