Stratospheres of giant gas planets of the Solar System (Jupiter and Saturn) extend above the cloud top layers near the tropopause to the lower thermosphere, and have a thickness of about 14 density scale heights. Their stratospheric dynamics are poorly understood, and are very distinctive from that of terrestrial-like planets due to peculiarities of the gas giants: the size, fast rotation, absence of solid surfaces, weak radiative forcing, and strong influence of the interiors. The main objectives of this work were to develop a three-dimensional general circulation model (GCM) suitable for simulating the stratospheres of gas giants, and to apply it for studying the global circulations in the stratospheres of Jupiter, Saturn, and generic extrasolar planets. Such models are computationally demanding, because they have to resolve horizontal scales shorter than the Rossby deformation radii that are very small compared to the planet sizes. In addition, weak radiative forcing requires long-time integration for equilibration of the fields, and small time steps for maintaining the stability. The developed model is based on a grid-point dynamical core, and solves the nonlinear primitive equations under the hydrostatic approximation. It covers altitudes from 1–2 bars to 1–10 microbars, and uses the observed distributions of zonal winds at the cloud layers as a lower boundary condition. Application of the GCM to the stratosphere of Saturn allowed to explore the sensitivity of the simulated fields to the numerical aspects like resolution, strength of horizontal diffusion, time-stepping algorithms. Further simulations were focused on studying the zonal mean circulation and the resolved wave activity on Saturn and Jupiter. They revealed, in particular, that the meridional transport on both planets is weak, and represents an upward extension of multiple cells imposed by the alternating zonal winds in the zones and belts at the lower boundary. The simulated mean fields and non-zonal disturbances were compared with available observations, and showed a good agreement in low latitudes, where the model resolution was the most sufficient. The developed GCM was applied to studying the change of the circulation regimes on gas giants induced by an increased heating due to stellar radiation absorption. Such "warm" gas exoplanets have been found in large quantities at distances intermediate between those for cold and hot transiting giants. The analysis showed that the meridional transport intensifies on such planets, and most of the changes are due to the momentum deposited by vertically propagating thermal tides. The developed GCM showed methodological suitability for studying atmospheric dynamics of giant gas planets under a variety of conditions. It represents a major step in developing model capabilities, and is in a great synergy with the planned Jupiter Icy Moon Explorer (JUICE) mission. The model can provide an insight into the stratospheric dynamics of Jupiter, and help with the interpretation of observational data.
|Advisor:||Dähne, MarioRauer, HeikeHartogh, Paul|
|School:||Technische Universitaet Berlin (Germany)|
|Source:||DAI-C 81/1(E), Dissertation Abstracts International|
|Subjects:||Planetology, Astronomy, Atmospheric sciences|
|Keywords:||Gas planets, Stratospheric circulation|
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