Physical Conditions in Coronal Structures About to Flare

We use Hinode observations to study coronal structures about to flare, based on their apparent footpoints as a guide to identification. The high resolution and excellent stability of the Hinode observations makes the identifications much more precise than those done with the soft X-ray telescope (SXT) on board Yohkoh. The physical conditions in the coronal structure about to flare are important in understanding the nature of the plasma processes leading to the eruption. We find examples of soft X-ray microflares that agree with the SXT conclusions: the structure is essentially invisible prior to the flare in most cases. We present a estimation of preflare temperature and density and find that in these cases, the flare appears to happen in flux tubes with undetectably low electron density, less than ∼10 cm. A similar program with the full instrument set of Hinode would be extremely powerful, owing to the broad temperature coverage available.