PARTICLE TRAJECTORIES ABOVE SINUSOIDAL TERRAIN

As heavy particles fall towards windswept topography, their motion is governed partly by gravitational forces and partly by fluid forces res ulting from the relative motion of the particles through the flow fiel d. Topographically induced perturbations of the flow field distort par ticle paths and ultimately modify deposition patterns at the surface. Here, we calculate trajectories of particles falling toward a series o f low-amplitude hills. Particle motion is obtained by simplifying the dynamical equations of particle motion to kinematic form and then appl ying perturbation techniques. This simplification is possible when the timescale of fluid motions is much longer than the characteristic res ponse-time of the particles. It is shown that, under the right atmosph eric conditions, alternating regions of convergent and divergent parti cle-paths will occur. An extension of the trajectory analysis yields e xpressions that predict the point of surface impact as functions of th e initial release point. This leads to a method for predicting the poi nt along the surface where deposition is either a maximum or a minimum .