HR: 0800h
AN: A31A-03    [Abstracts]
TI: An Observational and Modeling Study of an Atmospheric Internal Bore During NAME 2004
AU: * Martin, E R
EM: martin@atmos.colostate.edu
AF: Colorado State University, Department of Atmospheric Science, Fort Collins, CO 80523, United States
AU: Johnson, R H
EM: johnson@atmos.colostate.edu
AF: Colorado State University, Department of Atmospheric Science, Fort Collins, CO 80523, United States
AB: Atmospheric internal bores have been identified and studied in a variety of locations around the world. However, until now, atmospheric bores have not been explicitly reported in the North American monsoon region. Observations from the North American Monsoon Experiment (NAME) 2004, including soundings, surface observations, and wind profilers have been used to identify and describe the structure, dynamics and significance of an atmospheric internal undular bore in the NAME region along the Gulf of California (GoC). Such bores could potentially be important in GoC monsoon surges, which are often instrumental in bringing abundant moisture to the southwestern United States. An undular bore was identified at Bahia Kino in northwestern Mexico during the late evening of 31 July 2004, and was hypothesized to have developed from the interaction of an outflow from a large mesoscale convective system (MCS), which developed along the western slopes of the Sierra Madre Occidental during the afternoon, and a surface stable layer. The vertical structure and undular nature of the bore was initially identified from 915-MHz wind profiler data. Results show a series of waves along the bore's leading edge and turbulent mixing of air from above the stable layer to the surface on the downstream face of the leading undulation. The speed of the bore calculated from satellite imagery and surface observations (16.5 ms-1) compared favorably with the speed of a bore from hydraulic theory. In order to further investigate the formation and dissipation mechanisms of the bore, a real-data simulation of the event was performed using version 2.1.2 of the advanced research Weather and Forecasting model (WRF). Results show the model captured the structure of the bore but it was produced too far south compared to observations as the MCS also developed too far south. Results indicate the bore formed due to the collision between the MCS outflow and a stable layer formed by a sea breeze from the GoC and was maintained by wave trapping from an elevated stable layer. It is suggested that the bore dissipated due to enhanced turbulence as the surface stable layer on which it propagated reduced in depth. Explanations of the model results will be presented.
DE: 3307 Boundary layer processes
DE: 3329 Mesoscale meteorology
DE: 3355 Regional modeling
DE: 3374 Tropical meteorology
SC: Atmospheric Sciences [A]
MN: 2007 Joint Assembly