Numerical study of the motions within a slowly precessing sphere at low Ekman number
Numerical study of the motions within a slowly precessing sphere at low Ekman number
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DOI：
10.1017/s0022112001004311
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发表时间：
2001-06
影响因子：
3.7
通讯作者：
J. Noir;D. Jault;P. Cardin
中科院分区：
文献类型：
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作者：
J. Noir;D. Jault;P. Cardin
在缓慢进动的刚体中的球腔内产生地转环流和一对斜向振荡切变层。两者都是由两个临界圆处的Ekman边界层破裂造成的。对于非常小的Ekman数，我们依靠数值模拟来描述这些运动。振荡剪切层的速度幅值O(E_1/5)和斜层的宽度(E_(E_1/5))都是从Ekman层破裂区域进入内部的结果。振荡运动被限制在狭窄的剪切层内，其振幅在远离特征表面时呈指数衰减。边界层内部的非线性相互作用驱动着附着在临界圆上的地转切变层。这个稳定层的厚度也是O(e1/5)，包含O(E−3/10)的速度。我们的结果与Malkus对缓慢进动的椭球体中产生的地转速度的实验测量很好地一致。
A geostrophic circulation and a pair of oblique oscillating shear layers arise in a spherical uid cavity contained in a slowly precessing rigid body. Both are caused by the breakdown of the Ekman boundary layer at two critical circles. We rely on numerical modelling to characterize these motions for very small Ekman numbers. Both the O(E1/5) amplitude of the velocity in the oscillating shear layer and the width (also O(E1/5)) of these oblique layers are the result of in ux into the interior from the regions where the Ekman layer breaks down. The oscillating motions are confined to narrow shear layers and their amplitude decays exponentially away from the characteristic surfaces. Nonlinear interactions inside the boundary layer drive the geostrophic shear layer attached to the critical circles. This steady layer, again of O(E1/5) thickness, contains O(E−3/10) velocities. Our results are in good agreement with the experimental measurement by Malkus of the geostrophic velocity arising in a slowly precessing spheroid.