One day is not 24 hours, and the change of daily length is "reincarnation" every 8.6 years
Astronomy around
Intern reporter Yu Ziyue Correspondent Zuo Wenwen
People always think that holidays are short, and every day at work is very long. In fact, if we ignore the intervention of psychological senses and measure time with scientific means, we will find that each day we pass is indeed not an accurate 24 hours, but a very small change.
What is the regularity of the change of daily length? Recently, Chinese researchers have discovered for the first time that there is a significant amplitude enhancement signal with a period of about 8.6 years in the change in daily length, and for the first time found that there is a close correspondence between the extreme value of this oscillation and the occurrence of rapid changes in the geomagnetic field.
The research results have been published online in "Nature·Communication".
Separating and synthesizing the waves to find out the "unspoken rules" in the change of the day length
"Scientists have long discovered that the length of each day is not fixed. From a larger time scale, the length of the day is gradually becoming longer." Recently, the research participant, the Shanghai Astronomical Observatory of the Chinese Academy of Sciences, and the Key Laboratory of Planetary Sciences of the Chinese Academy of Sciences Researcher Huang Chengli said in an interview with a reporter from Science and Technology Daily.
The duration of a day in the Jurassic period was only about 23 hours and 10-20 minutes. As the lunar and sun’s tidal effects on the earth consume the earth’s energy, the earth’s rotation becomes slower and slower, and the day length becomes longer, averaging about 0.002 seconds per 100 years.
Huang Chengli pointed out that in addition to this long-term law, scientists also found that the change in daily length has a periodic law in a relatively short-term. It is generally believed that interdecadal changes with a scale of several decades and sub-decadal changes with a scale of about 5-10 years are likely related to the deep internal physics of the earth.
In this study, the researchers found that in addition to the previously recognized 6-year cycle, the change in daily length also "reincarnates" every 8.6 years. It is worth mentioning that the change in daily length resembles a sine curve, but the amplitude is gradually increasing. Generally speaking, with the passage of time, the daily length fluctuates up and down regularly on the average daily long-term line, sometimes a few milliseconds less than 24 hours, and sometimes a few milliseconds more than 24 hours, but the extreme value is getting more and more Large, that is, the change of time is becoming larger.
How can researchers find this pattern in the Nikon database collected over decades?
"We used the data of the change in daily length from 1962 to 2019 provided by the International Earth Rotation Service System, combined with a large number of numerical simulation examples, based on the standard wavelet time-frequency transform method and our independently developed "deletion of wavelet edge effect" strategy, For the first time, the phenomenon of signal amplitude increase for 8.6 years was discovered," said Duan Pengshuo, the first author of the paper and an associate researcher at the Shanghai Astronomical Observatory of the Chinese Academy of Sciences.
He further explained that the standard wavelet time-frequency transform method is a unique method in this field, which can quantitatively identify and extract periodic harmonic signals in the observation sequence. In daily life, 7 kinds of monochromatic light can be synthesized into white light, and white light can also be split into monochromatic light through a small prism, as is the exploration of the law of daily length change. In fact, the length of the sun is related to many factors, such as the influence of different physical structures or events inside the earth. The data of the actual measured length of the day can be regarded as a comprehensive wave, which can be split into many sub-waves dominated by different factors, which is called wavelet in academia. The standard wavelet time-frequency transform method is the "triangular prism" often used by scholars, which can split the data to be analyzed from the comprehensive data.
However, although this method has a high frequency resolution capability, it also has significant edge effect problems. The "wavelet edge effect removal" strategy independently developed by the research team can make up for this deficiency, allowing researchers to accurately separate the target harmonic signal and finally find out the hidden rule behind the change in daily length.
Reversing the Alfen wave or the "pushing hand" for the change of the daily cycle
In addition to the amplitude-enhanced signal of the 8.6-year cycle, the researchers also discovered a peculiar phenomenon. "Coincidentally, every 1-2 years before the extreme moment, the geomagnetic field will change rapidly, that is, the geomagnetic abrupt change." Huang Chengli told the Science and Technology Daily reporter, "We have consulted many previous geomagnetic records, and all This phenomenon coincides. This may help to uncover the mechanism of the cyclical change of the day length on the sub-decade scale."
The research team seized this clue and combined with a large number of previous research data, it was suggested that the 8.6-year periodic change in day length may be related to the torsional Alfyn wave oscillation near the equator on the surface of the Earth’s liquid core.
The earth is filled with a magnetic field. If the magnetic field lines of the magnetic field are imagined as individual strings, when the magnetic field is disturbed, the strings of the magnetic field lines will oscillate, and the oscillation will propagate along the magnetic field, forming an Alfen wave. When the lines of magnetic force are gathered into a tubular structure called a "magneto flow tube", the Alfen wave propagating in the magneto flow tube is a torsion Alfen wave.
Reversing the Alfen wave propagating outwards and coupling with the mantle will cause fluctuation signals of the same period to appear in the day length.
"Prediction of geomagnetic abrupt changes is currently an international problem. This study provides a new research portal that can accurately predict the moment of future geomagnetic abrupt changes by accurately separating the sub-decadal oscillation signals of the earth's rotation." Duan Pengshuo said At this stage, the periodic change signal with a daily length of 8.6 years is at a low point and is approaching the minimum. Therefore, it is predicted that there will be a new geomagnetic abrupt event in the most recent 1-2 years.
It is not difficult to see that through the study of the fine variation characteristics of the day length, you can gain a deeper understanding of the magnetohydrodynamic problems deep inside the earth. "Follow-up, we will pay close attention to the relevant information and reports of geomagnetic changes, and will also apply this independently developed data processing method to other fields of astronomical geodynamics." Huang Chengli said.