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Whistler waves observed by the DEMETER spacecraft
Záhlava, Jan ; Němec, František (advisor) ; Macúšová, Eva (referee)
Although lightning-generated whistlers have been studied for nearly a century, there are still questions to be answered. It is clear that, at least in a certain frequency range, these waves significantly contribute to the overall wave intensity in the inner magnetosphere. They also influence distribution functions of energetic particles in the Van Allen radiation belts. Thanks to the on-board implemented neural network for automated whistler detection, we can relate electromagnetic wave and energetic particle flux measurements performed by the low-altitude DEMETER spacecraft with the number and dispersion of whistlers detected during a certain time interval. We distinguish the cases with high and low whistler occurrence and we use this information to determine the overall effect of lightning-generated whistlers. Powered by TCPDF (www.tcpdf.org)
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Multipoint observations of magnetospheric wave phenomena
Bezděková, Barbora ; Němec, František (advisor) ; Grison, Benjamin (referee) ; Shklyar, David R. (referee)
Electromagnetic wave phenomena represent a crucial factor during the forma- tion of the Earth's magnetosphere, as they are responsible for the energy trans- fer in the collisionless plasma medium. Multipoint observations of such wave phenomena are particularly useful to distinguish between spatial and temporal intensity variations. Moreover, an approximate event spatial extent and prop- agation directions can be determined. The thesis is focused on the statistical study of conjugate observations of wave phenomena called quasiperiodic (QP) emissions observed by the Van Allen Probes spacecraft and ground-based Kan- nuslehto station. Altogether, 26 simultaneously observed events were analyzed. This approach is unique in the sense that most such analyses up to date were only case studies. The thesis further presents the analysis of the dependence of properties of another wave phenomena, called magnetospheric line radiation (MLR), on the geomagnetic activity indices and solar wind parameters. Geomag- netic activity effects on the event characteristics are revealed. Finally, the effect of interplanetary shocks on the overall very low frequency (VLF) wave intensity measured by the DEMETER spacecraft is studied.
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Selected Wave Phenomena in the Earth's Magnetosphere
Bezděková, Barbora ; Němec, František (advisor) ; Macúšová, Eva (referee)
Electromagnetic waves are crucial for energy transfer in the nearly collision- less plasma of the Earth's inner magnetosphere. The waves in the frequency range 1-8 kHz whose visualisation in the form of frequency-time spectrograms reveals a harmonic frequency modulation of the wave intensity are called magnetospheric line radiation (MLR). Waves characterized by a nearly periodic time modulation of the wave intensity observed at frequencies between about 0.5 and 4 kHz are called quasiperiodic (QP) emissions. Although both types of the events were re- peatedly observed by ground-based instruments and low-altitude satellites, their origin remains still unclear. Between 2004 and 2010 these wave events were me- asured by the DEMETER spacecraft (almost Sun-synchronous orbit, altitude of about 700 km). This thesis presents a systematic study of the properties of the observed events, a comparison of the observations by the spacecraft and ground- based instruments, and an investigation of a relation to solar wind parameters.
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Whistler waves observed by the DEMETER spacecraft
Záhlava, Jan ; Němec, František (advisor) ; Macúšová, Eva (referee)
Although lightning-generated whistlers have been studied for nearly a century, there are still questions to be answered. It is clear that, at least in a certain frequency range, these waves significantly contribute to the overall wave intensity in the inner magnetosphere. They also influence distribution functions of energetic particles in the Van Allen radiation belts. Thanks to the on-board implemented neural network for automated whistler detection, we can relate electromagnetic wave and energetic particle flux measurements performed by the low-altitude DEMETER spacecraft with the number and dispersion of whistlers detected during a certain time interval. We distinguish the cases with high and low whistler occurrence and we use this information to determine the overall effect of lightning-generated whistlers. Powered by TCPDF (www.tcpdf.org)
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Ray-tracing simulations of electromagnetic waves in magnetospheric plasmas
Nečada, Marek ; Santolík, Ondřej (advisor) ; Kouba, Daniel (referee)
This work deals with simulations of wave propagation in magnetospheric plasmas, particularly with numerical ray tracing. It mentions some of the earlier ray tracing implementations that were used in studies of wave propagation in Earth's magnetosphere. The most important parts of linear plasma wave theory are outlined. Some of the existing numerical methods for solving the hot plasma dispersion relation are described. A new ray tracing program, NPR, is presented. It is capable of ray-tracing simulations in cold plasmas and also in non-relativistic hot plasmas via the WHAMP procedure.
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