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Atmosphere 2018, 9(4), 116; https://doi.org/10.3390/atmos9040116

Micro-Scale Properties of Different Bora Types

1
Croatia Control Ltd., 10410 Velika Gorica, Croatia
2
Department of Geophysics, Faculty of Science, University of Zagreb, 10000 Zagreb, Croatia
3
EKONERG—Energy and Environmental Protection Institute, 10000 Zagreb, Croatia
4
Meteorological and Hydrological Service, 10000 Zagreb, Croatia
*
Author to whom correspondence should be addressed.
Received: 24 January 2018 / Revised: 15 March 2018 / Accepted: 16 March 2018 / Published: 21 March 2018
(This article belongs to the Special Issue Atmospheric Processes over Complex Terrain)
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Abstract

In this paper we use 20 Hz wind measurements on three levels (2, 5, and 10 m) to investigate the differences in micro-scale properties of different bora types, i.e., deep and shallow bora with further subdivision to cyclonic and anticyclonic bora cases. Using Fourier spectral analysis, we investigate a suitable turbulence averaging scale and bora gust pulsations. The obtained data set is further used to test the Monin–Obukhov similarity theory, the surface layer stratification, the behavior of the terms in the prognostic turbulence kinetic energy equation, and the wind profiles. One of our main goals is to identify possible micro-scale differences between shallow and deep bora types because of the possible different mountain wave dynamics in those flows. We found that a turbulence averaging scale of 30 min is suitable for this location and is in agreement with previous bora studies. The wind speed power spectral densities of all selected bora episodes showed pulsations with periods of 2–8 min. This suggests that mountain wave breaking was present in all cases, regardless of flow depth and synoptic type. The stability parameter analysis confirmed the near-neutral thermal stratification of bora; a consequence of intensive mechanical mixing. No significant differences related to bora type were observed in other micro-scale parameters. View Full-Text
Keywords: bora; turbulence; micro-scale; pulsations; wind profiles; surface layer; mountain wave bora; turbulence; micro-scale; pulsations; wind profiles; surface layer; mountain wave
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).
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Šoljan, V.; Belušić, A.; Šarović, K.; Nimac, I.; Brzaj, S.; Suhin, J.; Belavić, M.; Večenaj, Ž.; Grisogono, B. Micro-Scale Properties of Different Bora Types. Atmosphere 2018, 9, 116.

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