Spatial features of bora related turbulence

The downslope windstorm bora blows at the Eastern Adriatic coast from the northeast quadrant, most frequently during winter season. There is a wide spectrum of bora mean wind speeds, and due to gustiness the speed maxima may suprass 60 m/s. During a bora event, the turbulence is strongly developed in the lee of the mountain. The mesoscale bora structure in the along-coast direction, i.e. perpendicular to the mean bora direction, is characterized by interchange of jets and wakes related to mountain gaps and peaks, and has been studied extensively. Here we examine the along-coast structure of the bora turbulence.

A case study is presented of an early stage of a bora event over the northern Adriatic that occurred on 7 November 1999 during the Mesoscale Alpine Program (MAP) Intensive Observation Period 15. We use the aircraft data that were measured along the lee side of the Dinaric Alps over the Adriatic by the NCAR Electra aircraft. The study employs two vertically separated flight legs (lower at ~ 370 m, upper at ~ 680 m) and six dropsonde measurements along the legs. Main features of turbulence along the northern Adriatic are shown, including the spatial distribution of TKE dissipation rate that is calculated using inertial dissipation technique provided by the Kolmogorov's “-5/3 law”. The spatial structure of turbulence is studied with respect to the known bora mesoscale features such as mountain waves, wave breaking, jets, wakes, shear zones, etc.