Hybrid simulations of Titan's plasma interaction: Case studies of Cassini's T9, T63 and T96 flybys

In this thesis, we apply numerical simulations by means of the hybrid code A.I.K.E.F. (Adaptive Ion-Kinetic Electron-Fluid) to study the interaction of Saturn's magnetospheric plasma as well as the solar wind with Titan's ionosphere. The composition of Titan's ionosphere is represented by a 7-species model. The ionosphere is generated by a realistic wavelength dependent photoionization model of the main neutral species N2, CH4 and H2. We also included elastic ion-neutral collisions of the impinging plasma with Titan's neutral atmosphere to our model as well as a network of the most important chemical reactions of the ionosphere that converts between the ion species. In the first part of the thesis we investigate the physical processes that lead to the detection of 'split signatures' in the ion densities during several crossings of the Cassini spacecraft through Titan's mid-range plasma tail (T9, T63, and T75). During each of these flybys, the Cassini Plasma Spectrometer observed Titan's ionospheric ion population twice; i.e., the spacecraft passed through two spatially separated regions where cold ions were detected. Our simulation results show that the filamentation of Titan's tail is a common feature of the moon's plasma interaction. The transport of ionospheric ions of all species from the ramside to the moon's wakeside generates a cone-like structure on the downstream side, that contains a region of reduced density. In addition, light (mass 1-2 amu) ionospheric species are driven radially outwards by pressure gradients in the ionosphere and escape along draped magnetic field lines, forming a parabolically shaped filament structure which is mainly seen in planes that contain the upstream magnetospheric magnetic field and the upstream flow direction. Our results imply that the detections of split signatures during T9, T63 and T75 are consistent by Cassini penetrating through parts of these filament structures. In the second part of the thesis we study Titan's plasma interaction with the solar wind during the Cassini T96 flyby. The T96 encounter marks the only observed event of the entire Cassini mission where Titan was located in the supersonic solar wind in front of Saturn's bow shock. We show that the large-scale features of Titan's induced magnetosphere during T96 can be described in terms of a steady-state interaction with a high-pressure solar wind flow. About 40 minutes before the encounter, Cassini observed a rotation of the incident solar wind magnetic field by almost 90 degrees. We provide strong evidence that this rotation left a bundle of fossilized magnetic field lines in Titan's ionosphere that was subsequently detected by the spacecraft

Hybrid simulation of Titan's interaction with the supersonic solar wind during Cassini's T96 flyby

By applying a hybrid (kinetic ions and fluid electrons) simulation code, we study the plasma environment of Saturn's largest moon Titan during Cassini's T96 flyby on 1 December 2013. The T96 encounter marks the only observed event of the entire Cassini mission where Titan was located in the supersonic solar wind in front of Saturn's bow shock. Our simulations can quantitatively reproduce the key features of Cassini magnetic field and electron density observations during this encounter. We demonstrate that the large-scale features of Titan's induced magnetosphere during T96 can be described in terms of a steady state interaction with a high-pressure solar wind flow. About 40 min before the encounter, Cassini observed a rotation of the incident solar wind magnetic field by almost 90°. We provide strong evidence that this rotation left a bundle of fossilized magnetic field lines in Titan's ionosphere that was subsequently detected by the spacecraft.Fil: Feyerabend, Moritz. Georgia Institute Of Techology; Estados UnidosFil: Simon, Sven. Georgia Institute Of Techology; Estados UnidosFil: Neubauer, Fritz M.. Universitat Zu Köln; AlemaniaFil: Motschmann, Uwe. Deutsches Zentrum Fur Luft- Und Raumfahrt; Alemania. Technische Universitat Braunschweig; AlemaniaFil: 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: Edberg, Niklas J. T.. Instiutet For Rymdfysik; SueciaFil: Hospodarsky, George B.. University Of Iowa; Estados UnidosFil: Kurth, William S.. University Of Iowa; Estados Unido

The impact of Callisto's atmosphere on its plasma interaction with the Jovian magnetosphere

The interaction between Callisto's atmosphere and ionosphere with the surrounding magnetospheric environment is analyzed by applying a hybrid simulation code, in which the ions are treated as particles and the electrons are treated as a fluid. Callisto is unique among the Galilean satellites in its interaction with the ambient magnetospheric plasma as the gyroradii of the impinging plasma and pickup ions are large compared to the size of the moon. A kinetic representation of the ions is therefore mandatory to adequately describe the resulting asymmetries in the electromagnetic fields and the deflection of the plasma flow near Callisto. Multiple model runs are performed at various distances of the moon to the center of Jupiter's magnetospheric current sheet, with differing angles between the corotational plasma flow and the ionizing solar radiation. When Callisto is embedded in the Jovian current sheet, magnetic perturbations due to the plasma interaction are more than twice the strength of the background field and may therefore obscure any magnetic signal generated via induction in a subsurface ocean. The magnetic field perturbations generated by Callisto's ionospheric interaction are very similar at different orbital positions of the moon, demonstrating that local time is only of minor importance when disentangling magnetic signals generated by the magnetosphere-ionosphere interaction from those driven by induction. Our simulations also suggest that deflection of the magnetospheric plasma around the moon cannot alone explain the density enhancement of 2 orders of magnitude measured in Callisto's wake during Galileo flybys. However, through inclusion of an ionosphere surrounding Callisto, modeled densities in the wake are consistent with in situ measurements

Adaptive community-based biodiversity conservation in Australia's tropical rainforests

In the globally significant Australian tropical\ud rainforests, poor performance of community-based\ud natural resource management (CBNRM) approaches\ud mandated by national policy highlights the importance\ud of the global search for better models. This paper\ud reports on co-research to develop, apply and test\ud the transferability and effectiveness of a new model\ud and tools for CBNRM in biodiversity conservation.\ud Adaptive co-management, designed with specific communities\ud and natural resources, recognized as linked\ud multi-scalar phenomena, is the new face of CBNRM.\ud New tools used to achieve adaptive co-management\ud include a collaborative focal species approach focused\ud on the iconic southern cassowary, scenario analysis,\ud science brokering partnerships, a collaborative habitat\ud investment atlas and institutional brokering. An\ud intermediate-complexity analytical framework was\ud used to test the robustness of these tools and therefore\ud likely transferability. The tools meet multiple\ud relevant standards across three dimensions, namely\ud empowering institutions and individuals, ongoing\ud systematic scientific assessment and securing effective\ud on-ground action. Evaluation of effectiveness using\ud a performance criteria framework identified achievement\ud of many social and environmental outcomes.\ud Effective CBNRM requires multi-scale multi-actor\ud collaborative design, not simply devolution to localscale\ud governance. Bridging/boundary organizations\ud are important to facilitate the process. Further research\ud into collaborative design of CBNRM structures,\ud functions, tools and processes for biodiversity\ud conservation is recommended