21st century solar proton events and their influence on the middle atmosphere

Through a large solar disturbance like flare or coronal mass ejection a vast amount of protons and other ions with very high energies can be emitted from the Sun. If these particles reach Earth they evoke an occasion called Solar Proton Event (SPE). The charged particles enter the Earth's atmosphere causing ionization in the middle atmosphere. Ion chemistry leads to increased production of odd nitrogen (NO_x) and odd hydrogen (HO_x) in this atmospheric area. These gases participate in catalytic reaction cycles that decrease the amount of ozone in middle atmosphere. The ionization is greatest in the polar cap regions, where the magnetic field of the Earth provides least protection. For this stydy we have selected some of the largest solar proton events that have taken place in the 21st century, during which the flux of >10 MeV protons as measured by GOES satellites exceeded the value of 1000 particles cm^-2 s^-1 sr^-1. The influence that these events had in the middle atmosphere, particularly on ozone, has been studied using measurements of atmospheric minor species made by various satellite instruments (e.g. Odin/OSIRIS) and comparisons with modelled results from the Sodankylä Ion Chemistry model (SIC). In the presentation we will give a description of the selected events and present results from the measurements and modelling.