Ensemble inversion of time‐dependent core flow models
Ensemble inversion of time‐dependent core flow models
复制标题
随时间变化的核心流模型的集合反演
DOI：
10.1029/2008gc002290
复制
发表时间：
2009
期刊：
影响因子：
3.7
通讯作者：
D. Jault
中科院分区：
文献类型：
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作者：
N. Gillet;Maria Alexandra Pais;D. Jault
准地转核心流模式是由1960-2002年和1997-2008年两个长期变化模式建立的。我们依靠系综方法来解释未分辨的小尺度磁场与核心表面流动相互作用对观测到的磁场变化的贡献。系综解的不同核心流动成员在球谐和度ℓ≃10以下是一致的，且该分辨分量仅随正则化而微弱变化。考虑到小尺度隐含磁场的有限关联时间，我们发现，磁场在短时间尺度上的时间变化，如地磁突变，在很大程度上可以用流动的分辨(大尺度)部分来解释。我们的流动模型的残差在1995年后的最近时期内减少了30%。这一结果归因于地磁数据质量的提高。磁场模型显示，在我们估计的由空间分辨率误差引起的核-地幔边界的视磁通量变化范围内，最近几个历元的冻结磁通量破坏很小。我们将早期观测到的更重要的通量变化与高次谐场模型中的不确定性联系起来。我们的核心流动模型显示，在所有时期，在印度洋和太平洋下分别大约在30和60纬度处，一个偏心的和行星规模的反气旋回旋围绕与内核相切的圆柱面旋转。它们很好地解释了最近几个纪元核心角动量的变化。
Quasi‐geostrophic core flow models are built from two secular variation models spanning the periods 1960–2002 and 1997–2008. We rely on an ensemble method to account for the contributions of the unresolved small‐scale magnetic field interacting with core surface flows to the observed magnetic field changes. The different core flow members of the ensemble solution agree up to spherical harmonic degree ℓ ≃ 10, and this resolved component varies only weakly with regularization. Taking into account the finite correlation time of the small‐scale concealed magnetic field, we find that the time variations of the magnetic field occurring over short time scales, such as the geomagnetic jerks, can be accounted for by the resolved (large‐scale) part of the flow to a large extent. Residuals from our flow models are 30% smaller for recent epochs, after 1995. This result is attributed to an improvement in the quality of geomagnetic data. The magnetic field models show little frozen flux violation for the most recent epochs, within our estimate of the apparent magnetic flux changes at the core‐mantle boundary arising from spatial resolution errors. We associate the more important flux changes detected at earlier epochs with uncertainties in the field models at large harmonic degrees. Our core flow models show, at all epochs, an eccentric and planetary‐scale anticyclonic gyre circling around the cylindrical surface tangent to the inner core, at approximately 30 and 60 latitude under the Indian and Pacific oceans, respectively. They account well for the changes in core angular momentum for the most recent epochs.