July 12, 2013
Processes In The Earth’s Core Affect Length Of Day
April Flowers for redOrbit.com - Your Universe Online
The Earth rotates once a day, but this "day" isn't always the same length. For instance, 300 million years ago, a year was 450 days long, and the average day lasted 21 hours. The Earth's rotation has slowed since then, resulting in longer days and shorter years. A new study, led by the University of Liverpool, has shown variations in the length of day over periods of time between one and ten years are caused by processes in the Earth's core.The Earth's rotation is affected by a number of other factors beyond just slowing. For example, the force of the wind against pushing against mountain ranges can change the length of a day by more or less than a millisecond over a year's time.
The research team, led by Professor Richard Holme from University of Liverpool's School of Environmental Sciences, studied the variations and fluctuations in the length of day over a one to 10 year period between 1962 and 2012. Taking account of the effects on the Earth's rotation of atmospheric and oceanic processes, the researchers built a model of the variations in the length of a day on time scales longer than a year. The results of this study were published in Nature.
Professor Holme said, "The model shows well-known variations on decadal time scales, but importantly resolves changes over periods between one and 10 years. Previously these changes were poorly characterized; the study shows they can be explained by just two key signals, a steady 5.9 year oscillation and episodic jumps which occur at the same time as abrupt changes in the Earth's magnetic field, generated in the Earth's core.
"This study changes fundamentally our understanding of short-period dynamics of the Earth's fluid core. It leads us to conclude that the Earth's lower mantle, which sits above the Earth's outer core, is a poor conductor of electricity giving us new insight into the chemistry and mineralogy of the Earth's deep interior," Holme added.