Covariant Giant Gaussian Process Models With Improved Reproduction of Palaeosecular Variation
Covariant Giant Gaussian Process Models With Improved Reproduction of Palaeosecular Variation
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DOI：
10.1029/2020gc008960
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发表时间：
2020-08-01
影响因子：
3.5
通讯作者：
Bestard, Jack
中科院分区：
文献类型：
--
作者：
Bono, Richard K.;Biggin, Andrew J.;Bestard, Jack
一个常用的统计磁场模型族是基于巨高斯过程（GGP），它假设每个高斯系数可以从一个独立的正态分布实现。GGP模型能够产生一套合理的高斯系数，允许古地磁数据进行测试，对预期的分布所产生的时间平均地磁场。然而，现有的GGP模型不能同时再现过去1000万年来报告的场强分布和古长期变化估计，并且往往低估高纬度地区的虚拟地磁极（VGP）频散，除非对低纬度地区的拟合进行权衡。纬度。在这里，我们介绍了一个新的家庭的GGP模型，BB18和BB18.Z3（后者包括非零平均纬向项的球谐次数2和3）。我们的模型是不同的，从以前的GGP模型，同时处理轴偶极子方差分别从更高的程度，应用奇偶方差结构，并将某些高斯系数之间的协方差。高斯系数之间的协方差，预期从发电机理论和数值发电机模拟中观察到的属性，以前没有包括在GGP模型。引入某些高斯系数之间的协方差推断从合奏的“类地球”发电机模拟和预测的理论产生了减少错配VGP色散，使GGP模型产生改进的再现的场强分布和palaeosecular变化观察到的过去1000万年。
A commonly used family of statistical magnetic field models is based on a giant Gaussian process (GGP), which assumes each Gauss coefficient can be realized from an independent normal distribution. GGP models are capable of generating suites of plausible Gauss coefficients, allowing for palaeomagnetic data to be tested against the expected distribution arising from a time-averaged geomagnetic field. However, existing GGP models do not simultaneously reproduce the distribution of field strength and palaeosecular variation estimates reported for the past 10 million years and tend to underpredict virtual geomagnetic pole (VGP) dispersion at high latitudes unless trade-offs are made to the fit at lower latitudes. Here we introduce a new family of GGP models, BB18 and BB18.Z3 (the latter includes non-zero-mean zonal terms for spherical harmonic degrees 2 and 3). Our models are distinct from prior GGP models by simultaneously treating the axial dipole variance separately from higher degree terms, applying an odd-even variance structure, and incorporating a covariance between certain Gauss coefficients. Covariance between Gauss coefficients, a property both expected from dynamo theory and observed in numerical dynamo simulations, has not previously been included in GGP models. Introducing covariance between certain Gauss coefficients inferred from an ensemble of "Earth-like" dynamo simulations and predicted by theory yields a reduced misfit to VGP dispersion, allowing for GGP models which generate improved reproductions of the distribution of field strengths and palaeosecular variation observed for the last 10 million years.