Sand transport initiation and cessation occurs when the surface shear velocity exceeds a fluid threshold and falls below an impact threshold, respectively. Even when average shear velocity is below fluid threshold, turbulent fluctuations can initiate saltation, leading to turbulence‐driven transport intermittency. We leveraged the dynamic properties of large‐eddy simulation to recover a shear velocity time series due to atmospheric turbulence and recover a probability density function for saltation based on the frequency of events where wind has previously exceeded fluid threshold but not yet dropped below impact threshold. By conditionally sampling, we can quantitatively predict the frequency of intermediate saltation. Results show that a compensated, subthreshold shear velocity exhibits linear dependence upon the actual shear velocity. This compensated shear velocity compares favorably against field data. Model performance under terrestrial and Mars conditions is also shown.

Introduction BackgroundAerodynamically driven emission of dust is important for weather, climate, the hydrologic cycle, ecosystems, etc. On Earth, dust storms occur locally in arid and semiarid parts of the world and are responsible for injecting aerosols into the atmosphere that are eventually deposited in the oceans and elsewhere on the planet (Goudie, 1978). Iron-containing soil dust that is deposited in the ocean via dust storms can affect the climate and ocean biochemistry and hence can affect aquatic lives and nutrient distribution in the ocean (Jickells et al., 2005). Dust deposition can also affect ocean productivity (Martin et al., 1991) and CO 2 concentration (Broecker & Henderson, 1998;Martin, 1990). Suspended particles in the air due to dust storms can have a negative impact on human health (Griffin & Kellogg, 2004). Aerosols suspended in the air can travel thousands of kilometers away from the origin of the dust storm, affecting the weather in faraway places (Prospero, 2001;Tegen et al., 1996). Although dust storms occur locally on Earth, they can have global effects on climate and weather. Hence, it is extremely important to understand the origin, evolution, and entrainment mechanisms of dust storms. On Mars, dust affects performance of scientific instruments mounted upon campaigning rovers.

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