Mechanisms for Limiting the Depth of Zonal Winds in the Gas Giant Planets
Mechanisms for Limiting the Depth of Zonal Winds in the Gas Giant Planets
复制标题
限制气态巨行星纬向风深度的机制
DOI：
10.3847/1538-4357/ab698c
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发表时间：
2020
期刊：
影响因子：
--
通讯作者：
W. Dietrich
中科院分区：
文献类型：
--
作者：
U. Christensen;Johannes Wicht;W. Dietrich
朱诺号和卡西尼号任务观测到的与木星和土星外层强烈的纬向风相关的重力特征表明，这些气流延伸到了内部数千公里。人们注意到，在电导率变得显着的深度，风似乎减弱，这表明电磁效应在将风限制在外部弱导电区域方面发挥着关键作用。在这里，我们探索了在具有深度相关电导率和强制射流的两种模型设置中制动深度层流的可能机制，即轴对称壳模型和允许探索较宽参数范围的更简单的线性化盒模型。洛伦兹力直接制动风并不会降低风在传导区域的速度足以与推断的木星场的长期变化相一致。在电导率变得显着的深度之上的稳定分层可以解决这个问题。电磁力驱动微弱的经向环流，扰乱稳定区域的密度分布，从而由于热风平衡，风速随着深度的增加而强烈降低。为了使这种机制有效，稳定层必须向上延伸到低电导率区域。将线性化计算的结果应用于木星表明，与纬向风相关的耗散可能仅限于内部热流的一小部分，并且喷流可能会在 150-300 公里的深度范围内下降。
Gravity signatures observed by the Juno and Cassini missions that are associated with the strong zonal winds in Jupiter’s and Saturn’s outer envelopes suggest that these flows extend for several thousand kilometers into the interior. It has been noted that the winds seem to abate at a depth where electrical conductivity becomes significant, suggesting that electromagnetic effects play a key role for confining the winds to the outer weakly conducting region. Here, we explore the possible mechanisms for braking the zonal flow at depth in two model setups with depth-dependent conductivity and forced jet flow, i.e., in axisymmetric shell models and in more simple linearized box models that allow the exploration of a wide parameter range. Braking of the winds directly by Lorentz forces does not reduce their speed in the conducting region enough to be compatible with the inferred secular variation of Jupiter’s field. Stable stratification above the depth where conductivity becomes significant can solve the problem. Electromagnetic forces drive a weak meridional circulation that perturbs the density distribution in the stable region such that the wind speed decreases strongly with depth, due to a thermal wind balance. For this mechanism to be effective, the stable layer must extend upward into a region of low conductivity. Applying the results of the linearized calculations to Jupiter suggests that the dissipation associated with the zonal winds can be limited to a fraction of the internal heat flow and that the jets may drop off over a depth range of 150–300 km.
影响因子：
8.7
作者：
French, Martin;Becker, Andreas;Redmer, Ronald
通讯作者：
Redmer, Ronald
影响因子：
4.9
作者：
Nettelmann, N.;Becker, A.;Redmer, R.
通讯作者：
Redmer, R.
影响因子：
3.2
作者：
Gastine, T.;Wicht, J.
通讯作者：
Wicht, J.