engleski

Numerical simulation and analysis of the gap flow emanating from the Oštarijska Vrata Pass at the onset of Bora

The gap flow emanating from the Oštarijska Vrata Pass, locally called the Bora of Pag's ribs, can strongly affect the safety of maritime traffic in the Pag island area, Croatia due to the fact that strong and weak winds are sharply separated. Two cases with severe Bora have been selected for the analysis at the start of Bora. According to the measurements from automatic stations, the MM5 numerical model was successful in the 10-min mean wind speed prediction. The vertical analysis of the wind speed and potential temperature also gave satisfactory results for both cases. The model has proved successful in predicting the characteristics of the Bora of Pag’s ribs, and in the second Bora case the gap flow rotation was also successfully predicted. The vertical cross-sections through the centre of the gap point out a permanent hydraulic-like flow. The highest modeled turbulent kinetic energy was found in the jump-like region above the inversion and within the boundary layer, along the lower boundary. In both cases it was concluded that the dissipation in the hydraulic jumps and the wave breaking regions are the reasons for potential vorticity generation.

Bora onset ; gap flow ; potential vorticity

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