Here, we propose a conceptual framework of Aeolian sediment transport initiation that includes the role of turbulence. Upon increasing the wind shear stress
above a threshold value
, particles resting at the bed surface begin to rock in their
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Here, we propose a conceptual framework of Aeolian sediment transport initiation that includes the role of turbulence. Upon increasing the wind shear stress
above a threshold value
, particles resting at the bed surface begin to rock in their pockets because the largest turbulent fluctuations of the instantaneous wind velocity above its mean value
induce fluid torques that exceed resisting torques. Upon a slight further increase of
, rocking turns into a rolling regime (i.e., rolling threshold
) provided that the ratio between the integral time scale
(where
is the boundary layer thickness) and the time
required for entrainment (where
d is the particle diameter and
s the particle–air–density ratio) is sufficiently large. Rolling then evolves into mean-wind-sustained saltation transport provided that the mean wind is able to compensate energy losses from particle-bed rebounds. However, when
is too small, the threshold ratio scales as
, consistent with experiments. Because
controls
and the relative amplitude of turbulent wind velocity fluctuations, we qualitatively predict that Aeolian sediment transport in natural atmospheres can be initiated under weaker (potentially much weaker) winds than in wind tunnels, consistent with indirect observational evidence on Earth and Mars.
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