The Orinoco Low-Level Jet: An Investigation of Its Characteristics and Evolution Using the WRF Model

The structure and evolution 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, is characterized using finer horizontal, vertical, and temporal resolution than possible in previous studies via dynamical downscaling. The investigation relies 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. The Orinoco low-level jet (OLLJ) is found to be 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 stream tube, but also its diurnal and austral summer evolution. Having a better characterization and understanding of the OLLJ provides more accurate information to operational forecasters and pilots for making decisions that could save lives.