  Extreme ultraviolet imaging spectroscopic observations often show an increase
in line width around the loop-top or above-loop-top (ALT) region of solar
flares, suggestive of turbulence. In addition, recent spectroscopic
observations found the oscillation in the Doppler velocity around the ALT
region. We performed three-dimensional magnetohydrodynamic (MHD) simulations to
investigate the dynamics in the ALT region, with a particular focus on the
generation of turbulence and the excitation of the oscillatory motion. We found
a rapid growth of MHD instabilities around the upper parts of the ALT region
(arms of the magnetic tuning fork). The instabilities grow more rapidly than
the magnetic Rayleigh-Taylor-type instabilities at the density interface
beneath the reconnecting current sheet. Eventually, the ALT region is filled
with turbulent flows. The arms of the magnetic tuning fork have bad-curvature
and transonic flows. Therefore, we consider that the rapidly growing
instabilities are combinations of pressure-driven and centrifugally driven
Rayleigh-Taylor-type instabilities. Despite the presence of turbulent flows,
the ALT region shows a coherent oscillation driven by the backflow of the
reconnection jet. We examine the numerical results by re-analyzing the solar
flare presented in Reeves et al. 2020. We find that the highest non-thermal
velocity is always at the uppermost visible edge of the ALT region, where
oscillations are present. This result is consistent with our models. We also
argue that the turbulent magnetic field has a significant impact on the
confinement of non-thermal electrons in the ALT region.
