Modeling and Predicting the Short-Term Evolution of the Geomagnetic Field
Modeling and Predicting the Short-Term Evolution of the Geomagnetic Field
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DOI：
10.1029/2017jb015115
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发表时间：
2018-06-01
影响因子：
3.9
通讯作者：
Lesur, Vincent
中科院分区：
文献类型：
--
作者：
Baerenzung, Julien;Holschneider, Matthias;Lesur, Vincent
我们提出了一个简化的动力学系统，描述了1900年至2014年期间地球核心顶部的流体流动和磁场的耦合演化。流动的演变与一阶自回归过程建模，而磁场服从经典的冻结磁通方程。集合卡尔曼滤波算法用于约束与地磁场的动态和COV-OBS.x1模型给出的长期变化。使用具有40，000个成员的大型集合提供了有意义的统计数据，包括可靠的误差估计。该模型突出了两个不同的流量尺度。缓慢变化的大尺度元素包括已经记录在案的偏心环流。局部化的短寿命结构包括明显的非古地理特征，如北方半球的高纬度极地急流。与独立观测的日长变化的比较不仅验证了流量估计，但也表明在过去的世纪的地转流的加速。后测测试表明，我们的模型优于简单的预测基础（线性外推和平稳流）。磁偶极子分量的可预报性极限约为2,000年，主要取决于气流的随机快速变化动力学，而较少取决于地磁数据质量或缺乏小尺度信息。
We propose a reduced dynamical system describing the coupled evolution of fluid flow and magnetic field at the top of the Earth's core between the years 1900 and 2014. The flow evolution is modeled with a first-order autoregressive process, while the magnetic field obeys the classical frozen flux equation. An ensemble Kalman filter algorithm serves to constrain the dynamics with the geomagnetic field and its secular variation given by the COV-OBS.x1 model. Using a large ensemble with 40,000 members provides meaningful statistics including reliable error estimates. The model highlights two distinct flow scales. Slowly varying large-scale elements include the already documented eccentric gyre. Localized short-lived structures include distinctly ageostophic features like the high-latitude polar jet on the Northern Hemisphere. Comparisons with independent observations of the length-of-day variations not only validate the flow estimates but also suggest an acceleration of the geostrophic flows over the last century. Hindcasting tests show that our model outperforms simpler predictions bases (linear extrapolation and stationary flow). The predictability limit, of about 2,000years for the magnetic dipole component, is mostly determined by the random fast varying dynamics of the flow and much less by the geomagnetic data quality or lack of small-scale information.