Multi-wavelength observations and modelling of a canonical solar flare

¹ Astrophysics Research Group, School of Physics, Trinity College Dublin, Dublin 2, Ireland e-mail: rafteryc@tcd.ie
² Solar Physics Laboratory (Code 671), Heliophysics Science Division, NASA Goddard Space Flight Centre, Greenbelt, MD 20771, USA

Received: 20 June 2008
Accepted: 5 December 2008

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 , consistent with pre-flare heating and gentle chromospheric evaporation. During the impulsive phase, upflows of ~80 km s^-1 in and simultaneous downflows of ~20 km s^-1 in and 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 .

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.