The Lorentz Force at Work: Multi-Phase Magnetohydrodynamics Throughout a Flare Lifespan

The hour-long, gradual phase of solar flares is well-observed across theelectromagnetic spectrum, demonstrating many multi-phase aspects, where coldcondensations form within the heated post-flare system, but a completethree-dimensional (3D) model is lacking. Using a state-of-the-art 3Dmagnetohydrodynamic simulation, we identify the key role played by the Lorentzforce through the entire flare lifespan, and show that slow variations in thepost-flare magnetic field achieve the bulk of the energy release. Syntheticimages in multiple passbands closely match flare observations, and we quantifythe role of conductive, radiative and Lorentz force work contributions fromflare onset to decay. This highlights how the non-force-free nature of themagnetic topology is crucial to trigger Rayleigh-Taylor dynamics, observed aswaving coronal rays in extreme ultraviolet observations. Our C-class solarflare reproduces multi-phase aspects such as post-flare coronal rain. Inagreement with observations, we find strands of cooler plasma formingspontaneously by catastrophic cooling, leading to cool plasma draining down thepost-flare loops. As there is force balance between magnetic pressure andtension and the plasma pressure in gradual-phase flare loops, this haspotential for coronal seismology to decipher the magnetic field strengthvariation from observations.