A Case Study of Apparent Gravity Wave Initiation of Severe Convective Storms

Abstract

A detailed study of an outbreak of severe convective storms is presented which investigates the interaction between subsynoptic scale gravity waves and the convective activity. The gravity waves were isolated by passing digital forms of nearly 130 National Weather Service and FAA barograph traces through a normal weighted band pass filter and then analysing pressure perturbation p′ fields for the Midwest region at 15-minute intervals. The waves had periods of about 3 h, trace speeds between 35 and 45 m s−1and amplitudes between 0.5 and 2.5 mb. Analyses of surface weather reports, radar data, surface wind convergence, and surface p′ fields revealed that the intensity of the convective systems pulsated with periods ranging frown 2 to 4 h; and that the gravity waves were a precursor to storm development in Iowa and Wisconsin and appeared to initiate convection in those areas. Reintensification of preexisting storm cells or the development of new cells generally followed the passage of the wave trough, with maximum rainfall intensity coinciding with the passage of the ridge. The cycle is completed with a general weakening of the convective storms as the next trough approaches. To substantiate the proposed causal relationship, the observations were found to be consistent with a theoretical model of subsynoptic scale gravity waves.