Variations in Earth’s magnetic field maybe due to ebb and flow of world’s oceansJune 15th, 2009 - 11:53 am ICT by ANI
Washington, June 15 (ANI): A new research by scientists in the US has linked variations in the Earth’s magnetic field with the ebb and flow of the world’s oceans.
The origin and mechanism of the Earth’s magnetic field are amongst the biggest unsolved questions in the earth sciences.
Most geophysicists agree however that the main component of the field, which defines the magnetic poles, is a dipole generated by the convection of molten iron deep within the Earth’s interior.
From studying the way magnetic minerals align in volcanic rocks, scientists know that this dipole has flipped its orientation every million years or so throughout Earth history.
Given these huge time-scales, sailors and scouts need not worry about the North Pole suddenly becoming the South, but there is another shorter-term threat to old-fashioned navigation caused by slight drifting of the magnetic field over years-to-centuries.
The origin of this “secular variation” is also thought to originate in the molten iron core, due to fluctuations in the established convection pattern.
Although small in comparison with the main dipole field, secular variation can be difficult to predict with effects substantial enough to prompt a revision of the International Geomagnetic Reference Field every five years.
Now, according to a report in Physics World, Gregory Ryskin of Northwestern University, Illinois, is offering an alternative explanation for the origin of this secular variation.
Ryskin believes that electric currents induced in dissolved salts - as ocean waters circulate through the Earth’s magnetic field - can generate secondary magnetic fields strong enough to shift the orientation of the original field.
Comparing his own calculations with public geophysical data, Ryskin links circulation in the North Atlantic with observed trends in secular variation over Western Europe.
The physicist looked specifically at the North Atlantic in isolation from other models of the Earth’s field.
He calculated the expected variation in magnetic fields between 1995 and 2000 using equations of solute transport and magnetic diffusion, and ocean circulation data from ECCO - a global reference point funded in part by NASA and the National Science Foundation (NSF).
Ryskin then compared these figures with recorded secular variations in the International Geomagnetic Reference Field (IGRF) - a publicly available resource derived from satellites, observatories and surveys around the world.
Ryskin found strong temporal and spatial correlation between his calculated secular variation and the IGRF figures between 1995 and 2000.
“If secular variation 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,” he said. (ANI)
Tags: dipole field, earth history, earth sciences, electric currents, geomagnetic, geophysical data, geophysicists, magnetic field, magnetic minerals, magnetic poles, molten iron core, northwestern university, ocean waters, physics world, secular variation, term threat, time scales, university illinois, unsolved questions, volcanic rocks