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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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Lightning-Related Electromagnetic Wave Phenomena in the Earth's Magnetosphere
Záhlava, Jan ; Němec, František (advisor) ; Chum, Jaroslav (referee) ; Manninen, Jyrki (referee)
Title: Lightning-Related Electromagnetic Wave Phenomena in the Earth's Magnetosphere Author: Jan Záhlava Department: Department of Surface and Plasma Physics Supervisor: doc. RNDr. František Němec, PhD., Department of Surface and Plasma Physics Abstract: The thesis focuses on lightning-related electromagnetic wave phenomena observed by spacecraft in the Earth's inner magnetosphere. Two different approaches are used to identify the frequency and spatial extent where lightning generated emissions significantly contribute to the overall wave intensity. First, whistler detections onboard the DEMETER spacecraft are used to sort the measurements according to the whistler activity. Second, we use a geographic distribution of lightning activity and analyze a dependence of the overall wave intensity on geomagnetic longitude. We show that, especially during the night, the overall wave intensity observed in the plasmasphere is well correlated with lightning activity. The other focus of the study is on special electromagnetic wave events consisting of alternating frequency bands of enhanced and reduced wave intensity formed in the ionosphere due to lightning. We analyze their occurrence and parameters, and we suggest a possible mechanism of their formation. Keywords: lightning, waves in plasma, whistlers, plasmasphere
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Lightning-Related Electromagnetic Wave Phenomena in the Earth's Magnetosphere
Záhlava, Jan ; Němec, František (advisor)
Title: Lightning-Related Electromagnetic Wave Phenomena in the Earth's Magnetosphere Author: Jan Záhlava Department: Department of Surface and Plasma Physics Supervisor: doc. RNDr. František Němec, PhD., Department of Surface and Plasma Physics Abstract: The thesis focuses on lightning-related electromagnetic wave phenomena observed by spacecraft in the Earth's inner magnetosphere. Two different approaches are used to identify the frequency and spatial extent where lightning generated emissions significantly contribute to the overall wave intensity. First, whistler detections onboard the DEMETER spacecraft are used to sort the measurements according to the whistler activity. Second, we use a geographic distribution of lightning activity and analyze a dependence of the overall wave intensity on geomagnetic longitude. We show that, especially during the night, the overall wave intensity observed in the plasmasphere is well correlated with lightning activity. The other focus of the study is on special electromagnetic wave events consisting of alternating frequency bands of enhanced and reduced wave intensity formed in the ionosphere due to lightning. We analyze their occurrence and parameters, and we suggest a possible mechanism of their formation. Keywords: lightning, waves in plasma, whistlers, plasmasphere
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Lightning-Related Electromagnetic Wave Phenomena in the Earth's Magnetosphere
Záhlava, Jan ; Němec, František (advisor)
Title: Lightning-Related Electromagnetic Wave Phenomena in the Earth's Magnetosphere Author: Jan Záhlava Department: Department of Surface and Plasma Physics Supervisor: doc. RNDr. František Němec, PhD., Department of Surface and Plasma Physics Abstract: The thesis focuses on lightning-related electromagnetic wave phenomena observed by spacecraft in the Earth's inner magnetosphere. Two different approaches are used to identify the frequency and spatial extent where lightning generated emissions significantly contribute to the overall wave intensity. First, whistler detections onboard the DEMETER spacecraft are used to sort the measurements according to the whistler activity. Second, we use a geographic distribution of lightning activity and analyze a dependence of the overall wave intensity on geomagnetic longitude. We show that, especially during the night, the overall wave intensity observed in the plasmasphere is well correlated with lightning activity. The other focus of the study is on special electromagnetic wave events consisting of alternating frequency bands of enhanced and reduced wave intensity formed in the ionosphere due to lightning. We analyze their occurrence and parameters, and we suggest a possible mechanism of their formation. Keywords: lightning, waves in plasma, whistlers, plasmasphere
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Lightning-Related Electromagnetic Wave Phenomena in the Earth's Magnetosphere
Záhlava, Jan ; Němec, František (advisor) ; Chum, Jaroslav (referee) ; Manninen, Jyrki (referee)
Title: Lightning-Related Electromagnetic Wave Phenomena in the Earth's Magnetosphere Author: Jan Záhlava Department: Department of Surface and Plasma Physics Supervisor: doc. RNDr. František Němec, PhD., Department of Surface and Plasma Physics Abstract: The thesis focuses on lightning-related electromagnetic wave phenomena observed by spacecraft in the Earth's inner magnetosphere. Two different approaches are used to identify the frequency and spatial extent where lightning generated emissions significantly contribute to the overall wave intensity. First, whistler detections onboard the DEMETER spacecraft are used to sort the measurements according to the whistler activity. Second, we use a geographic distribution of lightning activity and analyze a dependence of the overall wave intensity on geomagnetic longitude. We show that, especially during the night, the overall wave intensity observed in the plasmasphere is well correlated with lightning activity. The other focus of the study is on special electromagnetic wave events consisting of alternating frequency bands of enhanced and reduced wave intensity formed in the ionosphere due to lightning. We analyze their occurrence and parameters, and we suggest a possible mechanism of their formation. Keywords: lightning, waves in plasma, whistlers, plasmasphere
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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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Frequencies of attenuation in the power spectra observed by the DEMETER spacecraft
Záhlava, Jan ; Němec, František (advisor) ; Sochorová, Zuzana (referee)
Předmětem bakalářské práce je analýza zvláštních efekt· pozorovaných ve frekvenčně-časových spektrogramech změřených družicí DEMETER v pásmu velmi nízkých frekvencí. Jedná se o periodické utlumení frekvenční závislosti elektrické intenzity, které se spojitě mění v čase. Při detailním zkoumání se ukazuje, že jsou tyto útlumové události tvořeny z hvizd· pocházejících z bleskových emisí. Porovnání závislosti doby trvání útlumových událostí na geomagnetické délce s délkovou závislostí četnosti výskytu blesk· ukazuje, že jsou útlumové události posunuty oproti blesk·m přibližně o 30◦ západním směrem. Podařilo se nám vysvětlit tento posun a vytvořit jednoduchý model možného formování útlumových událostí založený na módové teorii šíření vln ve vlnovodu. 1
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