3.6 Thermal flare
Most of the flare energy is thermalized in the solar atmosphere, some of which is heated to high
temperatures. This part is visible in soft X-rays (Figure 22). In the absence of further energy release the
plasma cools by thermal conduction to the chromosphere and by radiating X-rays. At high temperature and
low density, conductive cooling dominates, radiative cooling in the opposite case (Cargill et al., 1995). If
conductive cooling leads to evaporation of chromospheric material, the cooling time becomes longer as the
energy remains in the loop.
Flare loop cooling has been investigated by several authors. Radiative cooling and conduction losses
have been found to balance approximately (e.g., Jiang et al., 2006). In the late phase, radiative
cooling usually dominates, but considerable heat input is frequently observed (e.g., Milligan
et al., 2005).
mpg-Movie (1139 KB)
Soft X-ray images observed by Hinode on April 30, 2007. It shows an active region
during two hours. Some small flares or microflares occurred; the largest was of class B2.6 (prepared
by A. Savcheva).