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1.
Sensitivity of the Cherenkov Telescope Array to TeV photon emission from the Large Magellanic Cloud
A. Acharyya, R. Adam, Saptashwa Bhattacharyya, Samo Stanič, Veronika Vodeb, Serguei Vorobiov, Gabrijela Zaharijas, Danilo Zavrtanik, Marko Zavrtanik, Miha Živec, 2023, izvirni znanstveni članek

Opis: A deep survey of the Large Magellanic Cloud at ∼ 0.1−100 TeV photon energies with the Cherenkov Telescope Array is planned. We assess the detection prospects based on a model for the emission of the galaxy, comprising the four known TeV emitters, mock populations of sources, and interstellar emission on galactic scales. We also assess the detectability of 30 Doradus and SN 1987A, and the constraints that can be derived on the nature of dark matter. The survey will allow for fine spectral studies of N 157B, N 132D, LMC P3, and 30 Doradus C, and half a dozen other sources should be revealed, mainly pulsar-powered objects. The remnant from SN 1987A could be detected if it produces cosmic-ray nuclei with a flat power-law spectrum at high energies, or with a steeper index 2.3−2.4 pending a flux increase by a factor > 3−4 over ∼ 2015−2035. Large-scale interstellar emission remains mostly out of reach of the survey if its > 10 GeV spectrum has a soft photon index ∼ 2.7, but degree-scale 0.1 − 10 TeV pion-decay emission could be detected if the cosmic-ray spectrum hardens above >100 GeV. The 30 Doradus star-forming region is detectable if acceleration efficiency is on the order of 1 − 10% of the mechanical luminosity and diffusion is suppressed by two orders of magnitude within < 100 pc. Finally, the survey could probe the canonical velocity-averaged cross section for self-annihilation of weakly interacting massive particles for cuspy Navarro-Frenk-White profiles.
Ključne besede: very-high energy (VHE) gamma-rays, Cherenkov Telescope Array Observatory, Large Magellanic Cloud, pulsar wind nebulas, galaxiesstar-forming regions, cosmic rays, dark matter
Objavljeno v RUNG: 02.06.2023; Ogledov: 945; Prenosov: 0
.pdf Celotno besedilo (3,66 MB)

2.
Wind awareness : diploma thesis
Vasyl Kuzmich, 2022, diplomsko delo

Opis: Living at a time when the stress level is growing every year, or even day by day, the ecological situation is deteriorating, wars, pandemics, economic recession, racism, and nationalism. It is very important to find a way to connect with yourself and nature. Find a way to tap into spirituality. Find a way to improve our mental state so that later life will be in better ecological and mental conditions. If every person made himself happy, the world would be populated by happy people. With similar roots in spirituality, psychology, linguistics, and philosophy, this thesis mindset is about bringing people's mental health into balance while also understanding the structure and the research behind an audio-meditative installation "Breath of the Wind" based on the Bora wind. This work follows the interrelationship between body, mind, and spirit with a focus on breathing "Breath of the Wind" is a composition, meditative musical landscape, with spatialized sound samples driven by input from nature and digitally processed with MAX/MSP software
Ključne besede: Wind, atmosphere, air, spirituality, awareness, meditation, breathing, attention, music.
Objavljeno v RUNG: 20.12.2022; Ogledov: 1163; Prenosov: 48
.pdf Celotno besedilo (2,51 MB)
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3.
Bora flow characteristics in a complex valley environment
Marija Bervida, Samo Stanič, Griša Močnik, Longlong Wang, Klemen Bergant, Xiaoquan Song, 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.
Ključne besede: doppler wind lidar, Bora wind, turbulence intensity, complex terrain, turbulence integral length scale
Objavljeno v RUNG: 05.11.2021; Ogledov: 1936; Prenosov: 42
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4.
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.
Ključne besede: Vipava valley, Bora wind, Wind profile, Orography, Atmospheric boundary layer, Computational fluid dynamics, Numerical simulations
Objavljeno v RUNG: 17.06.2020; Ogledov: 5162; Prenosov: 47
.pdf Celotno besedilo (35,12 MB)

5.
Near-Ground Profile of Bora Wind Speed at Razdrto, Slovenia
Marija Bervida, Samo Stanič, Klemen Bergant, 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.
Ključne besede: Bora wind, logarithmic law, power law, roughness length, wind profile
Objavljeno v RUNG: 04.10.2019; Ogledov: 3387; Prenosov: 108
.pdf Celotno besedilo (5,90 MB)

6.
Bora wind, Wind speed vertical profile, Logarithmic law, Power law
Marija Bervida, Samo Stanič, Klemen Bergant, 2018, objavljeni znanstveni prispevek na konferenci

Opis: Bora is cold and gusty downslope wind with variable gust frequency and duration, appearing on the lee side of Dinaric Alps. Its flow characteristics are unique and theoretically still not fully described, especially for modeling purposes. We present an analysis of the wind speed vertical profiles at Razdrto, which lies in a gap between the Nanos and Javorniki plateau in southwest Slovenia and is strongly exposed to Bora. An analysis of the vertical wind speed profiles during Bora episodes is based on experimental wind data, provided by Helikopter energija, for six Bora events of different duration, appearing between April 2010 and May 2011. Average wind speed in 10-minute intervals was collected at four different heights (20, 31, 40 and 41.7 m above the ground)at the wind turbine site in Razdrto using cup anemometers. Wind direction data with same temporal resolution was obtained from a single wind vane placed at 40.9 m above the ground. Based on the collected data, the applicability of the empirical power-law and the logarithmic law profiles, commonly used for the description of neutrally stratified atmosphere, was investigated for the case of Bora. The parameters for the power-law and logarithmic law were obtained by fitting the wind speed data using linear regression method and are compared to standard values for that particular type of terrain. The quality of fits was very good with r2 above 0.9, indicating that both power-law and logarithmic law adequately describe mean horizontal Bora wind. The median value of the power-law coefficient was found to be 0.16±0.03, which is consistent with standard value for neutral atmosphere (0.143). The aerodynamic roughness varied from 0.003 m to 0.22 m with the median value of 0.09±0.07, which describes open level country terrain with some trees. The event in November 2010 with large roughness is expected to be due to specific wind direction and surface conditions.
Ključne besede: Bora wind, Wind speed vertical profile, Logarithmic law, Power law
Objavljeno v RUNG: 07.02.2019; Ogledov: 3906; Prenosov: 27
URL Povezava na celotno besedilo
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7.
Study of the properties of air flow over orographic barrier
Maruška Mole, 2017, doktorska disertacija

Opis: Earth’s atmosphere is a complex system. All weather phenomena take place in its lowest layer, the troposphere, which is strongly influenced by human activities and the underlying surface orography. A good example of the influence the orography has on the behavior of air flows is the appearance of strong north-east downslope wind in Vipava valley, called Bora. Numerical models used to analyze flows in complex terrain need meteorological data both for setting the initial conditions and the verification of modeling results. Obtaining spatial distributions of meteorological observables can be challenging, especially in the case of strong winds, such as Bora, where traditional methods may be inadequate due to prohibitive wind speeds. In most cases, vertical properties of the atmosphere can be obtained using remote sensing techniques. Contrary to vertical profile measurements with traditional methods, remote sensing techniques do not require the measuring device to be placed within the flow and are therefore more appropriate for measurements in severe weather conditions such as strong winds. The aim of this thesis is a detailed analysis of wind and tropospheric structure properties in and above the Vipava valley in a variety of typical atmospheric conditions, including strong wind events. It employs a combination of high resolution wind and lidar data in addition to standard meteorological measurements. In Ajdovščina, there are four predominant wind directions, two of them directly connected to Bora. In the case of Bora, periodicity analysis of wind data from Ajdovščina yielded a range of possible wind gust periods between 1 and 7 minutes. The periods were not stable, with the periodogram less noisy for stable wind directions. Wavelike structures were found to be present in the troposphere in half of the investigated cases, regardless of the presence of Bora. In statically stable conditions, gravity waves propagated throughout the planetary boundary layer (PBL). In the case of Bora, the PBL experienced oscillations with periods between 1 and 2 minutes. A shear layer was present above the PBL, causing Kelvin-Helmholtz waves at its boundaries with periods ranging from 3 to 6 minutes. In some cases, periodic structures were observed above the shear layer as well, which were found to have longer periods than those within the PBL.
Ključne besede: remote sensing, Vipava valley, wind properties, Bora, wind gusts, wind periodicity, tropospheric structures, Kelvin-Helmholtz waves
Objavljeno v RUNG: 18.09.2017; Ogledov: 6460; Prenosov: 199
.pdf Celotno besedilo (45,11 MB)

8.
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.
Ključne besede: Downslope wind Lidar observations Kelvin–Helmholtz waves Bora
Objavljeno v RUNG: 06.01.2017; Ogledov: 5259; Prenosov: 0
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9.
Measurements and modeling of air mass motion in the troposphere
Miha Živec, 2016, diplomsko delo

Opis: Throughout the history human race depended on weather, so one of the priorities for its survival was to understand weather patterns and to be able to forecast weather. With the development of powerful computers, atmospheric numerical methods and precision instruments for atmospheric monitoring, it is possible to predict weather with greater accuracy and for a longer period of time ahead. At the same time, we are able to gain improved understanding of physical processes that occur in the atmosphere and represent one of most important features in our world. This diploma thesis focuses on the lowest part of the atmosphere - troposphere only, as all weather occurs in the troposphere. Weather is a complete collection of momentary thermodynamic states in the atmosphere and is defined with thermodynamic variables and relations between them. The goal of this thesis is development and presentation of a new way to determine the direction and speed of air mass movement, based on the combination of passive and active remote sensing techniques. A lidar is being used to determine the range to an object, in our case a cloud, that can be used as a tracer in the air current. Simultaneously with lidar ranging of clouds that same clouds are being visually monitored in a series of optical photographs. Selecting and following the temporal evolution of distinct cloud features and their range allows us to calculate the speed of clouds. The performance of this method was tested on four cases in Feb. and Mar. 2016. Measurements were performed in Ajdovščina in different weather conditions. Along with remote sensing (infra-red lidar and optical cameras), ground measurements of wind at Ajdovščina were performed. Wind speeds and directions obtained from remote sensing were compared to atmospheric sounding data from Ljubljana and Udine at similar heights and performed within as small as possible time window. In all four cases remote sensing results for wind speeds and directions agree relatively well with atmospheric sounding. Deviations are expected to be primarily due to spatial and temporal mismatch between sounding and remote sensing measurements. Another source of uncertainties are the limitations of the present remote sensing method in the determination of the actual direction of the wind, however, theses limitations could be eliminated in the future by using an all-sky camera and vertical lidar configuration.
Ključne besede: remote sensing, wind, atmosphere
Objavljeno v RUNG: 13.10.2016; Ogledov: 7875; Prenosov: 200
.pdf Celotno besedilo (9,48 MB)

10.
H.E.S.S. observation of the Vela X nebula
Serguei Vorobiov, Bernhard Glück, 2010, objavljeni povzetek znanstvenega prispevka na konferenci

Ključne besede: ground based y-ray telescopes, H.E.S.S. system, Cherenkov telescopes, pulsar wind nebulae
Objavljeno v RUNG: 25.04.2014; Ogledov: 4951; Prenosov: 28
URL Povezava na celotno besedilo

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