General circulation modelling of close-in extrasolar giant planets
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A large fraction of the extrasolar planets detected so far are giant planets
that have such short orbital periods (a few days) that they are thought
to be tidally-synchronised with the host star. Such orbits lead to permanent
day/night sides on the planets and provide a forcing condition for
atmospheric dynamics that is not present in the Solar System. The main
subject of this thesis is to model the atmospheric dynamics of these close-in
extrasolar giant planets, using an accurate three-dimensional general
circulation model (GCM).
Using the GCM, the primitive equations are numerically solved, with
idealised forcing represented by Newtonian relaxation. A large number of
simulations is performed to thoroughly explore the relevant physical and
numerical parameter space.
First, it is found that different initial flow states lead to markedly different
flow and temperature distributions. This result is in contrast with
the results or assumptions of many published studies, and underlines the
fact that circulation models are currently unsuitable for quantitative predictions
without better constrained, and well-posed, initial conditions.
Second, the effects of artificial viscosity – particularly in relation to the
thermal relaxation timescale – are studied. It is demonstrated that using
a large range of thermal time scales, including very short ones ( 1 h), as
is common in the literature, leads to dominant noise and/or excessively
dissipated fields.
Finally, variations of the strength of thermal forcing are studied. Distinct
stationary or oscillatory states are identified for different sets of forcing
parameters. In addition, multiple long lasting states are observed for
a given forcing. Most of the states are characterised by a low number
( 4) of large-scale vortices and planetary waves, which exhibit a periodic time variability. The spatiotemporal variability can be important for observational
studies, and provides a strong argument for making repeated
measurements of a given planet.
Authors
Thrastarson, Heidar ThorCollections
- Theses [3705]