Frontal dynamics of powder snow avalanches Supplementary online material

Its gradient along a streamline is “favorable” (∂pus/∂s) < 0 for y > b′ − x, and “adverse” (∂pus/∂s) > 0 for y < b′ − x. On the interface where ψ = 0 and r = b′θ/ sin θ, pus(ψ = 0) vanishes at x = b′/2 ahead of the source (θ ' 10π/27), and is always < 0 downstream of that point. Because the interface has favorable pressure gradient until θ = θf ' 13π/20, and adverse ∀θ > θf , it is convenient to define the frontal region as bounded by the exit plane where ∂pus/∂s = 0 or, equivalently, as the region x > xf with