Hubert G., Pazianotto M. T., Federico C. A. (2017). Modeling of ground albedo neutrons to investigate seasonal cosmic ray?induced neutron variations measured at high?altitude stations (Vol. 121).
Abstract: Abstract This paper investigates seasonal cosmic ray?induced neutron variations measured over a long?term period (from 2011 to 2016) in both the high?altitude stations located in medium geomagnetic latitude and Antarctica (Pic?du?Midi and Concordia, respectively). To reinforce analysis, modeling based on ground albedo neutrons simulations of extensive air showers and the solar modulation potential was performed. Because the local environment is well known and stable over time in Antarctica, data were used to validate the modeling approach. A modeled scene representative to the Pic?du?Midi was simulated with GEANT4 for various hydrogen properties (composition, density, and wet level) and snow thickness. The orders of magnitudes of calculated thermal fluence rates are consistent with measurements obtained during summers and winters. These variations are dominant in the thermal domain (i.e., En??20?MeV) is weakly impacted. The role of hydrogen content on ground albedo neutron generation was investigated with GEANT4 simulations. These investigations focused to mountain environment; nevertheless, they demonstrate the complexity of the local influences on neutron fluence rates.
Keywords: albedo neutron cosmic ray spectrometer
Programme: 1112
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Marchaudon A., Blelly P.?L. (2015). A new interhemispheric 16?moment model of the plasmasphere?ionosphere system: IPIM (Vol. 120).
Abstract: Abstract We present a new interhemispheric numerical model: the IRAP plasmasphere?ionosphere model (IPIM). This model describes the transport of the multispecies ionospheric plasma from one hemisphere to the other along convecting and corotating magnetic field lines, taking into account source processes at low altitude such as photoproduction, chemistry, and energization through the coupling with a kinetic code solving the transport of suprathermal electron along the field line. Among the new developments, a 16?moment?based approach is used for the transport equations in order to allow development of strong temperature anisotropy at high altitude and we consider important but often neglected effects, such as inertial acceleration (centrifugal and Coriolis). In this paper, after presenting in detail the principle of the model, we focus on preliminary results showing the original contribution of this new model. For these first runs, we simulate the convection and corotation transport of closed flux tubes in the plasmasphere for tilted/eccentric dipolar magnetic field configuration in solstice and equinox conditions. We follow different flux tubes between 1.2 and 6 Earth Radii (RE) and demonstrate the capability of the model to describe a wide range of density (above 15 orders of magnitude). The relevance of the mathematical approach used is highlighted, as anisotropies can develop above 3000?km in the plasmasphere as a result of the mirroring effect related to the anisotropic pressure tensor. Moreover, we show that the addition of inertial acceleration may become critical to describe plasma interhemispheric transport above 4RE. The ability of the model to describe the external plasmasphere is demonstrated, and innovative studies are foreseen, regarding the dynamics of the plasma along the magnetic field lines (in particular interhemispheric exchanges and ?opening?/?closure? of a flux tube).
Keywords: centrifugal acceleration interhemispheric exchanges mirror force temperature anisotropy
Programme: 312
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Neala Creasy, Maureen D. Long, Heather A. Ford. (2017). Deformation in the lowermost mantle beneath Australia from observations and models of seismic anisotropy (Vol. 122).
Abstract: Observations of seismic anisotropy near the core-mantle boundary may yield constraints on patterns of lowermost mantle flow. We examine seismic anisotropy in the lowermost mantle beneath Australia, bounded by the African and Pacific Large Low Shear Velocity Provinces. We combined measurements of differential splitting of SKS-SKKS and S-ScS phases sampling our study region over a range of azimuths, using data from 10 long-running seismic stations. Observations reveal complex and laterally heterogeneous anisotropy in the lowermost mantle. We identified two subregions for which we have robust measurements of D?-associated splitting for a range of ray propagation directions and applied a forward modeling strategy to understand which anisotropic scenarios are consistent with the observations. We tested a variety of elastic tensors and orientations, including single-crystal elasticity of lowermost mantle minerals (bridgmanite, postperovskite, and ferropericlase), tensors based on texture modeling in postperovskite aggregates, elasticity predicted from deformation experiments on polycrystalline MgO aggregates, and tensors that approximate the shape preferred orientation of partial melt. We find that postperovskite scenarios are more consistently able to reproduce the observations. Beneath New Zealand, the observations suggest a nearly horizontal [100] axis orientation with an azimuth that agrees well with the horizontal flow direction predicted by previous mantle flow models. Our modeling results further suggest that dominant slip on the (010) plane in postperovskite aggregates provides a good fit to the data but the solution is nonunique. Our results have implications for the mechanisms of deformation and anisotropy in the lowermost mantle and for the patterns of mantle flow.
Keywords: anisotropy lowermost mantle mantle dynamics postperovskite shear wave splitting
Programme: 133
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. (2018). Global and Interregion Characterization of Subduction Interface Earthquakes Derived From Source Time Functions Properties (Vol. 123).
Keywords: global earthquake seismology radiated energy seismic coupling source time functions stress drop subduction earthquakes
Programme: 133
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Kiwamu Nishida, Takuto Maeda, Yoshio Fukao. (2019). Seismic Observation of Tsunami at Island Broadband Stations (Vol. 124).
Keywords: broadband seismometer tsunami propagation
Programme: 133
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Peji? Tanja, Tkal?i? Hrvoje, Sambridge Malcolm, Cormier Vernon F., Benavente Roberto. (2017). Attenuation tomography of the upper inner core (Vol. 122).
Keywords: attenuation inner core tomography
Programme: 133
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Creasy Neala, Long Maureen D., Ford Heather A. (2017). Deformation in the lowermost mantle beneath Australia from observations and models of seismic anisotropy (Vol. 122).
Abstract: Abstract Observations of seismic anisotropy near the core?mantle boundary may yield constraints on patterns of lowermost mantle flow. We examine seismic anisotropy in the lowermost mantle beneath Australia, bounded by the African and Pacific Large Low Shear Velocity Provinces. We combined measurements of differential splitting of SKS?SKKS and S?ScS phases sampling our study region over a range of azimuths, using data from 10 long?running seismic stations. Observations reveal complex and laterally heterogeneous anisotropy in the lowermost mantle. We identified two subregions for which we have robust measurements of D??associated splitting for a range of ray propagation directions and applied a forward modeling strategy to understand which anisotropic scenarios are consistent with the observations. We tested a variety of elastic tensors and orientations, including single?crystal elasticity of lowermost mantle minerals (bridgmanite, postperovskite, and ferropericlase), tensors based on texture modeling in postperovskite aggregates, elasticity predicted from deformation experiments on polycrystalline MgO aggregates, and tensors that approximate the shape preferred orientation of partial melt. We find that postperovskite scenarios are more consistently able to reproduce the observations. Beneath New Zealand, the observations suggest a nearly horizontal [100] axis orientation with an azimuth that agrees well with the horizontal flow direction predicted by previous mantle flow models. Our modeling results further suggest that dominant slip on the (010) plane in postperovskite aggregates provides a good fit to the data but the solution is nonunique. Our results have implications for the mechanisms of deformation and anisotropy in the lowermost mantle and for the patterns of mantle flow.
Keywords: anisotropy lowermost mantle mantle dynamics postperovskite shear wave splitting
Programme: 133
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Zhitu Ma, Colleen A. Dalton. (2017). Evolution of the lithosphere in the Indian Ocean from combined earthquake and ambient noise tomography (Vol. 122).
Keywords: ambient noise Indian Ocean surface wave
Programme: 133
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. (2014). Polar Front around the Kerguelen Islands: An up?to?date determination and associated circulation of surface/subsurface waters (Vol. 119).
Keywords: Kerguelen Polar Front Southern Ocean
Programme: 688
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. (2017). Antarctic boundary layer parametrization in a general circulation model: 1-D simulations facing summer observations at Dome C (Vol. 122).
Keywords: Antarctic Plateau atmospheric boundary layer GABLS4 general circulation model physical parametrizations
Programme: 1013
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