Reply to Comment by M. Dumberry [on “Could the Mw> = 9.3 Sumatra Earthquake trigger a geomagnetic jerk?”]
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Abstract:
We thank M. Dumberry for providing the opportunity to discuss further the article [ Florindo et al. , 2005] in which we suggested that the Sumatra earthquake could have triggered a geomagnetic jerk. Dumberry is against our hypothesis for different reasons: (1) The displacement pattern produced by this earthquake is incompatible with the core‐mantle boundary (CMB) deformations required for a torsional oscillation; (2) most of the deformations occurred locally, producing an actual mass displacement that has not involved the entire Earth; and (3) no abrupt change in the length of day (LOD) has been observed after this event.Keywords:
Jerk
Jerk
Geomagnetic secular variation
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Jerk
Intermittency
Geomagnetic secular variation
Morlet wavelet
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The results of instrumental observations of variations of Earth's magnetic field, which have been obtained on the basis of the North Caucasus Geophysical Observatory IPE (Elbrus volcanic area), and the incorporation of observation points Troitsk, located in the European part of Russia. Analyzed abnormal «quasi-harmonic» disturbance marked variations in the Earth's magnetic field at all stages of the seismic process. The experimental data give a general idea of the geomagnetic activity and some characteristics of the induced anomalous geomagnetic disturbances, which can be co-delivered with the development of related geodynamic and geoelectric processes in the subsurface of the focal zone.
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The nature of geomagnetic field behavior during polarity transitions is one of the most hotly debated issues in modern geophysics. Dynamo action in the earth's fluid outer core is known to be responsible for generating the earth's main magnetic field, however, the mechanism for polarity transition is still unknown. Polarity transitions are a fundamentally important property of the geomagnetic field, but because they have not taken place in historic time, it is necessary to turn to the paleomagnetic record to understand the mechanism by which they occur.
Polarity (international relations)
Polarity reversal
Geomagnetic secular variation
Ionospheric dynamo region
Geomagnetic pole
Geomagnetic reversal
Outer core
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Jerk model for tracking highly maneuvering targets is investigated. Through theoretical analysis, it is shown that the filter, based on jerk model, may suffer from deterministic steady state estimation errors. To find the solution to this question, a current statistic Jerk model, for a short CS Jerk, is developed, in which the jerk maneuvering is assumed to be an exponential correlated random process with nonzero mean. It consists of a CS Jerk model of target motion and a tracking filter with compatible order. The steady state performance of the CS Jerk model is also analyzed and the result indicates that the CS Jerk model eliminates the performance limitation of the jerk model. The improved performance of the CS Jerk model over the jerk model is illustrated through simulation.
Jerk
Tracking (education)
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The occurrence of geomagnetic jerks over the Arctic and Antarctic regions is here investigated. Maps of geomagnetic secular acceleration over the polar regions are produced from the CM4 and CHAOS models and the occurrence of geomagnetic jerks is associated with jumps in secular acceleration. The obtained results confirm that in Antarctica geomagnetic jerks systematically follow geomagnetic jerks in the Arctic region with a time delay from one to three years. Evidence is found of an abrupt change in secular acceleration in both polar regions around 1985, suggesting that the 1985 local jerk could actually be a worldwide event. Combining our results with the results previously obtained on the occurrence of a geomagnetic jerk at low‐mid latitudes around 2003, we support the hypothesis of a global extension of an event occurred at the beginning of the 21st century.
Jerk
Geomagnetic secular variation
Secular Variation
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Geomagnetic secular variation
Ionospheric dynamo region
Geomagnetic pole
Ring current
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The geomagnetic field is generated in the fluid outer core region of the Earth by electrical currents flowing in the slowly
moving molten iron. In addition to sources in the Earth’s core, the geomagnetic field observable on the Earth’s surface has
sources in the crust and in the ionosphere and magnetosphere. The signal from the core dominates, accounting for over 95%
of the field at the Earth’s surface. The geomagnetic field varies on a range of scales, both temporal and spatial; the
description of the variations made here concentrates on the recent spatial and temporal variations of the field with origins in
the Earth’s core that can be surmised from observations made over the last four centuries.
Geomagnetic secular variation
Ionospheric dynamo region
Outer core
South Atlantic Anomaly
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Theoretical work on the magnetohydrodynamics of the earth's liquid core indicates (a) that horizontal variations in the properties of the core-mantle interface that would escape detection by modern seismological methods might nevertheless produce measurable geomagnetic effects; (b) that the rate of drift, relative to the earth's surface, of nonaxisymmetric features of the main geomagnetic field might be much faster than the average zonal speed of hydrodynamic motion of core material relative to the surrounding mantle; and (c) why magnetic astronomical bodies usually rotate. Among the consequences of (a) and (b) are the possibilities that (i) the shortest interval of time that can be resolved in paleomagnetic studies of the geocentric axial dipole component of the earth's magnetic field might be very much longer than the value often assumed by many paleomagnetic workers, (ii) reversals in sign of the geomagnetic dipole might be expected to show some degree of correlation with processes due to motions in the mantle (for example, tectonic activity, polar wandering), and (iii) variations in the length of the day that have hitherto been tentatively attributed to core motions may be due to some other cause.
Geomagnetic secular variation
Outer core
Geomagnetic pole
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The detailed behaviour of the geomagnetic field during reversals is documented by palaeomagnetists to constrain models of the geomagnetic dynamo. Reversals are studied by measuring the magnetic remanence preserved in rocks to obtain both the direction and intensity of the ancient magnetic field.
Polarity (international relations)
Geomagnetic reversal
Geomagnetic secular variation
Magnetostratigraphy
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