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Your search keyword '"Velímský, J."' showing total 14 results
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14 results on '"Velímský, J."'

1. Satellite monitoring of long period ocean-induced magnetic field variations

Author

Finlay, C. C., Velímský, J., Kloss, C., and Blangsbøll, R. M.

Subjects
Physics - Geophysics
Abstract

Satellite magnetic field observations have the potential to provide valuable information on dynamics, heat content and salinity throughout the ocean. Here we present the expected spatio-temporal characteristics of the ocean-induced magnetic field at satellite altitude on periods of months to decades. We compare these to the characteristics of other sources of Earth's magnetic field, and discuss whether it is feasible for the ocean-induced magnetic field to be retrieved and routinely monitored from space. We focus on large length scales (spherical harmonic degrees up to 30) and periods from one month up to five years. To characterize the expected ocean signal we make use of advanced numerical simulations taking high resolution oceanographic inputs and solve the magnetic induction equation in 3D including galvanic coupling and self induction effects. We find the time-varying ocean-induced signal dominates over the primary source of the internal field, the core dynamo, at high spherical harmonic degree with the cross-over taking place at degree 15 to 20 depending on the considered period. The ionospheric and magnetospheric fields (including their Earth induced counterparts) have most power on periods shorter than one month and are expected to be mostly zonal in magnetic coordinates at satellite altitude. Based on these findings we discuss future prospects for isolating and monitoring long period ocean induced magnetic field variations using data collected by present and upcoming magnetic survey satellites.

Published
2024

2. Electrical conductivity of the suboceanic upper mantle constrained by satellite-derived tidal magnetic fields: three-dimensional inversion, validation and interpretation.

Author

Šachl, L, Knopp, O, and Velímský, J

Subjects
ROSSBY waves, FINITE element method, WATER distribution, ELECTRIC conductivity, MAGNETIC fields, ELECTRICAL conductivity measurement
Abstract

SUMMARY: We present the first 3-D upper-mantle conductivity models obtained by an inversion of the satellite-derived tidally induced magnetic fields (TIMFs). We primarily use the M $_2$ period, but the potential benefit of the O $_1$ period is also inspected. The inverse-problem solution is found using the recently developed frequency-domain, spherical harmonic finite-element method based on the adjoint approach. We tested two different TIMF data sets derived from the satellite measurements of the Swarm mission and two different regularizations; the solution is either required to be sufficiently smooth or reasonably close to the a priori 3-D conductivity model WINTERC-e Wd-emax. The reconstructed conductivity models are locally compared with the 1-D conductivity profiles from other studies. If we use one of the available TIMF data sets, the smooth reconstructed model gravitates towards Wd-emax and the TIMF-adjusted Wd-emax model is closer to the reference conductivity profiles than the original Wd-emax model. Finally, we use the obtained 3-D conductivity distributions to calculate the corresponding 3-D water distribution in the upper mantle using thermodynamical and compositional models coupled to the electrical-conductivity laboratory measurement of individual mantle constituents. [ABSTRACT FROM AUTHOR]

Published
2024
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3. Sensitivity of Swarm magnetic data to lateral variations of the electrical conductivity in the lower mantle

Author

Velímský, J. and Martinec, Z.

Abstract

The large-scale electrical conductivity structures in the deep Earth's mantle can be in principle determined from Swarm-observed induction response to time-variable magnetospheric currents. Here we present a new sensitivity study based on the 3-D time-domain modelling of the electromagnetic induction in the Earth's mantle, aimed at the lowermost mantle. So far, these efforts have been encumbered by limited spatio-temporal description of the magnetospheric field from moving satellite platforms. In particular, the polar electrojets (PEJs) and field-aligned currents (FACs) are sources of a strong bias in the spherical-harmonic analysis of Swarm magnetic data. Our approach exploits the recently introduced improvements to the processing of Swarm magnetic data. An electric circuit model of PEJs and FACs provides a novel data processing tool to suppress the bias and provide a reliable model of the large-scale magnetospheric field during magnetically disturbed times. In this contribution we determine the sensitivity and resolution of the inverse problem, and proceed with regularized 1-D and 3-D inversions to update the electrical conductivity model of the lower mantle., The 28th IUGG General Assembly (IUGG2023) (Berlin 2023)

Published
2023
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6. Benchmark study of magnetic induction codes forced by ocean tides

Author

Velímský, J., Einšpigel, D., Grayver, A., Irrgang, C., Kuvshinov, A., Martinec, Z., Petereit, J., Šachl, L., Saynisch, J., and Tyler, R.

Subjects
Physics::Geophysics
Abstract

We present a benchmark of magnetic induction codes driven by the ocean tidal flows. We concentrate on the principal lunar semi-diurnal tide M2, using the state-of-the-art TPXO8-atlas ocean flow model. We assess the effect of the two-dimensional thin-layer approximation, and the effect of self-induction. Large lateral variations of ocean electrical conductivity are assumed. For the underlaying Earth’s mantle we consider either a realistic one-dimensional conductivity profile, or use a perfect insulator approximation. Various numerical techniques are compared, including weak formulation in the spherical harmonic domain, contracting integral equations, and finite differences, both in the frequency and time domains. We compare the maps of magnetic field components at the ocean surface, as well as the spherical harmonic power spectra.

Published
2017

8. Decadal period external magnetic field variations determined via eigenanalysis

Author

Shore, R. M., Whaler, K. A., Macmillan, S., Beggan, C., Velímský, J., Olsen, Nils, Shore, R. M., Whaler, K. A., Macmillan, S., Beggan, C., Velímský, J., and Olsen, Nils

Abstract

We perform a reanalysis of hourly mean magnetic data from ground-based observatories spanning 1997-2009 inclusive, in order to isolate (after removal of core and crustal field estimates) the spatiotemporal morphology of the external fields important to mantle induction, on (long) periods of months to a full solar cycle. Our analysis focuses on geomagnetically quiet days and middle to low latitudes. We use the climatological eigenanalysis technique called empirical orthogonal functions (EOFs), which allows us to identify discrete spatiotemporal patterns with no a priori specification of their geometry-the form of the decomposition is controlled by the data. We apply a spherical harmonic analysis to the EOF outputs in a joint inversion for internal and external coefficients. The results justify our assumption that the EOF procedure responds primarily to the long-period external inducing field contributions. Though we cannot determine uniquely the contributory source regions of these inducing fields, we find that they have distinct temporal characteristics which enable some inference of sources. An identified annual-period pattern appears to stem from a north-south seasonal motion of the background mean external field distribution. Separate patterns of semiannual and solar-cycle-length periods appear to stem from the amplitude modulations of spatially fixed background fields.

Published
2016

10. The Swarm Satellite Constellation Application and Research Facility (SCARF) and Swarm data products

Author

Olsen, N., Friis-Christensen, E., Floberghagen, R., Alken, P., Beggan, Ciaran D., Chulliat, A., Doornbos, E., da Encarnação, J. T., Hamilton, Brian, Hulot, G., von den IJssel, J., Kushinov, A., Lesur, V., Lühr, H., Macmillan, Susan, Maus, S., Noja, M., Olsen, P. E. H., Park, J., Plank, G., Püthe, C., Rauberg, J., Ritter, P., Rother, M., Sabaka, T., Schachtschneider, R., Sirol, O., Stolle, C., Thébault, E., Thomson, Alan W.P., Tøffner-Clausen, L., Velímský, J, Vigneron, P., Visser, P. N., Olsen, N., Friis-Christensen, E., Floberghagen, R., Alken, P., Beggan, Ciaran D., Chulliat, A., Doornbos, E., da Encarnação, J. T., Hamilton, Brian, Hulot, G., von den IJssel, J., Kushinov, A., Lesur, V., Lühr, H., Macmillan, Susan, Maus, S., Noja, M., Olsen, P. E. H., Park, J., Plank, G., Püthe, C., Rauberg, J., Ritter, P., Rother, M., Sabaka, T., Schachtschneider, R., Sirol, O., Stolle, C., Thébault, E., Thomson, Alan W.P., Tøffner-Clausen, L., Velímský, J, Vigneron, P., and Visser, P. N.

Abstract

Swarm, a three-satellite constellation to study the dynamics of the Earth's magnetic field and its interactions with the Earth system, is expected to be launched in late 2013. The objective of the Swarm mission is to provide the best ever survey of the geomagnetic field and its temporal evolution, in order to gain new insights into the Earth system by improving our understanding of the Earth's interior and environment. In order to derive advanced models of the geomagnetic field (and other higher-level data products) it is necessary to take explicit advantage of the constellation aspect of Swarm. The Swarm SCARF (Satellite Constellation Application and Research Facility) has been established with the goal of deriving Level-2 products by combination of data from the three satellites, and of the various instruments. The present paper describes the Swarm input data products (Level-1b and auxiliary data) used by SCARF, the various processing chains of SCARF, and the Level-2 output data products determined by SCARF.

Published
2013

14. On the modelling of M 2 tidal magnetic signatures: effects of physical approximations and numerical resolution.

Author

Velímský J, Grayver A, Kuvshinov A, and Šachl L

Abstract

The magnetic signatures of ocean M 2 tides have been successfully detected by the low-orbit satellite missions CHAMP and Swarm. They have been also used to constrain the electrical conductivity in the uppermost regions of the Earth's mantle. Here, we concentrate on the problem of accurate numerical modelling of tidally induced magnetic field, using two different three-dimensional approaches: the contraction integral equation method and the spherical harmonic-finite element method. In particular, we discuss the effects of numerical resolution, self-induction, the galvanic and inductive coupling between the oceans and the underlying mantle. We also study the applicability of a simplified two-dimensional approximation, where the ocean is approximated by a single layer with vertically averaged conductivity and tidal forcing. We demonstrate that the two-dimensional approach is sufficient to predict the large-scale tidal signals observable on the satellite altitude. However, for accurate predictions of M 2 tidal signals in the areas with significant variations of bathymetry, and close to the coastlines, full three-dimensional calculations are required. The ocean-mantle electromagnetic coupling has to be treated in the full complexity, including the toroidal magnetic field generated by the vertical currents flowing from and into the mantle.

Published
2018
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