Simulation shows sand grain collisions increase strength of sandstorms

Science : Sandstorms are incredibly complex to model because of the number of sand grains they contain. A new model, created by Marcus Carneiro of ETH Zürich and his colleagues, that tracks just 4000 individual grains (less than a mouthful, according to Carneiro) is a major step forward in understanding the storms. Most models have not tracked individual sand grains and have ignored mid-air grain collisions because the effect of the collisions was thought to be negligible. Carneiro’s model includes both. It measures storm strength as the number of grains moving through a given volume in a given time. By turning collision modeling on and off, the researchers were able to see the effect of collisions on storm strength. They expected that collisions would dissipate energy, but found instead that they increased the storm strength, sometimes even doubling it. Further examination found that when particles fell into an area of slow-moving sand near the ground, they created a splash, which kicked more particles up into areas of fast-moving winds. The kicked-up particles then collided with other falling particles, sending the falling particles back up into even faster-moving areas. The repeated process of falling and splashing and colliding feeds the strength of the storm. The new model’s explanation of sandstorm strength will likely have a major effect on future storm modeling, though the findings need to be confirmed by experimentation or observation.