  Su et al. 2012 proposed a new explanation for filament formation and
eruption, where filament barbs are rotating magnetic structures driven by
underlying vortices on the surface. Such structures have been noticed as
tornado-like prominences when they appear above the limb. They may play a key
role as the source of plasma and twist in filaments. However, no observations
have successfully distinguished rotational motion of the magnetic structures in
tornado-like prominences from other motions such as oscillation and
counter-streaming plasma flows. Here we report evidence of rotational motions
in a tornado-like prominence. The spectroscopic observations in two coronal
lines were obtained from a specifically designed Hinode/EIS observing program.
The data revealed the existence of both cold and million-degree-hot plasma in
the prominence leg, supporting the so-called "the prominence-corona transition
region". The opposite velocities at the two sides of the prominence and their
persistent time evolution, together with the periodic motions evident in
SDO/AIA dark structures, indicate a rotational motion of both cold and hot
plasma with a speed of $\sim$5 km s$^{-1}$.
