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Thermal Convection in Terrestrial Planetary Mantles
Benešová, Nina ; Čížková, Hana (advisor) ; Hejda, Pavel (referee) ; Šrámek, Ondřej (referee)
In this thesis, we present results of a numerical modelling study focused on the thermal evolution of the Earth and terrestrial planets. We focus particularly on two problems: I) constraining the internal structure of Venus and Mercury using their geoid and surface topography data and II) evaluating the effects of a rhe- ologically distinct post-perovskite on the secular cooling of the Earth. In part I, we performed simulations in a broad group of models of the Venusian man- tle, characterised by different rheological descriptions, and we compared spectra of their geoid and their surface topography with the observed quantities. Our analysis suggested that the geoid and the surface topography of Venus are con- sistent with a radially symmetric viscosity model with a strong 200 km thick lithosphere, without an asthenosphere and with a gradual viscosity increase in the underlying mantle. In the case of Mercury, none of our models was able to predict observed data, thus suggesting other than a dynamic origin of observed geoid and topography. In part II, we investigated style of Earth's mantle con- vection and its long-term evolution in the models that take into account a weak post-perovskite. We conclude that the presence of the weak post-perovskite en- hances the core cooling. This effect is comparable in...
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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...
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Thermal Convection in Terrestrial Planetary Mantles
Benešová, Nina ; Čížková, Hana (advisor) ; Hejda, Pavel (referee) ; Šrámek, Ondřej (referee)
In this thesis, we present results of a numerical modelling study focused on the thermal evolution of the Earth and terrestrial planets. We focus particularly on two problems: I) constraining the internal structure of Venus and Mercury using their geoid and surface topography data and II) evaluating the effects of a rhe- ologically distinct post-perovskite on the secular cooling of the Earth. In part I, we performed simulations in a broad group of models of the Venusian man- tle, characterised by different rheological descriptions, and we compared spectra of their geoid and their surface topography with the observed quantities. Our analysis suggested that the geoid and the surface topography of Venus are con- sistent with a radially symmetric viscosity model with a strong 200 km thick lithosphere, without an asthenosphere and with a gradual viscosity increase in the underlying mantle. In the case of Mercury, none of our models was able to predict observed data, thus suggesting other than a dynamic origin of observed geoid and topography. In part II, we investigated style of Earth's mantle con- vection and its long-term evolution in the models that take into account a weak post-perovskite. We conclude that the presence of the weak post-perovskite en- hances the core cooling. This effect is comparable in...
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The effect of high long-lasting solar/geomagnetic activity on pressure fields in the winter northern lower atmosphere
Bochníček, Josef ; Davídkovová, Hana ; Hejda, Pavel ; Huth, Radan
The effect of high long-lasting solar/geomagnetic activity on stratospheric and tropospheric pressure distributions was investigated in the winter Northern Hemisphere. The analysis concerns winter period (December 1 – March 30) in 1952-2003. Solar activity is characterized by 30 day means of R number, geomagnetic activity by 30 day means of daily sum of Kp index. Stratospheric and tropospheric pressure distributions are described by 30 day mean anomalies in geopotential height (GPH) at 50 hPa/500 hPa. GPH anomalies are computed as the difference between the long-term 30 day averages (covering 33 year period, 1970-2003) and actual 30 day averages. Data are taken from the NCEP/NCAR reanalysis
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The influence of geomagnetic activity on the course of stratospheric warming
Davídkovová, Hana ; Bochníček, Josef ; Hejda, Pavel ; Huth, Radan
The temperature of the winter polar lower stratosphere is affected except the solar activity and atmospheric circulation by the geomagnetic activity as well. Plausible physical mechanism for its effect was described by Arnold and Robinson. According to this paper, warming in the lower thermosphere caused by geomagnetic activity produces the reduction of blending mid and high latitude air masses. In consequence of this reduction the temperature of solar insulated region (polar lower stratosphere)decreases. The aim of this work is to verify functionality of such mechanism.
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