Earth’s Magnetic Field and Ocean Circulation
Friday, 19. June 2009, 13:36:10
I have often written about the importance of ocean circulation for our climate. Is ocean circulation also responsible for the Earth’s magnetic field?
The earth is one big magnet with a magnetic north pole and a magnetic south pole. A magnetic field can be created by electrical currents. This is the base of the dynamo theory. Because liquid iron is a good conductor, it has been theorised that the Earth’s core might be the moving conductor required of a dynamo. Liquid iron in the core could be stirred into convective motion by heat generated from radioactivity in the core. How such a process would work is a bit of a mystery, but nevertheless this motion is thought to produce both the electric currents and the electric field needed to sustain a dynamo in the core. The existence of the magnetic field itself is taken as evidence that Earth’s outer core is liquid iron. Fortunately we also have seismic evidence that the outer core is fluid.
In short, scientists are not quite sure what creates the Earth's magnetic field, and that after 400 years of discussion, and in spite of text book explanations in line with my previous paragraph. Nevertheless the Earth's magnetosphere produced by the magnetic field is extremely important as the only buffer between us and deadly solar wind of charged particles (made up of electrons and protons). New research raises question marks about the forces behind the magnetic field and the structure of Earth itself. A controversial new paper on this topic published in New Journal of Physics titled ‘Secular variation of the Earth’s magnetic field: induced by the ocean flow?’ will no doubt cause vigorous debate, and possibly strong opposition. (The full text is freely available! - I strongly appreciate that).
The paper is full of equations, which I shall not comment. Interesting is a reference to Gallet et al 2005, who discovered a correlation between secular variation and the climate in Western Europe: the latter is strongly influenced by the atmospheric North Atlantic Oscillation, which is the driving force behind the variability of the North Atlantic gyre circulation (Curry and McCartney 2001).
Salt water conducts electricity, and according to the author there is a striking temporal correlation between the intensity of the North Atlantic oceanic circulation and the rate of secular variation in Western Europe; this explains, in particular, the hitherto unexplained geomagnetic jerks of 1969, 1978, 1991 and 1998 (De Michelis and Tozzi 2005), and the recently discovered correlation between secular variation and climate. Spatial correlation between ocean currents and secular variation is also strong.
At this stage I would like to stress that correlation as such does not imply causation!
If secular variation of the Earth’s magnetic field is caused by the ocean flow, the entire concept of the dynamo operating in the Earth’s core is called into question: there exists no other evidence of hydrodynamic flow in the core.
Note: The Earth's magnetic field is slowly changing on time scales that range from years to millennia. Such changes are referred to as secular variation (as opposed to periodic variation).
Reference:
Secular variation of the Earth's magnetic field: induced by the ocean flow?
By Gregory Ryskin
2009 New J. Phys. 11 063015 (23pp) doi: 10.1088/1367-2630/11/6/063015
• http://www.iop.org/EJ/abstract/1367-2630/11/6/063015
• http://www.eurekalert.org/pub_releases/2009-06/iop-tem061309.php
• http://www.sciencedaily.com/releases/2009/06/090615094038.htm
• http://www.physorg.com/news164253692.html
• http://www.geologytimes.com/research/The_Earths_magnetic_field_remains_a_charged_mystery.asp
• http://www.iop.org/News/news_35352.html
The earth is one big magnet with a magnetic north pole and a magnetic south pole. A magnetic field can be created by electrical currents. This is the base of the dynamo theory. Because liquid iron is a good conductor, it has been theorised that the Earth’s core might be the moving conductor required of a dynamo. Liquid iron in the core could be stirred into convective motion by heat generated from radioactivity in the core. How such a process would work is a bit of a mystery, but nevertheless this motion is thought to produce both the electric currents and the electric field needed to sustain a dynamo in the core. The existence of the magnetic field itself is taken as evidence that Earth’s outer core is liquid iron. Fortunately we also have seismic evidence that the outer core is fluid.
In short, scientists are not quite sure what creates the Earth's magnetic field, and that after 400 years of discussion, and in spite of text book explanations in line with my previous paragraph. Nevertheless the Earth's magnetosphere produced by the magnetic field is extremely important as the only buffer between us and deadly solar wind of charged particles (made up of electrons and protons). New research raises question marks about the forces behind the magnetic field and the structure of Earth itself. A controversial new paper on this topic published in New Journal of Physics titled ‘Secular variation of the Earth’s magnetic field: induced by the ocean flow?’ will no doubt cause vigorous debate, and possibly strong opposition. (The full text is freely available! - I strongly appreciate that).
The paper is full of equations, which I shall not comment. Interesting is a reference to Gallet et al 2005, who discovered a correlation between secular variation and the climate in Western Europe: the latter is strongly influenced by the atmospheric North Atlantic Oscillation, which is the driving force behind the variability of the North Atlantic gyre circulation (Curry and McCartney 2001).
Salt water conducts electricity, and according to the author there is a striking temporal correlation between the intensity of the North Atlantic oceanic circulation and the rate of secular variation in Western Europe; this explains, in particular, the hitherto unexplained geomagnetic jerks of 1969, 1978, 1991 and 1998 (De Michelis and Tozzi 2005), and the recently discovered correlation between secular variation and climate. Spatial correlation between ocean currents and secular variation is also strong.
At this stage I would like to stress that correlation as such does not imply causation!
If secular variation of the Earth’s magnetic field is caused by the ocean flow, the entire concept of the dynamo operating in the Earth’s core is called into question: there exists no other evidence of hydrodynamic flow in the core.
Note: The Earth's magnetic field is slowly changing on time scales that range from years to millennia. Such changes are referred to as secular variation (as opposed to periodic variation).
Reference:
Secular variation of the Earth's magnetic field: induced by the ocean flow?
By Gregory Ryskin
2009 New J. Phys. 11 063015 (23pp) doi: 10.1088/1367-2630/11/6/063015
• http://www.iop.org/EJ/abstract/1367-2630/11/6/063015
• http://www.eurekalert.org/pub_releases/2009-06/iop-tem061309.php
• http://www.sciencedaily.com/releases/2009/06/090615094038.htm
• http://www.physorg.com/news164253692.html
• http://www.geologytimes.com/research/The_Earths_magnetic_field_remains_a_charged_mystery.asp
• http://www.iop.org/News/news_35352.html
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