Jakub Velímský

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

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 (SatelliteConstellationApplication andResearchFacility) 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.

Determination of three-dimensional distribution of electrical conductivity in the Earth’s mantle from Swarm satellite data: Time-domain approach

One of the primary goals of the Swarm multisatellite mission is to determine the 3-D distribution of electrical conductivity in the Earth’s mantle. This paper presents an inversion method based on direct integration of magnetic fields in the time domain, and using the adjoint solution for fast evaluation of data sensitivities to model perturbations. Two tests of the method are presented. The first one is using a 3-D checkerboard conductivity model and noise-free synthetic data. The second test is based on the closed-loop simulation of Swarm mission, including recovery of external and induced fields from simulated data along satellite tracks, and realistic noise estimates.

Compositional and thermal equilibration of particles, drops, and diapirs in geophysical flows

Core formation, crystal/melt separation, mingling of immiscible magmas, and diapirism are fundamental geological processes that involve differential motions driven by gravity. Diffusion modifies the compo- sition or/and temperature of the considered phases while they travel. Solid particles, liquid drops and viscous diapirs equilibrate while sinking/rising through their surroundings with a time scale that depends on the physics of the flow and the material properties. In particular, the internal circulation within a liquid drop or a diapir favors the diffusive exchange at the interface. To evaluate time scales of chemical/thermal equilibration between a material falling/rising through a deformable medium, we propose analytical laws that can be used at multiple scales. They depend mostly on the non-dimensional Peclet and Reynolds numbers, and are consistent with numerical simulations. We show that equilibration between a particle, drop or diapir and its host needs to be considered in light of the flow structure complexity. It is of fundamental importance to identify the dynamic regime of the flow and take into account the role of the inner circulation within drops and diapirs, as well as inertia that reduces the thickness of boundary layers and enhances exchange through the interface. The scaling laws are applied to predict nickel equilibration between metals and silicates that occurs within 130 m of fall in about 4 minutes during the metal rain stage of the Earths core formation. For a mafic blob (10 cm diameter) sinking into a felsic melt, trace element equilibration would occur over 4500 m and in about 3 years.

Decadal period external magnetic field variations determined via eigenanalysis

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 mid- 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 (SHA) 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 semi-annual and solar-cycle-length periods appear to stem from the amplitude modulations of spatially fixed background fields.

Effect of a metallic core on transient geomagnetic induction

Magnetic fields due to the magnetospheric ring current, together with their induced counterparts, must be correctly taken into account when modeling the geomagnetic field using modern observatory and satellite measurements. It is common practice to parameterize the induced field using a response function depending on a spherically symmetric electrical conductivity model of the solid Earth. Here we show that Earths metallic core should be included in such conductivity models, which has not previously been the case. Abrupt changes in the amplitude of the ring current during geomagnetic storms excite a wide range of frequencies, some of which can induce electrical currents in the core. These currents decay very slowly because of the high conductivity of the core; the resulting induced field will therefore not be of zero mean even when averaged over many years. We present the results of time domain numerical simulations of induction that demonstrate the influence of a conducting core in an idealized experiment based on a synthetic geomagnetic storm. Moving to a more realistic scenario we show that taking 50 years of Dst(t) index as an input, an induced field Ist(t) with a mean value (when averaged over 10 years) of up to −1.5 nT is obtained. We conclude that transient induction in the metallic core caused by magnetospheric field variations must be included in accurate portrayals of the near-Earth magnetic environment.

Electromagnetic Induction by Sq Ionospheric Currents in a Heterogeneous Earth: Modeling Using Ground-based and Satellite Measurements

We have created a database consisting of hourly means of the geomagnetic field components observed on quiet days in years 2001–2002 on ground observatories, and Orsted and CHAMP satellite measurements covering the same time intervals. In the first part of our study, we use the potential method to estimate the model of external inducing field. Following 3-D simulations are used to evaluate the effect of heterogeneous surface conductance map on Orsted and CHAMP satellite measurements and to compare the results with observations. Improvement of up to 15% with respect to the best 1-D model was observed in surface observatory data as well as in the Orsted and CHAMP measurements.

The influence of adiabatic heating/cooling on magnetohydrodynamic systems

Abstract We have studied the influence of the dissipation number on the behaviour of a magnetohydrodynamic system in a rotating liquid Cartesian box in the presence of a finitely conducting solid box beneath the liquid. The dissipation number appears in dimensionless description of the three physical mechanisms in the heat equation: the adiabatic heating/cooling, the dissipative heating and the Joule heating. We have demonstrated that the adiabatic heating/cooling can strongly suppress the horizontal gradient of temperature, if the surface temperature is of the same order as the temperature drop over the liquid layer. This effect stabilizes the convection pattern. We hypothesize that the adiabatic heating/cooling could be the substantial stabilizing mechanism in systems with a high Rayleigh number, which seem to be suitable for the description of the magnetohydrodynamics of the Earths core.