  Magnetic reconnection is a universal process that powers explosive energy
release events such as solar flares, geomagnetic substorms, and some
astrophysical jets. A characteristic feature of magnetic reconnection is the
production of fast reconnection outflow jets near the plasma Alfv\'{e}n speeds.
In eruptive solar flares, dark, finger-shaped plasma downflows moving toward
the flare arcade have been commonly regarded as the principal observational
evidence for such reconnection-driven outflows. However, they often show a
speed much slower than that expected in reconnection theories, challenging the
reconnection-driven energy release scenario in standard flare models. Here, we
present a three-dimensional magnetohydrodynamics model of solar flares. By
comparing the model-predictions with the observed plasma downflow features, we
conclude that these dark downflows are self-organized structures formed in a
turbulent interface region below the flare termination shock where the outflows
meet the flare arcade, a phenomenon analogous to the formation of similar
structures in supernova remnants. This interface region hosts a myriad of
turbulent flows, electron currents, and shocks, crucial for flare energy
release and particle acceleration.
