Colloquia Abstracts

Thursdays, 4:00 pm, Workman 101 (unless noted*)

Physics 579 Graduate Seminar

Name: Branko Grisogono, Univ. of Zagreb

Title: Bora Downslope Windstorm

NOTE: Wednesday, March 22 — 4 pm***

Abstract:
Aside other things, the eastern Adriatic coast is well known for bora wind – a gusty downslope
windstorm that is dynamically similar to chinook and főehn wind. It blows typically from the NE
quadrant with sustained wind speeds between 5-20 ms -1 and gusts surpassing 50-70 ms -1 in the lee of
the coastal mountains over at least several hours, sometimes up to a few days. Similar bora-like
flows occur elsewhere, at least at a couple of tens of other places in the world, provided the
presence of mountain’s flow transcriticality. It has been studied at the NE coast more than at the
south; the latter bora cases appear as more complex but less frequent than their NE counterparts.
Occasional occurrence of pulsations and rotors may further be enriched by secondary low-level jets
(LLJs) that are up to a few tens of kilometers long and separated by only several kilometers (main LLJs
and wakes pertain to the mountain main passes and peaks). Spatial structures of O(1 km) may
appear further offshore in the convective marine atmospheric boundary layer more than 50 km in
the lee of the coast. A preliminary finding obtained via hotwire anemometer with sampling
frequency of 10 4 Hz, implies that the inertial dissipation method (IDM) provides an accurate estimate
of the bora turbulence kinetic energy (TKE) dissipation rate ( ε ) in the surface layer, that is about 1
m 2 s -3 , at least for moderate wind speeds, O(10 ms -1 ). Future bora research and applications are
outlined.

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