The existence of downward propagation mechanisms that couple stratospheric disturbances to the troposphere motivated the study of processes that can influence these stratospheric regimes. The dependence of the variability on the amplitude of the tropospheric wave forcing was studied on a stratosphere-mesosphere model, showing the atmosphere to be at a transition phase between the two regimes, with potential large amplification of the response to small perturbations. The recent discovery of transient luminous events (TLEs) such as sprites motivated the systematic study of the response of the middle atmosphere model to increasingly complex idealised ozone perturbation experiments. Within radioactively driven regions, the response of the middle atmosphere was found to be linear on the magnitude of the ozone reduction, within the location and time of the perturbation. In dynamically controlled regions, localised ozone perturbations (e.g. the ozone hole) could induce larger non-local responses compared to an equivalent uniform ozone change. Impulsive perturbations were found to be more capable of inducing changes to the variability compared to the equivalent forcing that was constant in time. The first estimates of the chemical impact of sprites were obtained using satellite data. Sprites were shown to cause no significant NOx or ozone changes at a global level, but to induce up to tens of percentage changes in NOx at 50 to 70 km height over active sprite-producing thunderstones, in reasonable agreement with ion-chemistry model estimates. Sprite ozone changes were found to be 3 to 4 orders of magnitude lower than the weakest ozone perturbation needed to induce significant responses in the model.