Do we need the first “Drop-Second”? A new ‘wobble’ by Earth has caused the shortest day since records began, scientists say
The Earth is suddenly spinning faster than it has since records began, and scientists will reveal the real reasons this week. It’s a rare situation that could call for the first “drop second”—the official subtraction of a second from world time.
Saving 1.59 milliseconds the usual 24 hours on June 29, 2022 was followed on July 26, 2022 by a day that lasted 1.50 milliseconds less. Although 2021 was normal, in 2020 scientists recorded the 28 shortest days since 1960.
All of this is very confusing to scientists, most of whom believed that the Earth was slowing down over the centuries. That’s what atomic clocks have been measuring since they were first used in 1973. Our planet’s gradual slowing is thought to be largely due to the Moon, whose Earth orbit creates a tidal friction that gradually slows the rotation of both Earth and of the Moon.
So why is the Earth’s rotation suddenly speeding up?
The “Chandler Wobble”
There are several short-term reasons for the sudden slowdown in Earth’s rotation, from seismic activity and movements of Earth’s molten core to melting glaciers meaning less weight at the poles.
However, experts believe something else may be at play—the “Chandler Wobble.” Essentially the theory holds that the different rotation is related to the Earth’s geographic poles moving across the surface of the globe.
“The Chandler wobble is a component of the Earth’s instantaneous rotation axis, the so-called polar motion, which changes the position of the point on the globe where the axis intersects the Earth’s surface,” said Leonid Zotov at Lomonosov’s Sternberg Astronomical Institute Moscow. State University. He is the lead author of two papers published earlier this year Advances in Space Research and Journal of Geophysical Research: Solid Earth on Earth’s polar motion and day length trends.
The theory holds that the different rotation is related to the Earth’s geographic poles moving across the surface of the globe. Zotov will present the theory at this week’s meeting of the Asia Oceania Geosciences Society.
“The amplitude of the Chandler oscillation is variable, averaging 3-4 meters over a period of 433 days,” Zotov said. “In 2017-2020 its width was less than 30 cm, which happened once before, around 1928.”
This is a big change – Chandler’s swing has fallen apart. “What we’re seeing nowadays is a rare event,” Zotov said.
Since 2016 the speed of the Earth’s rotation has been increasing and we have now reached the shortest day length on record.
So what’s going on?
Why do the Earth’s geographic poles move?
“They move because Earth is not a dead planet,” Zotov said. Although the position of the celestial pole changes gradually in 26,000 years due to precession, the movement of the poles on the surface of the planet is something more short-term. “Polar motion is caused by geophysical processes in the Earth’s systems, particularly currents in the ocean, winds in the atmosphere, internal processes in the Earth’s interior,” Zotov said.
Scientists believe that something is happening inside the Earth down to the core and mantle. “We’re not sure why the Earth is a very complex system, but I think it’s causing the decay of the Chandler oscillation and the modern shortening of day length.”
Earth is accelerating
“Nobody expected the Earth to accelerate,” Zotov said.
This is not the first time that the general tendency to slow down has been interrupted. Since the 1960s scientists have observed three periods of ups and downs with gaps of about 20 years between them.
However, the trend is for increased speed. “In each of the seasons it spins faster and faster,” Zotov said. “If the acceleration continues, the issue of subtracting a second from Universal Time would become real.”
Will we need the first ‘drop second’ in 2023?
Since 1962 anomalies in the Earth’s rotation speed have been accurately measured and compared to the atomic time scale. We discovered that our planet usually takes a little more than 24 hours to rotate. Consequently, the International Earth Rotation and Reference System (IERS) sometimes has to add leap seconds to compensate for the slower spin.
The IERS added leap seconds 28 times from 1972 to 2016. On July 28, 2022, it confirmed that it would not be a leap second addition at the end of 2022, which is not surprising given that the Earth now appears to be accelerating. For the first time the trend is clearly in the other direction.
Should IERS use a negative leap second – also known as a “drop second” – in 2023 and subtract a second from Universal Time?
This is the work of Christian Bizouard, director of The International Earth Rotation office in Paris, and co-author on the papers discussed here. “He carefully analyzes the situation, and if it does not change, he will make a first statement in history and remove a second one.”
A second drop is certainly not inevitable. “I hope the acceleration of the Earth stops and we don’t have to subtract a second, but who knows?” said Zotov. “Predicting fluctuations in the Earth’s rotation is almost as difficult as predicting stock prices.”
I wish you clear skies and open eyes.