Movie S1.

Consecutive image sequence of the isosurface of swirling strength λci=22×5.33×10−4Uf/θ0 over the transitional and early turbulent region 80<Reθ<1,160. Grayscale represents local values of y/δ, with white corresponding to y/δ≥1. The image sequence starts from instance t=110,000Δt and ends at t=115,000Δt. It is evident that infant TRTSs are caused by Λ vortices originating from spanwise vortex filaments. Infant TRTSs are simple hairpin packets; young TRTSs are elongated hairpin packet with noise, and matured TRTSs are a local concentration of hairpin vortices mixed with random vortex filaments. High-resolution and long-duration versions of this image sequence from instance t=100,000Δt to t=120,000Δt can be downloaded from the Center for Turbulence Research website at Stanford University.