Large-scale solar wind flow around Saturn's nonaxisymmetric magnetosphere

The interaction between the solar wind and a magnetosphere is fundamental to the dynamics of a planetary system. Here, we address fundamental questions on the large-scale magnetosheath flow around Saturn using a 3D magnetohydrodynamic (MHD) simulation. We find Saturn's polar-flattened magnetosphere to channel ~20% more flow over the poles than around the flanks at the terminator. Further, we decompose the MHD forces responsible for accelerating the magnetosheath plasma to find the plasma pressure gradient as the dominant driver. This is by virtue of a high-beta magnetosheath, and in turn, the high-MA bow shock. Together with long-term magnetosheath data by the Cassini spacecraft, we present evidence of how nonaxisymmetry substantially alters the conditions further downstream at the magnetopause, crucial for understanding solar wind-magnetosphere interactions such as reconnection and shear flow-driven instabilities. We anticipate our results to provide a more accurate insight into the global conditions upstream of Saturn and the outer planets.Comment: Accepted for publication in Journal of Geophysical Journal: Space Physic

A combined model of pressure variations in Titan's plasma environment

In order to analyze varying plasma conditions upstream of Titan, we have combined a physical model of Saturn's plasmadisk with a geometrical model of the oscillating current sheet. During modeled oscillation phases where Titan is furthest from the current sheet, the main sources of plasma pressure in the near-Titan space are the magnetic pressure and, for disturbed conditions, the hot plasma pressure. When Titan is at the center of the sheet, the main sources are the dynamic pressure associated with Saturn's cold, subcorotating plasma and the hot plasma pressure under disturbed conditions. Total pressure at Titan (dynamic plus thermal plus magnetic) typically increases by a factor of up to about three as the current sheet center is approached. The predicted incident plasma flow direction deviates from the orbital plane of Titan by ≲10°. These results suggest a correlation between the location of magnetic pressure maxima and the oscillation phase of the plasmasheet. Our model may be used to predict near-Titan conditions from ‘far-field’ in situ measurements

A combined model of pressure variations in Titan's plasma environment

In order to analyze varying plasma conditions upstream of Titan, we have combined a physical model of Saturn?s plasma disk with a geometrical model of the oscillating current sheet. During modeled oscillation phases where Titan is farthest from the current sheet, the main sources of plasma pressure in the near-Titan space are the magnetic pressure and, for disturbed conditions, the hot plasma pressure. When Titan is at the center of the sheet, the main sources are the dynamic pressure associated with Saturn?s cold, subcorotating plasma and the hot plasma pressure under disturbed conditions. Total pressure at Titan (dynamic plus thermal plus magnetic) typically increases by a factor of up to about 3 as the current sheet center is approached. The predicted incident plasma flow direction deviates from the orbital plane of Titan by ≲ 10◦ . These results suggest a correlation between the location of magnetic pressure maxima and the oscillation phase of the plasma sheet. Our model may be used to predict near-Titan conditions from ?far-field? in situ measurements.Fil: Achilleos, N.. University College London; Reino UnidoFil: Arridge, C. S.. University College London; Reino UnidoFil: Bertucci, Cesar. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; ArgentinaFil: Guio, P.. University College London; Reino UnidoFil: Romanelli, Norberto Julio. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; ArgentinaFil: Sergis, N.. Academy Of Athens. Office for Space Research and Technology; Greci

A new form of Saturn's magnetopause using a dynamic pressure balance model, based on in situ, multi‐instrument Cassini measurements

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95429/1/jgra19967.pd

Diamagnetic depression observations at Saturn’s magnetospheric cusp by the Cassini spacecraft

The magnetospheric cusp is a region where shocked solar wind plasma can enter a planetary magnetosphere, after magnetic reconnection has occurred at the dayside magnetopause or in the lobes. The dense plasma that enters the high‐latitude magnetosphere creates diamagnetic effects whereby a depression is observed in the magnetic field. We present observations of the cusp events at Saturn’s magnetosphere where these diamagnetic depressions are found. The data are subtracted from a magnetic field model, and the calculated magnetic pressure deficits are compared to the particle pressures. A high plasma pressure layer in the magnetosphere adjacent to the cusp is discovered to also depress the magnetic field, outside of the cusp. This layer is observed to contain energetic He++ (up to ∼100 keV) from the solar wind as well as heavy water group ions (W+) originating from the moon Enceladus. We also find a modest correlation of diamagnetic depression strength to solar wind dynamic pressure and velocity; however, unlike at Earth, there is no correlation found with He++ counts.Key PointsDiamagnetic depressions are found in the cusp and are observed to continue into the adjacent magnetosphereA heated plasma layer of mixed composition is found to depress the adjacent magnetospheric fieldDiamagnetic depression strength is correlated to solar wind dynamic pressure and velocity but not to the observed He++ counts, like at EarthPeer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/137687/1/jgra53517_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/137687/2/jgra53517-sup-0001-supinfo.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/137687/3/jgra53517.pd

Space Weather in the Saturn-Titan System

New evidence based on Cassini magnetic field and plasma data has revealed that the discovery of Titan outside Saturn’s magnetosphere during the T96 flyby on 2013 December 1 was the result of the impact of two consecutive interplanetary coronal mass ejections (ICMEs) that left the Sun in 2013 early November and interacted with the moon and the planet. We study the dynamic evolution of Saturn's magnetopause and bow shock, which evidences a magnetospheric compression from late November 28 to December 4 (at least), under prevailing solar wind dynamic pressures of 0.16-0.3 nPa. During this interval, transient disturbances associated with the two ICMEs are observed, allowing for the identification of their magnetic structures. By analyzing the magnetic field direction, and the pressure balance in Titan’s induced magnetosphere, we show that Cassini finds Saturn’s moon embedded in the second ICME after being swept by its interplanetary shock and amid a shower of solar energetic particles that may have caused dramatic changes in the moon’s lower ionosphere. Analyzing a list of Saturn's bow shock crossings during 2004-2016, we find that the magnetospheric compression needed for Titan to be in the supersonic solar wind can be generally associated with the presence of an ICME or a corotating interaction region. This leads to the conclusion that Titan would rarely face the pristine solar wind, but would rather interact with transient solar structures under extreme space weather conditions

Design and Operationalization of Connectivist Activities: an Approach through Business Process Management

International audienceThe work presented in this paper focuses on massive open online course (MOOC) environments, and more specifically on the activity of designing and implementing pedagogical scenarios for a connectivist MOOC (cMOOC). This paper presents a research work, which aims to propose a model and tool to support the design of connectivist MOOC scenarios. The major contribution of this work is a visual authoring tool that is intended for the design and deployment of cMOOC-oriented scenarios. The tool is based on the BPMN notation that we have extended to suit our objectives. The tool was evaluated primarily from the point of view of utility and usability. The findings confirm that the tool can be used to design connectivist pedagogical scenarios and can provide all the necessary elements to operationalize such courses