Towards the development of an automated electrical self-potential sensor of melt and rainwater flow in snow

To understand snow structure and snowmelt timing, information about flows of liquid water within the snowpack is essential. Models can make predictions using explicit representations of physical processes, or through parameterization, but it is difficult to verify simulations. In situ observations generally measure bulk quantities. Where internal snowpack measurements are made, they tend to be destructive and unsuitable for continuous monitoring. Here, we present a novel method for in situ monitoring of water flow in seasonal snow using the electrical self-potential geophysical method. A prototype geophysical array was installed at Col de Porte (France) in October 2018. Snow hydrological and meteorological observations were also collected. Results for two periods of hydrological interest during winter 2018-19 (a marked period of diurnal melting and refreezing, and a rain-on-snow event) show that the electrical self-potential method is sensitive to internal water flow. Water flow was detected by self-potential signals before it was measured in conventional snowmelt lysimeters at the base of the snowpack. This initial feasibility study shows the utility of the self-potential method as a non-destructive snow sensor. Future development should include combining self-potential measurements with a high-resolution snow physics model to improve prediction of melt timing

Bedforms of Thwaites Glacier, West Antarctica: Character and Origin

Bedforms of Thwaites Glacier, West Antarctica both record and affect ice flow, as shown by geophysical data and simple models. Thwaites Glacier flows across the tectonic fabric of the West Antarctic rift system with its bedrock highs and sedimentary basins. Swath radar and seismic surveys of the glacier bed have revealed soft-sediment flutes 100 m or more high extending 15 km or more across basins downglacier from bedrock highs. Flutes end at prominent hard-bedded moats on stoss sides of the next topographic highs. We use simple models to show that ice flow against topography increases pressure between ice and till upglacier along the bed over a distance that scales with the topography. In this basal zone of high pressure, ice-contact water would be excluded, thus increasing basal drag by increasing ice-till coupling and till flux, removing till to allow bedrock erosion that creates moats. Till carried across highlands would then be deposited in lee-side positions forming bedforms that prograde downglacier over time, and that remain soft on top through feedbacks that match till-deformational fluxes from well upglacier of the topography. The bedforms of the part of Thwaites surveyed here are prominent because ice flow has persisted over a long time on this geological setting, not because ice flow is anomalous. Bedform development likely has caused evolution of ice flow over time as till and lubricating water were redistributed, moats were eroded and bedforms grew

Seismic observations of a complex firn structure across the Amery Ice Shelf, East Antarctica

We use seismic refraction data to investigate the firn structure across a suture zone on the Amery Ice Shelf, East Antarctica, and the possible role of glacier dynamics in firn evolution. In the downstream direction, the data reveal decreasing compressional-wave velocities and increasing penetration depth of the propagating wave in the firn layer, consistent with 1 m firn thickening every 6 km. The boundary between the Lambert Glacier unit to the west and a major suture zone and the Mawson Escarpment Ice Stream unit to the east, is marked by differences in firn thicknesses, compressional-wave velocities and seismic anisotropy in the across-flow direction. The latter does not contradict the presence of a single-maximum crystal orientation fabric oriented 45– away from the flow direction. This is consistent with the presence of transverse simple shear governing the region's underlying ice flow regime, in association with elevated strain along the suture zone. The confirmation and quantification of the implied dynamic coupling between firn and the underlying ice requires integration of future seismic refraction, coring and modelling studies. Because firn is estimated to cover 98% of the Antarctic continent any such coupling may have widespread relevance to ice-sheet evolution and flow

Odcieleśnione ciało w filmie Nakarmić kruki Carlosa Saury

This article aims at providing an analysis of Carlos Saura’s Cria Cuervos [Raise ravens, 1976], focused mainly on the temporal and spatial structures of the film. It explores the dimensions of bodily presence, especially the means of representing spectral body in cinematic image.This article aims at providing an analysis of Carlos Saura’s Cria Cuervos [Raise ravens, 1976], focused mainly on the temporal and spatial structures of the film. It explores the dimensions of bodily presence, especially the means of representing spectral body in cinematic image

K+^+ production in proton-nucleus reactions and the role of momentum-dependent potentials

The production of $K^+$ mesons in proton-nucleus collisions from 1.0 to 2.5 GeV is analyzed with respect to one-step nucleon-nucleon $(NN\to N Y K^+$) and two-step $\Delta$-nucleon $(\Delta N \to K^+ Y N$) or pion-nucleon $(\pi N \to K^+ Y$) production channels on the basis of a coupled-channel transport approach (CBUU) including the kaon final state interactions. The influence of momentum-dependent potentials for the nucleon, hyperon and kaon in the final state are studied as well as the importance of $K^+$ elastic rescattering in the target nucleus. The transport calculations are compared to the experimental $K^+$ spectra taken at LBL Berkeley, SATURNE, CELSIUS, GSI and COSY-J\"ulich. It is found that the momentum-dependent baryon potentials effect the excitation function of the $K^+$ cross section; at low bombarding energies of $\sim$ 1.0 GeV the attractive baryon potentials in the final state lead to a relative enhancement of the kaon yield whereas the net repulsive potential at bombarding energies $\sim$ 2 GeV causes a decrease of the $K^+$ cross section. Furthermore it is pointed out, that especially the $K^+$ spectra at low momenta (or kinetic energy $T_K$) allow to determine the in-medium $K^+$ potential almost model independently due to a relative shift of the $K^+$ spectra in kinetic energy that arises from the acceleration of the kaons when propagating out of the nuclear medium to free space, i.e. converting potential energy to kinetic energy of the free kaon.Comment: 11 pages, LaTeX, including 10 postscript figures, submitted to Eur. Phys. J.

Transport analysis of K+ production in proton-nucleus reactions

The production of $K^+$ mesons in proton-nucleus collisions from 1.0 to 2.3 GeV is analyzed with respect to one-step nucleon-nucleon $(NN\to N Y K^+$) and two-step $\Delta$-nucleon $(\Delta N \to K^+ Y N$) or pion-nucleon $(\pi N \to K^+ Y$) production channels on the basis of a coupled-channel transport approach (CBUU) including the kaon final-state-interactions (FSI). Momentum-dependent potentials for the nucleon, hyperon and kaon in the final state are included as well as $K^+$ elastic rescattering in the target nucleus. The transport calculations are compared to the experimental $K^+$ spectra taken at COSY-J\"ulich. Our systematic analysis of $K^+$ spectra from $^{12}C$, $^{63}Cu$, $^{107}Ag$ and $^{197}Au$ targets as well as their momentum differential ratios gives a repulsive $K^+$ potential of $20\pm 5$ MeV at normal nuclear matter density.Comment: 7 pages, 5 figures, submitted to Eur. Phys. J.

Assessing the potential for ice flow piracy between Totten and Vanderford glaciers, East Antarctica

The largest regional drivers of current surface elevation increases in the Antarctic Ice Sheet are associated with ice flow reconfiguration in previously active ice streams, highlighting the important role of ice dynamics in responding to climate change. Here, we investigate controls on the evolution of the flow configuration of the Vanderford and Totten Glaciers – key outlet glaciers of the Aurora Subglacial Basin, the most rapidly thinning region of the East Antarctic Ice Sheet. We review factors that influence the ice flow in this region, and use an ice sheet model to investigate the sensitivity of the catchment divide location to thinning at Vanderford Glacier associated with ongoing retreat, and thickening at Totten Glacier associated with an intensification of the east-west snowfall gradient. The present-day catchment divide between the Totten and Vanderford Glaciers is not constrained by the geology or topography, but is determined by the large-scale ice sheet geometry and its long-term evolution in response to climate forcing. Furthermore, the catchment divide is subject to migration under relatively small changes in surface elevation, leading to ice flow and basal water piracy from Totten to Vanderford Glacier. Our findings show that ice flow reconfigurations do not only occur in regions of West Antarctica like the Siple Coast, but also in the east, motivating further investigations of past, and potential for future, ice flow reconfigurations around the whole Antarctic coastline. Such modelling of ice flow and basal water piracy may require coupled ice sheet thermomechanical and subglacial hydrology models, constrained by field observations of subglacial conditions. Our results also have implications for ice sheet mass budget studies that integrate over catchments, and the validity of the zero flow assumption when selecting sites for ice core records of past climate