Empirical orthogonal function analysis of magnetic observatory data : further evidence for non-axisymmetric magnetospheric sources for satellite induction studies

Although satellite electromagnetic induction studies have usually assumed a symmetric magnetospheric ring current source, there is growing evidence for significant source asymmetry. Here we apply empirical orthogonal function methods to mid-latitude night-side hourly mean geomagnetic observatory data to search for evidence of nonzonal low-frequency source fields. The dominant spatial mode of variability in residuals, obtained by subtracting symmetric ring current and ionospheric fields of the CM4 comprehensive model, has a substantial Y₂¯¹ quadrupole component and is highly correlated with Dst. This pattern of temporal variability, which implies enhanced ring current densities in the dusk sector, persists even when peak storm-time data are omitted. The observed asymmetry agrees with that inferred previously by Balasis et al. (2004), from the local time dependence of biases in satellite induction transfer functions. Temporal correlation of the leading mode with Dst, and consistency of its spatial structure with recent empirical ring current models, suggest a magnetospheric origin

Statistical Mechanics and Information-Theoretic Perspectives on Complexity in the Earth System

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Common solar wind drivers behind magnetic storm-magnetospheric substorm dependency

The dynamical relationship between magnetic storms and magnetospheric substorms presents one of the most controversial problems of contemporary geospace research. Here, we tackle this issue by applying a causal inference approach to two corresponding indices in conjunction with several relevant solar wind variables. We demonstrate that the vertical component of the interplanetary magnetic field is the strongest and common driver of both, storms and substorms, and explains their the previously reported association. These results hold during both solar maximum and minimum phases and suggest that, at least based on the analyzed indices, there is no statistical evidence for a direct or indirect dependency between substorms and storms. A physical mechanism by which substorms drive storms or vice versa is, therefore, unlikely.Comment: 18 pages, 6 figure

Local time effects in satellite estimates of electromagnetic induction transfer function

The current satellite magnetic missions offer new opportunities to determine the electrical conductivity of the Earth. However, satellites are nearly stationary in local time and therefore sample the inducing and induced fields quite differently than geomagnetic observatories, which rotate with the Earth. We show that estimates of induction transfer functions obtained from CHAMP magnetic data under the traditional symmetric magnetospheric ring current source (Y⁰₁ ) assumption depend systematically on local time, suggesting that source fields contain also a coherent nonaxisymmetric component. An extended magnetospheric source model that incorporates a coherent nonaxisymmetric quadrupole (Y¹₂), and allows for Earth rotation qualitatively explains the observations

Statistical mechanics and information-theoretic perspectives on complexity in the Earth system

This review provides a summary of methods originated in (non-equilibrium) statistical mechanics and information theory, which have recently found successful applications to quantitatively studying complexity in various components of the complex system Earth. Specifically, we discuss two classes of methods: (i) entropies of different kinds (e.g., on the one hand classical Shannon and R´enyi entropies, as well as non-extensive Tsallis entropy based on symbolic dynamics techniques and, on the other hand, approximate entropy, sample entropy and fuzzy entropy); and (ii) measures of statistical interdependence and causality (e.g., mutual information and generalizations thereof, transfer entropy, momentary information transfer). We review a number of applications and case studies utilizing the above-mentioned methodological approaches for studying contemporary problems in some exemplary fields of the Earth sciences, highlighting the potentials of different techniques

Temporal organization of magnetospheric fluctuations unveiled by recurrence patterns in the Dst index

This work has been financially supported by the joint Greek-German project “Transdisciplinary assessment of dynamical complexity in magnetosphere and climate: A unified description of the nonlinear dynamics across extreme events” funded by IKY and DAAD. Individual financial support of the authors has been granted by the LINC (Learning about Interacting Networks in Climate) project (project no. 289447) funded by the Marie Curie Initial Training Network (ITN) program (FP7-PEOPLE2011-ITN), the German Federal Ministry for Science and Education (BMBF) via the Young Investigator’s Group CoSy-CC2 (grant no. 01LN1306A) and the project GLUES, the Stordalen Foundation (Planetary Boundary Research Network PB.net), and the International Research Training Group IRTG 1740/TRP 2014/50151-0, jointly funded by the German Research Foundation (DFG, Deutsche Forschungsgemeinschaft) and the S˜ao Paulo Research Foundation (FAPESP, Funda¸c˜ao de Amparo `a Pesquisa do Estado de S˜ao Paulo). Numerical codes used for estimating RQA and RNA properties can be found in the software package pyunicorn70, which is available at https://github.com/pik-copan/pyunicorn. The Dst data have been obtained from the World Data Center for Geomagnetism, Kyoto (http://wdc.kugi.kyoto-u.ac.jp/index.html). We are grateful to three reviewers of an earlier version of this manuscript for their detailed comments.Peer reviewedPublisher PD