Earth’s seasonal gyration mass motion detected for the first time


A new research, performed by the scientist from the University of Newcastle (UON) suggests the Australian continent gyrates in response to seasonal mass change across the globe. This is the first time such a discovery has been made and it is expected to have a profound impact on the climate-change-related research questions.

The study was conducted by combining the GPS data with data from the Gravity Recovery and Climate Experiment (GRACE) satellites, using the sensitive instrumentation capable of detecting the ground deformation of the so-called "seasonal gyration", by relying on the Earth's center of mass.

Because the Earth's center of mass is shifting, the combination of data has provided the researcher with the most accurate reading of the surface deformation across the globe possible.

“The new research shows Australia sinks and rises between 3mm – 5mm in response to the mass change across the globe, as well as shifting northwest 1mm during the southern hemisphere’s summer and moving back during the winter. The whole continent is basically leaning toward where the earth is heavier. Australia experiences a larger mass shift than other continents due to its unique location in relation to global weather patterns, so understanding the impact these factors have is vital in understanding the reasoning behind the movement,” said Professor Shin-Chan Han, a geodesist with NASA and an academic in UON’s School of Engineering.

The seasonal change in mass is induced by numerous different factors, such as atmospheric pressure, ocean mass, ground water storage or the cycle of ice and snow. During the summer season in the southern hemisphere, more mass is concentrated in Europe because of the increased amounts of rainfall, snowfall, and water distribution in general. As the seasons change, so does the mass distribution, and the Australian continent tilts toward the heavier regions, consequently.

The natural continental drift in combination with this tilt produces the elliptical movement, named gyration. While the motion was anticipated, the expert didn't expect such a large motion will respond to weather.

Video credit: University of Newcastle, Australia

“It’s an exciting development in that we now know we can use these forms of surveillance to track the slightest of movements, which are vital in the long-term planning for our response to climate change,” said Han.

The significance of the new discovery was widely recognized by the scientific community.

“This study provides a new way to monitor Earth’s center of mass. There’s a need to be able to monitor it so that surveyors and scientists know what their satellite and GPS measurements are relative to and how their ‘reference point’ is moving,” said Matt King, a professor of polar geodesy at the University of Tasmania who wasn't involved in the research.

According to Professor Han, a next important step of the research will be to evaluate the impact of the pre-2010 drought and the La Nina event in the period between 2010 and 2012 on the continental movement.

The results are expected to affect the readings of the sea-level change, thus providing more accurate measurements, with a lesser systematic data error.

"If we want to have correct sea-level rise satellite data, as well as ground data, we have to have an understanding of where the central mass is so that we can link the satellite data with the ground data. This motion, this oscillation of the continent, is something we don't want to have in our sea level measurements — this is a systematic error in our data. Without knowing our systematic distortion, we cannot have a correct interpretation of our measurements for sea level rise," explained Han.


  • Seasonal clockwise gyration and tilt of the Australian continent chasing the center of mass of the Earth's system from GPS and GRACE – Shin-Chan Han – Journal of Geophysical Research: Solid Earth – DOI: 10.1002/2016JB013388

Featured image credit: NASA/JPL-Caltech

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