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International audience; Quasiperiodic (QP) electromagnetic emissions are whistler mode waves at typical frequencies of a few kHz characterized by a periodic time modulation of their intensity. The DEMETER spacecraft observed events where the QP emissions exhibit a sudden change in the wave vector and Poynting vector directions. The change happens in a short interval of latitudes. We explain this behavior by ionospheric reflection and present a ray-tracing simulation which matches resulting wave vector directions. We also attempt to locate the source region of these emissions and conclude that they are most probably generated at the inner boundary of the plasmapause which also acts as a guide during the propagation of the QP emissions.

The main objective of this thesis is to use the data measured by the MAVEN spacecraft and machine learning methods to develop models of the locations of bow shock and magnetic pileup boundary. Characteristic values of density, flow speed, and magnetic field magnitude in solar wind, magne- tosheath, and magnetosphere allows an automatic classification of measured data into respective regions using the SVM method, as well as the identi- fication of the boundary crossings. Models of the two boundaries based on multilayer neural networks are then developed. Two different approaches are used: i) model based directly on the classification of individual regions, and ii) model using only the identified boundary crossings. The accuracy of the developed models is validated both by using individual boundary crossings and by a comparison with former empirical models. 1

This thesis is focused on study of properties of the lightning strokes accompanying tropical cyclones. We investigated lightning densities, median energies of lightning strokes, their multiplicity, radial distribution of lightning and a correlation of lightning activity with the development of the cyclone wind speed. We used 429 cyclones occuring all over the world in the period 2012-2017 and lightning data provided by WWLLN (World Wide Lightning Location Network). We found substantial differences in the lightning densities and energies when comparing cyclones of different intensities appearing in both hemispheres and individual basins. Radial distribution of lightning in the cyclones shows a strong maximum of the stroke density and a minimum of the median stroke energy near the center of the cyclone. The increase in the lightning density often preceded the increase of wind, but the time interval between them varied substantially when considering the cyclone intensity and the hemisphere of cyclone occurrence. The analysis of properties of lightning accompanying nearly five hundred tropical cyclones (the largest data set so far) revealed that there isn't a fix delay between the time of the maximum lightning activity and the time of the maximum wind speed which can be globally used for predictions of the...

Title: Fine structure of quasiperiodic emissions observed in the Earth's magne- tosphere Author: Vojtěch Partík Supervisor: doc. RNDr. František Němec, Ph.D. Abstract: Quasiperiodic emissions are a type of electromagnetic waves detected in the Earth's inner magnetosphere which are not yet fully understood. In this thesis, we use high resolution electric field data obtained by the DEMETER satellite, at an altitude of about 700 km, to analyze their fine inner structure. Overall, we analyzed 251 events, which were classified into three categories (with fine inner structure, without fine inner structure, and borderline cases). Additionally, we determined the periods of the fine inner structure and studied their dependance on relevant parameters. We show that the periods of the fine inner structure (on the order of seconds) do not significantly change during individual events and they are typically larger for events with longer modulation periods. We also show that the modulation periods of events without the fine inner structure are longer than the modulation periods of events with the fine inner structure, indicating their possibly different generation mechanisms. Keywords: DEMETER, quasiperiodic emissions, spectral analysis

The main task of this bachelor thesis is to create a model of the bow shock and magnetopause at Mars by analysing data from the MAVEN spacecraft. There are three main regions around Mars, namely the magnetosphere, the magnetosheath and the solar wind, which are separated by these two boun- daries. For approximately half of measured data it is possible to determine in which region the spacecraft is located at a given time based on simple conditions. This region classification allows us to develop empirical models parameterized by the solar wind dynamic pressure, solar ionizing flux, crustal magnetic field and Mach number. The developed empirical model of the bow shock is tested by comparing with the boundary crossings identified using a semiautomatic procedure. Another task of this thesis is to classify the remai- ning unclassified half of the measured data using machine learning techniques and to use a neural network to determine in which region the spacecraft is located at a given time. Finally, the results obtained by the empirical model and by the neural network are compared. 1

Title: Satellite observations of military transmitter signals Author: Jan Pekař Department: Department of surface and plasma science Supervisor: doc. RNDr. František Němec, Ph.D., Department of surface and plasma science Abstract: Transmitters operating in the very low frequency range, used in military for their characteristic features, are powerful and localised sources of electromagnetic waves at known distinct frequencies. These waves can affect the ionosphere surrounding their passing as well as the dynamics of energetic particles trapped in the Van Allen radiation belts. A systematic analysis of data acquired by the low altitude satellite DEMETER in the vicinity of the transmitters and their magnetically conjugate regions during six years of its operation allows for the recognition and description of these potential influences. This work is focused primarily on changes of ionospheric plasma density and temperature and energetic particle precipitation due to wave-particle interactions. Keywords: Low frequency transmitters, DEMETER, ionosphere, particle precipitation

Historically, studying the Martian ionosphere has been difficult due to the lack of dedicated instruments for electron density measurements in the orbit of Mars. However, since 2005, radio occultation measurements have been supplemented by Mars Express MARSIS remote sounder data and, more recently, by data from the MAVEN LPW Langmuir probe since 2014. The ionosphere of Mars is an interesting system, because Mars as one of the two solar system planetary bodies without an intrinsic magnetic field has highly localised crustal magnetic fields. The Chapman model describes the main layer of the ionosphere surprisingly well. Nevertheless, the crustal magnetic fields and other parameters potentially influence the ionosphere formation and topology. Combining the recent vast electron density data set, the Mars Global Surveyor crustal magnetic field map, and F10.7 solar radio flux measurements carried out at the Earth, a detailed study of the influence of these parameters can be conducted. To study the influence of these parameters as well as solar zenith angle on electron densities in the Martian ionosphere, we study magnitude of deviations from the established Chapman model. Furthermore, we use the Kolmogorov's 5/3 power law to investigate a possible dependence of its parameters characterising power and dissipation...

The objective of this thesis is to evaluate the accuracy of two frequently used models of magnetic field within Earth's magnetosphere (Tsyganenko 1989, 1996). In order to do this, we use vector magnetic data from four satellites of the Cluster II mission, collected between 2001-2014 and covering almost the whole region of the Earth's inner magne- tosphere at radial distances from 2 to 20 Earth radii. We compare model predictions with spacecraft data and evaluate the spatial dependence of the magnitude differences and angular deviations. Furthermore, we compare model locations of the min-B equator with the locations determined using the four-point measurements, and we study the de- pendence of the respective latitudinal deviations on the level of geomagnetic activity. We show that, although both models are very well correlated with satellite data, the newer model is systematically more accurate. At the same time, we show that the accuracy of both models decreases significantly during the periods of increased geomagnetic activity. 1

This thesis deals with processing wave data obtained by the LPW instrument onboard the MAVEN satellite spanning a time frame from 10/2014 to 10/2018. We look for an evidence of lightning existence on Mars. We assume that while an electromagnetic pulse originally generated during a lightning stroke would have a form of a vertical intense line in the frequency-time spectrogram, the subsequent dispersion during the propagation through the plasma medium would lead to a formation of a characteristic shape of so-called whistler. We further use the data obtained by the LPW instrument and by the magnetometer MAG to analyze electromagnetic wave environment in the near-Mars space. We study the intensity of electric and magnetic eld uctuations as a function of the position, frequency, solar activity, and Sun-Mars distance. Multicomponent measurements performed by the MAG instrument allow us to carry out a detailed wave analysis of selected events, i.e., to determine the polarity and propagation directions of the observed emissions. We show that all the selected events have common characteristics. 1