CATURBO - ChAracteristics of TURbulence of the BOra wind
Scientific project of the Croatian Science Foundation
Keywords: atmosphere, wave breaking, atmospheric boundary layer, mesoscale, turbulent kinetic energy, dissipation, wind energy, air pollution, environmental issue
Turbulence is a principally unsolved problem in science; it occurs almost everywhere around us: in rivers, sea, air, plasma (in the higher atmosphere). Simultaneously, no other part of the atmosphere that we breathe is more important to Earth’s ecosystems than its lowest layer, the Atmospheric Boundary Layer (ABL), which is always under the influence of turbulence. The land-sea-ice surface exchanges heat, momentum and mass with the free atmosphere via the ABL. Naturally, characteristics of the ABL (and turbulence) is affected by orography, land use, external forcing like radiation, and Earth’s rotation. Environmental changes, either due to gradually evolving global warming or rapidly dispersing atmospheric pollutants, have a strong impact on all living organisms in the ABL because of its interactive role between the atmosphere and Earth's surfaces (land, sea or ice).
A turbulent downslope windstorm blowing at the eastern Adriatic coast from NE direction is called Bora. Similar winds exist at other places on virtually all continents. Related hourly mean wind speeds surpassing 20 m/s, with gusts reaching up to 50-70 m/s, in the (coastal) mountain lee areas are common (hurricane speeds!). It is known that various roles of turbulence in the Bora evolution and the related flow structures are still understood inadequately. This project aims at explaining the Bora turbulence main characteristics; these relate but are not limited to the Bora wave breaking, Turbulent Kinetic Energy (TKE production, dissipation, etc.) and overall spatio-temporal flow structures.
Recent research projects, conference presentations, workshops, peer-review publications, etc. show clearly the relevance, potential and international recognition of the importance of Bora-like turbulence. The most productive soon-ending national project in Geosciences over the last ~4 years is our project BORA, which serves as a basis for CATURBO. Although turbulence research is seldom done nowadays because it the subject is so difficult, this proposal also fits into scientific and technical applications and knowledge transfer. This will be achieved by assessing the specific type of relevant flows in Croatia, Bora wind, which affects daily life in terms of traffic, wind energy resources and air-pollution transport and near-coastal dispersion. Bora wind is clearly one of the few Croatian brands.
The study of above-mentioned phenomena such as waves, turbulence, transport and dispersion of air pollution, wind energy usage is based on the high-frequency wind and temperature measurements at various vertical levels at a few places. Such a (rare) type of measurements permit the calculation of turbulent fluxes and various TKE components essential for the calculation of materials properties (stress and strain), for atmospheric dispersion and validating research and operational numerical meteorological models that we also deploy (to some extent) to further study e.g., Bora rotors, pulsations and dangerous hydraulic jumps in Bora flows. We will come up with a better understanding of Bora turbulence, its finer numerical model treatment, i.e., its sub-grid scale parameterization, which will allow for rapid applications in wind energy and air-pollution calculations as well as detailed Bora forecasts (the beginning, the end and the spatial distribution).
With this project the Croatian meteorology (and geophysics) keeps its excellence and continues to provide the expertise in atmospheric turbulence, Bora research and further applications. Working in four different institutions on three continents, CATURBO collaborators are competent for further international developments and regional applications of the related research. It is evident from our references and the specific spread of the young, vigorous collaborators. Toward the end of CATURBO, we will deal with very-fine scale numerical simulations of Bora airflow and some of the turbulence and thus also the related, consequent transfer of knowledge and applications.