engleski

Turbulence averaging interval for summer bora flows at the middle of the NE Adriatic coast

At the Eastern Adriatic coast often blows a downslope windstorm called bora. It flows from the north-eastern (NE) quadrant, and it occurs most frequently during winter seasons. Bora mean wind speed can surpass 20 m s-1 and due to its gustiness it reaches speeds greater than 60 m s-1. During such events, the turbulence is strongly developed in the lee of the mountains ; moreover, sub-mesocale and turbulent structures are additionally complicated at the middle of the NE Adriatic coast due to the surrounding mountains. Bora is investigated at the NE Adriatic coast more intensively and systematically than at the middle-eastern, not to mention the southern Adriatic part, mainly because it occurs more often at the NE Adriatic and is stronger there. Nevertheless, severe bora at the middle-eastern and southern Adriatic coast is not a rarity at all. Partially inspired by this fact, we have installed three levels of horizontal and vertical wind and sonic temperature sensors at the middle-eastern Adriatic coast: on the hill of Pometeno Brdo (43.62°N, 16.47°E, 600 m above MSL), inland from the city of Split, at heights of 10, 20 and 40 m above the ground. Measurements are performed with WindMaster ultrasonic anemometers (Gill Instruments) with a sampling frequency of 5 Hz. In order to investigate turbulence, a suitable time/space averaging interval has to be used in order to define turbulent perturbations ; these quantities later on define turbulent kinetic energy, gustiness, etc. This study addresses the turbulence averaging interval for bora events on the hill of Pometeno Brdo (”Swept-Away Hill”) during three months of the last summer. The instruments remain there over a whole year. There are indications that the appropriate averaging interval for bora turbulence at the more studied NE Adriatic coast is not the same as that for the middle-eastern Adriatic coast studied here.

Bora; Ultrasonic anemometers; Turbulence averaging interval; Pometeno Brdo

nije evidentirano