42 Sensitivity of bora turbulence to the analysis procedures

Wednesday, 11 June 2014
Palm Court (Queens Hotel)
Zeljko Vecenaj, University of Zagreb, Faculty of Science, Zagreb, Croatia; and I. Odak, M. Hrastinski, and B. Grisogono

Bora is a famous downslope windstorm at the eastern Adriatic coast. It often causes difficulties in traffic, industry and generally in everyday life. Hence, it is a subject of intensive scientific research. Statistical and synoptic characteristics of the bora flow have been investigated intensively in the past few decades. However, some aspects of bora dynamics still remain unexplored, especially its turbulence. The main reason for such situation was the lack of suitable measurements which are needed to asses these aspects. This was especially the case for the middle and southern NE Adriatic coast where, until only recently, no turbulence measurements were conducted.

From April 2010 to June 2011, a three level tower (10, 20 and 40 m) was equipped with WindMaster Pro ultrasonic anemometers (Gill Instruments), measuring 3D wind speed and sonic temperature at 5 Hz sampling rate. The tower was mounted at the top of Pometeno brdo (Swept-away Hill, ≈ 600 m ASL) in Dugopolje, bora upwind site from the city of Split. During this period, anemometers captured multiple bora events in all annual seasons. Our focus here is on a strong, long-lasting winter bora event. We show that the obtained turbulence strength is highly sensitive not only to the length of the low-pass filter, but to its type as well. Also, we show that reconstructions of logarithmic wind profiles using required turbulence parameters are highly sensitive to the choice of statistical moments that represent these parameters.

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