CHAMOS

• Direct and indirect effects of energetic particle precipitation
• Related changes in the atmosphere, including the ionosphere
• Effects on middle atmospheric ozone, temperature, and dynamics
• Connections to ground level regional climate through dynamical coupling

Energetic particles from the Sun enter (precipitate into) the Earth's atmosphere. These precipitating particles are mostly electrons and protons. During large precipitation events, the particles can ionise and dissociate the neutral gases in significant amounts and disturb the chemical balance of the middle atmosphere. In chemical reactions between the neutral and ionic gas constituents, the products of impact ionisation and dissociation processes are converted to important minor species, such as NO and OH. These minor components may affect the ozone balance of the atmosphere because they can destroy ozone in a catalytic chemical reaction chains. Ozone is a key constituent for the thermal balance and UV radiation absorption characteristics of the atmosphere. Therefore, if the particle events affect ozone, they can also affect the atmosphere as a whole all the way down to ground level.

Growing concern about global change and the existence of an anthropogenic component in climate variability challenge our scientific understanding of the atmosphere. Still today we are lacking exact knowledge on to what extent the solar variability is causing natural variations in Earth's atmosphere. We need to know how important the different variable energy inputs into the atmosphere from above are to lower altitudes, and ultimately how a strong solar variability signal can be propagated into climate data. Solar proton precipitation at polar cap areas, auroral electron precipitation at the auroral zone, relativistic electron precipitation at auroral and sub-auroral latitudes, variable cosmic ray ionisation and solar extreme ultraviolet and X-radiation are ionising energy inputs to the mesosphere and lower thermosphere (MLT). They all show large variations on different time scales, causing changes in the ion and neutral composition in the MLT region. During extreme ionisation events, direct effects in the stratosphere can be seen. Since ozone plays a major role in determining the temperature profile of the atmosphere it is important to know quantitatively the share of all natural processes affecting its concentration. We are investigating how the thermospheric and mesospheric excess ionisation processes affect the composition and dynamics of the stratosphere. We aim to quantify the production of odd nitrogen (NOx) and calculate the transport of long-lived NOx in polar night conditions, so that we can finally resolve the consequent variations in stratospheric ozone.