# Penetration of MeV electrons into the mesosphere accompanying pulsating aurorae

## TL;DR

This study shows that pulsating aurorae cause high-energy electrons to penetrate the mesosphere, leading to ozone depletion similar to effects from solar flares.

## Contribution

The study reveals that high-energy electrons during pulsating aurorae cause immediate ozone depletion in the mesosphere.

## Key findings

- EISCAT radar observed electron precipitations from hundreds of keV to MeV during pulsating aurorae.
- Simulations showed immediate catalytic ozone depletion at mesospheric altitudes.
- PsA events may significantly impact mesospheric ozone chemistry in high latitudes.

## Abstract

Pulsating aurorae (PsA) are caused by the intermittent precipitations of magnetospheric electrons (energies of a few keV to a few tens of keV) through wave-particle interactions, thereby depositing most of their energy at altitudes ~ 100 km. However, the maximum energy of precipitated electrons and its impacts on the atmosphere are unknown. Herein, we report unique observations by the European Incoherent Scatter (EISCAT) radar showing electron precipitations ranging from a few hundred keV to a few MeV during a PsA associated with a weak geomagnetic storm. Simultaneously, the Arase spacecraft has observed intense whistler-mode chorus waves at the conjugate location along magnetic field lines. A computer simulation based on the EISCAT observations shows immediate catalytic ozone depletion at the mesospheric altitudes. Since PsA occurs frequently, often in daily basis, and extends its impact over large MLT areas, we anticipate that the PsA possesses a significant forcing to the mesospheric ozone chemistry in high latitudes through high energy electron precipitations. Therefore, the generation of PsA results in the depletion of mesospheric ozone through high-energy electron precipitations caused by whistler-mode chorus waves, which are similar to the well-known effect due to solar energetic protons triggered by solar flares.