The Impact of Solar Eruptions on the Upper Chromosphere, Transition Region, and Corona

We study how the solar atmosphere and wind respond to sudden and large increases in the coronal energy input, with the aim of better understanding the impact of fast coronal mass ejections on the lower solar atmosphere. We apply a gyrotropic multifluid model extending from the chromosphere to 1 AU and that accounts for radiative losses in the transition region. The energy is deposited as pushing of coronal plasma by a large-amplitude Alfvén wave (simulating expulsion of flux ropes) and by thermal heating of electrons and protons. Both mechanisms lead to rapid acceleration of coronal plasma close to the Sun, with speeds of order 1000-2000 km s -1 , and the resulting solar wind structures with large-amplitude shocks do not depend sensitively on the form of energy deposition in the corona. The response of the low corona and transition region does depend sensitively on the form of energy input, however. Alfvén wave pushing leads to very low coronal temperatures and densities and a strong reduction in Lyα radiation from the transition region, and only the plasma already present in the corona is expelled. Thermal heating leads to much higher coronal temperatures and densities and large downward heat fluxes, causing a strong heating of the upper chromosphere and a resulting large upflow of chromospheric material. In this case chromospheric material constitutes 50% or more of the matter ejected from the Sun as a result of the heating. Heating also leads to a sudden and large increase in the Lyα radiation during the event. Although the lower atmosphere responds rapidly to the increased energy input, it takes half a day or more for the transition region and corona to be restored to its preeruption state. Without electron or proton coronal heating, electrons never reach the temperatures required to produce the high ion charge states that are observed in some CMEs.