engleski

Microscale properties of bora turbulence at the new micrometeorological research facility

Bora macroscale and even mesoscale features have been intensively investigated in the past few decades, but the important details about bora microscale properties are yet not known well. One of the reasons for this inadequacy is the lack of measurements suitable for bora microscale investigations. Those are high-frequency in situ measurements of wind speed and temperature in space (e.g., detailed aircraft measurements) and in time (single point ground based measurements on e.g., meteorological towers/masts), as well as bora remote sensing. Therefore, Department of Geophysics, University of Zagreb, Croatia, conducted several projects in the past 10-15 years within which high-frequency measurements of the wind speed and temperature along the eastern Adriatic coast have been performed. These are single point measurements at the town of Senj, Vratnik Pass and Pometeno Brdo (Swept-Away Hill, hinterland of the city of Split). However, all those measurements were performed using sonic anemometers mounted on the towers/masts at 10 m and higher above the ground, leaving the turbulence structure of the bora wind below 10 m undisclosed (important for traffic and agriculture). Thus, here we present a new state- of-the-art micrometeorological tower measurements installed 200 m in the front of the new Maslenica Bridge (≈ 30 km NE of the city of Zadar, on the main motorway), in the lee of Velebit mountain. The tower 10 m tall, equipped with three levels of Gill WindMaster ultrasonic anemometers (2, 5 and 10 m), gathers continuously the 3D wind speed and sonic temperature with the sampling rate of 20 Hz since 09 October 2015. Most of the analysis and background theory is covered within our PhD course ‘Selected chapters in atmospheric turbulence’. Using Fourier spectral analysis, we investigate a suitable turbulence averaging scale and bora gust pulsations. The obtained data set is further used for testing the Monin-Obukhov similarity theory and the degree of closure of the prognostic TKE equation. These are expected to be considerably modified due to the complexity of the terrain and effects of vigorous air-sea- land interaction. Finally, the growing expertise in micrometeorological measurements is offered here for future collaboration within the scope of PannEx.

turbulence ; micromeasurements ; bora wind

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