ALBERT

Description: Fluid dynamical simulations were carried out in order to investigate the effect of the large-scale mantle flow field and the depth of the plume source on the structure of the Iceland plume through time. The time-dependent location and shape of the plume in the Earth's mantle was calculated in a global model and it was refined in the upper mantle using a 3D Cartesian model box. Global flow was computed based on density heterogeneities derived from seismic tomography. Plate motion history served as a velocity boundary condition in both models. Hotspot tracks of the plume conduits and the plume head were calculated and compared to actual bathymetry of the North Atlantic. If a plume source in the lowermost mantle is assumed, the calculated surface position of the plume conduit has a southward component of motion due to southward flow in the lower mantle. Depending on tomography model, assumed plume age and buoyancy the southward component is more or less dominating. Plume models having a source at the 660 km discontinuity are only influenced by flow in the upper mantle and transition zone and hence rather yield westward hotspot motion. Many whole-mantle plume models result in a V-shaped track, which does not match the straight Greenland–Iceland–Faroe ridge. Models without strong southward motion, such as for a plume source at 660 km depth, match actual bathymetry better. Plume tracks were calculated from both plume conduits and plume heads. A plume head of 120 K anomalous temperature gives the best match between plume head track and bathymetry.

Description: Field-aligned currents (FACs) are an important mechanism for transporting energy and momentum from the solar wind into the upper atmosphere at high latitudes. The efficiency of energy dissipation depends on the ionospheric conductivity and the transverse scale size of the field-aligned current circuits. According to Vogt (2002) the conversion of electric current into heat should be most effective for scales of the order of some 10 km when typical ionospheric conductivities are considered. In order to test this conclusion we have performed a statistical analysis with FACs of various scale sizes. This study is based on observations that are derived from CHAMP magnetic field measurements taken during the years 2002-2005. FAC densities within the medium-scale wavelength band of 15-150 km and large-scale FACs (〉150 km) are considered separately and their distributions are compared. The thermospheric mass density recorded simultaneously by CHAMP is used as a measure for the heat deposited in the ionospheric E-layer. The relation between current strength of the two FAC types and thermospheric heating is determined in a superposed epoch analysis. The analysis is performed separately for each season and covers all local time sectors.

Description: Earth's long-term sea-level history is characterized by widespread continental flooding in the Cretaceous period (~145 to 65 million years ago), followed by gradual regression of inland seas. However, published estimates of the Late Cretaceous sea-level high differ by half an order of magnitude, from ~40 to ~250 meters above the present level. The low estimate is based on the stratigraphy of the New Jersey margin. By assimilating marine geophysical data into reconstructions of ancient ocean basins, we model a Late Cretaceous sea level that is 170 (85 to 270) meters higher than it is today. We use a mantle convection model to suggest that New Jersey subsided by 105 to 180 meters in the past 70 million years because of North America's westward passage over the subducted Farallon plate. This mechanism reconciles New Jersey margin–based sea-level estimates with ocean basin reconstructions.

Description: Observations from the affected population can be an important source of information for disaster management and rapid loss estimation. New Internet technologies facilitate fast and easy data collection from the public. A major obstacle for using this information is its unknown quality. This research will develop methods to assess the quality of observations from the affected population for rapid loss estimation after flood events. It will yield an assessment of the fitness for use of flood observations from the public for empirical loss modeling and an automated procedure to evaluate the quality of these observations.

Description: A major part of the plasma in the Earth's magnetotail is populated through transport of plasma from the solar wind via the magnetotail lobes. In this paper, we present a statistical study of plasma convection in the lobes for different directions of the interplanetary magnetic field and for different geomagnetic disturbance levels. The data set used in this study consists of roughly 340 000 one-minute vector measurements of the plasma convection from the Cluster Electron Drift Instrument (EDI) obtained during the period February 2001 to June 2007. The results show that both convection magnitude and direction are largely controlled by the interplanetary magnetic field (IMF). For a southward IMF, there is a strong convection towards the central plasma sheet with convection velocities around 10 km s−1. During periods of northward IMF, the lobe convection is almost stagnant. A By dominated IMF causes a rotation of the convection patterns in the tail with an oppositely directed dawn-dusk component of the convection for the northern and southern lobe. Our results also show that there is an overall persistent duskward component, which is most likely a result of conductivity gradients in the footpoints of the magnetic field lines in the ionosphere.

Description: Sea-level variability as observed by satellite altimetry reflects the integral effect of various dynamic processes in the oceans including the response to atmospheric loading, density changes in the water column as well as re- distribution of ocean mass. Since the first two effects are reasonably estimated and removed from the data, altimetric observations of the remaining mass induced height changes can be used to validate direct measurements of ocean mass variations as obtained with the satellite gravimetry mission GRACE. In order to assess the accuracy of various GRACE products, recently released gravity field solutions from, e.g., GFZ Potsdam, CSR Austin, JPL Pasadena and the Universities of Bonn and Delft will be contrasted both against sterically corrected Jason 1 observations and mass anomalies simulated with the numerical ocean model OMCT. Focussing on the time period 2003 until 2007, regional distribution, intensity, and shape of mass variabilities as well as corresponding barotropic current anomalies are used to assess the accuracy and reliability of the latest GRACE results over the oceans separately for individual monthly solutions. The cross- comparisons will additionally allow for first order error estimates of the data sets involved, which are necessary to know for using these data in any type of inversion experiment.

Description: The measurement of glacial isostatic adjustment (GIA) is one of the key ways in which geophysicists probe the long-term mantle rheology and Pleistocene ice history. GIA models are also tied to global and regional relative sea-level (RSL) histories, to 20th century tide-gauge (TG) data and to space and terrestrial geodetic measurements. Two new types of observation are related to the high-resolution space–gravity data recovered from the Gravity and Climate Experiment (GRACE) satellite pair and the soon-to-be launched Gravity and Ocean Circulation Experiment (GOCE) with on-board three-component gradiometer. Gravity mapping has the unique capability of isolating those regions that lack isostatic equilibrium. When coupled with other space and terrestrial geodetic measurements, such as those of the Global Positioning System (GPS) networks and with multi-decade terrestrial gravity data, new constraints on GIA are in the offing and should soon illuminate new interpretations of ice-sheet history and mantle response. GIA studies also incorporate space-based altimetry data, which now provide multi-decadal coverage over continents, oceans and lakes. As we are approaching 72 monthly solutions of GRACE gravity coefficients for determining the Earth's secular component of gravity change over the continents, a new issue has surfaced: the problem of relying on interannual hydrological modeling to determine the hydrological contribution to the linear trend in the gravity field. Correctly extracting this contribution is germane to using the GIA-driven component for modeling solid-Earth and paleo-climatic parameters. Seismic and heat-flux-based models of the Earth's interior are emerging with ever higher levels of sophistication regarding material strength (or viscosity). A basic question raised is: how good are traditional Newtonian and non-Newtonian viscosity models that only allow radial variations of Earth parameters? In other words: under what circumstances must this assumption be abandoned for joint interpretations of new and traditional data sets. In this short review we summarize the issues raised in the papers forming this special issue (SI) dedicated to GIA.

Description: Operational global mass transport data of the atmosphere and the oceans are widely used for studies of earth rotation excitation and gravity field simulations and are essential for GRACE dealising purposes, too. Seasonal and short periodic variations are also caused by continental water mass redistributions. In order to account for the continental hydrology processes as well and to close the global water cycle, continental water mass storage fields and fluxes are needed in the same operational manner as for the atmosphere and ocean. To simulate continental water mass redistributions a land surface scheme (SLS) is combined with a hydrological discharge model (HDM). The SLS generates components of the land water budget like soil moisture, snow accumulation and evaporation as well as surface fluxes like runoff and drainage. The latter is applied as input data for the HDM simulating the lateral water flow. Both models work on daily time steps. The new extended model combination (LSXM+HDXM) for the operational use, provides daily variations of the global water mass storage and the corresponding water fluxes as well as the hydrological angular momentum functions and low degree gravity coefficients in near real time. Since both, LSXM+HDXM and OMCT, are consistently forced with operational analyses from ECMWF, the complete data set of atmospheric, oceanic and hydrologic mass variations allows a realistic representation of mass transports in the global hydrological cycle.

Description: In this work two Co53.5Fe10X5.5B31 (X = Ta, W) alloys were synthesized from high purity (〉= 99.9%) powder elements by means of mechanical alloying. In case of Ta-addition, mechanical alloying resulted in formation of two component material with nanocrystalline phase embedded in amorphous matrix. On the other hand, substitution of Ta by W retards partial amorphization induced by mechanical alloying. High pressure-temperature stability of both alloys was monitored using in situ energy dispersive X-rays.

Description: A new approach to estimate surface soil moisture from reflectance data in the solar spectral range (350-2500 nm) is presented, called the Normalized Difference Soil Moisture Index (NSMI). The motivation for this new index is to make use of spectral features that fulfill the criteria of robustness against covariates, physical comprehensibility and easy applicability in the field and from remote sensing platforms. Spectral measurements were taken in the laboratory from 121 prepared as well as 467 natural soil samples consisting of different sands and clayey substrates originating from a lignite mine reclamation site. While the preparation procedure performed on samples from the first group removed the covariates' influence on the reflectance spectra, the natural samples in the second group maintained the influencing factors like impurity, crusts, and organic matter. In a systematic way all wavelengths were combined in different spectral feature approaches and optimum bands or band combinations were found for linear correlation with soil moisture. For the natural samples, the NSMI achieved best results in this study with R 2 of 0.61 by combining reflectance values at 1800 and 2119 nm. This value increased to 0.71 when samples with significant xylite proportions had been removed. Analyses on the effect of single covariates showed that neither surface crusts nor substrate heterogeneity changed the correlation between soil moisture and the NSMI significantly. The NSMI can therefore be seen as a new index for quick assessment of surface or near-surface soil moisture directly in the field using spectral instruments.

Description: This paper presents a compilation of intensity data covering the past 10 millennia (ArcheoInt). This compilation, which upgrades the one of Korte et al. (2005), contains 3648 data and incorporates additional intensity and directional data sets. A large majority of these data (∼87%) were acquired on archeological artifacts, and the remaining ∼13% correspond to data obtained from volcanic products. The present compilation also includes important metadata for evaluating the intensity data quality and providing a foundation to guide improved selection criteria. We show that ∼50% of the data set fulfill reasonable reliability standards which take into account the anisotropic nature of most studied objects (potsherds), the stability of the magnetization, and the data dispersion. The temporal and geographical distributions of this sub–data set are similar to those of the main data set, with ∼72% of the data dated from the past three millennia and ∼76% obtained from western Eurasia. Approximately half of the selected intensity data are associated with at least an inclination value. To constrain the axial and full dipole evolution over the past three millennia requires that we avoid any overrepresentation of the western Eurasian data. We introduce a first-order regional weighting scheme based on the definition of eight widely distributed regions of 30° width within which the selected data are numerous enough. The regional curves of virtual axial dipole moments (VADM) and of mixed VADM-virtual dipole moments (VDM) averaged over sliding windows of 200 years and 500 years testify for strong contributions from either equatorial dipole or nondipole components. The computation of global VADM and mixed VADM/VDM variation curves, assuming an equal weight for each region, yields a dipole evolution marked by a distinct minimum around 0 B.C./A.D. followed by a maximum around the third-fourth century A.D. A second minimum is present around the eighth century A.D. This variation pattern is compatible with the one deduced from earlier, more sophisticated analysis based on the inversion of both intensity and directional data. In particular, there is a good agreement among all VADMs and dipole moment estimates over the historical period, which further strengthens the validity of our weighting scheme.

Description: In addition to seismically mapped fault structures, a large number of faults below the limit of seismic resolution contribute to subsurface deformation. However, a correlation between large- and small-scale faults is difficult because of their strong variation in orientation. A workflow to analyze deformation over different scales is described here. Based on the combination of seismic interpretation, coherency analysis, geostatistical analysis, kinematic modeling, and well data analysis, we constrained the density and orientation of subseismic faults and made predictions about reactivation and opening of fractures. We interpreted faults in seismic and coherency volumes at scales between several kilometers and a few tens of meters. Three-dimensional (3-D) retrodeformation was performed on a detailed interpreted 3-D structural model to simulate strain in the hanging wall at the time of faulting, at a scale below seismic resolution. The modeling results show that (1) considerable strain is observed more than 1 km (0.62 mi) away from the fault trace and (2) deformation around the fault causes strain variations, depending on the fault morphology. This strain variation is responsible for the heterogeneous subseismic fracture distribution observed in wells. We linked the fracture density from the well data with the modeled strain magnitude and used the strain magnitude as a proxy for fracture density. With this method, we can predict the relative density of small-scale fractures in areas without well data. Furthermore, knowing the orientation of the local strain axis, we predict a fault strike and opening or reactivation of fractures during a particular deformation event.