Mechanisms for dynamic coronal mass supply via evaporative solar “micro-events”

The idea that the corona is at least in part supplied by chromospheric evaporation in loop “micro-events” is quantified in terms of the power requirements of evaporation mechanisms, using recent analyses of data on such events in high temperature EUV lines from the SoHO EIT instrument. Estimates are derived for the pre-event and event values of loop density and temperature and it is shown, using the conductive scaling law, that the event emission measure enhancements are too large to be accounted for solely by enhanced conductive flux from coronal heating. That is, observations demand that supply of coronal mass by evaporation events need a mechanism which enhances upper chromospheric heating and not just conductively driven evaporation. Thus coronal mass supply in transients is inextricably linked to direct chromospheric heating processes. Using parametric models of a chromospheric heating function and of the pre-event chromosphere, an estimate is made of the extra power required to yield the emission measure enhancement of a large event evaporatively. The dependence of the result on just how the EUV solar images are interpreted is emphasised and observational tests are discussed for the case of heating by fast particles. Implications of the results in terms of the global supply of the hot corona and wind mass loss are briefly mentioned.