  Sandstorms are frequently accompanied by the generation of intense electric
fields and lightning. In a very narrow region close to the ground level, sand
particles undergo a charge exchange mechanism whereby larger (resp. smaller)
sized sand grains become positively (resp. negatively) charged are then
entrained by the turbulent fluid motion. Our central hypothesis is that
differently sized sand particles get differentially transported by the
turbulent flow resulting in a large-scale charge separation, and hence a
large-scale electric field. We utilize our simulation framework, comprising of
large-eddy simulation of the turbulent atmospheric boundary layer along with
sand particle transport and an electrostatic Poisson solver, to investigate the
physics of electric fields in sandstorms and thus, to confirm our hypothesis.
We utilize the simulation framework to investigate electric fields in weak to
strong sandstorms that are characterized by the number density of the sand
particles. Our simulations reproduce observational measurements of both mean
and RMS fluctuation values of the electric field. We propose a scaling law in
which the electric field scales as the two-thirds power of the number density
that holds for weak-to-medium sandstorms.
