Recent high-resolution and high-cadence observations have
surprisingly suggested that prominence barbs exhibit apparent rotating
motions suggestive of a tornado-like structure. Additional evidence has been
provided by Doppler measurements. The observations reveal opposite velocities
for both hot and cool plasma on the two sides of a prominence barb. This
motion is persistent for several hours and has been interpreted in terms of
rotational motion of prominence feet. Several authors suggest that such barb
motions are rotating helical structures around a vertical axis similar to
tornadoes on Earth. One of the difficulties of such a proposal is how to
support cool prominence plasma in almost-vertical structures against
gravity. In this work we model analytically a tornado-like structure and try
to determine possible mechanisms to support the prominence plasma. We have
found that the Lorentz force can indeed support the barb plasma provided the
magnetic structure is sufficiently twisted and/or significant poloidal flows
are present.