Dense and sparse vortices in excitable media drift in opposite directions in electric field

Two mechanisms for vortex drift in an advective field are described. The velocity of vortex tip movement in an advective held is periodically modulated. It results in the periodical modulations of the core size of the vortex. While periodical changes of the core size (mechanism 1) result in vortex drift parallel to the electric field, periodical changes of the velocity (mechanism 2) result in the vortex drift in the opposite direction. Mechanism 1 dominates in sparse vortices, mechanism 2 dominates in dense vortices. Arguments used to predict the effect suggest its generic nature.