  We present the first observational study of the onset and evolution of solar
flare turbulence in the lower solar atmosphere on an unprecedented time scale
of 1.7 s using the Interface Region Imaging Spectrograph observing plasma at a
temperature of 80,000 K. At this time resolution, nonthermal spectral line
broadening, indicating turbulent velocity fluctuations, precedes the flare
onset at this temperature and is coincident with net blue-shifts. The
broadening decreases as the flare brightens and then oscillates with a period
of ~10 s. These observations are consistent with turbulence in the lower solar
atmosphere at the flare onset, heating that region as it dissipates. This
challenges the current view of energy release and transport in the standard
solar flare model, suggesting that turbulence partly heats the lower
atmosphere.
