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Spectral characteristics of the bora wind (CROSBI ID 490441)

Prilog sa skupa u zborniku | sažetak izlaganja sa skupa | međunarodna recenzija

Orlić, Mirko ; Pasarić, Miroslava ; Pasarić, Zoran Spectral characteristics of the bora wind // Book of Abstracts B / . (ur.). 2003. str. B.77-x

Podaci o odgovornosti

Orlić, Mirko ; Pasarić, Miroslava ; Pasarić, Zoran

engleski

Spectral characteristics of the bora wind

Bora is a cold, dry wind that blows above the Adriatic from the northeast quadrant, most often during winter season. Its average speed is usually not high, but - due to the gustiness - the bora speed maxima may surpass 60 m/s. Thus, bora is one of the severest local winds in the world. Previous measurements of the bora speed and direction were performed either with the large sampling intervals (greater than 1 min) over a day or more or with the small sampling intervals (1-16 s) over an hour at most, thus tending to emphasize low- or high-frequency part of the spectrum, respectively. Measurements caried out recently at Senj, east Adriatic station which is notorious for its strong bora outbreaks, with a 1 s sampling interval over two months (December 2001 - January 2002), enabled for the first time broad characteristics of the wind spectrum to be determined. Micro-m-asta TM anemometer was positioned at the coast, 15 m above sea level. During the two-month measurement interval it recorded more than 20 bora episodes, the longest lasting over 82 hours. The maximum wind speeds surpassed 40 m/s, and they were - as expected - related to gusts, the low-pass filtered speeds being smaller than 20 m/s. Spectral analysis revealed (1) an increase of energy from the smallest resolved period (2 s) to about 1 min, (2) further increase of energy between 1 and 10 min with frequently occuring maxima, (3) a spectral gap between about 10 min and 1 h, and (4) renewed increase of energy from 1 h to the largest periods as determinsd by the length of bora episodes. The last two are well-known characteristics of wind spectra observed worldwide. What makes the bora wind special is the energy continuum extending from 2 s to 1 min and accounting for more than 50% of the total wind variance - an obvious sign of strongly turbulent wind regime, and significant spectral peaks observed at periods from 3 to 8 min during most bora episodes. The position and intensity of the peaks vary from one bora episode to the other, and even within an episode, but no regularity could be noticed in their occurrence. This seems to agree with the prevailing wisdom, according to which the bora gustiness is related to unstable gravity waves that develop at the upper boundary of the bora layer.

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Podaci o prilogu

B.77-x.

2003.

objavljeno

Podaci o matičnoj publikaciji

Book of Abstracts B

.

Podaci o skupu

XXIII General Assembly of the International Union of Geodesy and Geophysics

predavanje

30.06.2003-11.07.2003

Sapporo, Japan

Povezanost rada

Geologija