Dust ring width as a function of the ring location. We set ℳ_hw = 0.03 and α_diff = 10⁻⁴. The dashed and dotted lines are given by Eq. (33) with St = 10⁻³ and 10⁻⁴, where we converted the units of ${\mathcal{W}}_{\text{ring\hspace{0.17em}}}^{\text{SA}}$ from H to au using Eq. (A.3). The blue and orange solid lines denote H and 5 H, respectively. We hatched the region where the time required for ring formation exceeds 3 Myr for the assumed dimensionless time, t. The observational data with pink and purple markers are from Bae et al. (2023) and Huang et al. (2018) (DSHARP sample), respectively.