Impact of energetic electron precipitation on the northern and southern polar vortex

Electrons precipitate into the Earth’s atmosphere from magnetospheric plasma regions as a continuously varying flux. Energetic electron precipitation (EEP) forms reactive odd nitrogen (NO_X) and hydrogen (HO_X) oxides which catalytically destroy ozone in the high-latitude thermosphere and mesosphere. Moreover, during polar darkness, the NO_X radicals formed by EEP descend to the stratosphere and spread the EEP effect down to the wintertime polar middle atmosphere. Several studies have shown that EEP affects the temperature in the polar middle atmosphere and the strength of the polar vortex, a westerly wind system around the winter pole. The EEP effect is strong in the northern hemisphere but has so far remained unclear in the southern polar vortex. Here we examine the EEP effect on the chemical and dynamical features of the mesosphere and stratosphere both in the northern and southern hemisphere using satellite observations of the EEP by POES/MEPED and atmospheric parameters by Aura/MLS. We also utilize the geomagnetic aa index as a proxy for EEP and the ERA5 reanalysis dataset for atmospheric variables to extend the temporal coverage of observations. We show that, while the effect of EEP on the polar vortex is stronger in the northern than southern hemisphere, the EEP also affects the southern polar vortex in the late winter and spring. This is, e.g., seen in the timing of the final warming.