Movie S2.

Consecutive image sequence of the isosurface of temperature φ=0.25φwall in 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. The meandering and breakdown of long streaks occur later when the streaks are contaminated by existing neighboring TRTSs, which in turn, provides a means for the existing spots to grow in size. 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.