Solar variability impacts on the chemical composition of the middle atmosphere: measurements and model predictions

Principial investigator:

Dr. Miriam Sinnhuber
Universität Bremen
Institut für Umweltphysik
Otto-Hahn Allee 1
28359 Bremen

Co investigator:

Dr. Christian von Savigny


Large events of highly energetic solar particles precipitation - solar proton events (SPEs) and energetic electron precipitation events (EEPs) - are well known sources of NOx (N, NO, NO2) and HOx (H, OH, HO2) and lead to ozone loss in the middle atmosphere. SPE effects have been studied in some detail in the past, and it has been shown that significant amounts of NOx are produced by large SPEs in the mesosphere and upper stratosphere during solar maximum which can be transported down into the middle and lower stratosphere during polar winter. As ozone is one of the key species of radiative heating in the stratosphere, the additional ozone loss due to particle precipitation has an impact on stratospheric temperatures as well. In contrast, the impact of EEPs has not been studied in as much detail, though it has been emphasized that their impact on mesospheric and stratospheric NOx, ozone and temperature could be comparable or even larger than that of SPEs, because they more occur frequently. We propose to investigate in detail the impact of EEPs on the chemical composition of the middle atmosphere, combining measurements of mesospheric and stratospheric parameters from different platforms with model studies with global stratosphere-mesosphere chemistry-transport and radiation models. Model runs with EEP and SPE impacts will be carried out covering a complete solar cycle, and the total impact of energetic particle precipitation on the middle atmosphere as well as the contribution of SPEs versus EEPs will be quantified and assessed.