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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.
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Ključne besede: Downslope wind Lidar observations Kelvin–Helmholtz waves Bora
Objavljeno: 06.01.2017; Ogledov: 3269; Prenosov: 0
.pdf Polno besedilo (3,02 MB)

Study of the properties of air flow over orographic barrier
Maruška Mole, 2017, doktorska disertacija

Najdeno v: ključnih besedah
Povzetek najdenega: ...north-east downslope wind in Vipava valley, called Bora. Numerical models used to analyze flows in...
Objavljeno: 18.09.2017; Ogledov: 3811; Prenosov: 124
.pdf Polno besedilo (45,11 MB)

Klemen Bergant, Samo Stanič, Marija Bervida, 2018, objavljeni znanstveni prispevek na konferenci

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Ključne besede: Bora wind, Wind speed vertical profile, Logarithmic law, Power law
Objavljeno: 07.02.2019; Ogledov: 2024; Prenosov: 15
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Near-Ground Profile of Bora Wind Speed at Razdrto, Slovenia
Klemen Bergant, Samo Stanič, Marija Bervida, Benedikt Strajnar, 2019, izvirni znanstveni članek

Najdeno v: ključnih besedah
Ključne besede: Bora wind, logarithmic law, power law, roughness length, wind profile
Objavljeno: 04.10.2019; Ogledov: 1474; Prenosov: 59
.pdf Polno besedilo (5,90 MB)

Bora wind effects on common structures in the Vipava valley
Marija Bervida, 2020, doktorska disertacija

Opis: Strong and gusty north-east wind called Bora is common in south-west regions of Slovenia, as well as along the Adriatic coast. Its intermittent behavior, related to variable strength, frequency and duration, has brought out scientific curiosity for decades. Bora affects human life and causes problems for structures built in Bora affected areas. In Slovenia, Bora is the strongest in the Vipava valley. The motivation for this research is the need to evaluate Bora wind effects on structures, commonly found in the Vipava valley region, using a high resolution computational fluid dynamics (CFD) modeling approach. To date, there are several experimental and computational constraints for accurate representation of Bora in a CFD model, therefore, the main aim of this dissertation is to build foundations for Bora wind simulations using CFD and its method of finite volumes. The dissertation incorporates the analysis of experimental measurements of Bora wind, as well as numerical modeling studies. Vertical mean wind speed profile characteristics of Bora were analyzed based on experimental measurements at Razdrto just above the Vipava valley. The obtained results contributed to the choice of Bora mean wind profiles applied at the inflow of computational models. Guidelines regarding the choice of the associated wind profile parameters were given and a new relationship between these parameters was found. As orographic barriers to the north of the Vipava valley are known to give rise to Bora and to define the specific properties of the Bora flow, numerical modeling studies were in the first place focused on the implementation of the real-scale complex terrain into a CFD model. Simulation of wind flow over orographic barrier in Vipava valley was performed using Raynolds averaged Navier-Stokes approach, providing a first estimation of the flow field over a small hill of Zemono. As resolving the turbulence characteristics of Bora is very important for the estimation of wind loads on structures, modeling studies converged towards a more appropriate approach - Large eddy simulations (LES). A crucial step in setting up an accurate LES is the generation of appropriate inflow, which was investigated for the case of atmospheric boundary layer (ABL) flow. The synthetic method PRFG^3 for the generation of unsteady inflow was tested and adapted as a source of an ABL flow with desired turbulence flow properties. Based on its performance, in particular on adequate reproduction of target turbulence intensities and length scales, it was found that PRFG^3 method may be used to generate velocity inflow with desired turbulence properties in LES. Finally, simulations of wind flow coming from Bora direction over the Vipava valley were performed with the aim to depict the effects of underlying orography on the flow within and above the valley. Modeling results were found to be comparable with the results of lidar based remote sensing of vertical atmospheric structures within and above the valley.
Najdeno v: ključnih besedah
Ključne besede: Vipava valley, Bora wind, Wind profile, Orography, Atmospheric boundary layer, Computational fluid dynamics, Numerical simulations
Objavljeno: 17.06.2020; Ogledov: 1870; Prenosov: 16
.pdf Polno besedilo (35,12 MB)

Bora flow characteristics in a complex valley environment
Xiaoquan Song, Klemen Bergant, Longlong Wang, Griša Močnik, Samo Stanič, Marija Bervida, 2021, izvirni znanstveni članek

Opis: This paper complements the existing studies of Bora flow properties in the Vipava valley with the study of Bora turbulence in a lower region of the troposphere. The turbulence characteristics of Bora flow were derived from high resolution Doppler wind lidar measurements during eight Bora wind episodes that occurred in November and December 2019. Based on the vertical profiles of wind velocity, from 80 to 180 m above the valley floor, the turbulence intensity related to all three spatial directions and the along-wind integral length scales related to three velocity components were evaluated and compared to the approximations given in international standards. The resulting turbulence characteristics of Bora flow in a deep mountain valley exhibited interesting behaviour, differing from the one expected and suggested by standards. The intensity of turbulence during Bora episodes was found to be quite strong, especially regarding the expected values for that particular category of terrain. The specific relationship between along-wind, lateral and vertical intensity was evaluated as well. The scales of turbulence in the along-wind direction were found to vary widely between different Bora episodes and were rather different from the approximations given by standards, with the most significant deviations observed for the along-wind length scale of the vertical velocity component. Finally, the periodicity of flow structures above the valley was assessed, yielding a wide range of possible periods between 1 and 10 min, thus confirming some of the previous observations from the studies of Bora in the Vipava valley.
Najdeno v: ključnih besedah
Povzetek najdenega: ...flow were derived from high resolution Doppler wind lidar measurements during eight Bora wind episodes...
Ključne besede: doppler wind lidar, Bora wind, turbulence intensity, complex terrain, turbulence integral length scale
Objavljeno: 05.11.2021; Ogledov: 122; Prenosov: 3
URL Polno besedilo (0,00 KB)
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