Solar winds trigger ozone depletion in the mesosphere | Polarjournal
The color explosions of the auroras fascinate just about everyone. Often in shades of green, sometimes red-violet-pink or bluish, they race or dance across the skies of the polar regions under the right conditions. Responsible for auroras are electrically charged particles of the solar wind from the magnetosphere. When these electrons and protons hit oxygen and nitrogen atoms in the Earth’s upper atmosphere (thermosphere), they get ionized and emit light, mostly green light from oxygen atoms, sometimes red light, and violet to blue light from nitrogen atoms. Photo: Dr. Michael Wenger

Solar winds are the cause of auroras – but not just that. They not only cause the color spectacle dancing in the sky above the polar regions, but are also responsible for another effect, as Japanese researchers have now discovered. According to a new study, the electrically charged particles coming from the sun also cause local ozone depletion in the mesosphere, which could be of significance for global climate change.

Electrons coming from the Sun are actually intercepted by the Earth’s magnetosphere. However, when the electrons interact with plasma waves, the electrons can enter the Earth’s upper atmosphere, the thermosphere, which is called electron precipitation. This phenomenon is responsible for the auroras. The current study, led by Professor Yoshizumi Miyoshi of Nagoya University, Japan and published in Nature’s Scientific Reports, shows that electron precipitation is also responsible for the local depletion of the ozone layer located in the mesosphere. The mesosphere lies between the stratosphere and the thermosphere at an altitude of 50 to 80 kilometers. Scientists cannot rule out effects of this ozone depletion on our climate.

In space, the Arase satellite observes chorus waves and energetic electrons, while on the ground EISCAT and optical instruments observe pulsating auroras and electron precipitation in the mesosphere. Image: the ERG science team

Scientists suspect that ozone depletion in the mesosphere occurs during auroras. Previous studies have investigated the relationship between electron precipitation and auroras, but no sufficient explanation for the cause of mesospheric ozone depletion has yet been found.
During a moderate geomagnetic storm over Scandinavia in 2017, Miyoshi and his team observed “pulsating aurorae” (PsA), a type of faint aurora. Their observations were made possible by coordinated experiments with the European Incoherent Scatter (EISCAT) radar (at altitudes between 60 and 120 km, where the PsA occur), the Japanese Arase spacecraft, and the All-Sky Camera Network.

According to the study, Arase’s data showed that the trapped electrons in the Earth’s magnetosphere have a wide energy range. They also indicated the presence of chorus waves, a type of electromagnetic plasma wave, in this region of space. Computer simulations then showed that Arase had observed plasma waves that caused precipitation of these electrons over a wide energy range, consistent with EISCAT observations in Earth’s thermosphere.

The non-profit international research organisation EISCAT (European Incoherent Scatter Scientific Association) operates several research facilities, including one in Longyearbyen on Svalbard. The facilities are designed to gain knowledge about interactions between the sun and the Earth, which are expressed in perturbations of the magnetosphere and the ionosphere. Photo: Dr. Michael Wenger

Analysis of the EISCAT data showed that electrons in a wide energy range, from a few kiloelectron volts to megaelectron volts, precipitate and cause pulsating auroras. These electrons have enough energy to penetrate our atmosphere to an altitude of about 60 km, where mesospheric ozone is found. Computer simulations using EISCAT data have shown that these electrons immediately deplete (by more than 10%) local ozone in the mesosphere when they hit it.

“PsAs occur almost daily, are spread over large areas, and last for hours. Therefore, the ozone depletion from these events could be significant,” Miyoshi explains. On the larger significance of these findings, he adds, “This is only a case study. Further statistical studies are needed to confirm how much ozone destruction occurs in the middle atmosphere because of electron precipitation. After all, the impact of this phenomenon on the climate could potentially impact modern life.”

Julia Hager, PolarJournal / Original text: Nagoya University

Link to the study: Y. Miyoshi, K. Hosokawa, S. Kurita, S.-I. Oyama, Y. Ogawa, S. Saito, I. Shinohara, A. Kero, E. Turunen, P. T. Verronen, S. Kasahara, S. Yokota, T. Mitani, T. Takashima, N. Higashio, Y. Kasahara, S. Matsuda, F. Tsuchiya, A. Kumamoto, A. Matsuoka, T. Hori, K. Keika, M. Shoji, M. Teramoto, S. Imajo, C. Jun, S. Nakamura. Penetration of MeV electrons into the mesosphere accompanying pulsating aurorae. Scientific Reports, 2021; 11 (1) DOI: 10.1038/s41598-021-92611-3

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