Multi-wavelength observations and modelling of a canonical solar flare

Abstract

Aims. We investigate the temporal evolution of temperature, emission measure, energy loss, and velocity in a C-class solar flare from both observational and theoretical perspectives. Methods. The properties of the flare were derived by following the systematic cooling of the plasma through the response functions of a number of instruments - the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI; >5 MK), GOES-12 (5-30 MK), the Transition Region and Coronal Explorer (TRACE 171 Å 1 MK), and the Coronal Diagnostic Spectrometer (CDS; ∼0.03-8 MK). These measurements were studied in combination with simulations from the 0-D enthalpy based thermal evolution of loops (EBTEL) model. Results. At the flare onset, upflows of ∼90 km s -1 and low-level emission were observed in Fe XIX, consistent with pre-flare heating and gentle chromo spheric evaporation. During the impulsive phase, upflows of ∼80 km s-1 in FeXIX and simultaneous downflows of ∼20 km s-1 in He I and O V were observed, indicating explosive chromospheric evaporation. The plasma was subsequently found to reach a peak temperature of ≳13 MK in approximately 10 min. Using EBTEL, conduction was found to be the dominant loss mechanism during the initial ∼300 s of the decay phase. It was also found to be responsible for driving gentle chromospheric evaporation during this period. As the temperature fell below ∼8 MK, and for the next ∼4000 s, radiative losses were determined to dominate over conductive losses. The radiative loss phase was accompanied by significant downflows of ≲40 km s-1 in O V. Conclusions. This is the first extensive study of the evolution of a canonical solar flare using both spectroscopic and broad-band instruments in conjunction with a 0-D hydrodynamic model. While our results are in broad agreement with the standard flare model, the simulations suggest that both conductive and non-thermal beam heating play important roles in heating the flare plasma during the impulsive phase of at least this event. © ESO 2009.