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 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 to March 2014) performed with the Weather Research and Forecasting model, with initial and boundary conditions provided by the Global Forecast System analysis. Dynamical downscaling is demonstrated to be an effective method to better resolve the horizontal and vertical characteristics of the Orinoco low-level jet (OLLJ), improving not only the representation of small-scale jet streaks within the broader region of low-level wind enhancement but also its diurnal and austral-summer evolution. The OLLJ is found to be a single stream tube over Colombia and Venezuela with wind speeds greater than 8 m/s and four distinctive cores varying in height under the influence of sloping terrain. The OLLJ has its maximum monthly mean wind speed (13 m/s) and largest spatial extent (2,100 km × 400 km) in January. The maximum mean wind speeds (13–17 m/s) in the diurnal cycle occur in the early morning, whereas wind speeds are a minimum (8–9 m/s) in the late afternoon when a deep, convective boundary layer is present. The intraseasonal variability of the wind speed and potential temperature only presents significant periodicity in the diurnal and semidiurnal scales, with no other meaningful cycles evident during the austral summer.