A Proposed Mechanism of Squall Lines: The Pressure Jump Line

The squall line of 16 May 1948 in the area of the Cloud Physics Project, U. S. Weather Bureau micro-meteorological network of weather recording stations near Wilmington, Ohio, is analyzed by means of one-minute synoptic maps, x–t diagrams and isochrone maps. The relative behavior of the pressure jump, wind shift, temperature fall, maximum wind velocity, rain gush and pressure maximum forms the basis of a hypothesis concerning the physical mechanism of the squall line. Following the theory developed by Freeman, it is proposed that a squall line might be considered as a disturbance generated by accelerations along the cold front and which travels along the warm sector inversion as a gravitational wave. It is recommended that any series of meteorological events similar to this mechanism be called a Pressure Jump Line. The weather associated with the passage of a pressure jump line is then indicated. Speculatively it is proposed, by analogy to the theory of supersonic flow and shock waves, that the zone of interaction of two pressure jump lines is a preferred zone for tornado formation. The importance of the intensity and the time of passage of a pressure jump over a station, as the primary tools for identifying and following the progress of pressure jump lines, is emphasized.