An improved parameterization of wind‐blown sand flux on Mars that includes the effect of hysteresis

Abstract

[1] Saltation, the wind-driven hopping motion of sand grains, forms dunes and ripples, and ejects fine dust particles into the atmosphere on Mars. Although the wind speed at which saltation is initiated, the "fluid threshold," has been studied extensively, the wind speed at which saltation is halted, the "impact threshold," has been poorly quantified for Mars conditions. I present an analytical model of the impact threshold, which is in agreement with measurements and numerical simulations for Earth conditions. For Mars conditions, the impact threshold is approximately an order of magnitude below the fluid threshold, in agreement with previous studies. Saltation on Mars can thus be sustained at wind speeds an order of magnitude less than required to initiate it, leading to the occurrence of hysteresis. I include the effect of hysteresis into an improved parameterization of sand transport on Mars.

The Noise Model of the SEIS Seismometer of the InSight Mission to Mars

“…Therefore, this saltation effect is limited to a reduced period of time, when the wind velocity is over a threshold u . Following Kok (2010), the minimum wind shear speed (u ) for saltation is about 0.5 m/s (for 100 µm grains). We can estimate the wind shear speed from the wind speed at one measurement location, U x (z), if we make an assumption on the surface roughness, z o :…”

“…The saltation is initiated when the shear stress exerted by wind on the soil surface exceeds the fluid threshold Kok (2010), at which point surface particles are lifted Kok et al (2012). These lifted particles undergo ballistic trajectories during which they are accelerated by wind drag.…”

“…-A secondary impact coming from "saltation particles" flux from saltation models Kok (2010): these heavier particles have mostly a ballistic trajectory and impact the WTS with a ≈45 deg angle. The saltation is initiated when the shear stress exerted by wind on the soil surface exceeds the fluid threshold Kok (2010), at which point surface particles are lifted Kok et al (2012).…”

Recent developments in planetary Aeolian studies and their terrestrial analogs

“…Calculations show that Mars sand grains should saltate in trajectories that are 100 times longer and higher, and reach velocities that are 5-10 times higher, than equivalent sand grains on Earth (Almeida et al, 2008a), leading to models of dune formation and modification under diverse wind regimes (Parteli et al, 2009a, b). Similarly, a recent comprehensive numerical model of steady state saltation (Kok and Renno, 2009) was used to calculate that the wind speed needed to maintain saltation on Mars is an order of magnitude less than the wind speed required to initiate saltation (Kok, 2010a), leading to the possibility of a hysteresis effect that would allow for maintenance of saltation at wind speeds much lower than previously thought (Kok, 2010b). The on-going monitoring of documented sand movement rates on Mars should provide a steadily growing data set for future applications to a variety of numerical modeling efforts.…”

Preparing for InSight: An Invitation to Participate in a Blind Test for Martian Seismicity

“…Because the electrical tether linking SEIS to the lander is sensitive to electric fields, this creates an electric-field noise that will be detected by SEIS. Using the wind shear velocity (LES data), the induced saltation mass flux and resulting electric field are derived following Kok and Renno (2009) and Kok (2010). This electric-field noise is equivalent to an additional voltage noise at the integrator level.…”