The bow shock current is hypothesized to connect to the Earth's magnetosphere on open field lines and to contribute as a field aligned current to the polar ionospheric currents. In order to investigate this, two years of AMPERE data are used to compute the average region 1 currents, and average currents within the polar cap boundary, under different interplanetary magnetic field (IMF) clock angles and IMF magnitudes. The average currents are studied for stable IMF conditions. Therefore data is selected if the IMF By and Bz components do not change sign in a 30 minutes time interval to ensure sufficiently stable conditions. In addition, the AMPERE current maps are renormalized and recentered such that the region 1 currents have a fixed extent. These averaged current maps are then used to discuss the sources of the currents in the polar cap and their possible connection to the bow shock current. The currents in the polar ionosphere are found to generally agree with the statistical convection pattern. For a strong east-west IMF there are some discrepancies for the region 0 currents which indicates a possible bow shock current closure. Furthermore there are currents in the polar cap of the northern hemisphere for a strong southward IMF, which however do not have the expected polarity for bow shock current closure. Therefore they must have another, but unknown, origin. In addition, SuperDARN data is used to confirm that currents on the dayside of the polar cap and polwards of the Region 1 currents are on open field lines for a strong eastward or westward IMF. Further investigations are needed to confirm the bow shock closure in the ionosphere. Additional investigations are needed to identify the source of the polar cap currents for a strong southward IMF.

No description available.

L'objectif principal du présent travail était d'étudier, comment la cinétique du plasma change dans les conditions de dépôt d'énergie spécifique élevé dans des champs électriques réduits élevé. La décharge capillaire nanoseconde a été utilisée comme outil expérimental. Les mesures sont effectuées dans l'azote pur et dans les mélanges azote/oxygène. Les paramètres électriques de la décharge sont mesurés: la tension appliquée, le dépôt d'énergie, le champ électrique et le courant électrique. Les spectres de l'émission optique de la décharge sont obtenus. La densité électronique dans les impulsions de décharge est mesurée. La décroissance du plasma est étudiée par les mesures de la densité électronique dans la post‐luminescence de la décharge. Les processus contrôlant la décroissance du plasma sont déterminés. La dépopulation de molécules excitées sur l'exemple de l'azote moléculaire N2(C) est étudié dans des mélanges azote/oxygène. Les processus responsables de la dépopulation des espèces excitées lors de la post‐luminescence de la décharge de nanoseconde à les conditions de dépôt d'énergie spécifique élevé dans des champs électriques réduits élevé sont examinés. La distribution radiale des espèces excitées à différentes compositions de gaz sont étudiée et comparées. L'étude expérimentale et numérique des processus responsables du chauffage rapide du gaz dans l'azote pur et dans les mélanges azote/oxygène dans la post‐luminescence de la décharge capillaire à la nanoseconde sont effectuées. Les particularités du chauffage rapide du gaz aux conditions de la décharge de nanoseconde à de dépôt d'énergie spécifique élevé dans des champs électriques réduits élevé sont étudués. La modification du schéma cinétique actuellement utilisé est proposée. / The main aim of the present work was to investigate, how the plasma kinetics changes at the conditions of high specific energy deposition at high reduced electric fields. The nanosecond capillary discharge was used as an experimental tool. The measurements are performed for pure nitrogen and nitrogen/oxygen mixtures. Electric parameters of the discharge are measured: the applied voltage, the energy deposition, the electric field, and the electric current. The spectra of the optical emission of the discharge are obtained. The electron density in the discharge pulses is measured. The plasma decay is studied by the measurements of the electron density in the afterglow of the discharge as well. The processes controlling the plasma decay are determined. Depopulation of excited molecules on the example of N2(C) state of molecular nitrogen is studied in nitrogen/oxygen mixtures. The processes responsible for depopulation of excited species in the afterglow of the nanosecond discharge at high specific deposited energy at high reduced electric field are discussed. The radial distributions of the excited species at different gas compositions are investigated and compared. The experimental and numerical studies of the processes responsible for fast gas heating in pure nitrogen and in nitrogen/oxygen mixtures in the afterglow of nanosecond capillary discharge are performed. The peculiarities of the fast gas heating at conditions of the nanosecond discharge at high specific deposited energy at high reduced electric field are discussed. The modification of the kinetic scheme currently in use is proposed.

In this report we present spacecraft and ground-based observations of magnetosheath jets impacting the magnetosphere, both as a case study and a statistical study. In the case study, jets were detected in the magnetosheath by the Magnetospheric MultiScale mission, MMS. By utilizing a data-based magnetosphericmodel (Tsyganenko T96 [29]), we estimated which jets were likely to impact the magnetopause and where they would do so. We examined ground based magnetometers, GMAGs, at the expected foot-point to the affected magnetic fieldline and compared this with the spacecraft observations. Theoretical transfertimes for a jet to be detectable by GMAGs have been estimated and compared with the observed time delay, from detection to GMAG response, and they were in good agreement for all cases. The times found for this geoeffective responsewere found to be around 1-2 min, and the response in the GMAGs was in the form of a pulse with an amplitude of around 50 nT. We suggest that jets of along enough time duration can be geoeffective in a way that they are detectable at ground level by GMAGs. It was also found that GMAGs fluctuate more during periods containing many detected jets. We performed our statistical study with the intention of comparing fluctuations in GMAG observations during Interplanetary Magnetic Field, IMF, configurations which is suggested to be favorable for jet creation. The IMF observationswas provided by the THEMIS (Time History of Events and Macroscale Interactions during Substorms) spacecraft. This was done by selecting periods of steady IMF with different orientations, and examining the GMAGs observed variations. GMAGs were selected based on a region where most of our foot-points were found in our previous case study. We performed this study over a three year interval, and found that GMAGs observe about 2 nT higher variation, according to their standard deviations, during radial IMF compared to northward IMF. During northward IMF we expect less effects from magnetopause phenomena, thus making it suitable to compare with radial IMF. Our statistical investigation support our findings that magnetosheath jets can be geoeffective in a waythat GMAGs can detect them.

This work is part of a bigger project on analyzing the ionospheric dynamics in the equatorial region using simulations. The main objective of this study is to determine and characterize the parameters needed to trigger instabilities and thus the formation of plasma bubbles. An ambition is to keep the calculations as complete as possible by not oversimplifying the process itself as a classic Rayleigh-Taylor instability and by introducing the more realistic Generalized Eccentric Dipole description of the magnetic field. In this way, we aspire to avoid the neglect of convoluted interactions in the ionospheric system as well as the distorted nature of the geomagnetic field. After an in-depth study of the existing literature and getting to know the data generated by IPIM, I derived the equations describing the relevant physical processes based on fundamental plasma physics. In a MATLAB environment, I proceeded to develop the necessary tools for a computation of the quantities needed in the equations to then assemble and interpret the results for a simple study case. The found growth rate values are high enough and thus the characteristic time for the occurrence of instabilities short enough for them to be the principal process in the examined time and altitude range. It has been verified that the computed growth rate is such that instabilities may occur with a higher probability in the Southern Hemisphere due to the elevated amplitudes and the time delay between the foot points. We managed to derive a complete description of the equatorial ionosphere without using unreasonable approximations and the simplicity of the chosen configuration did not hinder the successful computation of instability seeds. The preparations that I undertook during this internship are an important first step for the subsequent development of the ionospheric model.

Measurements are made to investigate the nature of a fast current disruptionappearing in one of the experimental devices at the Alfven Laboratory. Thedisruption appears when we let the induced electric field ( -vxB) in a transverselymagnetized flowing plasma drive a current between two short circuited plasmaprobes. It is the current measured in the circuit connecting the two probes thatshow the disruptive behaviour. The parameters of the typical disruption are a 5 Adrop in 25 ns.The results of the measurements indicate that the disruption is a relatively generalprocess. Instead of being a consequence of some special detail in the probeconfiguration it turns out to be a process appearing whenever we draw a currentbetween two probes in the plasma.The origin of the disruption is located and it turns out to be at, or at least near,the negatively biased probe.Simultaneous current and plasma density measurements indicate that the currentin the probe circuit generally exceeds the theoretical ion saturation current. Forthis to be possible there has to be some sort of electron emission process present atthe surface of the negatively biased probe. The conclusion is that it is this processthat fails when the current disrupts. Cathode spots are sometimes observed on thenegative probe, and they are believed to be the emission process in question.An analysis of the probe circuit gives that the measured current-voltagebehaviour during a disruption in a good way agrees with the assumption that acathode spot is extinguished at the negatively biased probe. When combining themodel of the circuit with a negative current-voltage characteristic for the cathodespot we get an unstable system. The disruption is believed to reflect this instability.The negative current-voltage characteristic needed to make this descriptionsuccessful is well described by curves found in literature on cathode spots.

No description available.

No description available.

No description available.

No description available.