engleski

"Zadar calm" during severe Bora

In this study, we investigate small-scale characteristics and spatial variability of severe Bora flow in the wider Zadar area with the objective of identifying reasons for the “ Zadar calm” . A detailed analysis of several severe Bora events that occurred in the winter-spring 2004/5 season is undertaken, during which a new sodar system was deployed at the Zadar-Zemunik airport, which provided continuous vertical soundings from 40 to 700 m MSL at the temporal resolution of 10 minutes. The Zadar sodar data reveals a significant variability in the wind speed and direction during the severe Bora events. The maximum Bora speeds were observed in the layer between 300 and 500 m MSL, while the low-level flow was characterized by weak winds. This observational analysis also includes surface data from Zadar and several automatic weather stations located inside the target area, as well as the Zadar - Zemunik radio-sounding data. Initial simulation results indicate that the Bora flow never fully penetrated to the surface near the coast in the Zadar area. The simulation results also suggest that the primary mountain wave could be responsible for low-level flow separation over the steep terrain, leading to weak surface winds over Zadar, downstream of Velebit.

Bora flow; sodar; flow separation; mesoscale variability

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