Examination of Gravity Waves Associated with the 13 March 2003 Bow Echo

Abstract

umerical simulations of the 13 March 2003 bow echo over Oklahoma are used to evaluate bow echo development and its relationship with gravity wave generation. Multiple fast-moving (with speeds of 30?35 m s?1) gravity waves are generated in association with fluctuations in the first vertical mode of heating in the convective line. The surface impacts of four such waves are observed in Oklahoma Mesonet data during this case. Observations of surface pressure surges ahead of convective lines prior to the bowing process are reproduced; a slower gravity wave produced in the simulation is responsible for a prebowing pressure surge. This slower gravity wave, moving at approximately 11 m s?1, is generated by an increase in low-level microphysical cooling associated with an increase in rear-to-front flow and low-level downdrafts shortly before bowing. The wave moves ahead of the convective line and is manifested at the surface by a positive pressure surge. The pattern of low-level vertical motion associated with this wave, in conjunction with higher-frequency gravity waves generated by multicellularity of the convective line, increases the immediate presystem CAPE by approximately 250 J kg?1 just ahead of the bowing segment of the convective line. Increased presystem CAPE aids convective updraft strength in that segment despite amplified updraft tilt due to a stronger cold pool and surface-based rear-to-front flow, compared to updraft strength in other, nonbowing segments of the convective line.