|
|
Wave-particle interactions in the Earth's magnetosphere
Tomori, Alexander ; Santolík, Ondřej (advisor) ; Němec, František (referee)
Wave-particle interactions in the Earth's mag- netosphere Abstract: In this work we analyse wave-particle interactions in the Earth's magnetosphere. After the theoretical introduction we find the dispersion relation of plasma described by parameters obtained from the particle anal- yser PEACE aboard Cluster spacecraft and we identify possible wave modes. The dispersion relation is derived using software WHAMP, which uses nu- merical approach and works with hot plasma theory. Various directions of wave propagation are analysed in order to find instabilities. We look at how maximal found instability changes while varying plasma parameters and we try to find plasma parameters leading to higher instabilities. Using numerical integration we try to verify dependency of instabilities on different plasma components and its parameters, especially on loss cone.
|
|
|
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)
|
|
| |
|
|
Verification of empirical models of magnetic field around Earth
Kotková, Marie ; Němec, František (advisor) ; Výbošťoková, Tatiana (referee)
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
|
|
|
Satellite observations of military transmitter signals
Pekař, Jan ; Němec, František (advisor) ; Bezděková, Barbora (referee)
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
|
|
|
Martian bow shock and magnetic pileup boundary locations
Linzmayer, Václav ; Němec, František (advisor) ; Gončarov, Oleksandr (referee)
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
|
|
|
Variability of the Martian ionosphere
Maruška, Jakub ; Němec, František (advisor) ; Pitňa, Alexander (referee)
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...
|
|
|
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
|
|
| |
|
|
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
|
guest ::
RSS feed.