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  • Author or Editor: J. E. Stout x
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G. E. Stout and J. C. Neill

Areal rainfall distribution over a 50-square-mile area was observed by 3-cm radar and by a rain-gage network of 33 rain gages. Isohyetal maps were prepared from both rain-gage and radar observations in order to compare the rainfall distribution as observed by the two rainfall observation techniques. The computed rainfall values were at least as accurate as those obtained by a rain-gage network of one gage per 200 square miles and in some cases they were considerably more accurate.

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J. E. Stout, S. P. Arya, and E. L. Genikhovich

Abstract

The effects of nonlinear drag on the motion and settling velocity of heavy particles in a turbulent atmosphere are investigated. The authors approach the problem rather systematically by first considering the response of particles to much simpler fluid motions that are subprocesses of the more complex turbulent field. The authors first consider the motion and time response of particles falling under gravity in still fluid. Then the effects of a sudden gust or step change in relative velocity between a falling particle and its surrounding fluid are investigated. The authors demonstrate that horizontal relative motion produced by a sudden gust tends to reduce the settling velocity of a panicle. In simple oscillating fluids it is shown that the reduction of settling velocity increases with increasing amplitude of fluid oscillation. The authors also explore the effects of oscillation frequency on the settling velocity and show that if the period of fluid oscillation is less than the particle response time, then the settling velocity reduction becomes independent of oscillation frequency. Finally, the authors explore the motion of heavy particles within simulated isotropic turbulence and show that the effect of nonlinear drag is to produce a slowing of particle settling velocity.

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J. E. Stout, Y-L. Lin, and S. P. S. Arya

Abstract

Trajectories of 500- and 1000-μm diameter particles are calculated as they fall through the spatially varying flow field above sinusoidal terrain for various combinations of atmospheric stability, wind speed, and terrain wavelength. In each case, a set of 20 uniformly spaced particles are released simultaneously above sinusoidal topography and their trajectories are obtained numerically by coupling a linear wave solution for flow over sinusoidal topography with equations for particle motion. The flow field and the associated patterns of deposition are shown to be strongly influenced by atmospheric stratification. For strong stratification, the presence of vertically propagating waves produces relatively concentrated “particle streams.” For less stratified conditions with evanescent waves, little focusing of particle trajectories is apparent. The ability of the atmosphere to focus or concentrate falling particles may ultimately produce regions along the surface with enhanced deposition.

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