National Repository of Grey Literature 16 records found  1 - 10next  jump to record: Search took 0.00 seconds. 
Helioseismic inversions of plasma flows and sound-speed perturbations
Korda, David ; Švanda, Michal (advisor) ; Komm, Rudolf (referee) ; Roth, Markus (referee)
Local helioseismology consists of methods which study the propagation of the waves through the solar interior. The properties of the waves encode conditions in the plasma along their propagation trajectories. Local helioseismology allows us to learn about these conditions. The principal method utilised in this thesis is the time-distance local helioseismology. The time-distance method is based on measurements of travel times of the waves, hence it is sensitive especially to plasma flows and sound-speed perturbations, to which we focus. We utilised the inverse modelling, mainly using subtractive optimally localised averaging method with a minimisation of the cross-talk. This method was modified to allow for a simultaneous inversion of vector flows and sound-speed perturbation. This combination makes use of both the difference and the mean point-to-annulus averaging geometries of wave travel times in both the ridge and the phase-speed filtering approaches. The combined inversion provides us with more information about the inverted quantities. Moreover, the user can control the cross-talk and other important mathematical properties of the objects involved. The modified methodology was thoroughly tested. The main results may be summarised in five points. First, for successful inversions of the sound-speed...
Helioseismic inversions of plasma flows and sound-speed perturbations
Korda, David ; Švanda, Michal (advisor) ; Komm, Rudolf (referee) ; Roth, Markus (referee)
Local helioseismology consists of methods which study the propagation of the waves through the solar interior. The properties of the waves encode conditions in the plasma along their propagation trajectories. Local helioseismology allows us to learn about these conditions. The principal method utilised in this thesis is the time-distance local helioseismology. The time-distance method is based on measurements of travel times of the waves, hence it is sensitive especially to plasma flows and sound-speed perturbations, to which we focus. We utilised the inverse modelling, mainly using subtractive optimally localised averaging method with a minimisation of the cross-talk. This method was modified to allow for a simultaneous inversion of vector flows and sound-speed perturbation. This combination makes use of both the difference and the mean point-to-annulus averaging geometries of wave travel times in both the ridge and the phase-speed filtering approaches. The combined inversion provides us with more information about the inverted quantities. Moreover, the user can control the cross-talk and other important mathematical properties of the objects involved. The modified methodology was thoroughly tested. The main results may be summarised in five points. First, for successful inversions of the sound-speed...
Solar photosphere under an eruptive filament
Wollmann, Jiří ; Švanda, Michal (advisor) ; Zemanová, Alena (referee)
Filaments are enlongated structures of plasma in solar atmosphere held by solar magnetic field. The aim of this thesis is to study the photosphere near the eruptive filament. An eruptive filament is a filament that erupts in the final stage of its life. The studied filament was located at 10◦ of heliographic longiitude close to the central meridian on October 21 2010. The measurements of the vector velocity fields with a cadence of 6 hours were analysed, as well as the observations in the Hα line with a cadence of 1 min and the maps of the line-of-sight component of the magnetic field with a cadence of 45 s. From the Hα measurements first the evolution of the filament was studied, including the phase of its activation and eruption. Then the 6-hour averages were studied and mutually compared. The velocity field was used to study the flows in the vicinity of the filament. It was found that before the phase of activation convergent flows towards the spine of the filament was enhanced, which disappeared after the filament eruption. From the magnetograms the potential-approximation magnetic field in the region of the filament was also computed and its evolution was studied. 1
Effects of solar activity in power-distribution grids
Výbošťoková, Tatiana ; Švanda, Michal (advisor) ; Hejda, Pavel (referee)
Eruptive events on the Sun have an impact on immediate cosmic surround- ings of the Earth. Through induction of electric current also affect Earthbound structures such as the electric power distribution networks. Inspired by recent studies we investigate the correlation between the disturbances recorded by the Czech electric-power distributors with the geomagnetic activity represented by the K index. We found that in the case of the datasets recording the disturbances on the power lines with the high and very high voltage levels and disturbances on elec- trical substations, there was a statistically significant increase of failure rates in the periods of maxima of geomagnetic activity compared to the adjacent minima of activity. There are hints that the disturbances are more pronounced shortly after the maxima than shortly before the maxima of activity. Our results provide hints that the geomagnetically induced currents may af- fect the power-grid equipment even in the mid-latitude country in the middle of Europe. A follow-up study that includes the modelling of geomagnetically induced currents is needed to confirm our findings. The second part of our research includes modelling of geoelectric field using one-minute geomagnetic measurements from Intermagnet database. We applied this model to the long-term...
Vortical motions in supergranules
Grund, Lubomír ; Švanda, Michal (advisor) ; Jurčák, Jan (referee)
In this thesis, we study vortical flows in solar supergranules in a specific dataset of velocity fields. In particular, the relation between heliographic latitude and vorticity near the respective centers of the supergranules is examined. There is a supported hypothesis that supergranular motions are influenced by Coriolis force, so we attempt to verify the hypothesis using aforementioned data. The thesis further validates our understanding of several aspects of the solar supergranulation. Our results also suggest possible systematic errors of used helioseismological measurements and data analysis.
Multi-wavelength study of white-light flares
Mravcová, Lucia ; Švanda, Michal (advisor) ; Zemanová, Alena (referee)
Solar flares are common and strong demonstrations of solar activity. They are observable throughout the whole electromagnetic spectrum. If they show a broadband emission in the visible continuum, then we speak of white-light flares. The origin of white-light flares is not fully understood. We detected 24 white-light flares in SDO/HMI data and analyzed them using SDO/AIA wavelength bands at 1 700 ̊A and 304 ̊A and GONG Hα observations. According to our work, the emission in the 1 700 ̊A band is similar to the white-light emission but usually starts sooner. The positions of intensity enhancements in the 1 700 ̊A band are similar to the positions of the white-light flares and are connected by ribbons visible in the 304 ̊A band and in the Hα line. Then we studied the decay time of white-light flares and found that for most of the white-light flare points the typical decay time ranges in 2 - 3 min. 1
The influence of solar activity on failure rate of components of Czech power-distribution network
Výbošťoková, Tatiana ; Švanda, Michal (advisor) ; Mošna, Zbyšek (referee)
We analyse the impact of solar activity on Czech power grid. Massive solar flares are responsible for the formation of spaceweather and have a certain impact on technological infrastructures on the Earth and in its surroundings. We elaborated this issue and studied possible effects of spaceweather events on failure rate recorded in Czech power grid. The basis of the practical part is a program that processes the data recording the disturbances on power grid in the Czech Republic obtained by ČEPS (Czech Transmission System Operator) and compared those with the measured values of geomagnetic activity from Budkov station in Šumava by the statistical analysis methods. Our study revealed that there possibly exists some connection between the intensity of solar activity and disturbances in the Czech eletrical power grid. It turns out that the number of faults on the grid during the period of increased solar activity is appreciably higher than in the period of lower solar activity. Our work contributes to the propagation of awareness of disturbances in the Czech electrical power grid that can also arise due to solar activity
Flare stars
Kára, Jan ; Wolf, Marek (advisor) ; Švanda, Michal (referee)
The works deals with the study of the flare stars, which is a group of stars for which sudden brightening can be observed. The work focuses on a star GJ 3236, which is a low-mass eclipsing binary and on which numerous flares have been observed. For the analysis of this system spectroscopic and photometric data were used, which were obtained at various observatories. Parameters of the binary system have been determined by analysing spectroscopic and photometric data with the program PHOEBE. A total of 241 flares have been detected in the photometric data and for 190 flares, which light curves were not affected by eclipses, released energies were estimated. The set of flares was used for the study of stellar activity of the binary. The energy distribution of observed flares is similar to the flares observed on other flare stars and also on the Sun. This suggests, that the flare mechanism is the same for these stars.
Road safety inspection in the Zlin region
Holcová, Veronika ; Švanda, Michal (referee) ; Matuszková, Radka (advisor)
The topic of this Diploma's thesis is Road safety inspection in the Zlín region. To start off, I was given 14 dangerous locations in the region of Zlín by the Road Services of Kroměříž; 7 of them at crossroads and 7 outside of crossroads. Then I analysed accident risks and compared the locations among each other according to safety features. Based on the outcome of my analysis, then I chose 2 locations at crossroads and 2 outside of crossroads which I personally visited and conducted analysis on how safe they are. I uncovered potential risks which could lead to traffic accidents and suggested solutions that eliminate or minimise that risk.
Study of white-light flares
Mravcová, Lucia ; Švanda, Michal (advisor) ; Heinzel, Petr (referee)
Solar flares are a relatively common and strong demonstration of the solar ac- tivity and are observable throughout the whole electromagnetic spectrum. Some- times, solar flares are also accompanied with an emission in white-light contin- uum, then we speak of white-light flares. The origin of white-light flares is not entirely understood up to this day. The detection of white-light flares can be difficult, therefore we developed a program for automatic detection of white-light flares in SDO/HMI observations. After that, we studied properties of the detected white-light flares. Our work implies that there are two types of white-light flares depending on an X-ray flux of a solar flare. The difference between these two groups can be caused by a different behaviour of the magnetic field in the neigh- bourhood of the detected white-light flares. Our discovery could help in a better understanding of the origin of white-light flares. 1

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