Posted on 01/11/2003 10:28:03 AM PST by blam
Magnetic effect of ocean flow revealed
19:00 09 January 03
NewScientist.com news service
Tiny magnetic fields created by ocean tides have been mapped globally for the first time, after researchers filtered out the signal from satellite data.
Improving the technique so that the magnetic fields created by all the ocean's motions can be picked out would provide a valuable new way to track global ocean circulation and climate change. It would be especially useful for monitoring deep water currents, as these cannot be seen by the current measurements of water colour or wave height.
This is possible - at least in theory - says Robert Tyler, at the University of Washington in Seattle, who created the new map with colleagues in Germany.
"It opens up a new area of research," comments geophysicist Michael Purucker, at the NASA Goddard Space Flight Center, near Washington DC. "But we're not going to know if tracking is possible until we try."
Positive and negative
The Earth's magnetic field is created primarily by the flow of molten iron in the planet's core. But other factors affect the field too, like the magnetisation of rocks in the crust and the flow of the ocean.
Dissolved salts in ocean waters exist as positive and negative ions, like sodium and chloride. As water flows around the planet, these ions are deflected by the Earth's magnetic field - positive ions are pushed one way, negative ions the other.
This builds up volumes of positively and negatively charged water, sometimes on a scale of thousands of kilometres. As the particles move to reduce this charge separation they create loops of electric current in the water. These, in turn, induce magnetic fields.
These induced fields are tiny compared to the Earth's overall field, which is 6000 times stronger. But it is still the biggest part of the Earth's field left to be modelled and mapped by geophysicists. So Tyler's team looked at magnetic field data from the CHAMP satellite to see if they could pick out the ocean's contribution.
Frequency match
They found a signal that matched their computer model of the effect by filtering out tiny fluctuations that had the same frequency as the tides. The biggest fields were generated, unsurprisingly, in parts of the ocean where the tide is strongest.
"Finding the tides is the easiest problem, that's why we started with it," says Tyler. Filtering out the magnetic fields made by other kinds of ocean circulation will be much harder since there is no regular frequency to identify them.
Tyler also hopes that historical data of the Earth's magnetic field - a record from land-based magnetometers stretching back 100 years - could someday be used to infer changes in ocean circulation in the past. "But that's a much harder problem," he admits.
Journal reference: Science (vol 299, p 239)
Nicola Jones
I'll bet it's a good way to pick up on enemy submarines, too. It wouldn't surprise me if this information was seized by the government and made top-secret.
Or it might be the other way around. While trying to find alternate ways to detect submarines, they discovered this and now want to be able to offer it to the highest bidder. Note the language "we won't know until we try". Translation:"some government needs to provide us a "grant" and we will then help them develop the technology."
Resuming my post scanning the skies for black helicopters...
Some flow is periodic. Harmonic analysis will pop it right up.
That is true of both subcrustal and oceanic flows. The problem lies with separating them all. I don't think it's that easy.
We are dealing with a LOT of periodic driving forces here some of which are likely drive constructive and destructive interference in the system response. Some may be harmonics of solar cycles, both magnetic and radiative but the responses to both are different enough to put them quickly out of phase. Others may involve rotation of the elliptical axis of lunar orbit. Then there is possible harmonic activity within the earth driven by gravitational forces that would affect heat transfer through the crust.
There are identified ocean inversions that operate on (approximately) ten, twenty-five, and possibly hundred year cycles, all of which are influenced by basin shape, much as are tides. Then there is interbasin interaction and responses to chaotic activity in weather patterns. Throw in a few singularities (such as volcanic activity, or a breakup of an ice sheet) and the whole thing becomes rather chaotic. How then do you subtract harmonics?
Nor do I think anybody knows how much feedback there is from oceanic temperature cycles to heat transfer through the crust affecting subcrustal magma flows.
In short, if they have just managed to cancel tidal effects, I don't think it is that simple to remove the rest.
Tiny magnetic fields created by ocean tides
Two components, of roughly 24 hours period each, with a changing phase angle between. Fourier filter it and: done.
Kindergarten. What about the rest of it?
Needs work. Send money.
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