INAF-IFSI

Solar activity influences the Earth’s environment, in particular the atmospheric ozone, by the direct output of the e.m. radiation or through the variability of the incoming cosmic ray flux (solar and galactic particles). Especially energetic particles, arising from huge explosions on the Sun’s surface, travel in the interplanetary medium and, if the circumstances were favorable, they could enter the terrestrial atmosphere (driven by the geomagnetic field lines of our planet) and reach the polar cap regions (geomagnetic latitude > 60°). There, they provide additional external energy and are able to produce ionizations, dissociations, dissociative ionizations and excitations phenomena by interacting with the minor constituents. The induced changes are not confined to the ion chemistry but also to the neutral components. In this way a rise of the concentration of HOx and NOx species and the triggering of catalytic cycles which lead to short (hours) and medium (days) term ozone destruction occur. Finally, also no-reactive reservoir species (e.g., HNO3, HCl, HOCl) are involved in these processes and endure large variations. The present thesis highlights the chemical variability of the middle atmosphere during and after some Solar Energetic Particle (SEP) events recorded during the current solar cycle. Special attention has been paid to the relationship between ozone and HOx data (retrieved from the Microwave Limb Sounder of EOS AURA satellite) for four events referred to 2005. The HOx data, recorded for the first time during the intense ionization caused by the SEP flux, have pointed out some features related to these phenomena not wholly captured by the current theoretical models. In addition, they have highlighted that the HOx rise is able to destroy the so-called third ozone peak at the polar latitudes of the winter hemisphere and it occurs also during medium intensity events. Besides, the analyses of January 2005 SEP events have shown that the changes on the hydrogen species leaded to variability in the concentration and partitioning of chlorine family, not discernible in the summer hemisphere. Further, the use of data coming from the HALOE instrument, referred to SEP events occurred in July 2000 and April 2002, has in short confirmed past experimental results. Finally, the study of a little SEP event occurred during May 2003 has pointed out that SEP events are not the unique ionization source inside the polar latitudes during the winter.