Daedalus will measure the characteristics of energetic particle precipitation, which is known to impact the atmosphere from the surface up to the mesosphere or lower thermosphere, albeit in a yet unquantified way. EPP significantly affects stratospheric and mesospheric atmospheric composition below 100 km altitude via the production of odd hydrogen species (HOx ) and odd nitrogen species (NOx) which are involved in catalytic destruction of ozone. NOx can be long-lived during polar winter and can then be transported down into the lower mesosphere and stratosphere, where it is one of the main participants in catalytic ozone destruction. It is also known that energetic particle precipitation can affect temperature and the dynamics of the atmosphere down to the stratosphere and possibly even propagating down to the surface, due to a coupling of chemical composition changes affecting atmospheric heating and cooling rates, the mean circulation, and wave propagation and breaking. However, there are still a number of open questions in the theoretical description of the energetic particle precipitation impact; the most important are related to uncertainties in the formation rate of different NOx species due to a lack of knowledge regarding energetic particle precipitation characteristics, and the complex coupling between chemical changes, atmospheric heating and cooling rates, and atmospheric dynamics.
Daedalus will measure the key characteristics of energetic charged particles that precipitate directly in the LTI and also charged particles of much higher energy that precipitate in the mesosphere and even below. These measurements will answer the unsolved question of what is the particle flux distribution as it precipitates into the Earth’s atmosphere, and provide more realistic fluxes needed for climate modelling leading to IPCC input [Matthes et al., 2017]. Recent estimates suggest that the under-estimate in EPP flux levels could be as large as a factor of 10 [Hilde, 2018] during moderate geomagnetic storms. Even so, coupled climate models have shown that enhanced wintertime mesospheric NOx is associated with surface air temperature changes in mid- to high-latitudes [Rozanov et al., 2005; Baumgartner et al., 2011]. In terms of HOx/NOx chemistry, this entails LTI local production that can be advected downwards in the polar night, as well as direct generation in the stratosphere/mesosphere that will immediately impact ozone chemistry.