Propagation of whistler-mode chorus to low altitudes: divergent ray trajectories and ground accessibility

We investigate the ray trajectories of nonductedly propagating lower-band chorus waves with respect to their initial angle θ<sub>0</sub>, between the wave vector and ambient magnetic field. Although we consider a wide range of initial angles θ<sub>0</sub>, in order to be consistent with recent satellite observations, we pay special attention to the intervals of initial angles θ<sub>0</sub>, for which the waves propagate along the field lines in the source region, i.e. we mainly focus on waves generated with &theta<sub>0</sub> within an interval close to 0° and on waves generated within an interval close to the Gendrin angle. We demonstrate that the ray trajectories of waves generated within an interval close to the Gendrin angle with a wave vector directed towards the lower L-shells (to the Earth) significantly diverge at the frequencies typical for the lower-band chorus. Some of these diverging trajectories reach the topside ionosphere having θ close to 0°; thus, a part of the energy may leak to the ground at higher altitudes where the field lines have a nearly vertical direction. The waves generated with different initial angles are reflected. A small variation of the initial wave normal angle thus very dramatically changes the behaviour of the resulting ray. Although our approach is rather theoretical, based on the ray tracing simulation, we show that the initial angle θ<sub>0</sub> of the waves reaching the ionosphere (possibly ground) is surprisingly close - differs just by several degrees from the initial angles which fits the observation of magnetospherically reflected chorus revealed by CLUSTER satellites. We also mention observations of diverging trajectories on low altitude satellites

Simultaneous observations of quasi-periodic ELF/VLF wave emissions and electron precipitation by DEMETER satellite: A case study

International audience[1] We present results of case studies of quasi-periodic (QP) ELF/VLF hiss emissions detected onboard the DEMETER satellite. Three events with simultaneous periodic modulation in VLF wave intensity and energetic electron precipitation are found. In each event we observe exact coincidence of one or two busts of VLF wave intensity with energetic electron precipitation peaks. To our knowledge, such observations made onboard satellites have not been reported earlier. All events are observed at fairly quiet geomagnetic conditions (Kp < 3). The dynamic spectrum of the VLF waves in these QP events was characterized by a regular frequency increase in each burst, and the repetition period was less than or about 20 s. These features allow us to suggest that the observed events belong to the QP2-class, i.e., events which are not associated with geomagnetic pulsations. We also analyze energetic electron data from NOAA-17 spacecraft which has helio-synchronous circular orbit similar to DEMETER spacecraft and measured in the same region of the magnetosphere within 30 min for the analyzed events. NOAA-17 data confirm that the QP emissions were detected by DEMETER in the region of isotropization of energetic electrons, which is typically associated with the development of the cyclotron instability. Modulation of electron flux with a period close to the QP emission period is observed in two events. Based on the observed correlation between bursts of wave intensity and energetic particle flux, we estimate the location and spatial extent of the source region for QP emissions. Citation: Hayosh, M., D. L. Pasmanik, A. G. Demekhov, O. Santolik, M. Parrot, and E. E. Titova (2013), Simultaneous observations of quasi-periodic ELF/VLF wave emissions and electron precipitation by DEMETER satellite: A case study

Influence of power line harmonic radiation on the VLF wave activity in the upper ionosphere: Is it capable to trigger new emissions?

International audience[1] We analyze the influence of Power Line Harmonic Radiation (PLHR) events on the overall VLF wave activity as observed by the low‐altitude (about 700 km) DEMETER spacecraft. We take advantage of a unique set of 148 PLHR events identified in the Burst mode data, where a waveform of one electric and one magnetic field component is measured. It is shown that the occurrence rate of PLHR events over the industrialized areas is quite large (more than about 8%). However, among all the identified events, we have found only two cases of possibly PLHR‐triggered emissions. There is no evidence that the total power spectral density of electromagnetic waves over industrialized regions and geomagnetically conjugate regions is larger than what would be expected without man‐made influence. Finally, we have analyzed the presence of the weekend effect (i.e., a different behavior during the weekends as compared to the weekdays due to the lower power consumption), demonstrating that no such phenomenon seems to be present in the analyzed data set. Citation: Němec, F., M. Parrot, and O. Santolík (2010), Influence of power line harmonic radiation on the VLF wave activity in the upper ionosphere: Is it capable to trigger new emissions?

Vznik a vývoj davelského vulkanického komplexu

Davelský vulkanický komplex (DVC), který je součástí tepelsko-barrandienské jednotky Českého masivu, představuje vulkanický oblouk neoproterozoického až kambrického stáří, zformovaný během kadomské akreční orogeneze na severním okraji superkontinentu Gondwana. Tato diplomová práce kombinuje data získaná z terénního výzkumu, petrografie, mikroanalýzy horninotvorných minerálů, analýzy hlavních a stopových prvků, izotopů Sr-Nd- Pb a U-Pb geochronologie na zirkonech za účelem objasnění petrogeneze a vývoje DVC. Na základě těchto dat je zřejmá minimálně třístupňová metamorfóza zahrnující alteraci během extruze magmatu na mořské dno, variskou regionální metamorfózu a variskou kontaktní metamorfózu související s intruzí Středočeského plutonického komplexu. Zkoumané horniny vykazují vápenato-alkalický trend, zatímco bazalty vykazující tholeiitický trend, dříve popsané z této oblasti, jsou považovány za produkty mladších událostí. V severní části DVC dominují felsické subvulkanické (plagiogranit), vulkanické (dacit-ryolit) a pyroklastické (daciticko- ryolitické tufy a brekcie) členy s několika výchozy bazalto-andezitových až andezitových polštářových láv dokumentující mořské prostředí extruze. Tyto horniny mají vysoký podíl sodíku, a naopak nízký podíl draslíku, přičemž plagiogranit obsahuje albit, který se...The Davle Volcanic Complex (DVC) situated in the Teplá-Barrandian unit (TBU) of the Bohemian Massif, is considered as a Neoproterozoic-Cambrian magmatic arc that developed on the northern active margin of Gondwana supercontinent during Cadomian accretionary orogeny. This study combines data obtained from fieldwork, petrography, rock-forming mineral microanalysis, major and trace element analysis, Sr-Nd-Pb isotopic systematics and U-Pb zircon geochronology in order to reveal the petrogenesis and evolution of the DVC. At least three-stage metamorphism including Cadomian seafloor alteration, Variscan regional metamorphism as well as contact metamorphism related to the emplacement of the Central Bohemian Plutonic Complex affected the DVC. The studied rocks follow calc-alkaline trend whereas tholeiitic trend previously reported is rather related to younger magmatic events. The northern part of the DVC is dominated by felsic subvolcanic (plagiogranite), volcanic (dacite- rhyolite) and pyroclastic (dacitic-rhyolitic tuffs and breccias) rocks with a few outcrops of basaltic andesite-andesite pillow lavas documenting the subaqueous activity of the DVC. These rocks are Na-rich, but K-poor, the plagiogranite contains albite most likely primary in origin, and exhibit highly radiogenic εNd values (~ +6 to +11),...Institute of Geochemistry, Mineralogy and Mineral ResourcesÚstav geochemie, mineralogie a nerostných zdrojůPřírodovědecká fakultaFaculty of Scienc

Analysis of fine ELF wave structures observed poleward from the ionospheric trough by the low-altitude satellite DEMETER

International audienceDEMETER was a three-axis stabilized Earth-pointing spacecraft launched on 29 June 2004 into a low-altitude (710 km) polar and circular orbit that was subsequently lowered to 650 km until the end of the mission in December 2010. DEMETER measured electromagnetic waves all around the Earth except at magnetic invariant latitudes >65°. The frequency range for the electric field was from DC up to 3.5 MHz and for the magnetic field from a few hertz up to 20 kHz. Electromagnetic ion cyclotron (EMIC) waves have been previously observed by DEMETER close to the ionospheric trough during high magnetic activity, and this paper describes another type of EMIC waves. These waves are also observed close to the trough, but they extend poleward, with the trough acting as a boundary. They are observed exclusively during the night and preferentially during geomagnetic substorms. The analysis of wave propagation shows that they propagate nearly along the ambient magnetic field and that they come from larger radial distances

Using the cold plasma dispersion relation and whistler mode waves to quantify the antenna sheath impedance of the Van Allen Probes EFW instrument

Cold plasma theory and parallel wave propagation are often assumed when approximating the whistler mode magnetic field wave power from electric field observations. The current study is the first to include the wave normal angle from the Electric and Magnetic Field Instrument Suite and Integrated Science package on board the Van Allen Probes in the conversion factor, thus allowing for the accuracy of these assumptions to be quantified. Results indicate that removing the assumption of parallel propagation does not significantly affect calculated plasmaspheric hiss wave powers. Hence, the assumption of parallel propagation is valid. For chorus waves, inclusion of the wave normal angle in the conversion factor leads to significant alterations in the distribution of wave power ratios (observed/ calculated); the percentage of overestimates decreases, the percentage of underestimates increases, and the spread of values is significantly reduced. Calculated plasmaspheric hiss wave powers are, on average, a good estimate of those observed, whereas calculated chorus wave powers are persistently and systematically underestimated. Investigation of wave power ratios (observed/calculated), as a function of frequency and plasma density, reveals a structure consistent with signal attenuation via the formation of a plasma sheath around the Electric Field and Waves spherical double probes instrument. A simple, density-dependent model is developed in order to quantify this effect of variable impedance between the electric field antenna and the plasma interface. This sheath impedance model is then demonstrated to be successful in significantly improving agreement between calculated and observed power spectra and wave powers

Statistical investigation of VLF quasiperiodic emissions measured by the DEMETER spacecraft

International audienceWe present a survey of quasiperiodic (QP) ELF/VLF emissions detected onboard the DEMETER (Detection of Electro-Magnetic Emissions Transmitted from Earthquake Regions) satellite (altitude of about 700 km, nearly Sun-synchronous orbit at 10:30/22:30 LT). Six years of data have been visually inspected for the presence of QP emissions with modulation periods higher than 10 s and with frequency bandwidths higher than 200 Hz. It is found that these QP events occur in about 5% of daytime half orbits, while they are basically absent during the night. The events occur predominantly during quiet geomagnetic conditions following the periods of enhanced geomagnetic activity. Their occurrence and properties are systematically analyzed. QP emissions occur most often at frequencies from about 750 Hz to 2 kHz, but they may be observed at frequencies as low as 500 Hz and as high as 8 kHz. Modulation periods of QP events may range from about 10 to 100 s, with typical values of 20 s. Frequency drifts of the identified events are generally positive, but they are lower for events with larger modulation periods. The events are usually limited to higher L values (L > 2). The upper L shell boundary of their occurrence could not be identified using the DEMETER data, but they are found to extend up to at least L ~ 6. The occurrence rate of the events is significantly lower at the longitudes of the South Atlantic anomaly (by a factor of more than 2)

Geochemistry and petrology of plagiogranites from the Jílové belt

This thesis is focused on the study of the subvolcanic rocks from the northern part of the Jílové belt. The Jílové belt is a strip of magmatic rocks belonging to the Davle Volcanic Complex situated in the center of the Bohemian Massif, south of Prague, close to the border between the Teplá-Barandian and Moldanubian units. The sub-volcanic facies of its northern part has been previously ascribed to trondhjemite, alaskite or plagiogranite. In this study, we provide new geochemical data such as major and trace element analyses paralleled by Sr-Nd isotopic data, which indicate the origin of these rocks in the mantle wedge. They probably represent a final product of a magmatic differentiation of an island arc series. Here, we consider two possible models for their origin, according to which we could also choose the correct classification of these peculiar rocks: adakite, or plagiogranite. Adakites are rocks formed by melting of a subducted slab which are predominantly related to the volcanic arc settings. In comparison, plagiogranites are rocks formed by an extreme differentiation of a mantle- derived basaltic melt in the oceanic crust environment. Our new geochemical data, especially the low degree of light rare earth enrichment (LaN/YbN = 0.8-1.3), is clearly inconsistent with the genetic association...Tato práce se zabývá studiem subvulkanických hornin v severní části jílovského pásma. Jílovské pásmo je pruh magmatických hornin nacházející se ve středu českého masivu jižně od Prahy, na hranici tepelsko-barandienské oblasti s oblastí moldanubickou. Subvulkanická facie jeho severní části byla v minulosti nazývána různými jmény, např. trondhjemit, alaskit, nebo plagiogranit. V této práci jsou prezentována nová geochemická data zahrnující analýzy hlavních a stopových prvků a zejména izotopického složení Sr- Nd, která dokládají původ těchto hornin v plášťovém klínu. Pravděpodobně se jedná o jeden z finálních produktů vulkanické diferenciační série ostrovního oblouku. Uvažujeme zde dva možné modely vzniku, podle kterých bychom mohli zvolit rovněž správný název pro zkoumané horniny: adakity, nebo plagiogranity. Adakity jsou horniny vzniklé tavením subdukované desky a nachází se především ve vulkanických obloucích. Plagiogranity jsou naopak horniny vzniklé extrémní diferenciací taveniny plášťového zdroje a nachází se především v oceánské kůře. Geochemická data stopových prvků, zejména nízký stupeň frakcionace vzácných zemin (LaN/YbN = 0,8-1,3) jasně vyvrací genetickou spojitost s adakity a potvrzuje spojitost subvulkanických hornin jílovského pásma s plagiogranity.Ústav geochemie, mineralogie a nerostných zdrojůInstitute of Geochemistry, Mineralogy and Mineral ResourcesFaculty of SciencePřírodovědecká fakult

Isolated Electrostatic Structures Observed Throughout the Cluster Orbit: Relationship to Magnetic Field Strength

Isolated electrostatic structures are observed throughout much of the 4 Re by 19.6 Re Cluster orbit. These structures are observed in the Wideband plasma wave instrument's waveform data as bipolar and tripolar pulses. These structures are observed at all of the boundary layers, in the solar wind and magnetosheath, and along auroral field lines at 4.5-6.5 Re. Using the Wideband waveform data from the various Cluster spacecraft we have carried out a survey of the amplitudes and time durations of these structures and how these quantities vary with the local magnetic field strength. Such a survey has not been carried out before, and it reveals certain characteristics of solitary structures in a finite magnetic field, a topic still inadequately addressed by theories. We find that there is a broad range of electric field amplitudes at any specific magnetic field strength, and there is a general trend for the electric field amplitudes to increase as the strength of the magnetic field increases over a range of 5 to 500 nT. We provide a possible explanation for this trend that releates to the structures being Bernstein-Greene-Kruskal mode solitary waves. There is no corresponding dependence of the duration of the structures on the magnetic field strength, although a plot of these two quantities reveals the unexpected result that with the exception of the magnetosheath, all of the time durations for all of the other regions are comparable, wheras the magnetosheath time durations clearly are in a different category of much smaller time duration. We speculate that this implies the structures are much smaller in size.Comment: 24 pages plus 8 figures; paper presented at Spatio-Temporal Analysis and Multipoint Measurements in Space (STAMMS) conference, held in Orleans, France on 12-16 May 200

Quasiperiodic emissions observed by the Cluster spacecraft and their association with ULF magnetic pulsations

International audience[1] Quasiperiodic (QP) emissions are electromagnetic waves at frequencies of about 0.5–4 kHz characterized by a periodic time modulation of the wave intensity, with a typical modulation period on the order of minutes. We present results of a survey of QP emissions observed by the Wide-Band Data (WBD) instruments on board the Cluster spacecraft. All WBD data measured in the appropriate frequency range during the first 10 years of operation (2001–2010) at radial distances lower than 10 R E were visually inspected for the presence of QP emissions, resulting in 21 positively identified events. These are systematically analyzed, and their frequency ranges and modulation periods are determined. Moreover, a detailed wave analysis has been done for the events that were strong enough to be seen in low-resolution Spatio-Temporal Analysis of Field Fluctuations-Spectrum Analyzer data. Wave vectors are found to be nearly field-aligned in the equatorial region, but they become oblique at larger geomagnetic latitudes. This is consistent with a hypothesis of unducted propagation. ULF magnetic field pulsations were detected at the same time as QP emissions in 4 out of the 21 events. They were polarized in the plane perpendicular to the ambient magnetic field, and their frequencies roughly corresponded to the modulation period of the QP events. Citation: Němec , F., O. Santolík, J. S. Pickett, M. Parrot, and N. Cornilleau-Wehrlin (2013), Quasiperiodic emissions observed by the Cluster spacecraft and their association with ULF magnetic pulsations