Scientists discover changes in the Earth's core rotation and its impact throughout the day
About 1,800 miles below our feet, Earth's inner core is a dense, hot ball of steel roughly the size of the dwarf planet Pluto.
The rotation of the Earth's inner core changes according to a six-year cycle — a cycle that also changes the length of the day — according to the study of seismic waves.
Due to the impossibility of direct observation, scientists who study the inner nucleus are forced to resort to the interpretation of indirect measurements to identify its nature.
Despite this, our understanding of the Earth's inner core has expanded greatly over the past three decades, as geologists have shown that the motion of the core has changed over time.
In 1996, for example, researchers first suggested that the inner core is spinning eastward faster than the rest of the planet, at a rate of about one degree per year — a phenomenon known as "super-spin".
However, subsequent research indicated that this may have been an overestimation.
Using a new technique, the researchers found that the inner core was spinning slower than previously expected, at a rate of about 0.1 degrees per year.
In their new study, the researchers applied the same approach to seismic waves generated by a pair of previous atomic weapons tests conducted by the United States.
These tests - dubbed "Milrow" and "Cannikin" - were conducted under Amchitka Island, at the tip of the Alaskan archipelago, in 1969 and 1971, respectively.
By measuring the compressive seismic waves from nuclear explosions, the team concluded that the inner core was spinning in the opposite direction relative to the rest of the planet, "partially spinning" by at least 0.1 degrees each year.
This is the first time that the hypothesis that the core's internal rotation undergoes six-year oscillations has been confirmed by direct seismic observations.
The oscillations are regular variations around a central point - much like the movement of a pendulum in a long watch.
The researchers explained that the transformations of the Earth's surface compared to its inner core can be seen, as people have confirmed for 20 years. However, recent observations show that the inner core was slightly slower from 1969-1971 and then moved in the other direction from 1971 to 1974.
The length of the day changes by plus or minus 0.2 seconds over every six years - an oscillation offset by differences in the Earth's magnetic field.
The full results of the study were published in the journal Science Advances.
Source: Express
https://shahbapress.net/archives/25838?fbclid=IwAR3breopFXvW_FY_seMS91GKnVc8M0JIN46NwTkHe106u0UFDZN477e3ebY