  Planetary-scale waves are thought to play a role in powering the
yet-unexplained atmospheric superrotation of Venus. Puzzlingly, while Kelvin,
Rossby and stationary waves manifest at the upper clouds (65--70 km), no
planetary-scale waves or stationary patterns have been reported in the
intervening level of the lower clouds (48--55 km), although the latter are
probably Lee waves. Using observations by the Akatsuki orbiter and ground-based
telescopes, we show that the lower clouds follow a regular cycle punctuated
between 30$^{\circ}$N--40$^{\circ}$S by a sharp discontinuity or disruption
with potential implications to Venus's general circulation and thermal
structure. This disruption exhibits a westward rotation period of $\sim$4.9
days faster than winds at this level ($\sim$6-day period), alters clouds'
properties and aerosols, and remains coherent during weeks. Past observations
reveal its recurrent nature since at least 1983, and numerical simulations show
that a nonlinear Kelvin wave reproduces many of its properties.
