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arXiv 1807.08433astro-ph.EP
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棕矮星和木星及类土星行星的大气环流:纬向喷流、长期变率和QBO型振荡

Atmospheric Circulation of Brown Dwarfs and Jupiter and Saturn-like Planets: Zonal Jets, Long-term Variability, and QBO-type Oscillations

Adam P. Showman, Xianyu Tan, Xi Zhang

摘要:

棕矮星和直接成像的巨行星显示了活跃的大气环流的重要证据,这导致了云结构中的大规模斑块,随着时间的推移显着演变,如红外线曲线和多普勒地图所证明的那样。这些观测结果提出了关于环流的基本性质,其时间变化以及与木星和土星环流的整体关系的关键问题。木星和土星本身在云层中也有许多强劲的纬向(东西向)喷流;此外,这两颗行星都有长期的平流层振荡,包括纬向风和温度的扰动,这些扰动会在约4年(木星)和约15年(土星)的时间尺度上向下传播。这些振荡被称为木星的准四年振荡(QQO)和土星的半年振荡(SAO),被认为类似于地球上的准两年振荡(QBO),这是由对流层赤道波向上传播驱动的。为了研究这些问题,我们在这里提出了全球性的,三维的,高分辨率的数值模拟流在分层的大气-覆盖对流内部-褐矮星和类星体行星。内部对流的影响参数化诱导小尺度,随机变化的扰动的辐射对流边界的基础上的模型。在模拟中,对流扰动产生大气波和湍流,与旋转相互作用,产生大量的纬向喷流。此外,赤道平流层呈现出堆叠的东向和西向喷流,随着时间的推移向下迁移,正是发生在地球的QBO,木星的QQO,土星的SAO。这是第一次在巨行星的3D数值模拟中展示类似QBO的现象。

英文摘要:

Brown dwarfs and directly imaged giant planets exhibit significant evidence for active atmospheric circulation, which induces a large-scale patchiness in the cloud structure that evolves significantly over time, as evidenced by infrared light curves and Doppler maps. These observations raise critical questions about the fundamental nature of the circulation, its time variability, and the overall relationship to the circulation on Jupiter and Saturn. Jupiter and Saturn themselves exhibit numerous robust zonal (east-west) jet streams at the cloud level; moreover, both planets exhibit long-term stratospheric oscillations involving perturbations of zonal wind and temperature that propagate downward over time on timescales of ~4 years (Jupiter) and ~15 years (Saturn). These oscillations, dubbed the Quasi Quadrennial Oscillation (QQO) for Jupiter and the Semi-Annual Oscillation (SAO) on Saturn, are thought to be analogous to the Quasi-Biennial Oscillation (QBO) on Earth, which is driven by upward propagation of equatorial waves from the troposphere. To investigate these issues, we here present global, three-dimensional, high-resolution numerical simulations of the flow in the stratified atmosphere--overlying the convective interior--of brown dwarfs and Jupiter-like planets. The effect of interior convection is parameterized by inducing small-scale, randomly varying perturbations in the radiative-convective boundary at the base of the model. In the simulations, the convective perturbations generate atmospheric waves and turbulence that interact with the rotation to produce numerous zonal jets. Moreover, the equatorial stratosphere exhibits stacked eastward and westward jets that migrate downward over time, exactly as occurs in the terrestrial QBO, Jovian QQO, and Saturnian SAO. This is the first demonstration of a QBO-like phenomenon in 3D numerical simulations of a giant planet.

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