Institute for Space and Earth Environment, Nagoya University

University of Electro-Communications

Kyoto University

National Institute of Polar Research

National Institute of Information and Communications Technology

Japan Aerospace Exploration Agency

Geophysical Institute of Sodankyla, Finland

Finnish Meteorological Institute

Graduate School of Science, The University of Tokyo

Osaka University

Kanazawa University

Tohoku University

Kyushu Institute of Technology

Abstract

A combination of space observations by JAXA's AASE satellite, ground-based radar observations, and aurora imaging has revealed that the "flickering aurora" and "mesospheric ozone depletion," phenomena that at first glance seem unrelated, are in fact both triggered by electromagnetic waves in space at the same time. The research has revealed that electromagnetic waves are triggered at the same time by space waves.

The aurora shining in the Arctic and Antarctic regions is a luminous phenomenon caused when electrons with energy of several kiloelectron volts fall from space and collide with the atmosphere at a height of around 100 kilometers. There is a type of aurora called a "pulsating aurora" that flickers with a period of a few seconds. Observations by the Arase satellite and others have shown that these pulsating auroras are caused by the scattering of electrons in space by an electromagnetic wave (with a frequency of several kilohertz) called a chorus.

On the other hand, it is also known that electrons with extremely high energy of several thousand kiloelectron volts fall into the Earth's atmosphere. These high-energy electrons are thought to be electrons in the radiation belts (Van Allen belts) that exist around the Earth, and are also called "killer electrons" because they cause satellite failures and other problems. Theoretical studies by this research group have predicted that pulsating auroras and killer electrons in the Van Allen zone would simultaneously enter the atmosphere due to "chorus" waves, resulting in changes in the atmospheric conditions in the mesosphere at an altitude of 60 to 80 km.

This study comprehensively analyzed the relationship between the "chorus" waves, the pulsating aurora, and the killer electrons, as well as the effects of the killer electrons on the atmosphere, through a combination of satellite (Arase), ground-based observations (European Incoherent Scattering Radar and optical auroral observations), and simulations, and verified the above theoretical predictions. The results of this research have been used to verify the above theoretical predictions.

The results of this research are important because they suggest the possibility that the descent of electrons from space may affect the middle atmosphere and, in turn, climate change.

Figure: Overview of this study: The AASE satellite observed the "chorus" radio waves and van Allen-band electrons in space, and EISCAT and optical observations on the ground were used to observe the "pulsating aurora" and mesosphere.

The research results were published in the British online journal Scientific Reports at 19:00 (JST) on July 13, 2021.

Associate Professor Satoshi Kasahara and Assistant Professor Kunihiro Katsuraka of the Department of Earth and Planetary Science participated in this research achievement.

For more information, please visit the website of Nagoya University.