Abstract
On 20 May 1977 a periodic pressure disturbance over the upper Midwest was detected by synoptic and mesoscale microbarograph arrays. Analysis indicates that a pressure wave with an amplitude of approximately 1.0 mb, a phase speed of approximately 14 m s−1, a period of between 1.5 and 3 h, and a horizontal wavelength of approximately 100 km moved through Illinois, Iowa and Wisconsin from the south within the warm sector of an occluded cyclone. We interpret them pressure data as the signature of an internal atmospheric gravity wave. At several locations convective precipitation occurred coincident with the advancing ridges of the pressure wave, suggesting that the gravity wave influence convection. Openings in the cloud cover correlated with the location of the gravity wave. Simple modeling confirms the destabilization potential of the gravity wave.
