Science

We finally know why mysterious waves seem to survive traveling through Earth’s turbulent “impact” region.

The waves created by the solar winds acting on the Earth’s magnetic field appear to escape from the turbulent region around our planet, but how they do so remains a mystery.

Now the research team has discovered how these waves appear to survive: they continue past the leading “foreshock” region into an area called “shock” and then create “clone” waves with identical properties, which explains how they cross that region. . regions in near-Earth space. So, what astronomers have observed for decades were not waves created by the solar winds, but rather newly created “clones” of waves.

“How the waves survive the impact has been a mystery since waves were first discovered in the 1970s,” Lucille Turk, a research fellow at the University of Helsinki in Finland and lead researcher, said in a statement. “No evidence of the existence of these waves on the other side of the shock wave has been found.”

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The magnetosphere is a magnetic bubble that shields the Earth from the Sun’s charged particles, called the solar wind, by directing these particles along magnetic field lines to the other side of our planet. The interaction between the supersonic solar wind and the Earth’s magnetic field creates a shock region, also known as a bow shock. The foreshock then forms “upstream” of that impact area.

The impact of solar winds causes the appearance of electromagnetic waves in the form of small fluctuations in the Earth’s magnetic field. Waves with the same oscillations as those in this foreshock region have been seen on the sun-facing side of the Earth, suggesting that they may enter the magnetosphere and travel all the way to the planet’s surface. But how could these waves cross the region of strong impact and remain unchanged?

Turk and colleagues have been studying wave propagation in the foreshock region for three years, using a computer model called the Vlasiator to recreate and understand the physical processes involved in wave transmission. By studying simulations performed by Vlasiator, a system developed at the University of Helsinki under the direction of Minna Palmroth, the team found waves on the other side of the impact region that had properties almost the same as those of the previous foreshock. region.

They followed this discovery by looking for signs of these waves in satellite data and confirmed that the simulations were correct. But they still doubted that the waves would be able to cross the shock wave and reach the Earth.

“At first we thought that the original theory proposed in the 1970s was correct: waves can cross the shock without change,” Turk said. “But there was a discrepancy in the wave properties that this theory could not reconcile, so we continued the study. In the end, it became clear that everything was much more complicated than it seemed.

“The waves we saw behind the shock were not the same as in the foreshock, but new waves created at the impact by the periodic impact of the foreshock waves,” Turk said.

The team believes that when the solar winds pass through the shock wave, they compress and heat it up, and the strength of the shock wave determines the extent to which this occurs. Peaks and troughs in the waves emanating from the foreshock “tune” the shock wave as they reach it and cause it to alternate between weak and strong space weather periodically. This then creates new waves from the shock, which are thus consistent with the foreshock waves. The Vlasiator simulation suggests that these waves should only be detected in a narrow region behind the shock wave and that they can be easily obscured by turbulence in this region. This may explain why these waves have not been observed before.

The team’s study was published Dec. 19 in the journal Nature Physics. (will open in a new tab).

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