Climatology of bora wind derived from high-frequency wind measurements

Bora is a downslope windstorm that blows at the Eastern Adriatic coast from the north-eastern quadrant, most often during the winter season. It possesses a wide spectrum of average wind speeds and due to its gustiness the speed maxima may surpass 60 m/s. During a bora event the turbulence is strongly developed in the lee of the mountain.

Horizontal and vertical wind is measured at Senj (44.99°N, 14.90°E, 2 m above MSL) at a height of 13 m above the ground with the WindMaster ultrasonic anemometer (Gill Instruments). It recorded the data with a sampling frequency of 4 Hz. The anemometer was operating from 18 March 2004 to 19 June 2006 with approximately three months break due to the lighting strike (summer 2005). During this two years period, more than 300 bora episodes are extracted that lasted from several hours to several days. The only criterion for extracting episodes was the wind direction. In this way, bora episodes with a whole range of mean wind speeds are taken into the analysis. We present basic statistics related to this data set (bora episodes) concerning wind speeds, seasons, time of the day and duration, etc. Some considerations about the bora turbulent properties are pointed out as well.