Excess Diffusion of a Driven Colloidal Particle in a Convection Array

We numerically investigate the transport of a passive colloidal particle in a periodic array of planar counter-rotating convection rolls, at high Peclet numbers. It is shown that an external bias, oriented parallel to the array, produces a huge excess diffusion peak, in cases where bias and advection drag become comparable. This effect is not restricted to one-dimensional convection geometries, and occurs independently of the array's boundary conditions.