Earth Interior I: Core & Mantle

By far the largest part of the Earth's magnetic field is generated by motions taking place within our planet's liquid metal outer core.  Variations of this core-generated field thus provide us with a unique means of probing the dynamics taking place in the deepest reaches of the Earth.  In this contribution, we will present the core-generated magnetic field, and its recent time changes, as seen by ESA's Earth explorer mission Swarm.    

We will present a new time-dependent geomagnetic field model, called CHAOS-6, derived from satellite data collected by the Swarm constellation, as well as data from the previous missions CHAMP and Oersted together with ground observatory data.  Advantage is taken of the constellation aspect of the Swarm mission by ingesting field differences along track and across track between the lower pair of Swarm satellites. Evaluating the global field model at the outer boundary of the source region, the core-mantle boundary, we present maps of the detailed structure of the geodynamo, and how this is presently evolving.  Both the trend (secular variation) and accelerations in the field changes since the launch of the Swarm mission will be presented.  

Assuming that field changes are primarily a result of advective processes, thanks to the high electrical conductivity of the core, and that the responsible core flows are essentially columnar, due to the organizing influence of the Coriolis force, we derive maps of the underlying core flow. The structure of this core flow, its changes over recent years, and implications for our understanding of the geodynamo process will be discussed.

A time-domain approach to the global inversion of observatory and satellite data in terms
of 3-D electrical conductivity structure of the mantle has been developed in the
preparation of the L2 products for the Swarm mission (Velímský 2013). This approach
relies on the separation of individual contributions to the total geomagnetic
field by means of comprehensive modeling (Sabaka et al. 2013), and inversion of the
series of spherical harmonic coefficients of magnetospheric fields and their
induced counterparts by regularized quasi-Newton minimization of data misfit.
The results based on the inversion of first 2.5 years of data will be presented.

The study of the South Atlantic Anomaly is an important challenge nowadays not only for the geomagnetic and paleomagnetic community, but also for other areas focused on the Earth Observation. This large magnetic anomaly is characterized by values of geomagnetic field intensity around 30% lower than expected for those latitudes and covers a large area in the South Atlantic Ocean between Southwest Brazil and South Africa. This great depression of the geomagnetic field strength at the Earth's surface has an internal deep origin: it is caused by a prominent patch of reversed polarity flux in the terrestrial outer core, and could be even a precursor of an imminent geomagnetic polarity reversal or excursion. Since the Earth's magnetic field has an important protective role for the all geosphere because it deflects a large part of the solar radiation that would otherwise reach the Earth's surface, a larger increase of this anomaly could have dramatic consequences for human health and technologies. In this context, we present TEMPO (Is The Earth's Magnetic field POtentially reversing? New insights from Swarm mission) a 2-year research project co-funded by The Living Planet Programme of ESA and the INGV (Rome, Italy). The main objective of TEMPO is to analyse in detail the evolution of the South Atlantic Anomaly using the new magnetic dataset provided by the Swarm three-satellite mission and all the available data over the area of interest covering the geomagnetic instrumental period.

Oceans cover about seventy percent of the Earth and yet the overwhelming majority of seismological or electromagnetic (EM) observatories are found on continents. This provides a challenge for understanding composition, structure, and dynamics of Earth’s lithosphere and upper mantle in oceanic regions. The recent expansion in magnetic data from low-Earth orbiting satellite missions (Ørsted, CHAMP, SAC-C, and Swarm) has led to a rising interest in probing Earth from space. The largest benefit of using satellite data is much improved spatial coverage. Additionally, and in contrast to ground-based data, satellite data are overall uniform and very high quality.

Probing the conductivity of the lithosphere and upper mantle requires EM variations with periods of a few hours. Electric currents generated by oceanic tides are a well-suited source within this period range. Ocean tides interact galvanically with Earth’s lithosphere (i.e. by direct coupling of the source currents in the ocean with the underlying substrate), enabling conductivity estimations at shallower depths.

Here we present the results of determining a 1-D conductivity-depth profile of oceanic lithosphere and upper mantle using  satellite and seafloor magnetic signals from the M2 ocean tide. With these data we also make an attempt to detect lateral variability of the Earth’s conductivity.

A major uncertainty in determining the mass balance of the Antarctic ice sheet from satellite gravimetry, and to a lesser extent altimetry, measurements is the poorly known correction for the ongoing deformation of the solid Earth caused by glacial isostatic adjustment (GIA). Although much progress has been made in consistently modelling ice-sheet evolution and related bedrock deformation, predictions of GIA remain ambiguous due to the lack of observational constraints. Here, we present an improved regional GIA estimate based on GRACE, Envisat/ICESat/CryoSat-2 and GPS measurements. Making use of the different sensitivities of the satellite observations to surface-mass and solid Earth processes, we estimate GIA using viscoelastic response functions to a disc load forcing, distributed according to estimates of the variation of lithosphere thickness and mantle viscosity in Antarctica. The estimated GIA signal is interpreted for recent ice load changes in West Antarctica in the presence of a low-viscosity upper mantle and a ductile layer in the elastic lithosphere. We compare the GIA estimate with published GIA estimates and results from numerical modelling, and evaluate its impact on the determination of ice-mass balance in Antarctica from GRACE and CryoSat-2. The results presented here are the final results of the Support To Science Element Project REGINA and its Supplementary Study of the European Space Agency, www.regina-science.eu.