  This article investigates the formation of spanwise vorticity in the velocity
streaks of the oblique laminar- turbulent bands of plane Couette flow (PCF) by
mean of Direct Numerical Simulations (DNS). The spanwise vorticity is created
by a roll-up type development of the streamwise-wall normal shear layer of the
velocity streaks. It is advected by the large scale flow along the bands. We
propose a criterion on spanwise vorticity which detects these events in order
to perform systematic measurements. Beside of the streamwise and spanwise
correlation lengths of the rolls, their advection velocity is measured and
shown to match the large scale flow along the band near the turbulent region.
Eventually, we discuss the possible relation between ejection of vorticity away
from the bands near the laminar region and the size of said laminar region.
