Nylonathatep wrote:Earth’s magnetic field overdue for a chaos-causing (possibly life-altering) fliphttp://news.nationalpost.com/2012/10/03 ... ring-flip/
Scientists say earth’s magnetic field is weakening and could all but disappear in as little as 500 years as a precursor to flipping upside down.
It has happened before – the geological record suggests the magnetic field has reversed every 250,000 years, meaning that, with the last event 800,000 years ago, another would seem to be overdue.
“Magnetic north has migrated more than 1,500 kilometres over the past century,” said Conall Mac Niocaill, an earth scientist at Oxford University. “In the past 150 years, the strength of the magnetic field has lessened by 10 percent, which could indicate a reversal is on the cards.”
Just wondering if there's any truth in this article.
It's impossible to predict magnetic field reversals. The cartoon story is that the dipole weakens and then reverses polarity every 250,00 years, but there are several problems with this account, the most important of which is the variance on that number. Chrons (polarity eras) are nowhere near uniform in length. The longest one we know about is the cretaceous superchron, which lasted 40 million years. The field is not really a dipole, but the dipole term usually dominates, and assuming it's dipolar simplifies discussions and analysis. When it starts to 'weaken', though, things get more complicated and it becomes unclear whether its best analyzed as a wandering dipole or simply a more complex field. Sometimes the pole wanders away from north and then returns, sometimes it wanders all the way south. There's no way to know whether it will go all the way south until after the fact
When transitions do occur, they take ~1000 years (huge variance again) and the field never really fades to zero, but becomes less dipolar. This makes it difficult to talk about the 'strength' of the field because it can no longer be described by a single number. It's not easy to analyze exactly how strong the field is when averaged over the whole Earth because there are not enough usable rock samples to make complete field maps of different eras.
There is no consensus on exactly why the field reverses (physics-wise). There are numerical and physical simulations of magnetic fluid eddies (liquid sodium in rotating spherical containers, extremely dangerous), but you can only get them to behave like the Earth's field if you use parameters that are many orders of magnitude different from what are believed to realistic. Some of these simulations show reversals, some don't. Contrary to The Core, Earth's core is not spinning with respect to the mantle, although it probably oscillates just a little. Some whole-Earth seismologists would disagree, but even they would only estimate a maximum rotation of about 1 degree per year. Geomagnetists point out that such a rotation would cause electrojets at the Earth's equator that should be measurable but are not observed.
Fun fact: the north geographic pole is magnetically a south pole. Almost every illustration you seen of the Earth's magnetic field in a textbook shows it as a bar magnet with magnetic north pointing at geographic north. It's actually more similar to a disk magnet with magnetic south pointing at geographic north.
Also, the fading of the Earth's field during a reversal does not leave us unprotected from cosmic rays, as is commonly feared. These are scattered by the atmosphere, not blocked by the magnetic field. We would
be more exposed to the solar wind, but the increased risk of cancer over a lifetime is estimated to be roughly equivalent to smoking a pack a day for one year, which is not that bad. Satellites would be more likely to be damaged, though.
the article wrote:The European Space Agency is taking the issue seriously. In November, it plans to launch three satellites to improve our fairly blurry understanding of the magnetosphere.
The project – Swarm – will send two satellites into a 450 kilometre high polar orbit to measure changes in the magnetic field, while a third satellite 530 kilometres high will look at the influence of the sun.
The Swarm mission has little or nothing to do with the possibility of impending reversals. It will measure spatial
variations and very short-term
temporal variations of the field in order to make more detailed maps of the current magnetic field. It will tell us nothing at all about how likely the field is to reverse.