The electrostatic force in blowing snow.

摘要

In blizzards and sand storms, wind transport of particles is associated with separation of electrostatic charge. Moving particles develop charge of sign opposite the electrostatic charge on stationary surface particles. This electrification produces forces, in addition to the gravitational and fluid friction forces, that determine trajectories for particles being transported in saltation. Evaluating electrostatic forces requires the electric field strength very near the saltation surface and charge-to-mass ratios for the moving particles.; Measurements in a blizzard provide an electric field profile, with measured fields as high as 30 kV m-1 measured at the 4-cm height. Reversal of charge sign on samples of saltation particles collected in a blizzard indicates a mixture of positive and negative particles in transport. This result points out the need for measurements of charge on individual particles, and an apparatus designed to make these measurements is detailed. Using measured charge-to-mass ratio for individual saltation particles (Schmidt et al., 1998) of +72 mC kg--1 and --208 mC kg-1 we estimate electrostatic forces as large as the gravitational force on some saltating particles. Including forces of this magnitude in the equations of motion for saltating particles shows saltation trajectories altered as much as 60% from those for uncharged particles.; These results show that the electrostatic force has a significant effect on the saltation process which brings up questions about the effects of the electrostatic force on the transfer of momentum from the atmospheric boundary layer to the planetary surface and wind transport of particles by suspension in the atmosphere.