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Lidar measurements of Bora wind effects on aerosol loading
Maruška Mole, Longlong Wang, Samo Stanič, Klemen Bergant, William Eichinger, Francisco Ocaña, Benedikt Strajnar, Primož Škraba, Marko Vučković, William Willis, 2017, izvirni znanstveni članek

Opis: The Vipava valley in Slovenia is well known for the appearance of strong, gusty North-East Bora winds, which occur as a result of air flows over an adjacent orographic barrier. There are three revealing wind directions within the valley which were found to give rise to specific types of atmospheric structures. These structures were investigated using a Mie scattering lidar operating at 1064 nm, which provided high temporal and spatial resolution backscatter data on aerosols, which were used as tracers for atmospheric flows. Wind properties were monitored at the bottom of the valley and at the rim of the barrier using two ultrasonic anemometers. Twelve time periods between February and April 2015 were selected when lidar data was available. The periods were classified according to the wind speed and direction and investigated in terms of appearance of atmospheric structures. In two periods with strong or moderate Bora, periodic atmospheric structures in the lidar data were observed at heights above the mountain barrier and are believed to be Kelvin–Helmholtz waves, induced by wind shear. No temporal correlation was found between these structures and wind gusts at the ground level. The influence of the wind on the height of the planetary boundary layer was studied as well. In periods with low wind speeds, the vertical evolution of the planetary boundary layer was found to be governed by solar radiation and clouds. In periods with strong or moderate Bora wind, convection within the planetary boundary layer was found to be much weaker due to strong turbulence close to the ground, which inhibited mixing through the entire layer.
Najdeno v: osebi
Ključne besede: Downslope wind Lidar observations Kelvin–Helmholtz waves Bora
Objavljeno: 06.01.2017; Ogledov: 1937; Prenosov: 0
.pdf Polno besedilo (3,02 MB)

Near-Ground Profile of Bora Wind Speed at Razdrto, Slovenia
Klemen Bergant, Samo Stanič, Marija Bervida, Benedikt Strajnar, 2019, izvirni znanstveni članek

Opis: Southwest Slovenia is a region well-known for frequent episodes of strong and gusty Bora wind, which may damage structures, affect traffic, and poses threats to human safety in general. With the increased availability of computational power, the interest in high resolution modeling of Bora on local scales is growing. To model it adequately, the flow characteristics of Bora should be experimentally investigated and parameterized. This study presents the analysis of wind speed vertical profiles at Razdrto, Slovenia, a location strongly exposed to Bora during six Bora episodes of different duration, appearing between April 2010 and May 2011. The empirical power law and the logarithmic law for Bora wind, commonly used for the description of neutrally stratified atmosphere, were evaluated for 10-min averaged wind speed data measured at four different heights. Power law and logarithmic law wind speed profiles, which are commonly used in high resolution computational models, were found to approximate well the measured data. The obtained power law coefficient and logarithmic law parameters, which are for modeling purposes commonly taken to be constant for a specific site, were found to vary significantly between different Bora episodes, most notably due to different wind direction over complex terrain. To increase modeling precision, the effects of local topography on wind profile parameters needs to be experimentally assessed and implemented.
Najdeno v: osebi
Ključne besede: Bora wind, logarithmic law, power law, roughness length, wind profile
Objavljeno: 04.10.2019; Ogledov: 416; Prenosov: 20
.pdf Polno besedilo (5,90 MB)

Lidar Observations of Mountain Waves During Bora Episodes
Longlong Wang, Marija Bervida, Samo Stanič, Klemen Bergant, William Eichinger, Benedikt Strajnar, 2020, objavljeni znanstveni prispevek na konferenci

Opis: Airflows over mountain barriers in the Alpine region may give rise to strong, gusty downslope winds, called Bora. Oscillations, caused by the flow over an orographic barrier, lead to formation of mountain waves. These waves can only rarely be observed visually and can, in general, not be reliably reproduced by numerical models. Using aerosols as tracers for airmass motion, mountain waves were experimentally observed during Bora outbreak in the Vipava valley, Slovenia, on 24-25 January 2019 by two lidar systems: a vertical scanning lidar positioned just below the peak of the lee side of the mountain range and a fixed direction lidar at valley floor, which were set up to retrieve two-dimensional structure of the airflow over the orographic barrier into the valley. Based on the lidar data, we determined the thickness of airmass layer exhibiting downslope motion, observed hydraulic jump phenomena that gave rise to mountain waves and characterized their properties.
Najdeno v: osebi
Ključne besede: Bora, mountain waves, lidar observations
Objavljeno: 08.07.2020; Ogledov: 73; Prenosov: 0
.pdf Polno besedilo (3,66 MB)

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