"Advisor: Dr. Paul Markowski"

Abstract:

Horizontal low-level wind speed maxima, referred as low-level jets, have important impacts on a wide range of fields, including aviation. The spatial structure, evolution and mechanisms of formation of the low-level jet over the Orinoco River basin, which poses a risk to aerial operations at ten regional airports and three Colombian Air Force bases, will be characterized using finer horizontal, vertical, and temporal resolution than possible in previous studies via dynamical downscaling. The investigation will rely on a 5-month-long simulation (November 2013-March 2014) performed with the Weather Research and Forecasting model, with initial and boundary conditions provided by the Global Forecast System analysis. Preliminary results indicate that the Orinoco low-level jet (OLLJ) is a single stream tube over Colombia and Venezuela with wind speeds greater than 8 m s^-1.  The OLLJ exhibits its maximum wind intensity and largest spatial extent (2,100 km × 450 km) in January. OLLJ wind speeds are a maximum in the morning (~12–14 m s^-1; 0700 LST), when low-level static stability is maximized; wind speeds are a minimum in the afternoon (~8 m s^-1, 1500 LST), when the boundary layer is approximately neutrally stratified. The peak winds tend to develop within three distinct cores; these cores are found in the vicinity of the most steeply sloped terrain.  Dynamical downscaling is demonstrated to be an effective method to better resolve the horizontal and vertical characteristics of the OLLJ, not only improving the identification and location of the cores within the broader OLLJ, but also its diurnal and austral-summer evolution. Additional simulations will be performed to test the sensitivity of the OLLJ structure and behavior to different model configurations, such as using different planetary-boundary-layer and surface-layer schemes, topography height reduction, or increased grid spacing. These sensitivity experiments are expected to identify the most important mechanisms for the development of the OLLJ and the suggested model configuration to represent it adequately. Having a better characterization and understanding of the OLLJ will provide more accurate information to operational forecasters and pilots for making decisions that could save lives.