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| Scientists are trying to answer the question of how changes in the Earth's rotational speed affect tectonic activity. Photo Credit: NASA |
Scientists from Moscow State University, together with colleagues from the Ural Federal University, the University of Helsinki and the University of Oxford, have studied the response of viscous incompressible fluid flow in a spherical layer of the Earth to random external forcing. The results help scientists understand how random changes in the planet's rotation speed affect the tectonic activity that leads to earthquakes, volcanic eruptions and tsunamis. The research has been published in the Philosophical Transactions of the Royal Society, the world's oldest scientific journal.
"In our research we considered flows of a viscous incompressible fluid induced either by rotation of the inner sphere only or by co-rotation of the spheres. The magnitude of the rotation speed of the inner sphere was subjected to the influence of noise - random deviations in time of the angular rotation speed from the average values. Mean flow generation was found to occur under the action of additive noise. Calculations have shown that the response to noise depends on how the flow was created - by rotation of the inner sphere only or by rotation of both spheres," explains Maria Gritsevich, Senior Researcher at the Ural Federal University and Assistant Professor at the University of Helsinki.
As we know, increasing the angular velocity of the inner sphere causes a transition from stationary to oscillating flow. This creates a flow with periodic velocity variations at each location. More than 30 years ago it was shown that in noisy dynamical systems precursors of instability are observed near the bifurcation point. The mean values of the parameters characterizing the state of the dynamical system decrease and their fluctuating amplitudes increase. The same precursors of instability in the case of hydrodynamic flows with noise were discovered by the researchers for the first time in the world.
"One of the burning scientific questions is how changes in the Earth's spin rate affect tectonic activity. Until now, the modeling of such phenomena has been dominated by the approach in which the Earth's rotational velocity changes strictly periodically over time. We have had a look at the change of the rotation velocity under the influence of random and small changes. Both cases are idealized in a polar sense. The real rotation of the Earth takes place somewhere "in the middle", and its true nature is not yet known. However, our work contributes to the knowledge of these complex and very important processes," explains the importance of the scientific work of Olga Krivonosova, Senior Researcher at the Laboratory of Experimental Fluid Dynamics of Moscow State University and Head of the research team.
Reference: The flow caused by rotation of one or two coaxial spheres is commonly called Couette flow, after the French scientist who first systematically studied flows caused by boundary rotation. The Couette's spherical flow can be considered a simplified model of atmospheres, oceans, Earth's liquid core and other planets. It is known that the parameters of the Earth's rotation tend to change randomly over time.
The development of the study of the Coutte flows is associated with the name of Geoffrey Taylor, who studied the stability of the cylindrical flow. In 1923, he published a study that became one of the most important in the development of the theory of hydrodynamic stability. On the 100th anniversary of this seminal work by Geoffrey Taylor, the oldest English-language scientific journal, the Philosophical Transactions of the Royal Society, decided to publish a commemorative issue. This anniversary issue included the work of researchers from Moscow State University, the Ural Federal University, the University of Helsinki, and the University of Oxford. Professor Peter Read of Oxford University was part of the research team.
Published in journal: Philosophical Transactions of the Royal Society
Source/Credit: Ural Federal University
Reference Number: es041823_01
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