187 research outputs found
Magnetic configurations, reconnection and energy transfers in space plasmas
No full textNello spazio interplanetario, particelle cariche e campi magnetici sono continuamente soggetti a processi fisici responsabili di scambi di energia e che ne modellano le configurazioni. Un processo chiave in questo contesto è la riconnessione magnetica. La complessa dinamica che ne risulta, responsabile dell’accellerazione delle particelle e della loro entrata nella magnetosfera terrestre (il che è potenzialmente pericoloso per alcune tecnologie ed il personale che se ne occupa) costituisce il soggetto principale di questa tesi. Nella prima parte del lavoro, il focus è la struttura locale del campo magnetico. Si mette a punto una tecnica per determinare le caratteristiche locali della configurazione di campo magnetico e la si applica a dati raccolti da satellite, dimostrandone l’applicabilità e l’efficacia. Nella seconda parte del lavoro di tesi vengono studiati i trasferimenti di energia fra campo elettromagnetico e plasma in prossimità di un sito di riconnessione, con l’aiuto di una simulazione numerica. In particolare si dimostra come i diversi canali di trasferimento dell’energia sono legati statisticamente gli uni agli altri, e correlati alle caratteristiche locali del sistema.
Throughout interplanetary space, plasma particles and magnetic fields play an endless game of re-shaping themselves and exchanging energy. A key process in this regard is magnetic reconnection. The complex dynamics resulting from this process is responsible for particle acceleration and entry into the Earth’s magnetosphere, potentially dangerous for people and machinery, and is the basic subject of this thesis. In the first part of the work, I focus on the local shape of magnetic configurations. To this aim, I devise a technique to retrieve relevant local characteristics of magnetic configurations, which I apply to multi-spacecraft data, demonstrating its efficacy. In the second part of the thesis I discuss how energy is exchanged among its different forms in the neighbourhood of a reconnection site using a numerical simulation. I show in particular how different energy conversions are statistically related to one another and to local features of the system
Kelvin-Helmholtz instability and induced magnetic reconnection at the Earth’s magnetopause: 3D simulation based on satellite data
No full textA 3D two-fluid simulation, using plasma parameters as measured by MMS on 8 September 2015, shows the nonlinear development of the Kelvin–Helmholtz instability at the Earth’s magnetopause. It shows extremely rich dynamics, including the development of a complex magnetic topology, vortex merging and secondary instabilities. Vortex induced and mid-latitude magnetic reconnection coexist and produce an asymmetric distribution of magnetic reconnection events. Off-equator reconnection exhibits a predominance of events in the Southern Hemisphere during the early nonlinear phase, as observed by satellites at the dayside magnetopause. The late nonlinear phase shows the development of vortex pairing for all latitudes while secondary Kelvin–Helmholtz instability develops only in the Northern Hemisphere, leading to an enhancement of the occurrence of off-equator reconnection there. Since vortices move tailward while evolving, this suggests that reconnection events in the Northern Hemisphere should dominate at the nightside magnetopause
Modeling the effects of cold-dense and hot-tenuous plasma sheet on proton ring current energy and peak location
No full textCaracterització de cordes de flux en el vent solar lent amb la missió Parker Solar Probe
No full textLa reconexión magnética es un importante mecanismo para la formación del viento solar. Probablemente está relacionado con la formación del viento solar lento en particular, que se observa en las proximidades de la lámina de corriente heliosférica (HCS) en el plano eclíptico. Un escenario posible es que la reconexión al HCS entre campos magnéticos de orientaciones opuestas (desde los polos solares opuestos) se vuelva a conectar de forma secuencial para formar pequeñas estructuras similares a cuerdas de flujo al viento solar, que nos interesan especialmente. En 2018 se lanzó la misión Parker Solar Probe (PSP) de la NASA con uno de sus principales objetivos ser determinar la estructura y la dinámica del plasma y los campos magnéticos en las fuentes del viento solar. Hemos tomado datos de la PSP durante su primera orbita en la aproximación más cercana al Sol. En particular, hemos analizado las observaciones del campo magnético, la velocidad de los iones y los electrones strahl, con el fin de identificar y caracterizar cuerdas de flujo pequeñas, principalmente en su orientación de eje y tamaño radial. El propósito es interpretar estas estructuras en el contexto de los procesos de reconexión magnética X-line. Más concretamente, este proyecto implementa un algoritmo de Fargette et al. (2020) que ajusta el campo magnético de las observaciones a un campo magnético modelo. Este método de ajuste permite determinar la orientación del eje de la cuerda de flujo ajustada, la distancia de aproximación más cercana desde la nave espacial al eje de la cuerda de flujo, el tiempo de aproximación más cercana y un parámetro adicional que describe las propiedades geométricas de las cuerdas de flujo. La implementación de este método marca la primera aplicación del algoritmo en cuerdas de flujo a pequeña escala liberadas secuencialmente en las puntas de los streamers del casco cerca de la eclíptica del Sol. Se desarrolló un método de muestreo bootstrap para adaptarse a 20 subintervalos dentro de un intervalo de tiempo máximo determinado por cada cuerda de flujo, dando lugar a distribuciones estadísticas de los parámetros. El análisis cubrió tres cruces HCS distintos, identificando inicialmente más de 30 intervalos de tiempo máximos. Este proceso dio 22 intervalos ajustados. La consistencia entre los ángulos ajustados y el comportamiento esperado del campo magnético bipolar demuestra la capacidad del algoritmo para moldear con precisión la geometría del campo magnético previsto. Los resultados muestran que las orientaciones de los ejes de la cuerda de flujo eran mayoritariamente perpendiculares al eje radial, de acuerdo con la explicación de la formación de la cuerda de flujo mediante la reconexión secuencial en la punta de los streamers del casco del Sol . Por último, las medidas de las cuerdas de flujo oscilaban entre medio radio solar y 2 radios solares, confirmando su pequeña escala en comparación con fenómenos mayores como los CME.Magnetic reconnection is an important mechanism for the formation of the solar wind. It is likely related to the formation of the slow solar wind in particular, which is observed in the vicinity of the heliospheric current sheet (HCS) in the ecliptic plane. A possible scenario is that reconnection at the HCS between magnetic fields of opposite orientations (from the opposite solar poles) leads to the formation of sequential small flux rope-like structures in the solar wind, which we are particularly interested in. In 2018, NASA’s Parker Solar Probe (PSP) mission was launched with one of its main objectives being to determine the structure and dynamics of the plasma and magnetic fields at the sources of the solar wind. We have taken data from the PSP during closest approach to the Sun on its first orbit around it. In particular, we have looked at observations from the magnetic field, ion velocity and strahl electrons, in order to identify and characterize small flux ropes, primarily in their axis orientation and their radial size. The purpose is to interpret these structures in the context of the X-line magnetic reconnection processes. More specifically, this project implements an algorithm from Fargette et al. (2020) that fits the magnetic field from observations to a model magnetic field. This fitting method permits to determine the fitted flux rope axis orientation, the distance of closest approach from the spacecraft to the flux rope’s axis, the time of closest approach and an additional parameter that describes the geometric properties of the flux ropes. The implementation of this method marks the first application of the model to small-scale flux ropes released sequentially at the tips of helmet streamers near the Sun’s ecliptic. A bootstrap resampling method was developed to fit 20 flux rope subintervals within a given maximum interval, resulting in statistical distributions of fitting parameters for each flux rope. The analysis covered three distinct HCS crossings, initially identifying over 30 maximum time intervals. This process yielded 22 well-fitted intervals. The consistency between the fitted angles (‘ and ‘) and expected bipolar magnetic field signatures demonstrates the algorithm's ability to accurately model the intended magnetic field geometry. The results show that the orientations of the flux rope’s axes were mostly perpendicular to the radial axis, consistent with the explanation of flux rope formation through the sequential reconnection at the tip of the Sun’s helmet streamers. Lastly, flux rope sizes ranged from half a solar radius to 2 solar radii, confirming their small scale compared to larger phenomena like CME
Correcting moments of in situ particle distribution functions for spacecraft electrostatic charging
No full textCaracterització de cordes de flux en el vent solar lent amb la missió Parker Solar Probe
No full textLa reconexión magnética es un importante mecanismo para la formación del viento solar. Probablemente está relacionado con la formación del viento solar lento en particular, que se observa en las proximidades de la lámina de corriente heliosférica (HCS) en el plano eclíptico. Un escenario posible es que la reconexión al HCS entre campos magnéticos de orientaciones opuestas (desde los polos solares opuestos) se vuelva a conectar de forma secuencial para formar pequeñas estructuras similares a cuerdas de flujo al viento solar, que nos interesan especialmente. En 2018 se lanzó la misión Parker Solar Probe (PSP) de la NASA con uno de sus principales objetivos ser determinar la estructura y la dinámica del plasma y los campos magnéticos en las fuentes del viento solar. Hemos tomado datos de la PSP durante su primera orbita en la aproximación más cercana al Sol. En particular, hemos analizado las observaciones del campo magnético, la velocidad de los iones y los electrones strahl, con el fin de identificar y caracterizar cuerdas de flujo pequeñas, principalmente en su orientación de eje y tamaño radial. El propósito es interpretar estas estructuras en el contexto de los procesos de reconexión magnética X-line. Más concretamente, este proyecto implementa un algoritmo de Fargette et al. (2020) que ajusta el campo magnético de las observaciones a un campo magnético modelo. Este método de ajuste permite determinar la orientación del eje de la cuerda de flujo ajustada, la distancia de aproximación más cercana desde la nave espacial al eje de la cuerda de flujo, el tiempo de aproximación más cercana y un parámetro adicional que describe las propiedades geométricas de las cuerdas de flujo. La implementación de este método marca la primera aplicación del algoritmo en cuerdas de flujo a pequeña escala liberadas secuencialmente en las puntas de los streamers del casco cerca de la eclíptica del Sol. Se desarrolló un método de muestreo bootstrap para adaptarse a 20 subintervalos dentro de un intervalo de tiempo máximo determinado por cada cuerda de flujo, dando lugar a distribuciones estadísticas de los parámetros. El análisis cubrió tres cruces HCS distintos, identificando inicialmente más de 30 intervalos de tiempo máximos. Este proceso dio 22 intervalos ajustados. La consistencia entre los ángulos ajustados y el comportamiento esperado del campo magnético bipolar demuestra la capacidad del algoritmo para moldear con precisión la geometría del campo magnético previsto. Los resultados muestran que las orientaciones de los ejes de la cuerda de flujo eran mayoritariamente perpendiculares al eje radial, de acuerdo con la explicación de la formación de la cuerda de flujo mediante la reconexión secuencial en la punta de los streamers del casco del Sol . Por último, las medidas de las cuerdas de flujo oscilaban entre medio radio solar y 2 radios solares, confirmando su pequeña escala en comparación con fenómenos mayores como los CME.Magnetic reconnection is an important mechanism for the formation of the solar wind. It is likely related to the formation of the slow solar wind in particular, which is observed in the vicinity of the heliospheric current sheet (HCS) in the ecliptic plane. A possible scenario is that reconnection at the HCS between magnetic fields of opposite orientations (from the opposite solar poles) leads to the formation of sequential small flux rope-like structures in the solar wind, which we are particularly interested in. In 2018, NASA’s Parker Solar Probe (PSP) mission was launched with one of its main objectives being to determine the structure and dynamics of the plasma and magnetic fields at the sources of the solar wind. We have taken data from the PSP during closest approach to the Sun on its first orbit around it. In particular, we have looked at observations from the magnetic field, ion velocity and strahl electrons, in order to identify and characterize small flux ropes, primarily in their axis orientation and their radial size. The purpose is to interpret these structures in the context of the X-line magnetic reconnection processes. More specifically, this project implements an algorithm from Fargette et al. (2020) that fits the magnetic field from observations to a model magnetic field. This fitting method permits to determine the fitted flux rope axis orientation, the distance of closest approach from the spacecraft to the flux rope’s axis, the time of closest approach and an additional parameter that describes the geometric properties of the flux ropes. The implementation of this method marks the first application of the model to small-scale flux ropes released sequentially at the tips of helmet streamers near the Sun’s ecliptic. A bootstrap resampling method was developed to fit 20 flux rope subintervals within a given maximum interval, resulting in statistical distributions of fitting parameters for each flux rope. The analysis covered three distinct HCS crossings, initially identifying over 30 maximum time intervals. This process yielded 22 well-fitted intervals. The consistency between the fitted angles (‘ and ‘) and expected bipolar magnetic field signatures demonstrates the algorithm's ability to accurately model the intended magnetic field geometry. The results show that the orientations of the flux rope’s axes were mostly perpendicular to the radial axis, consistent with the explanation of flux rope formation through the sequential reconnection at the tip of the Sun’s helmet streamers. Lastly, flux rope sizes ranged from half a solar radius to 2 solar radii, confirming their small scale compared to larger phenomena like CME
Four-Spacecraft Magnetic Curvature and Vorticity Analyses on Kelvin-Helmholtz Waves in MHD Simulations
No full textThis is the final version of the article. Available from AGU/Wiley via the DOI in this record.Four-spacecraft missions are probing the Earth's magnetospheric environment with high potential for revealing spatial and temporal scales of a variety of in situ phenomena. The techniques allowed by these four spacecraft include the calculation of vorticity and the magnetic curvature analysis (MCA), both of which have been used in the study of various plasma structures. Motivated by curved magnetic field and vortical structures induced by Kelvin- Helmholtz (KH) waves, we investigate the robustness of the MCA and vorticity techniques when increasing (regular) tetrahedron sizes, to interpret real data. Here for the first time, we test both techniques on a 2.5-D MHD simulation of KH waves at the magnetopause. We investigate, in particular, the curvature and flow vorticity across KH vortices and produce time series for static spacecraft in the boundary layers. The combined results of magnetic curvature and vorticity further help us to understand the development of KH waves. In particular, first, in the trailing edge, the magnetic curvature across the magnetopause points in opposite directions, in the wave propagation direction on the magnetosheath side and against it on the magnetospheric side. Second, the existence of a "turnover layer" in the magnetospheric side, defined by negative vorticity for the duskside magnetopause, which persists in the saturation phase, is reminiscent of roll-up history. We found significant variations in the MCA measures depending on the size of the tetrahedron. This study lends support for cross-scale observations to better understand the nature of curvature and its role in plasma phenomena.R. K. acknowledges financial support from CEMPS at the University of Exeter. C. F. acknowledges financial support from the UK Science and Technology Facilities Council (STFC) under her Advanced Fellowship ST/I003649
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In situ signatures of interchange reconnection between magnetic clouds and open magnetic fields: a mechanism for the erosion of polar coronal holes?
No full textWe outline a method to determine the direction of solar open flux transport that results from the opening of magnetic clouds (MCs) by interchange reconnection at the Sun based solely on in-situ observations. This method uses established findings about i) the locations and magnetic polarities of emerging MC footpoints, ii) the hemispheric dependence of the helicity of MCs, and iii) the occurrence of interchange reconnection at the Sun being signaled by uni-directional suprathermal electrons inside MCs. Combining those observational facts in a statistical analysis of MCs during solar cycle 23 (period 1995 – 2007), we show that the time of disappearance of the northern polar coronal hole (1998 – 1999), permeated by an outward-pointing magnetic field, is associated with a peak in the number of MCs originating from the northern hemisphere and connected to the Sun by outward-pointing magnetic field lines. A similar peak is observed in the number of MCs originating from the southern hemisphere and connected to the Sun by inward-pointing magnetic field lines. This pattern is interpreted as the result of interchange reconnection occurring between MCs and the open field lines of nearby polar coronal holes. This reconnection process closes down polar coronal hole open field lines and transports these open field lines equatorward, thus contributing to the global coronal magnetic field reversal process. These results will be further constrainable with the rising phase of solar cycle 24
Statistical Properties of Lower Hybrid Waves in the Magnetopause Reconnection Exhaust Region
No full textInternational audienceAbstract Lower hybrid waves (LHWs) are frequently observed associated with magnetic reconnection. A general picture of the statistical properties of LHWs in magnetopause reconnection, however, has not yet been established. Here we report such a statistical study of LHWs using magnetospheric multiscale mission data in the magnetopause reconnection exhaust region. LHWs are identified in reconnection outflow regions over a broad range of magnetic local time. Most of the LHWs are near strong density gradients located on the low‐density magnetospheric side of the reconnection layer. The wave amplitude is typically several mV/m but can occasionally reach a few tens of mV/m. Compared with intervals that do not exhibit LHWs, intervals with LHWs show a ∼50% increase in parallel electron temperature, providing statistical evidence that LHWs contribute to parallel electron heating in reconnection exhausts and the dayside low‐latitude boundary layer
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