The dynamics of subhaloes in warm dark matter models

We present a comparison of the properties of substructure haloes ( subhaloes ) orbiting within host haloes that form in cold dark matter (CDM) and warm dark matter (WDM) cosmologies. Our study focuses on selected properties of these subhaloes, namely their anisotropic spatial distribution within the hosts; the existence of a 'backsplash' population; the age–distance relation; the degree to which they suffer mass loss; and the distribution of relative (infall) velocities with respect to the hosts. We find that the number density of subhaloes in our WDM model is suppressed relative to that in the CDM model, as we would expect. Interestingly, our analysis reveals that backsplash subhaloes exist in both the WDM and CDM models. Indeed, there are no statistically significant differences between the spatial distributions of subhaloes in the CDM and WDM models. There is evidence that subhaloes in the WDM model suffer enhanced mass loss relative to their counterparts in the CDM model, reflecting their lower central densities. We note also a tendency for the (infall) velocities of subhaloes in the WDM model to be higher than in the CDM model. Nevertheless, we conclude that observational tests based on either the spatial distribution or the kinematics of the subhalo population are unlikely to help us to differentiate between the CDM model and our adopted WDM model.     

Model-reduced gradient-based history matching

Gradient-based history matching algorithms can be used to adapt the uncertain parameters in a reservoir model using production data. They require, however, the implementation of an adjoint model to compute the gradients, which is usually an enormous programming effort. We propose a new approach to gradient-based history matching which is based on model reduction, where the original (nonlinear and high-order) forward model is replaced by a linear reduced-order forward model and, consequently, the adjoint of the tangent linear approximation of the original forward model is replaced by the adjoint of a linear reduced-order forward model. The reduced-order model is constructed with the aid of the proper orthogonal decomposition method. Due to the linear character of the reduced model, the corresponding adjoint model is easily obtained. The gradient of the objective function is approximated, and the minimization problem is solved in the reduced space; the procedure is iterated with the updated estimate of the parameters if necessary. The proposed approach is adjoint-free and can be used with any reservoir simulator. The method was evaluated for a waterflood reservoir with channelized permeability field. A comparison with an adjoint-based history matching procedure shows that the model-reduced approach gives a comparable quality of history matches and predictions. The computational efficiency of the model-reduced approach is lower than of an adjoint-based approach, but higher than of an approach where the gradients are obtained with simple finite differences.     

Infrasound produced by debris flow: propagation and frequency content evolution

Rapid mass movements such as avalanches, debris flows, and rock fall are periodic or episodic phenomena that occur in alpine regions. Recent studies have shown that debris flows generate characteristic signals in the low-frequency infrasonic spectrum (4–15 Hz). Infrasound can travel thousands of kilometers and can still be detectable. This characteristic provides a basis for the development of wide area automated monitoring systems that can operate in locations unaffected by the activity of the process. This study focuses on the infrasound vibrations produced by a debris flow at the Lattenbach torrent, Tyrol (Austria), and by two events at the Illgraben torrent, Canton of Valais (Switzerland). The Lattenbach torrent is a very active torrent, which is located in the west of Tyrol in a geologic fault zone between the Silvrettakristallin and the Northern Limestone Alps. It has a large supply of loose sediment. The Illgraben torrent, which is well known for its frequent sediment transport and debris flow activity, has been equipped with instruments for debris flow monitoring since the year 2000. This study shows that debris flow emits low-frequency infrasonic signals that can be monitored and correlated with seismic signals. During the passage of the debris flow, several surges were identified by ultrasonic gauges and detected in the time series and the running spectra of infrasonic data.     

Energy budget and imaging spectroscopy of a compact flare

We present the analysis of a compact flare that occurred on 26 February 2002 at 10:26 UT, seen by both RHESSI and TRACE. The size of the nearly circular hard X-ray source is determined to be 5.6 (±0.8)′′, using different methods. The power-law distribution of non-thermal photons is observed to extend down to 10 keV without flattening, and to soften with increasing distance from the flare kernel. The former indicates that the energy of the precipitating flare electron population is larger than previously estimated: it amounts to 2.6 (±0.8)×10³⁰ erg above 10 keV, assuming thick-target emission. The thermal energy content of the soft X-ray source (isothermal temperature of 20.8 (±0.9) MK) and its radiated power were derived from the thermal emission at low energies. TRACE has observed a low-temperature ejection in the form of a constricted bubble, which is interpreted as a reconnection jet. Its initial energy of motion is estimated. Using data from both satellites, an energy budget for this flare is derived. The kinetic energy of the jet bulk motion and the thermal and radiated energies of the flare kernel were more than an order of magnitude smaller than the derived electron beam energy. A movie is available on the CD-ROM accompanying this volume. Supplementary material to this paper is available in electronic form at http://dx.doi.org/10.1023/A:1022478300679     

Image compression by means of wavelet transform - application to solar observations

Images and spectra contain a large amount of data. Therefore the question arises, how this data can be decreased or compressed without losing important detail. The discrete wavelet transform is a tool which can be used to compress data because of its good approximation properties. It is very easy to implement and requires approximately the same amount of calculation as the fast Fourier transform. It has the advantage of giving information both in time and frequency. Since most of the coefficients in the transformed data are very small compared to the maximum values, which means that they do not contribute much to the transform, a large number of them can be neglected. Although some data get lost, the physical results deduced from the data remain the same, as is demonstrated by various examples. By this method it is even possible to compress data containing much noise to high-compression ratios.     

Dependency of geodynamic parameters on the GNSS constellation

Significant differences in time series of geodynamic parameters determined with different Global Navigation Satellite Systems (GNSS) exist and are only partially explained. We study whether the different number of orbital planes within a particular GNSS contributes to the observed differences by analyzing time series of geocenter coordinates (GCCs) and pole coordinates estimated from several real and virtual GNSS constellations: GPS, GLONASS, a combined GPS/GLONASS constellation, and two virtual GPS sub-systems, which are obtained by splitting up the original GPS constellation into two groups of three orbital planes each. The computed constellation-specific GCCs and pole coordinates are analyzed for systematic differences, and their spectral behavior and formal errors are inspected. We show that the number of orbital planes barely influences the geocenter estimates. GLONASS’ larger inclination and formal errors of the orbits seem to be the main reason for the initially observed differences. A smaller number of orbital planes may lead, however, to degradations in the estimates of the pole coordinates. A clear signal at three cycles per year is visible in the spectra of the differences between our estimates of the pole coordinates and the corresponding IERS 08 C04 values. Combinations of two 3-plane systems, even with similar ascending nodes, reduce this signal. The understanding of the relation between the satellite constellations and the resulting geodynamic parameters is important, because the GNSS currently under development, such as the European Galileo and the medium Earth orbit constellation of the Chinese BeiDou system, also consist of only three orbital planes.     

Landslide-dam paleolakes in the Central Pyrenees,Upper Gállego River Valley,NE Spain: timing and relationship with deglaciation

The production of a cartographic landslide inventory in the glaciated headwaters of the upper Gállego River, Axial Zone of the Spanish Pyrenees, revealed several paleolakes. These relict lake basins are related to the blockage of drainages by postglacial earthflows and slides, mainly developed on Paleozoic slates. The paleolakes are recorded either by non-dissected infilled basins or by hanging and incised lacustrine terraces that persisted for thousands of years. The development of lakes upstream of landslides, was favored, despite their erodibility, by high-displacement rates and the occurrence of paired landslides on both sides of the valley. Radiocarbon and single-grain optically stimulated luminescence (OSL) ages obtained on the lake sediments range between 41.5?±?3.9 ka and 15.1?±?0.3 ka. These chronologies indicate prolonged landslide activity long after the early deglaciation in the upper Gállego River Valley. The landslide-lake dating results support the interpretation that the regional maximum ice extent (MIE) in the Pyrenees occurred during the marine isotope stage 4 (MIS 4), long before the global Last Glacial Maximum (LGM).     

Field data and flow system response in clay (vertisol) shale terrain,north central Texas,USA

The water budget in clay shale terrain is controlled by a complex interaction between the vertisol soil layer, the underlying fractured rock, land use, topography, and seasonal trends in rainfall and evapotranspiration. Rainfall, runoff, lateral flow, soil moisture, and groundwater levels were monitored over an annual recharge cycle. Four phases of soil–aquifer response were noted over the study period: (1) dry‐season cracking of soils; (2) runoff initiation, lateral flow and aquifer recharge; (3) crack closure and down‐slope movement of subsurface water, with surface seepage; (4) a drying phase. Surface flow predominated within the watershed (25% of rainfall), but lateral flow through the soil zone continued for most of the year and contributed 11% of stream flow through surface seepage. Actual flow through the fractured shale makes up a small fraction of the water budget but does appear to influence surface seepage by its effect on valley‐bottom storage. When the valley soil storage is full, lateral flow exits onto the valley‐bottom surface as seasonal seeps. Well response varied with depth and hillslope position. FLOWTUBE model results and regional recharge estimates are consistent with an aquifer recharge of 1·6% of annual precipitation calculated from well heights and specific yield of the shale aquifer. Copyright © 2005 John Wiley & Sons, Ltd.