Semi-empirical Studies Of Solar Supergranulation And Related Phenomena
Abstract
In recent years, solar observations have moved from ground-based
telescopes to observatories on Earth orbiting satellites, such as
SOHO. They provide us with a clear and uninterrupted view of the
solar disk. One instrument upon SOHO, the Michelson Doppler Imager
(MDI), has proved fruitful in providing not only important
information of the solar photosphere but, in combination with
helioseismic methods, a method for probing the solar interior.
This dissertation discusses current investigations by myself and my
collaborators into surface manifestations of convection phenomena,
using Doppler velocity data from MDI and produced from computer
simulations. The Doppler data reveal convection cells much larger
than the granulation seen easily by optical telescopes. These
'supergranules' originate deeper within the convection layer than
the granules and, like their smaller counterparts, are heavily
influential in structuring the magnetic field and subsequently play
an important role in controlling aspects of the solar activity
cycle.
My work presented in this dissertation shows that the
supergranulation pattern seems to rotate faster than the surface
plasma. It has been suggested that the pattern is driven by
wave-like phenomena, but instead we find the reason is a geometric
effect with respect to the observer. We further find that
supergranules are also responsible for observed corrugation features
on the solar surface, which previously had been interpreted as
Rossby wave hills.
We extend our convection spectrum and Doppler map production
simulations to include axisymmetric flows such as differential
rotation, which contribute to the evolution of the velocity field.
These models assist in understanding how such large-scale surface
flows influence the surface motions of supergranules.
Lastly, I describe the construction of a numerical experiment to
study the influence of a 'giant-cell' velocity field on the
supergranule pattern. Such non-axisymmetric flows would further
contribute to supergranule advection and the results of such
experiments may assist in the observation of these hitherto elusive
'giant-cells'.