During the initial stages of a solar flare, accelerated electrons propagate along closed magnetic field lines to the dense underlying chromosphere, where they lose their energy via Coulomb collisions and heat the local plasma. The resulting expansion of this material is known as chromospheric evaporation. Although much observational evidence has been provided to lend support to this fundamental principle, the detailed theories that predict a relationship between the energy released and the dynamic response of the atmosphere, remain largely unchallenged.
Recently we have provided strong evidence for both 'gentle' (Milligan et al. ApJL, 642, 169) and 'explosive' (Milligan et al. ApJL, 638, 117) chromospheric evaporation as predicted by current solar flare models using co-spatial and co-temporal observations by RHESSI and SOHO/CDS. Through a combination of X-ray imaging and spectroscopy using RHESSI we were able to infer the properties of the driving electron beam, while the dynamic response of the solar atmosphere was measured from Doppler shifts in EUV emission lines using CDS. We showed that electron fluxes that differ by an order of magnitude produced upflow velocities in the 8 MK Fe XIX line that differ by approximately a factor of 2.
|
|