Monday, June 15, 2009
The controversial new paper published in New Journal of Physics
(co-owned by the Institute of Physics and the German Physical
Society), 'Secular variation of the Earth's magnetic field: induced
by the ocean flow?', will deflect geophysicists' attention from
postulated motion of conducting fluids in the Earth's core, the
twentieth century's answer to the mysteries of geomagnetism and
magnetosphere.
Professor Gregory Ryskin from the McCormick School of Engineering
and Applied Science at Northwestern University in Illinois, US, has
defied the long-standing convention by applying equations from
magnetohydrodynamics to our oceans' salt water (which conducts
electricity) and found that the long-term changes (the secular
variation) in the Earth's main magnetic field are possibly induced
by our oceans' circulation.
With calculations thus confirming Ryskin's suspicions, there were
also time and space correlations - specific indications of the
integral relationship between the oceans and our magnetospheric
buffer. For example, researchers had recorded changes in the
intensity of current circulation in the North Atlantic; Ryskin
shows that these appear strongly correlated with sharp changes in
the rate of geomagnetic secular variation ("geomagnetic
jerks").
Tim Smith, senior publisher of the New Journal of Physics, said,
"This article is controversial and will no doubt cause vigorous
debate, and possibly strong opposition, from some parts of the
geomagnetism community. As the author acknowledges, the results by
no means constitute a proof but they do suggest the need for
further research into the possibility of a direct connection
between ocean flow and the secular variation of the geomagnetic
field."
In the early 1920s, Einstein highlighted the large challenge that
understanding our Magnetosphere poses. It was later suggested that
the Earth's magnetic field could be a result of the flow of
electrically-conducting fluid deep inside the Earth acting as a
dynamo.
In the second half of the twentieth century, the dynamo theory,
describing the process through which a rotating, convecting, and
electrically conducting fluid acts to maintain a magnetic field,
was used to explain how hot iron in the outer core of the Earth
creates a magnetosphere.
The journal paper also raises questions about the structure of our
Earth's core.
Familiar text book images that illustrate a flow of hot and highly
electrically-conducting fluid at the core of the Earth are based on
conjecture and could now be rendered invalid. As the flow of fluids
at the Earth's core cannot be measured or observed, theories about
changes in the magnetosphere have been used, inversely, to infer
the existence of such flow at the core of the Earth.
While Ryskin's research looks only at long-term changes in the
Earth's magnetic field, he points out that, "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."
On a practical level, it means the next time you use a compass you
might need to thank the seas and oceans for influencing the force
necessary to guide the way.
Dr Raymond Shaw, professor of atmospheric physics at Michigan
Technological University, said, "It should be kept in mind that the
idea Professor Ryskin is proposing in his paper, if valid, has the
potential to deem irrelevant the ruling paradigm of geomagnetism,
so it will be no surprise to find individuals who are strongly
opposed or critical."
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Institute of Physics
Thanks to Institute of Physics for this article.