1. A disturbance in the troposphere of wave length 1000–4000 km (cyclonic scale). They are recognized on synoptic charts as migratory high and low pressure systems. These waves have been identified with the unstable perturbations discussed in connection with baroclinic instability and shearing instability. See short wave, barotropic disturbance. 2. A frontal wave at the crest of which there is a center of cyclonic circulation; therefore, the frontal wave of a wave cyclone.