A pair of researchers, Richard Holme of the University of Liverpool in the U.K. and Olivier de Viron of the University of Paris, in France has found that the length of Earth’s days follows a cyclic oscillation pattern every 5.9 years. As the two describe in their paper published in the journal Nature, the variations in day length were discovered as part of a study examining day-length over the past 50 years.
The time it takes the Earth to spin once around its axis varies by milliseconds on any given day. This is due to the impact of weather patterns, ocean currents and other factors. But the Earth is also subject to other forces that can cause the length of day to vary over the long term or even for short “jumps” of time. In this new effort, the researchers looked at data from the past 50 years and then filtered out those short term forces that cause daily fluctuations in day-length. In so doing, they found what they describe as a ten year “decadally varying trend” a 5.9 year cycle of day-length oscillations and times when the planet seems to jerk, temporarily changing the length of the days that follow.
Unlike the ten year trend (believed to be caused by changes in the Earth’s core) and the episodic jerks (scientists have detected 10 such events since 1969) the 5.9 year cycle was unexpected. Every 5.9 years, they claim, the planet undergoes a period of several months where the length of each day is longer or shorter than “normal.” The researchers don’t know what causes the cycle but suspect it has something to do with the core-mantle boundary.
Scientists are also interested in learning more about the episodic jerks that alter day-length for several months at a time—this new research has revealed that during each event, the Earth’s geomagnetic field undergoes a similar effect. Scientists don’t know why either occurs, but suspect they are connected.
Research into Earth’s day-length changes as well as studies seeking to better understand the true makeup of the planet are not just academic pursuits—gains in understanding are used by geologists and engineers in mining and exploration efforts.