Dynamics of the Tokar Gap Jet

Fluid dynamics of winds occurring during the peak hours of the Tokar Gap Jet are described using a number of analyses of WRF model output data of a hindcast of an extreme jet event occurring the evening of July 11th into the following day of July 12th, 2008.  Vertical profiles of wind velocity and buoyancy frequency at points upstream of the gap led to assumptions of stratification and constant flow, which were then used in calculations describing the flow regimes existing during jet events, including the calculation of a ‘Mountain Parameter’ or ∈=(Nh)/U.  Analysis of the mountain parameter over time correlates to values calculated in existing literature that indicates a flow regime featuring mountain lee wave as well as weak upstream blocking. With the goal of better understanding leeward turbulence and what causes the jet winds to accelerate, a matlab script was developed simulating lagrangian trajectories in the region. These trajectories were then used to calculate characteristics related to energy, as well as basic air properties.  Conservation of Bernoulli’s function of air parcels following trajectories through the gap and extending over the Red Sea attributes the acceleration of the jet winds during peak hours to a change in potential energy regulated by a change in enthalpy, as indicated by the relative scale of energy terms. Later analysis using the trajectory simulations include a comparison of trajectories passing through the Tokar Gap as well as those that pass through secondary gaps and those that experience hydraulic jumps. A general Lagrangian view of the gap winds is also considered, looking at trajectories starting at various upstream locations and different times during the WRF hindcast.