Heating events observed in the quiet corona

The emission measure of the quiet corona, defined by the plasma hotter than one million degrees, has been observed by EIT on SoHO to fluctuate in a alrge majority of the 1900km x 1900km pixels during the observing time of 42 minutes. In the average, the larger the emission measure in a pixel, the more it fluctuates. Increases in emission measure constitute a major energy input into the corona, suggesting that the lower corona is not just heated, but continuously replenished by chromospheric material heated to coronal temperatures. We test the hypothesis that the coronal heat input may be largely by chromospheric evaporation. The total energy input by an evaporative event consists of thermal energy, gravitational energy, expansion work and is reduced by radiative and conduction losses at various temperatures during heating. The evaluation of just the thermal energy is critically discussed. It depends on several assumptions and model parameters. Thus the published values of the energy input are only order of magnitude estimates. We conclude that heating events have revelled an exciting view on coronal heating, but definite statements on their ability to provide all the energy for coronal heating are premature.