论文标题
全球超级旋转对行星旋转速率的依赖性
The dependence of global super-rotation on planetary rotation rate
论文作者
论文摘要
如果大气的总纬向动量超过与基础行星的固体共旋转相关的,则可以将大气描述为全球超级旋转。在本文中,我们讨论了陆地大气中全球超级旋转对行星旋转速率的依赖性。与太阳系大气中的全球超级旋转相比,在理想化的通用循环模型实验中对全球超级旋转的分析来揭示了这种依赖性。进行了轴对称和三维实验。我们发现,在三维实验中,全局超旋转程度与轴对称实验的程度密切相关,详细差异。轴对称气氛中全局超级旋转的缩放理论来自held-hou模型。以高旋转速度,我们的数值实验居住在一个全球超级旋转范围的范围内,我们建议地球和火星占据了这一制度。以较低的旋转速率,我们的实验占据了由角动量保护确定的状态,在该方案中,整体超级旋转与旋转速率无关。我们的实验中的全球超级旋转的饱和,其值明显低于金星和泰坦大气中所达到的值,而金星和泰坦的大气中则占据了全球超级旋转尺度环形循环的状态。只有当涡感诱导的上梯度动量传输足够大时,才能访问该机制,在我们理想化的数值实验中并非如此。我们建议,缓慢旋转的行星的“默认”制度是保护方案的角动量,其特征是轻度的全球(局部)超级脱位。
An atmosphere may be described as globally super-rotating if its total zonal angular momentum exceeds that associated with solid-body co-rotation with the underlying planet. In this paper, we discuss the dependence of global super-rotation in terrestrial atmospheres on planetary rotation rate. This dependence is revealed through analysis of global super-rotation in idealised General Circulation Model experiments with time-independent axisymmetric forcing, compared with estimates for global super-rotation in Solar System atmospheres. Axisymmetric and three-dimensional experiments are conducted. We find that the degree of global super-rotation in the three-dimensional experiments is closely related to that of the axisymmetric experiments, with some differences in detail. A scaling theory for global super-rotation in an axisymmetric atmosphere is derived from the Held-Hou model. At high rotation rate, our numerical experiments inhabit a regime where global super-rotation scales geostrophically, and we suggest that the Earth and Mars occupy this regime. At low rotation rate, our experiments occupy a regime determined by angular momentum conservation, where global super-rotation is independent of rotation rate. Global super-rotation in our experiments saturates at a value significantly lower than that achieved in the atmospheres of Venus and Titan, which instead occupy a regime where global super-rotation scales cyclostrophically. This regime can only be accessed when eddy induced up-gradient angular momentum transport is sufficiently large, which is not the case in our idealised numerical experiments. We suggest that the 'default' regime for a slowly rotating planet is the angular momentum conserving regime, characterised by mild global (and local) superrotation.