Observations of a Mesoscale Ducted Gravity Wave

Abstract

This paper reports coordinated observations of a mesoscale gravity wave made during the FRONTS 84 field experiment conducted in southwestern France in the summer of 1984. The observations were unique in the sense that all relevant wave characteristics, including its detailed vertical structure, could be directly ascertained and shown to be mutually consistent. The wave was observed to be ducted. The static stability structure of the atmosphere was favorable for the existence of such a duct. A critical level (where the phase velocity of the wave matches the wave-parallel background wind speed) was present in or just above a layer of low static stability that capped a stabler layer at a still lower level. The observed vertical structure was that of a standing wave with the top of the stable lower layer corresponding roughly to an antinode and one-half the vertical wavelength below the critical level. The wave was observed when there was extensive activity associated with two line of deep convection. No define conclusion could be drawn, however, about the interaction between the wave and the convection.