Dynamics of fibril magnetic fields. IV. Trapping in closed convective rolls

The equations of motion for a slender, buoyant flux tube extending horizontally along a closed convective roll are solved to illustrate the motion of the flux tube relative to the fluid. The principal effect of the buoyant rise u of the flux tube is to offset the path of the tube (which remains closed) from the closed circulation pattern of the fluid. Further investigation shows that an upward decrease of rhou causes the position of the tube to spiral inward to the dynamical equilibrium point where the convective downdraft is equal to the buoyant rise. Any variation of the convective velocity along the length of the roll has the same effect, so that flux tubes, or fibrils, are stably trapped in closed convective flow that exceeds u