Yohkoh has revealed the existence of persistent high temperature plasmas in solar active regions where major flare activity takes place. Density at the energy release site for coronal heating determines the efficiency of magnetic heating, and hence the heating energy flux. Temperatures and densities of solar (and stellar) flares at the pre-flare states are compiled. Preflare conditions are basically derived from the data taken with the same instruments several tens of minutes before the onset of the impulsive phase of subsequent flares. It is found that the temperature increase from the preflare to flare states is only ∆ log T ∼ 0.2, and that density and flux increases are roughly independent of the flare thermal energy. Namely large flares take place at the coronal loops where both temperatures and densities are already high. Several line pairs exist in the EIS observing wavelengths, which are suitable for plasma density diagnostics, covering wider temperature ranges. Combining with the emission measure information, ``differential'' filling factors will reveal the fundamental structures of coronal loops proceeding to abrupt magnetic activity.
The Solar-B Mission and the Forefront of Solar Physics
- Pub Date:
- December 2004