General description of the SOHO data sets needed:
High resolution ultra-violet (UV) spectra taken with HRTS and SUMER show transient enhancements of the wings of lines formed in the solar transition region, often referred to as explosive events. Observations to date show: (i) the observed velocities range between 50 - 250 km/s, (ii) a particular explosive event may present different time histories with distinct activity episodes (iii) the life time distribution ranges between 20 - 200 sec.
We have recently starting an observational and modelling programme whereby numerical simulations are compared to observational data. However, many outstanding questions remain, e.g. (i) why is the upflow plasma not observed in the corona? (ii) why is the enhanced activity in the transition region not observable in the lower atmosphere? Perhaps it is observable but has been labelled under a different header under what can be termed the solar zoo.
Using simulations we find that thermal energy perturbations drive flows along the flux tube. Our computational results are converted also into UV line profiles in (non)-equilibrium ionisation. These simulations are only a first approximation, however to advance further requires additional observational data. Here we propose a joint observation involving simultaneous H alpha (via Tenerife), SUMER, MDI, CDS & EIT.