  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.
