Bora wind characteristics for engineering applications

  • Lepri, Petra (Meteorological and Hydrological Service) ;
  • Vecenaj, Zeljko (Department of Geophysics, Faculty of Science, University of Zagreb) ;
  • Kozmar, Hrvoje (Faculty of Mechanical Engineering and Naval Architecture, University of Zagreb) ;
  • Grisogono, Branko (Department of Geophysics, Faculty of Science, University of Zagreb)
  • Received : 2017.03.03
  • Accepted : 2017.04.20
  • Published : 2017.06.25


Bora is a strong, usually dry temporally and spatially transient wind that is common at the eastern Adriatic Coast and many other dynamically similar regions around the world. One of the Bora main characteristics is its gustiness, when wind velocities can reach up to five times the mean velocity. Bora often creates significant problems to traffic, structures and human life in general. In this study, Bora velocity and near-ground turbulence are studied using the results of three-level high-frequency Bora field measurements carried out on a meteorological tower near the city of Split, Croatia. These measurements are analyzed for a period from April 2010 until June 2011. This rather long period allows for making quite robust and reliable conclusions. The focus is on mean Bora velocity, turbulence intensity, Reynolds shear stress and turbulence length scale profiles, as well as on Bora velocity power spectra and thermal stratification. The results are compared with commonly used empirical laws and recommendations provided in the ESDU 85020 wind engineering standard to question its applicability to Bora. The obtained results report some interesting findings. In particular, the empirical power- and logarithmic laws proved to fit mean Bora velocity profiles well. With decreasing Bora velocity there is an increase in the power-law exponent and aerodynamic surface roughness length, and simultaneously a decrease in friction velocity. This indicates an urban-like velocity profile for smaller wind velocities and a rural-like velocity profile for larger wind velocities. Bora proved to be near-neutral thermally stratified. Turbulence intensity and lateral component of turbulence length scales agree well with ESDU 85020 for this particular terrain type. Longitudinal and vertical turbulence length scales, Reynolds shear stress and velocity power spectra differ considerably from ESDU 85020. This may have significant implications on calculations of Bora wind loads on structures.


Supported by : Croatian Science Foundation


  1. Aboshosha, H. and El Damatty, A. (2015), "Dynamic response of transmission line conductors under downburst and synoptic winds", Wind Struct., 21(2), 241-272.
  2. Agustsson, H. and Ólafsson, H. (2007), "Simulating a severe windstorm in complex terrain", Meteorologische Zeitschrift, 16, 111-122.
  3. Babic, N., Vecenaj, Z., Kozmar, H., Horvath, K., De Wekker, S.F. and Grisogono, B. (2016), "On turbulent fluxes during strong winter bora wind events", Bound.-Lay. Meteorol., 158, 331-350.
  4. Belusic, D. and Klaic, Z.B. (2004), "Estimation of Bora wind gusts using a limited area model", Tellus, 56, 296-307.
  5. Belusic, D. and Klaic, Z.B. (2006), "Mesoscale dynamics, structure and predictability of a severe Adriatic Bora case", Meteorologische Zeitschrift, 15, 157-168.
  6. Belusic, D., Hrastinski, M., Vecenaj, Z. and Grisogono, B. (2013), "Wind regimes associated with a mountain gap at the northeastern Adriatic coast", J. Appl. Meteorol. Clim., 52, 2089-2105.
  7. Belusic, D., Pasaric, M. and Orlic, M. (2004), "Quasi-periodic bora gusts related to the structure of the troposphere", Q. J. Roy. Meteor. Soc., 130, 1103-1121.
  8. Belusic, D., Pasaric, M., Pasaric, Z., Orlic, M. and Grisogono, B. (2006), "A note on local and non-local properties of turbulence in the bora flow", Meteorologische Zeitschrift, 15, 301-306.
  9. Belusic, D., Zagar, M. and Grisogono, B. (2007), "Numerical simulation of pulsations in the Bora wind", Q. J. Roy. Meteor. Soc., 133, 1371-1388.
  10. Cao, Y. and Fovell, R.G. (2016), "Downslope windstorms of San Diego county. Part I: A case study", Mon. Weather Rev., 144, 529-552.
  11. Counihan, J. (1975), "Adiabatic atmospheric boundary layers: a review and analysis of data from the period 1880-1972", Atmos. Environ., 9, 871-905.
  12. Enger, L. and Grisogono, B. (1998), "The response of bora-type flow to sea surface temperature", Q. J. Roy. Meteor. Soc., 124, 1227-1244.
  13. ESDU Data Item No. 74030. (1976), "Characteristics of atmospheric turbulence near the ground. Part I: definitions and general information", Engineering Science Data Unit, London, UK.
  14. ESDU Data Item No. 85020. (1985), "Characteristics of atmospheric turbulence near the ground. Part Ii: single point data for strong winds (neutral atmosphere)", Engineering Science Data Unit, London, UK.
  15. Grisogono, B. and Belusic, D. (2009), "A review of recent advances in understanding the meso-and micro-scale properties of the severe Bora wind", Tellus, 61, 1-16.
  16. Grubisic, V. (2004), "Bora-driven potential vorticity banners over the Adriatic", Q. J. Roy. Meteor. Soc., 130, 2571-2603.
  17. Heimann, D. (2001), "A model-based wind climatology of the eastern Adriatic coast", Meteorologische Zeitschrift, 10, 5-16.
  18. Hellman, G. (1916), "Uber die Bewegung der Luft in den untersten Schichten der Atmosphare", Meteorologische Zeitschrift, 34, 273-285.
  19. Jackson, P.L., Mayr, G. and Vosper, S. (2013), "Dynamically-Driven Winds", (Eds., Chow F.K., De Wekker S.F.J. and Snyder B.J.), Mountain Weather Research and Forecasting. Recent Progress and Current Challenges, Springer, Dordrecht, Netherlands.
  20. Jurcec, V. (1981), "On mesoscale characteristics of Bora conditions in Yugoslavia", Pure Appl. Geophys., 119, 640-657.
  21. Jurcec, V. and Viskovic, S. (1994), "Mesoscale characteristics of southern Adriatic Bora storms", Geofizika, 11, 33-46.
  22. Klemp, J.B. and Durran, D.R. (1987), "Numerical modelling of Bora winds", Meteorol. Atmos. Phys., 36, 215-227.
  23. Kozmar, H., Allori, D., Bartoli, G. and Borri, C. (2016), "Complex terrain effects on wake characteristics of a parked wind turbine", Eng. Struct., 110, 363-374.
  24. Kozmar, H., Butler, K. and Kareem A. (2015), "Downslope gusty wind loading of vehicles on bridges", J. Bridge Eng., 20(11), 04015008.
  25. Kozmar, H., Butler, K. and Kareem, A. (2012a), "Transient cross-wind aerodynamic loads on a generic vehicle due to bora gusts", J. Wind Eng. Ind. Aerod., 111, 73-84.
  26. Kozmar, H., Procino, L., Borsani, A. and Bartoli, G. (2012b), "Sheltering efficiency of wind barriers on bridges", J. Wind Eng. Ind. Aerod., 107, 274-284.
  27. Kozmar, H., Procino, L., Borsani, A. and Bartoli, G. (2014), "Optimizing height and porosity of roadway wind barriers for viaducts and bridges", Eng. Struct., 81, 49-61.
  28. Kuzmic, M., Grisogono, B., Li, X.M. and Lehner, S. (2015), "Discerning a deep and a shallow Adriatic bora event", Q. J. Roy. Meteor. Soc., 141, 3434-3438.
  29. Lepri, P., Kozmar, H., Vecenaj, Z. and Grisogono, B. (2014), "A summertime near-ground velocity profile of the Bora wind", Wind Struct.,19(5), 505-522.
  30. Lepri, P., Vecenaj, Z., Kozmar, H. and Grisogono, B. (2015), "Near-ground turbulence of the Bora wind in summertime", J. Wind Eng. Ind. Aerod., 147, 345-357.
  31. Lou, W.J., Wang, J.W., Chen, Y., Lv, Z.B. and Lu, M. (2016), "Effect of motion path of downburst on wind-induced conductor swing in transmission line", Wind Struct., 23(3), 41-59.
  32. Magjarevic, V., Vecenaj, Z., Horvath, K. and Grisogono, B. (2011), "Turbulence averaging interval for summer Bora flows at the middle of the NE Adriatic coast", Proceedings of the Poster, 31st International Conference on Alpine Meteorology, Aviemore, Scotland, 23-27 May 2011.
  33. Makjanic, B. (1978), "Bura, jugo, etezija", Prilozi poznavanju vremena i klime u SFRJ, 5, 1-43.
  34. Neiman, P.J., Hardesty, R.M., Shapiro, M.A. and Cupp, R.E. (1988), "Doppler lidar observations of a downslope windstorm", Mon. Weather Rev., 116, 2265-2275.<2265:DLOOAD>2.0.CO;2
  35. Pandzic, K. (2002), "Analiza meteoroloskih polja i sustava", HINUS, Zagreb, Croatia.
  36. Papoulis, A. and Pillai, S.U. (2002), "Probability, Random Variables, and Stochastic Processes", McGraw-Hill Europe.
  37. Petkovsek, Z. (1976), "Periodicity of Bora gusts", Rasprave-Papers SMD, 20, 67-75.
  38. Petkovsek, Z. (1982), "Gravity waves and Bora gusts", Annalen der Meteorologie, 19, 108-110.
  39. Petkovsek, Z. (1987), "Main Bora gusts-a model explanation", Geofizika, 4, 41-50.
  40. Poje, D. (1992), "Wind persistence in Croatia", Int. J. Climatol., 12, 569-586.
  41. Rakovec, J. (1987), "Preliminary report on spectral characteristics of Bora on the island of Rab", Geofizika, 4, 35-40.
  42. Simiu, E. and Scanlan, R.H. (1996), "Wind effects on structures", John Wiley, New York, NY, USA.
  43. Smith, R.B. (1987), "Aerial observations of Yugoslavian Bora", J. Atmos. Sci., 44, 269-297.<0269:AOOTYB>2.0.CO;2
  44. Solari, G. (2014), "Emerging issues and new frameworks for wind loading on structures in mixed climates", Wind Struct., 19(3), 295-320.
  45. Solari, G., Burlando, M., De Gaetano, P. and Repetto, M.P. (2015), "Characteristics of thunderstorms relevant to the wind loading of structures", Wind Struct., 20(6), 763-791.
  46. Stull, R.B. (1988), "An introduction to boundary layer meteorology", Kluwer, Dordrecht, Netherlands.
  47. Thuillier, R.H. and Lappe, U.O. (1964), "Wind and temperature profile characteristics from observations on a 1400 ft tower", J. Appl. Meteorol. Clim., 3, 299-306.<0299:WATPCF>2.0.CO;2
  48. Vecenaj, Z., Belusic, D. and Grisogono, B. (2010), "Characteristics of the near-surface turbulence during a bora event", Ann. Geophys., 28, 155-163.
  49. von Karman, T. (1948), "Progress in the statistical theory of turbulence", Proceedings of the National Academy of Sciences, 34(11), 530-539.
  50. Yang, F.L. and Zhang, H.J. (2016), "Two case studies on structural analysis of transmission towers under downburst", Wind Struct., 22(6), 685-701.

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