Periodical Characteristics of the Geomagnetic Secular Variation and Decadal Length‐of‐Day Variation

Kang, Guofa; Chen, Bai; Gao, Guoming

doi:10.1002/cjg2.1215

Cited by 4 publications

(2 citation statements)

References 30 publications

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“…Xu et al [2006] studied the periodicity of the geomagnetic field from the IGRF-9 model to demonstrate a 30 year signal over the last 100 years. Kang et al [2008] used the wavelet transform method upon GUFM1 and IGRF-10 and inferred 32, 66 and 82 year signals. Table 2 compares the periods we have found in the geomagnetic times series with the modal solutions from three different core flow models.…”

Section: Resultsmentioning

confidence: 99%

Geomagnetic variation on decadal time scales: What can we learn from Empirical Mode Decomposition?

Jackson

Mound

2010

Geophysical Research Letters

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[1] The effects of core fluid dynamics are observable as variations in the geomagnetic field at time scales of decades to many thousands of years. A non-classical method, Empirical Mode Decomposition (EMD) is performed on globally distributed observatory records of declination and inclination to study decadal variations of the geomagnetic field. We use waveform analysis to test the robustness of EMD and find an 11.5 year signal consistent with the solar cycle. Periods of 30.5, 62 and 81 years are also identified in the observations and compared with results from core flow inversions. These signals are likely to be of internal origin, potentially the manifestation of torsional oscillations, in the fluid core. Finally, we analyse a new 600 year time series from Munich and suggest that a longer, 160 year period exists.

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Section: Resultsmentioning

confidence: 99%

Geomagnetic variation on decadal time scales: What can we learn from Empirical Mode Decomposition?

Jackson

Mound

2010

Geophysical Research Letters

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“…A second mode was identified, which concentrates variations of core angular momentum, with a quasi-periodicity of 80 to 90 yrs. Periods close to 80 or 90 yrs have been found in magnetic field observatory data [Jackson and Mound, 2010], geomagnetic field models [Kang et al, 2008] and inverted flows [Zatman and Bloxham, 1997, 1998, Dickey and de Viron, 2009, Buffett et al, 2009. Never before, however, have they been put forward without focusing the analysis on the zonal component of the flow and resorting to flows inverted from different geomagnetic field models.…”

Section: Discussionmentioning

confidence: 99%

Variability modes in core flows inverted from geomagnetic field models

Pais

Morozova

Schaeffer

2014

Geophysical Journal International

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The flow of liquid metal inside the Earth's core produces the geomagnetic field and its time variations. Understanding the variability of those deep currents is crucial to improve the forecast of geomagnetic field variations, which affect human spacial and aeronautic activities. Moreover, it may provide relevant information on the core dynamics. The main goal of this study is to extract and characterize the leading variability modes of core flows over centennial periods, and to assess their statistical robustness. To this end, we use flows that we invert from two geomagnetic field models (gufm1 and COV-OBS), and apply Principal Component Analysis and Singular Value Decomposition of coupled fields. The quasi geostrophic (QG) flows inverted from both geomagnetic field models show similar features. However, COV-OBS has a less energetic mean and larger time variability. The statistical significance of flow components is tested from analyses performed on subareas of the whole domain. Bootstrapping methods are also used to extract significant flow features required by both gufm1 and COV-OBS.Three main empirical circulation modes emerge, simultaneously constrained by both geomagnetic field models and expected to be robust against the particular a priori used to build them (large scale QG dynamics). Mode 1 exhibits three large vortices at medium/high latitudes, with opposite circulation under the Atlantic and the Pacific hemispheres. Mode 2 interestingly accounts for most of the variations of the Earth's core angular momentum. In this mode, the regions close to the tangent cylinder and to the equator are correlated, and oscillate with a period between 80 and 90 years. Each of these two modes is energetic enough to alter the mean flow, sometimes reinforcing the eccentric gyre, and other times breaking it up into smaller circulations. The three main circulation modes added together to the mean flow account for about 70% of the flows variability, 90% of the root mean square total velocities, and 95% of the secular variation induced by the total flows.Direct physical interpretation of the computed modes is not straightforward. Nonetheless, similarities found between the two first modes and time/spatial features identified in different studies of core dynamics, suggest that our approach can help to pinpoint the relevant physical processes inside the core on centennial timescales.

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Characteristics of the Secular Variation and Secular Acceleration Distributions of the Main Geomagnetic Field from the CHAMP Satellite

Kang

Gao

Chen

et al. 2009

Chinese J of Geophysics

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Using the new geomagnetic model POMME‐4.2S derived from the CHAMP satellite data, we have analyzed the characteristics of the distributions of seven secular variation components and three secular acceleration components , Ÿ , in China and the world. We also compared the differences of the distributions between the secular variation models POMME‐4.2S and CGRF‐SV (Chinese Geomagnetic Reference Field‐Secular Variation). The results suggest that the quadrupole plays the main role in the geomagnetic secular variation, and the octupole occupies the largest portion in the contribution to the secular acceleration. The decrease of global secular variation is much larger than its increase in 2004.0 A.D. in the background of a decreasing trend of the geomagnetic field. The secular acceleration changes more at middle and low latitudes than that at higher latitudes. Moreover, the negative and positive magnetic anomalies of Ÿ and components form several alternating areas along longitudes, and these two kinds of anomalies of component are nearly symmetrical to the equator. An evident relationship is present for the magnetic anomaly distributions of the three secular acceleration components , Ÿ , . That is, the foci of magnetic anomalies exist in the south and north, and Ÿ in the east and west sides of the foci of magnetic anomalies. The amounts of change of the secular variation and acceleration in China are small and their distributions are relatively uniform.

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Periodical Characteristics of the Geomagnetic Secular Variation and Decadal Length‐of‐Day Variation

Cited by 4 publications

References 30 publications

Geomagnetic variation on decadal time scales: What can we learn from Empirical Mode Decomposition?

Geomagnetic variation on decadal time scales: What can we learn from Empirical Mode Decomposition?

Variability modes in core flows inverted from geomagnetic field models

Characteristics of the Secular Variation and Secular Acceleration Distributions of the Main Geomagnetic Field from the CHAMP Satellite

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