Variations in peak intensity ratio, peak intensity, and nonthermal width of QS from the disk center to limb. Panel a: scatter plot of peak intensity ratios of Si IV 1394 Å to Si IV 1403 Å and the nonlinear fitting (blue curve) performed using Eq. (A.5). The upper and lower dashed curves are calculated according to Eq. (A.5) with τ₀ ± 3σ (σ is the standard deviation of τ₀) respectively. The red line is a linear fitting of peak intensity ratios in the range of μ = 1.0−0.4. Panel b: scatter plot of normalized peak intensities of Si IV 1394 Å and the theoretical normalized peak intensities (blue curve) calculated using τ₀ and Eq. (B.2). Panel c: scatter plot of nonthermal widths of Si IV 1394 Å and the theoretical nonthermal widths (blue curve) obtained using τ₀ and Eq. (C.1). The red line is a linear fitting of nonthermal widths in the range of μ = 1.0−0.4. The vertical dashed lines in the three images mark the location of μ = 0.4. We note that μ = 1.0 corresponds to closer to the disk center, whereas μ = 0.0 corresponds to closer to the limb.