A mesoscale gravity wave event observed during CCOPE. Part III: wave environment and probable source mechanisms

Abstract

Synoptic-scale analysis reveals that the waves were excited north of a stationary front and within the right exit region of the jet streak as it approached a stationary ridge in the 300 mb height field. Strong indications of unbalanced flow were diagnosed within the gravity wave source region. Hence, it is suggested that the propagation of the jet streak, toward the ridge resulted in the shedding of a gravity-inertia wave packet in association with a geostrophic adjustment process, which in turn triggered severe thunderstorms along the preexisting outflow boundary. A shear instability analysis conducted upon a representative CCOPE sounding shows that the vertical shear associated with the jet also could have served as a wave energy source, since a wave critical level was found at which the calculated Richardson number fell to a value Ri~ 1/4 . Additional analyses indicate that the observed waves were nondispersive and hydrostatic and that vertical energy propagation was impeded by a wave duct associated with the presence of the critical level and lower-tropospheric static stability. -from Authors