Modelling of explosive events in the solar atmosphere

High-resolution ultraviolet (UV) spectra of the solar outer atmosphere show transient brightenings often referred to as explosive events. These are localized regions with small spatial extent that show sudden enhancements of line intensities associated with strong non-Gaussian broadenings at temperatures between 20,000 - 200,000 K. The present work describes the progress made on their numerical simulations. Computational results are converted into UV line profiles in (non)-equilibrium ionization. Observational derived signatures (e.g emission measures) are calculated as a function of time at different locations on the solar disk. Explosive events are simulated in semi-circular magnetic flux tubes. Thermal energy perturbations representing explosive events drive flows along the flux tube. The time evolution of explosive events shows (i) a sudden rise in temperature at the perturbation site; (ii) ejections of cool and dense gas bullets and generation of sound waves; (iii) and the appearance of 'new' transition regions moving at different velocities. Recent data obtained with the SUMER instrument on board SOHO also show these kind of events. They are described elsewhere in this volume (Erdélyi et al. 1997).