“…In the smooth case (h = 1), the limit value Γ decreases from Γ = 1 for St = 0, which corresponds to a differentiable particle velocity field, to Γ = 0 for St → ∞, which means that particles move with uncorrelated velocities [16]. The fact that Γ < 1 is due to the contribution of caustics appearing in the particle velocity field [15,18,24,25,26] (see Sect. V for a discussion in d = 1).…”