A day lost 1.59 milliseconds, the Earth set a record for the fastest rotation! Experts from Sun Yat-Sen University unveil the reason behind
Source: Yangcheng Evening News - Yangcheng Pai
"How do I feel that the day has passed so quickly?" This may not be an "illusion", but a phenomenon that is being played out in reality - the recent acceleration of the Earth's rotation has led to a day longer and shorter. Recently, according to the latest publicly available data, on June 29, 2022, the Earth's rotation speed set the fastest record since 1969, but also the fastest record since there is an accurate record of the Earth's rotation speed, 1.59 milliseconds less than the standard 24 hours (86,400 seconds).
Earth's rotation Photo/Visual China
In order to unveil the "mystery" of the Earth's accelerated rotation, the Yangcheng Evening News full media reporter interviewed Professor Min Zhong and Professor Wei Feng from the School of Geospatial Engineering and Science of Sun Yat-Sen University. The interviewed experts said, "Every day is actually not the exact 24 hours, short-term view, the Earth will sometimes rotate a little faster, the length of the day becomes shorter; but from hundreds of thousands of years or even longer, the Earth is slowing down in the rotation, the length of the day is becoming longer."
The Earth's rotation is like a skater's rotation on ice
Yangcheng Evening News - Yangcheng faction: In addition to June 29, the Earth's rotation speed set a record for the fastest, what other "fast" performance of the Earth in recent years?
Experts interviewed: on July 26 this year, the Earth again appeared less than 24 hours a day, its rotation speed is 1.5 milliseconds less than the standard 24 hours. The Earth's rotation has accelerated frequently in recent years, the last shortest record was on July 19, 2020, the Earth's rotation broke the fastest daily record since 1969, 1.47 milliseconds less than the standard 24 hours, a total of 28 less than 24 hours a day was recorded that year.
Yangcheng Evening News - Yangcheng Pai: Why is the length of each day not fixed? How does the Earth speed up the rotation speed?
Experts interviewed: The rotation of the earth mainly consists of the revolution around the sun and the rotation of the earth itself. The motion of the Earth's revolution around the sun forms the four seasons, while the rotation of the Earth itself forms the daily sunrise and sunset. The speed of the Earth's rotation and revolution is roughly stable, so the length of our year and day is basically the same.
However, as people use modern astronomical and geodetic means to observe the Earth's movement with increasing precision, we find that the speed of these rotations varies, so the length of the year and the day are not constant.
Earth's rotation Photo/Visual China
In physics, the rotation of the earth needs to conform to the law of conservation of angular momentum. This is like figure skaters, who spin on the ice with constant angular momentum, but can speed up or slow down their rotation by retracting and opening their arms. The same is true for the Earth. The "arms" of the Earth are extended and bent, which means that the mass of the Earth's surface runs from one place to another, and the speed of the Earth's rotation changes to ensure that the Earth's angular momentum is conserved.
Earth's rotation speeds up in summer and slows down in winter every year
Yangcheng Evening News - Yangcheng Pai: Is the Earth's rotation speed is always accelerating?
Interviewed experts: Not so, there is a long-term trend of slowing down the Earth's rotation speed, periodic changes, special irregular changes.
In the long term, the Earth's rotation speed is getting slower and slower because of tidal friction, especially the influence of the Moon on the Earth. In other words, the day is getting longer and longer, and the days are getting "harder". Geologically, we find that the Earth's rotation is getting slower and slower through early coral fossils. Calculated from the growth lines preserved in ancient coral fossils, 400 million years ago, there were about 400 days in a year, instead of 365 days today. In other words, at that time, when the Earth circled the sun, the Earth rotated more than 400 revolutions, and the speed of rotation was greater than that of today.
In addition to long-term slowing, the Earth's rotation also has obvious seasonal changes, mainly affected by seasonal changes in the wind field in the east-west direction (latitudinal direction) of the Earth, such as changes in the westerly surge wind field that often drastically affects aircraft flight speed at high altitudes in the mid-latitude belt. The wind speed of this wind field usually decreases in summer and increases in winter, resulting in an annual process of the Earth's rotation that speeds up in summer and slows down in winter (the law of conservation of the Earth's angular momentum). The amplitude of the annual change in rotation is about 20 to 25 ms, which is mainly related to the monsoon. The Earth's rotation speed varies from fast to slow throughout the year and is not uniform.
The Earth's rotation speed varies irregularly, i.e., it varies irregularly when it is fast and slow. There are also three kinds of such variations: (i) variations of decades or longer, whose relative change is less than ±5×10-10 per year; (ii) variations of several years to 10 years, whose relative change is less than ±8×10-9 per year; and (iii) variations of a few weeks to a few months, whose relative change is less than ±5×10-8 per year.
The 1-second variation due to fast and slow rotation is crucial
Yangcheng Evening News - Yangcheng Pai: Since the Earth's rotation has been slowing down for a long time, why has the Earth's rotation accelerated frequently recently?
Interviewed experts: Our team, after studying more than 60 years of day-length change observations (see Figure 1), analyzed that the recent frequent acceleration of the Earth's rotation is mainly due to the following two major factors together:
First, from the observed diurnal length change graph, we can see that the reason for the recent acceleration of the Earth's rotation is influenced by the change of the electromagnetic coupling moment of the Earth's nucleus and mantle (the principle of the Earth's nucleus and mantle dynamo), and the diurnal length change in recent years is in the low value period of about 18 years of large cycle change, that is, the diurnal length becomes shorter and the rotation accelerates. Belonging to the first case of irregular changes in the speed of Earth's rotation;
Second, the recent frequent acceleration of the Earth's rotation all occur in June and July in summer, which is mainly influenced by the seasonal change of the Earth's latitudinal wind field, resulting in the annual acceleration of the Earth's rotation in summer, which belongs to the seasonal change of the Earth's rotation speed.
Figure 1: Changes in the length of day (LOD) of Earth's rotation from 1962 to 2022, in milliseconds Contributed by the interviewer
According to reports, some international research colleagues believe that the recent acceleration of the Earth's rotation may be related to the Chandler oscillation of the Earth's rotation (Chandler oscillation refers to the small free oscillation of the Earth's rotation axis relative to the north and south poles of the Earth's surface, as the Earth is not a standard sphere, rotating the tiny periodic oscillation of the rotation axis around the north and south poles of the Earth's surface), global warming, the melting of Arctic glaciers, tidal movements and other reasons The results are still inconclusive.
In addition, the Chandler oscillation was once "silent" from 1920 to 1930, and why was it "silent" again after nearly 100 years in 2017-2020? It is worth scientists to explore in depth in the future.
Yangcheng Evening News - Yangcheng Pai: What is the most direct impact of the accelerated rotation of the Earth? Does it have an impact on our daily life?
Experts interviewed: the study of the Earth's rotation is commonly used to indicate the speed of the Earth's rotation by the term "day length change", which refers to the difference between the time required for the Earth to make one revolution around its axis and the average day length of 86,400 seconds (i.e. 24 hours). As the Earth's rotation slows or becomes faster, the "length of the Earth's rotation day" increases or decreases. In order to be consistent with standard atomic clock time, the World Time Service occasionally ensures, in the form of leap seconds, that the difference between solar time based on the Earth's rotation and UTC based on the atomic clock is within 0.9 seconds.
In the long term, leap seconds tend to be an increase of 1 second due to the unevenness of the Earth's rotation speed and the slow decrease and therefore the slow lengthening of the day length. If the Earth's rotation continues to increase in speed, then it is likely that negative leap seconds may also exist in the future. The time system is ubiquitous in our daily lives, and precise time is essential in all aspects of society, including scientific research, financial services, and transportation navigation. Therefore the increase or decrease of 1 second in time due to the fast or slow rotation of the Earth is also very important.
Yangcheng Evening News - Yangcheng Pai: Will the Earth's rotation still be accelerated? Do we need to do countermeasures?
Interviewed experts: The above graph shows that the day length variation in recent years is in the low value period of about 18 years large cycle variation, the low value period means that the day length becomes shorter and the Earth's rotation accelerates period. The first two low periods correspond to 1985-1987 and 2003-2005, respectively. The current low value period of day length variation should be 2020-2023, and the Earth's rotation should be at the maximum of this acceleration, followed by a phase of deceleration of the Earth's rotation cycle. This is the natural law of the Earth's rotation movement, and the public does not need to have special countermeasures.
