A University of Alberta geophysicist has the honour of introducing readers to the latest developments in research about the rotation of the earth's inner core.
Dumberry wrote about a UK team's research into the rotation speed of the earth's inner core, a topic that he is well versed on through his own research into changes in the Earth's rotation, both in amplitude and direction.
Fifteen years ago, scientists discovered that the earth's inner core rotates at a faster rate of speed than the mantle, causing a number of interesting effects. New research by the University of Cambridge examined the travel time of seismic waves through the top 100 kilometres of the inner core.
"With careful analysis, they were able to observe that seismic waves travel slightly faster in the East than in the western hemisphere," Dumberry says. "Moreover, they showed that the location of the boundary between the two hemispheres is sharp, and is displaced eastward with depth."
Dumberry adds that the eastward shift is consistent with an inner core rotating just barely faster than the mantle at a rate of between 0.1 and 1 degrees in angular velocity per million years. "When the inner core rotates one full turn with respect to the mantle, it rotates by 360 degrees, so 1 degree per million years means that it would take 360 million years for the inner core to complete one full turn with respect to a fixed mantle. Other seismic observations had previously reported much faster differential inner core rotation, of the order of 0.1 degrees per year!"
The older and newer theories about rotation speed may seem to contradict each other, but Dumberry says they add up to create a scenario similar to one that he and French colleague Julien Aubert described in a paper published by Geophysical Journal International earlier this year.
"I was asked by Nature Geoscience to write an introductory article -- a News & Views -- on a specific research article," says Mathieu Dumberry, who joined the Department of Physics as an assistant professor in 2008. The article appears in the April 2011 edition of Nature Geophysics.
"The goal of the exercise is to present to a general Earth Science audience the results of the paper and why they are significant. It is, of course, an honour to be asked to write such a piece, as they always select world experts in specific topics."Dumberry wrote about a UK team's research into the rotation speed of the earth's inner core, a topic that he is well versed on through his own research into changes in the Earth's rotation, both in amplitude and direction.
Fifteen years ago, scientists discovered that the earth's inner core rotates at a faster rate of speed than the mantle, causing a number of interesting effects. New research by the University of Cambridge examined the travel time of seismic waves through the top 100 kilometres of the inner core.
"With careful analysis, they were able to observe that seismic waves travel slightly faster in the East than in the western hemisphere," Dumberry says. "Moreover, they showed that the location of the boundary between the two hemispheres is sharp, and is displaced eastward with depth."
Dumberry adds that the eastward shift is consistent with an inner core rotating just barely faster than the mantle at a rate of between 0.1 and 1 degrees in angular velocity per million years. "When the inner core rotates one full turn with respect to the mantle, it rotates by 360 degrees, so 1 degree per million years means that it would take 360 million years for the inner core to complete one full turn with respect to a fixed mantle. Other seismic observations had previously reported much faster differential inner core rotation, of the order of 0.1 degrees per year!"
The older and newer theories about rotation speed may seem to contradict each other, but Dumberry says they add up to create a scenario similar to one that he and French colleague Julien Aubert described in a paper published by Geophysical Journal International earlier this year.
"All other studies were tailored to capture the present-day speed of inner core rotation, in a snapshot so to speak," says Dumberry. "So it may just be that the inner core has large fluctuations in its rotation speed on timescales of decades to centuries, but that overall these almost cancel out, leaving only a very slow super-rotation over geological times."