A case study of a severe Adriatic bora on 28 December 1992

Abstract

Most bora research, until now, considered the appearance of the severe bora only on the northern Adriatic. However, the important topic of this paper is the internationally less known southern Adriatic bora. Preliminary results, including ours, begin to change the traditional view of bora as a local small-scale phenomenon by suggesting that bora-related airflow has a multiscale nature. Here, we present a rare synoptic situation which was characterised by the strong NE flow through the entire depth of the troposphere, which could be responsible for the appearance of the unusually severe wind over the continental part of Croatia and the bora on the southern Adriatic at 27 /29 December 1992. The results of isentropic diagnostics show that the southern Adriatic bora mechanism could not be explained by 2-D hydraulic theory with simpler upstream conditions as was mainly the case on the northern Adriatic. The downstream effects, due to the isallobaric component of the ageostrophic motion, play an essential role in the southern Adriatic bora genesis. This does not diminish the importance of upstream effects on the bora flow. From the theoretical approach, it is considered that upstream conditions for the southern Adriatic bora should be based on 3-D theories and numerical simulation which could explain the flow splitting, divergence and steep lowering of isentropic surfaces.

Transient cross-wind aerodynamic loads on a generic vehicle due to bora gusts

“…Their most prominent feature is strong gustiness. In severe bora cases, mean hourly wind speeds exceed 17 m/s (Ivančan-Picek and Tutiš, 1996;Belušić et al, 2004aBelušić et al, , 2004bKoračin, 1984;Yoshino, 1976), while gusts may reach values to 69 m/s (Bajić and Peroš, 2005). Spectral analyses of bora gusts (Petkovšek, 1982(Petkovšek, , 1987 reveal spectral peaks between 3 min and 11 min, often with doubling of periods (Petkovšek and Rakovec, 1983;Koračin, 1982;Petkovšek, 1984), and a possibility of cessation and even reappearance of the pulsations in the course of a single bora episode (Watanabe, 1976) that highlights a transient, irregular nature of the bora wind.…”

Dense water generation on a shelf: the case of the Adriatic Sea

“…It is generated in a shallow area ( Fig. 1) largely affected by: (1) severe winter outbreaks of the cold and dry northeast Bora wind (Ivancˇan-Picek and Tutisˇ1996;Belusˇic´et al 2004;Grubisˇic´2004), which shows large year-to-year variability, and (2) large rivers, of which the Po River is the largest (average discharge of 1,500 m 3 /s, Raicich 1996), flooding the surface layers during most of the year, but confined to the western coast, especially during severe winters (Hendershott and Rizzoli 1976; Zore-Armanda and Gacˇic1 987; Supic´and Ivancˇic´2002). All these factors acting together contribute to NAdDW generation (Beg-Paklar et al 2001), resulting in: (1) buoyancy-driven circulation due to river runoff, (2) surface cooling due to large heat loss during Bora events, and (3) wind-driven circulation and vertical mixing due to large wind inhomogeneity over the region.…”

Development of an atmosphere‐ocean coupled model and its application over the Adriatic Sea during a severe weather event of Bora wind

“…The speed and direction of the Bora largely depend on orographic details, hence mountain and coastal features are clearly responsible for daily variation in wind speed and direction during Bora periods. In spite of these local effects, the onset of the Bora, (its longevity and its severity) have been shown to be closely related to larger subsynoptic features, in particular, those resulting from the interaction processes of synoptic scale flow with the Alpine massif [ Jurcev and Vishovic , 1994; Ivancan‐Picek and Tutis , 1996].…”