Atmospheric impact of extreme solar eruptions

Abstract

Large solar eruption -solar flares and coronal mass ejections- can have a significant impact on the chemical composition and dynamics of the polar middle atmosphere. For solar events of the space age since 1957, this is well quantified and understood. However, evidence for much larger events has been derived from paleonucleide records within the last 10000 years. Here, we show results from model experiments comparing the well-known "Halloween" solar storm of October 2003 with an extreme event of AD 774/775. Both events had a significant impact on atmospheric composition which lasted for several months. Due to its harder spectrum and larger fluxes, this impact affected lower atmospheric layers during and after the AD 774 event. Due to radiative-dynamical feedbacks, both events affected atmospheric temperatures and dynamics as well with larger changes during the event and during polar summer for the stronger AD 774 event. However, during polar winter, the preconditioning of the atmosphere seems to play a role as well.