October 26th, 2012 by James Ayre
Short-term changes in the Earth’s magnetic field that occur over periods of just years or decades have now been shown in new research to have a very close relationship with changes in gravity. The research focused on a specific area, stretching from the Atlantic to the Indian Ocean. In this area, changes in the magnetic field correlate very closely with variations in gravity. The researchers concluded that this means that processes occurring in the outer core have an influence on gravity.
The primary field of the Earth’s magnetic field is created by the swirling masses of liquid iron that are in the outer core. Without the magnetic field, there would be vastly more cosmic radiation reaching the surface of the Earth. Improving our understanding of the processes that occur in the outer core is therefore essential to understanding the magnetic shield, and it’s influence on life. “Key to this are measurements of the geomagnetic field itself,” a news release on this matter notes. “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 (theoretically) with mass displacements. The research group has now succeeded to provide the first evidence of such a connection of fluctuations in Earth’s gravity and magnetic field.”
The researchers utilized magnetic field measurements taken by the GFZ-satellite CHAMP and some extremely accurate measurements of Earth’s gravity field derived from the GRACE mission.
“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. “The 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.”
“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.”
For the research, the work was focused on an area located between the Atlantic and the Indian Ocean. The currents flows in this area had previously been determined to be the highest in this region. “Extremely fast changes (so-called magnetic jerks) were observed in the year 2007 at 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 Earth’s core. Using the satellite data, a clear signal of gravity data from Earth’s core could be received for the first time.”
The findings of this research upends many existing conceptual models, contradicting assumptions made by them. As an example, it has long been assumed that density differences in the molten iron of the Earth’s core were too limited to create “a measurable signal in Earth’s gravitational field.” This research has resulted in the need for new approaches to the study of the Earth’s core hydrodynamics.
The new research was just published in the latest issue of Proceedings of the National Academy of Sciences of the United States.
Source: Helmholtz Centre Potsdam – GFZ German Research Centre for Geosciences
Image Credits: University of Liverpool
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