Geomagnetic storms deplete the ozone layer of Earth’s atmosphere

Geomagnetic storms that cause auroras – beautiful streaks of green light often visible from the Earth’s polar regions – cause depletion of the ozone layer in the mesosphere. This depletion can have implications for global climate change, so understanding this phenomenon is very important.

Now, a team of scientists led by Professor Yoshizumi Miyoshi of Nagoya University, Japan, has observed, analyzed and provided a better understanding of this phenomenon. The results of the study are published in Nature’s Scientific Reports.

In the Earth’s magnetosphere, the region of magnetic field around the Earth, electrons from the Sun remain trapped. Interactions between electrons and plasma waves can cause trapped electrons to escape and enter Earth’s upper atmosphere (thermosphere). This phenomenon, called electron precipitation, is responsible for the occurrence of auroras. However, recent studies show that this phenomenon is also responsible for the local destruction of the ozone layer in the mesosphere (below the thermosphere) and may have some effect on our climate.

Moreover, this destruction of the ozone layer in the mesosphere may occur precisely during the auroras. And although scientists have studied electron precipitation in connection with auroras (auroras), none of them have been able to sufficiently figure out how they cause the destruction of mesospheric ozone.

Professor Miyoshi and his team took the opportunity to change this view during a moderate geomagnetic storm over the Scandinavian Peninsula in 2017. Their observations focused on “pulsating auroras” (PCA), a type of weak aurora. Their observations were made possible by coordinated experiments with the European Incoherent Scattering Radar (EISCAT) (at heights of 60 to 120 km, where PSAs occur), the Japanese Arase spacecraft, and a network of all-sky cameras.

The Arase data showed that trapped electrons in the Earth’s magnetosphere had a wide energy range. They also indicated the presence of chorus waves, a type of electromagnetic plasma waves, in this region of space. Computer simulations showed that Arase observed plasma waves causing the deposition of these electrons in a wide energy range, which is consistent with EISCAT observations in Earth’s thermosphere.

Analysis of the EISCAT data showed that electrons in a wide energy range, from a few keV (kiloelectronvolts) to MeV (megaelectronvolts), precipitate, causing PCA. These electrons have enough energy to penetrate our atmosphere below 100 km, all the way up to ~60 km, where mesospheric ozone is located. In fact, computer simulations using EISCAT data have shown that these electrons immediately destroy local ozone (by more than 10%) upon entering the mesosphere.

Professor Miyoshi explains, “SARs occur almost daily, spread over large areas and last for hours. Therefore, the ozone depletion from these events can be significant.”

Speaking of the greater significance of these results, Professor Miyoshi continues, “This is only a separate study. Further statistical studies are needed to confirm how much ozone destruction occurs in the middle atmosphere due to electron deposition. After all, the effects of this phenomenon on the climate could potentially affect modern life.”

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