Nonlinear force-free reconstruction of the global solar magnetic field: methodology

We present a novel numerical method that allows the calculation of nonlinear force-free magnetostatic solutions above a boundary surface on which only the distribution of the normal magnetic field component is given. The method relies on the theory of force-free electrodynamics and applies directly to the reconstruction of the solar coronal magnetic field for a given distribution of the photospheric radial field component. The method works as follows: we start with any initial magnetostatic global field configuration (e.g. zero, dipole), and along the boundary surface we create an evolving distribution of tangential (horizontal) electric fields that, via Faraday's equation, give rise to a respective normal field distribution approaching asymptotically the target distribution. At the same time, these electric fields are used as boundary condition to numerically evolve the resulting electromagnetic field above the boundary surface, modelled as a thin ideal plasma with non-reflecting, perfectly absorbing outer boundaries. The simulation relaxes to a nonlinear force-free configuration that satisfies the given normal field distribution on the boundary. This is different from existing methods relying on a fixed boundary condition - the boundary evolves toward the a priori given one, at the same time evolving the three-dimensional field solution above it. Moreover, this is the first time a nonlinear force-free solution is reached by using only the normal field component on the boundary. This solution is not unique, but depends on the initial magnetic field configuration and on the evolutionary course along the boundary surface. To our knowledge, this is the first time that the formalism of force-free electrodynamics, used very successfully in other astrophysical contexts, is applied to the global solar magnetic field.Comment: 18 pages, 5 figures, Solar Physic

A CsI(Tl) Scintillating Crystal Detector for the Studies of Low Energy Neutrino Interactions

Scintillating crystal detector may offer some potential advantages in the low-energy, low-background experiments. A 500 kg CsI(Tl) detector to be placed near the core of Nuclear Power Station II in Taiwan is being constructed for the studies of electron-neutrino scatterings and other keV-MeV range neutrino interactions. The motivations of this detector approach, the physics to be addressed, the basic experimental design, and the characteristic performance of prototype modules are described. The expected background channels and their experimental handles are discussed.Comment: 34 pages, 11 figures, submitted to Nucl. Instrum. Method

4pi Models of CMEs and ICMEs

Coronal mass ejections (CMEs), which dynamically connect the solar surface to the far reaches of interplanetary space, represent a major anifestation of solar activity. They are not only of principal interest but also play a pivotal role in the context of space weather predictions. The steady improvement of both numerical methods and computational resources during recent years has allowed for the creation of increasingly realistic models of interplanetary CMEs (ICMEs), which can now be compared to high-quality observational data from various space-bound missions. This review discusses existing models of CMEs, characterizing them by scientific aim and scope, CME initiation method, and physical effects included, thereby stressing the importance of fully 3-D ('4pi') spatial coverage.Comment: 14 pages plus references. Comments welcome. Accepted for publication in Solar Physics (SUN-360 topical issue

Systematic behaviour of 3He/4He in Earth’s continental mantle

Helium isotopes are unrivalled tracers of the origins of melts in the Earth’s convecting mantle but their role in determining melt contributions from the shallower and rigid lithospheric mantle is more ambiguous. We have acquired new 3He/4He data for olivine and pyroxene separates from 47 well-characterised mantle xenoliths from global on- and off-craton settings. When combined with existing data they demonstrate a new systematic relationship between fluid-hosted 3He/4He and major and trace element composition of host minerals and whole rock. We show that a significant proportion (>70 %) of mantle peridotites from continental off-craton settings with depleted major element compositions (e.g., olivine Mg# ≥ 89.5) have 3He/4He in the range of modern-day mid-ocean ridge basalt (MORB) source mantle (7–9 Ra) and we propose that they represent underplated melt residues, which initially formed in the convecting upper mantle. Furthermore, we observe that off-craton mantle xenoliths with signatures often attributed to enrichment by melts or fluids from ‘ancient’ subducted oceanic lithosphere have lower 3He/4He (<7 Ra). Modest correlations between 3He/4He and whole rock incompatible trace element signatures commonly used as proxies for metasomatism by small-fraction carbonatite and silicate melts or C-O-H fluids characterise lithospheric mantle with 3He/4He ranging from 5 to 8 Ra. [...

Provenance and correlation of Permian successions from the Falkland/Malvinas Islands with West Gondwana: implications for a Natal Embayment palaeo-location

Detrital zircon U-Pb and Lu-Hf data from the youngest (upper Permian) sedimentary succession of the Falkland/Malvinas Islands is used to constrain depositional age, provenance and palaeogeography, and test the Natal Embayment model for the Falkland/Malvinas Islands microplate. The upper Permian was a period of extensive magmatism and sediment recycling along the accretionary margin of West Gondwana. Deposition into retroarc foreland basins was widespread across South Africa, Antarctica, South America and the Falklands Islands, forming thick successions of fluvial, deltaic and shallow-marine units. Our analysis links the upper Permian (c. 260 Ma) Bay of Harbours Formation of the Falkland/Malvinas Islands with deltaic/fluvial volcaniclastic units from the Karoo Basin of South Africa, Theron Mountains of East Antarctica and sandstone of the Ellsworth Mountains and southern Antarctic Peninsula. These units all have a shared provenance from the Antarctic sector of the West Gondwana margin. Although the detrital zircon age profiles of the Falkland/Malvinas Islands sedimentary units overlap with those from the accretionary and volcanic complexes of Patagonia, Lu-Hf isotope compositions are clearly distinct indicating that there was no direct link between the upper Permian successions of the Falkland/Malvinas Islands (eHf -3 to +3) to the volcano sedimentary successions of southern South America (eHf <-5)