MessageToEagle.com - Rapid, almost sudden, changes take place in the Earth’s magnetic field.
A German-French group of geophysicists observed that - changes in the earth's magnetic field in
a region stretching from the Atlantic to the Indian Ocean - have a close relationship with variations of gravity in this area.
From this it can be concluded that outer core processes are reflected in gravity data. This is the result presented by scientists
in the latest issue of PNAS.
The main field of the Earth's magnetic field is generated by flows of liquid iron in the outer core. The Earth's magnetic
field protects us from cosmic radiation particles.
Therefore, understanding the processes in the outer core is important
to understand the terrestrial shield. Key to this are measurements of the geomagnetic field itself.
A second, independent access could be represented by the measurement of minute changes in gravity caused by the fact that
the flow in the liquid Earth's core is associated with mass displacements.
The research group has now succeeded to provide the first evidence of
such a connection of fluctuations in the Earth's gravity and magnetic field.
They used magnetic field measurements of the GFZ-satellite CHAMP and extremely accurate measurements of the Earth's gravity
field derived from the GRACE mission, which is also under the auspices of the GFZ.
"The main problem was the separation of the individual components of the gravity data from the total signal," explains
Vincent Lesur from the GFZ German Research Centre for Geosciences, who is involved in the study.
Simulated three-dimensional structure of Earth's magnetic field, with inward (blue) and outward (yellow) directed field lines. Field lines extend two Earth radii from the core.
The location of the core-mantle boundary is evident where the structure becomes complex. Credits: G. Glatzmaier, Los Alamos National Laboratory.
P. Roberts, University of California-Los Angeles
A satellite only measures the total gravity, which consists of the
mass fractions of Earth's body, water and ice on the ground and in the air. To determine the mass redistribution by flows
in the outer core, the thus attained share of the total gravity needs to be filtered out.
Cutaway views showing the internal structure of the Earth. Left: This scale drawing shows that the Earth's crust is literally only skin deep.
Right: A view not drawn to scale showing the Earth's three main layers (crust, mantle, and core) in more detail.
"Similarly, in order to capture the smaller changes in the outer core, the proportion of the magnetic crust and the
proportion of the ionosphere and magnetosphere need to be filtered out from the total magnetic field signal measured by
the satellite," Vincent Lesur explains. The data records of the GFZ-satellite missions CHAMP and GRACE enabled this for
the first time.
During the investigation, the team focused on an area between the Atlantic and the Indian Ocean, as the determined currents
flows were the highest here. Extremely fast changes (so-called magnetic jerks) were observed in the year 2007 at the
Earth's surface. These are an indication for sudden changes of liquid flows in the upper outer core and are important for
understanding the magneto-hydrodynamics in the Earth's core.
Using the satellite data, a clear signal of gravity data from the Earth's core could be received for the first time.
This results in consequences for the existing conceptual models. Until now, for example, it was assumed that the differences
in the density of the molten iron in the earth's core are not large enough to generate a measurable signal in the earth's
gravitational field. The newly determined mass flows in the upper outer core allow a new approach to Earth's core hydrodynamics.
“Recent changes of the Earth’s core derived from satellite observations of magnetic and gravity fields”, Mioara Mandea,
Isabelle Panet, Vincent Lesur, Olivier de Viron, Michel Diament, and Jean-Louis Le Mouël,
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