藉助衛星而發現地核中的噴流

原始網址：www.sciencedaily.com/releases/2016/12/161219134450.htm

藉助衛星而發現地核中的噴流

科學家藉助衛星產生的最新資料，而做出了地球的「X光」影像。從中他們發現有道噴流存在於地球的液態鐵核心內部。

領導這項研究的里茲大學Phil Livermore博士表示：「歐洲太空總署的Swarm衛星正提供給我們有史以來最清楚的地核X光影像。從中我們不但能首度清楚看見這道噴流(jet stream)的存在，同時也可以藉此了解為何它會於此形成。」

「我們可以清楚看出這是一道環繞北極的液態鐵加速帶，如同大氣中的噴射氣流一般。」里茲大學地球與環境學院的Livermore博士說。

由於地核所處的位置遠在3,000公里厚的岩石下方，因此多年以來科學家是透過測量地球磁場的性質來研究地核―這是少數可用選項之一。

過往的研究中已經發現，磁場變化意味著外核的鐵在北半球的流動速度比較快，尤其是阿拉斯加和西伯利亞下方。

但是由Swarm衛星提供的新數據顯示，這些變化實際上是由一道噴流導致，其流動速度高達每年40公里。

這是一般外核流速的三倍，更是地球板塊移動速度的數百倍至數千倍以上。

歐洲太空總署的Swarm任務，主要是利用三顆衛星同步測量並分離產生自地球不同區域的磁場訊號，這些來源包括了地核、地函、地殼、海洋、電離層和磁層。這些衛星對地核產生的磁場提供了迄今最清楚的資訊。

刊登於《自然―地質科學》的研究發現此噴流的方向，跟地核內部兩塊不同區域之間邊界的方向一致。他們認為這道噴流可能是因為地核內部的流體，從兩個方向往這道邊界匯聚，接著往側邊擠出而形成。

共同作者，里茲大學數學院的Rainer Hollerbach表示：「當然，你需要一股力量才能將流體推往這道邊界。它可能由浮力提供，或許更有可能是來自於地核內部磁場的變化。」

歐洲太空總署Swarm任務的主持人，Rune Floberghagen表示：「[這項計畫]還可能帶來更驚人的發現。磁場無時無刻都在變動著，甚至會改變這道噴流的方向。」

「這道特徵是因為Swarm才得以對地球深部首度作出的發現之一。有了現今可以達到的前所未見高解析度，這是相當令人振奮的時刻—我們只是還不知道對地球的下一步發現會是什麼。」

共同作者，丹麥科技大學的Chris Finlay博士表示：「關於地核我們所知的還遠遠不及太陽。在更加理解我們地球內部的運作方式上，這道噴流的發現無疑是激勵人心的一步。」

 

Satellites help discover a jet stream in the Earth's core

A jet stream within the Earth's molten iron core has been discovered by scientists using the latest satellite data that helps create an 'x-ray' view of the planet.

Lead researcher Dr Phil Livermore, from the University of Leeds, said: "The European Space Agency's Swarm satellites are providing our sharpest x-ray image yet of the core. We've not only seen this jet stream clearly for the first time, but we understand why it's there."

"We can explain it as an accelerating band of molten iron circling the North Pole, like the jet stream in the atmosphere," said Dr Livermore, from the School of Earth and Environment at Leeds.

Because of the core's remote location under 3,000 kilometres of rock, for many years scientists have studied the Earth's core by measuring the planet's magnetic field -- one of the few options available.

Previous research had found that changes in the magnetic field indicated that iron in the outer core was moving faster in the northern hemisphere, mostly under Alaska and Siberia.

But new data from the Swarm satellites has revealed these changes are actually caused by a jet stream moving at more than 40 kilometres per year.

This is three times faster than typical outer core speeds and hundreds of thousands of times faster than the speed at which the Earth's tectonic plates move.

The European Space Agency's Swarm mission features a trio of satellites which simultaneously measure and untangle the different magnetic signals which stem from Earth's core, mantle, crust, oceans, ionosphere and magnetosphere. They have provided the clearest information yet about the magnetic field created in the core.

The study, published today in Nature Geoscience, found the position of the jet stream aligns with a boundary between two different regions in the core. The jet is likely to be caused by liquid in the core moving towards this boundary from both sides, which is squeezed out sideways.

Co-author Professor Rainer Hollerbach, from the School of Mathematics at Leeds, said: "Of course, you need a force to move the liquid towards the boundary. This could be provided by buoyancy, or perhaps more likely from changes in the magnetic field within the core."

Rune Floberghagen, ESA's Swarm mission manager, said: "Further surprises are likely. The magnetic field is forever changing, and this could even make the jet stream switch direction.

"This feature is one of the first deep-Earth discoveries made possible by Swarm. With the unprecedented resolution now possible, it's a very exciting time -- we simply don't know what we'll discover next about our planet."

Co-author Dr Chris Finlay, from the Technical University of Denmark said: "We know more about the Sun than the Earth's core. The discovery of this jet is an exciting step in learning more about our planet's inner workings."

原始論文：Philip W. Livermore, Rainer Hollerbach, Christopher C. Finlay.An accelerating high-latitude jet in Earth’s core. Nature Geoscience, 2016; DOI: 10.1038/ngeo2859

引用自：University of Leeds. "Satellites help discover a jet stream in the Earth's core." ScienceDaily. ScienceDaily, 19 December 2016.