engleski

Quasi-periodic bora gusts related to the structure of the troposphere

This study provides a new insight into the behaviour of the bora wind gusts. Wind speed and direction measured with a 1 s sampling interval between 1 December 2001 and 31 January 2002 at Senj (east Adriatic) provided a sufficiently large database for a study of the gusts behaviour. The performed spectral analysis confirmed the occurrence of pulsations in the bora flow. Moreover, a new type of dynamics, involving the onset, cessation and reappearance of the pulsations within a single episode, has been observed in several cases. Suggested mechanisms responsible for generating these phenomena have been determined from comparisons of surface wind data with the upstream tropospheric thermodynamical structure derived from Zagreb radiosonde data. In particular, it has been shown that the appearance of an upper-tropospheric jet stream results in cessation of the pulsations, and the decrease in the jet stream supports quasi-periodic gust behaviour. As the pulsations are generated by wave breaking, the jet stream appearance has been related to the disappearance of the wave-breaking region in the lee of the mountain, which is in accordance with previous studies of downslope windstorms.

Downslope windstorm; Jet stream; Quasi-periodic pulsations

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