Impact of Thermally Forced, Nonperiodic Internal Gravity Waves on Convective Development

The thermal forcing in the upper troposphere resulting from deep convection produces internal gravity-wave like disturbances called buoyancy bores. Although they propagate in a manner similar to gravity waves, their structure in time and space is nonperiodic; they travel as a pulse, propagating radially in all directions from the source of thermal forcing. The passage of these bores through the troposphere causes vertical displacements throughout the column in which they occupy. The actual displacements depend upon the vertical structure, or mode, of the bore. Some bores cause local subsidence, while other bores are characterized low-level ascent and upper-level subsidence. Based upon idealized simulations, theories about the contribution of bores to the suppression or enhancement of convection differ. One holds that bores are capable of suppressing convection away from a mesoscale convective system (MCS) while another holds that low-level convergence is supported by bores near an MCS. This paper investigates buoyancy bore behavior in a mesoscale model simulation using initial and boundary conditions from an actual convective outbreak in the central plains of the United States. Despite low-level forcing produced by colliding outflow boundaries on this day, convection failed to initiate between two MCSs due to mid- to upper-level subsidence. Through manipulation of the convective parameterization scheme within the model, the initiation and suppression of convective heating regions is explicitly controlled. This technique of manual convective initiation allows for a better isolation of the specific sources of thermal forcing. Once the behavioral characteristics of buoyancy bores are ascertained, an analysis of buoyancy bore behavior during the simulated convective outbreak is conducted. The bores suspected of enhancing low-level convergence near MCSs never manifest themselves in the simulations.Air Force Inst of Tech Wright-Patterson AFB OH is the author of 'Impact of Thermally Forced, Nonperiodic Internal Gravity Waves on Convective Development', published 2001 under ISBN 9781423527077 and ISBN 1423527070.