1. Measurements and modeling of air mass motion in the troposphereMiha Živec, 2016, undergraduate thesis Abstract: 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.
Found in: osebi
Keywords: remote sensing, wind, atmosphere
Published: 13.10.2016; Views: 4497; Downloads: 128
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2. Meritve hitrosti gibanja zračnih masMiha Živec, Maruška Mole, Samo Stanič, 2017, published scientific conference contribution Abstract: V prispevku predstavljamo novo metodo merjenja smeri in hitrosti gibanja zračnih mas, ki temelji na kombinaciji aktivnega (lidarski sistem) in pasivnega (kamera) daljinskega zaznavanja atmosfere. S pomočjo lidarja smo določili razdaljo do oblakov, ki so služili kot sledilci v zračnem toku. Sočasno z lidarskimi meritvami smo fotografirali del neba, v katerega je bil usmerjen lidar. Iz meritev oddaljenosti oblakov ter njihovega premikanja smo izračunali hitrost potovanja oblakov in s tem tudi spodnjo mejo hitrosti zračne mase, ki je oblake nosila. Metodo merjenja hitrosti gibanja zračnih mas smo preizkusili na štirih testnih primerih v februarju in marcu 2016. Meritve so potekale v Ajdovščini v različnih vremenskih pogojih. Poleg naprav za daljinsko zaznavanje (lidar in optične kamere) smo za primerjavo uporabili tudi prizemne meritve vetra v Ajdovščini ter podatke vertikalne sondaže atmosfere v Vidmu in Ljubljani. Rezultati meritev vetra z daljinskim zaznavanjem se v vseh štirih opazovanih primerih relativno dobro ujemajo z rezultati sondaž, do odstopanj pa prihaja zaradi krajevnega in časovnega neujemanja sondaž z daljinskim zaznavanjem.
Found in: osebi
Keywords: daljinsko zaznavanje, veter, atmosfera
Published: 10.02.2017; Views: 2664; Downloads: 0
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3. Space weather research with the Pierre Auger ObservatoryMiha Živec, 2019, master's thesis Abstract: Space weather refers to environmental conditions in the interplanetary space and Earth’s
magnetosphere, ionosphere and exosphere and can influence the performance and reliability
of electronics based technological systems. The major role in space weather
changes plays the solar wind, a stream of charged particles (mostly electrons and protons)
with energies of approximately 1 keV, that can cause geomagnetic storms and auroras.
During their entry into the atmosphere, high energy cosmic rays collide with atomic
nuclei of atmospheric gasses. When scattering occurs extensive air showers are created.
Those cascades of secondary particles create flashes of light due to the Cherenkov
effect as well as excite molecules of nitrogen gas in atmosphere, which then glow in
fluorescent light. In order to observe the light created by air showers, it has to be
collected with telescopes. The particles from the cascades that reach ground can be
detected with surface detectors. The Pierre Auger Observatory is the largest observatory
for cosmic ray measurements. It is located in Argentinian pampas covering an area of
3000 km2. It consists of 1660 surface detectors and 27 fluorescence telescopes. For
cosmic rays with energies above few 1017 eV, a precise reconstruction of energy and
direction of primary particle is achievable. Observatory also allows measurement of
flux of incoming particles down to primary energies in ca. 10 GeV - 10 TeV interval, with a median energy ca. 80-90 GeV. This measurement capability is called "scaler"
mode, since the corresponding data consist of scaler counted cascade particles with
deposited energy between 15 and 100 MeV, at the average rate of 2 kHz per individual
surface detector.
For the purpose of this master thesis I compared the data from scaler mode measurements
with measurements of neutron monitors, which are commonly used for space weather
observations. With the correlation received from the comparison, I showed that scaler
mode operation of Pierre Auger observatory can be used to monitor space weather events
such as solar cycle and the decreases in the observed galactic cosmic ray intensity due
to solar wind (Forbush decrease).
Found in: osebi
Keywords: Pierre Auger Observatory, cosmic rays, space weather, Forbush decrease
Published: 17.09.2019; Views: 1862; Downloads: 80
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5. Sensitivity of the Cherenkov Telescope Array to a dark matter signal from the Galactic centreChristopher Eckner, A. Aguirre-Santaella, I. Agudo, C. Adams, R. Adam, A. Acharyya, Samo Stanič, Serguei Vorobiov, Gabrijela Zaharijas, Marko Zavrtanik, Danilo Zavrtanik, Miha Živec, 2021, original scientific article Found in: osebi
Keywords: dark matter, gamma ray, astrophysics
Published: 26.02.2021; Views: 214; Downloads: 8
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6. Sensitivity of the Cherenkov Telescope Array for probing cosmology and fundamental physics with gamma-ray propagationSerguei Vorobiov, Samo Stanič, Christopher Eckner, R. Adam, A. Acharyya, F. Acero, H. Abe, H. Abdalla, Gabrijela Zaharijas, Marko Zavrtanik, Danilo Zavrtanik, Miha Živec, 2021, original scientific article Abstract: The Cherenkov Telescope Array (CTA), the new-generation ground-based observatory for γ astronomy, provides unique capabilities to address significant open questions in astrophysics, cosmology, and fundamental physics. We study some of the salient areas of γ cosmology that can be explored as part of the Key Science Projects of CTA, through simulated observations of active galactic nuclei (AGN) and of their relativistic jets. Observations of AGN with CTA will enable a measurement of γ absorption on the extragalactic background light with a statistical uncertainty below 15% up to a redshift z=2 and to constrain or detect γ halos up to intergalactic-magnetic-field strengths of at least 0.3 pG . Extragalactic observations with CTA also show promising potential to probe physics beyond the Standard Model. The best limits on Lorentz invariance violation from γ astronomy will be improved by a factor of at least two to three. CTA will also probe the parameter space in which axion-like particles could constitute a significant fraction, if not all, of dark matter. We conclude on the synergies between CTA and other upcoming facilities that will foster the growth of γ cosmology.
Found in: osebi
Keywords: Cherenkov Telescope Array, active galactic nuclei, gamma-ray experiments, axions, extragalactic magnetic fields
Published: 02.03.2021; Views: 169; Downloads: 5
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