Ionisation of the terrestrial atmosphere caused by energetic particles

Solar energetic particle (SEP) events are known to cause changes in constituents of the Earth's polar neutral middle atmosphere. During the past years several large SEP events have been observed to generate such atmospheric variations. Furthermore, Galactic Cosmic Rays (GCRs)are known to be the principal agents of ionization in the atmosphere above certain altitudes. A combination of derivatives of the GEANT 4 code, MAGNETOCOSMICS and PLANETOCOSMICS, allows to compute the GCR produced particle fluxes as well as the level of ionization at different altitudes and geographic/geomagnetic locations. In order to determine the accuracy of our model, we compare our results with balloon measurements of the ion pair production over Palestine, Texas, in 1969 and 1970. In this contribution we present results from our investigation of the ionization rate above 50 km in response to different levels of solar modulation of GCRs and compare the effect of the latter with that of large SEP events