Eccentric geomagnetic dipole drift

A recalculation of the rate of westward drift of the eccentric geomagnetic dipole since 1900 has confirmed its correlation with irregularities in the excess length-of-day (LOD) as originally reported by Vestine. The major changes in the LOD curve since 1900 are shown to be well correlated with the westward drift rate from a number of magnetic models covering the interval. A new Magsat model of secular variation for 1980.0 shows no increase in the drift rate which dropped by a factor of three in the interval 1965–1970.     

Limit states and failure mechanisms of viscous dampers and the implications for large earthquakes

Fluid viscous dampers are used to control story drifts and member forces in structures during earthquake events. These elements provide satisfactory performance at the design‐level or maximum considered earthquake. However, buildings using fluid viscous dampers have not been subjected to very large earthquakes with intensities greater than the design and maximum considered events. Furthermore, an extensive database of viscous damper performance during large seismic events does not exist. To address these issues, a comprehensive analytical and experimental investigation was conducted to determine the performance of damped structures subjected to large earthquakes. A critical component of this research was the development and verification of a detailed viscous damper mathematical model that incorporates limit states. The development of this model and the laboratory and simulation results conclude good correlation with the new model and the damper limit states and provide superior results compared with the typical damper model when considering near collapse evaluation of structures. Copyright © 2010 John Wiley & Sons, Ltd.     

Spatial interpolation of snow water equivalency using surface observations and remotely sensed images of snow‐covered area

As demand for water continues to escalate in the western Unites States, so does the need for accurate monitoring of the snowpack in mountainous areas. In this study, we describe a simple methodology for generating gridded‐estimates of snow water equivalency (SWE) using both surface observations of SWE and remotely sensed estimates of snow‐covered area (SCA). Multiple regression was used to quantify the relationship between physiographic variables (elevation, slope, aspect, clear‐sky solar radiation, etc.) and SWE as measured at a number of sites in a mountainous basin in south‐central Idaho (Big Wood River Basin). The elevation of the snowline, obtained from the SCA estimates, was used to constrain the predicted SWE values. The results from the analysis are encouraging and compare well to those found in previous studies, which often utilized more sophisticated spatial interpolation techniques. Cross‐validation results indicate that the spatial interpolation method produces accurate SWE estimates [mean R² = 0·82, mean mean absolute error (MAE) = 4·34 cm, mean root mean squared error (RMSE) = 5·29 cm]. The basin examined in this study is typical of many mid‐elevation mountainous basins throughout the western United States, in terms of the distribution of topographic variables, as well as the number and characteristics of sites at which the necessary ground data are available. Thus, there is high potential for this methodology to be successfully applied to other mountainous basins. Copyright © 2010 John Wiley & Sons, Ltd.     

Uncertainty in hydrologic modelling for estimating hydrologic response due to climate change (Santiam River,Oregon)

This paper explores the predicted hydrologic responses associated with the compounded error of cascading global circulation model (GCM) uncertainty through hydrologic model uncertainty due to climate change. A coupled groundwater and surface water flow model (GSFLOW) was used within the differential evolution adaptive metropolis (DREAM) uncertainty approach and combined with eight GCMs to investigate uncertainties in hydrologic predictions for three subbasins of varying hydrogeology within the Santiam River basin in Oregon, USA. Predictions of future hydrology in the Santiam River include increases in runoff in the fall and winter months and decreases in runoff for the spring and summer months. One‐year peak flows were predicted to increase whereas 100‐year peak flows were predicted to slightly decrease. The predicted 10‐year 7‐day low flow decreased in two subbasins with little groundwater influences but increased in another subbasin with substantial groundwater influences. Uncertainty in GCMs represented the majority of uncertainty in the analysis, accounting for an average deviation from the median of 66%. The uncertainty associated with use of GSFLOW produced only an 8% increase in the overall uncertainty of predicted responses compared to GCM uncertainty. This analysis demonstrates the value and limitations of cascading uncertainty from GCM use through uncertainty in the hydrologic model, offers insight into the interpretation and use of uncertainty estimates in water resources analysis, and illustrates the need for a fully nonstationary approach with respect to calibrating hydrologic models and transferring parameters across basins and time for climate change analyses. Copyright © 2012 John Wiley & Sons, Ltd.     

Spectroscopy of Loose and Cemented Sulfate-Bearing Soils: Implications for Duricrust on Mars

The goal of this work is to determine the spectroscopic properties of sulfate in martian soil analogs over the wavelength range 0.3 to 25 μm (which is relevant to existing and planned remotely sensed data sets for Mars). Sulfate is an abundant component of martian soil (up to 9% SO₃ by weight) and apparently exists as a particulate in the soil but also as a cement. Although previous studies have addressed the spectroscopic identity of sulfates on Mars, none have used laboratory mixtures of materials with sulfates at the abundances measured by landed spacecraft, nor have any works considered the effect of salt-cementation on spectral properties of soil materials. For this work we created mixtures of a palagonitic soil (JSC Mars-1) and sulfates (MgSO₄ and CaSO₄·2H₂O). The effects of cementation were determined and separated from the effects of packing and hydration by measuring the samples as loose powders, packed powders, cemented materials, and disaggregated materials. The results show that the presence of particulate sulfate is best observed in the 4-5 μm region. Soils cemented with sulfate exhibit a pronounced restrahlen band between 8 and 9 μm as well as well-defined absorptions in the 4-5 μm region. Cementation effects are distinct from packing effects and disaggregation of cemented samples rapidly diminishes the strength of the restrahlen bands. The results of this study show that sulfate in loose materials is more detectable in the near infrared (4-5 μm) than in the thermal infrared (8-9 μm). However, cemented materials are easily distinguished from loose mixtures in the thermal infrared because of the high values of their absorption coefficient in this region. Together these results suggest that both wavelength regions are important for determining the spatial extent and physical form of sulfates on the surface of Mars.     

Dynamic simulation of littoral zone habitats in low Chesapeake Bay. II. Seagrass habitat primary production and water quality relationships

Seagrasses are indicators of ecosystem state because they are sensitive to variations in water composition and clarity resulting from watershed-level impacts. A simulation model designed to studyZostera marina (eelgrass) habitat dynamics in a variable littoral zone environment was used to address the potential ecological responses to eutrophication in lower Chesapeake Bay. The adjacent channel boundary environment is a source of dissolved and particulate materials to the littoral zone. In the simulations, concentrations of key water quality variables in the adjacent estuarine channel boundary were either halved or doubled relative to the base case to investigate light versus nitrogen effects. The role of the seagrass meadow in littoral zone carbon and nitrogen dynamics was evaluated when meadow size was changed in the model. Particulate and dissolved organic carbon accounted for 83% of the submarine light attenuation in the seagrass meadow. In all model runs, the water column concentrations of chlorophylla and dissolved inorganic nitrogen (DIN) were below the habitat criteria proposed as critical to seagrass survival. Eelgrass community production was carefully regulated by the interactive effects of light, nitrogen, and grazing on epiphyte growth. Increased eelgrass coverage in the littoral zone led to a simulated doubling of ecosystem primary production but reduced the fraction of production by planktonic and sediment microalgae. The simulation model presented here demonstrated the importance of material input from the channel in littoral zone biogeochemical dynamics. Submarine ligh regulated primary production more strongly than inorganic nitrogen concentrations in the model. External DIN concentrations influenced seagrass survival indirectly: enrichment stimulated growth of epiphytes and phytoplankton and promoted shading of the seagras leaf. The model was based upon a unimpacted ecosystem and deteriorated water quality negatively influenced primary production greater than the increases triggered by improved condition. Increased material loading to the littoral zone reduced submarine light availability, increased phytoplankton production, lowered ecosystem production, and reduced subtidal vegetated habitat. This simulation model of the estuarine littoral zone model combines hydrodynamics, biogeochemical sources and sinks, and living resources in order to better understand structure, function, and change in aquatic ecosystems.     

60Fe–60Ni systematics in the eucrite parent body: A case study of Bouvante and Juvinas

Eucrites are basaltic meteorites that cooled rapidly but are in many instances thermally metamorphosed and impact brecciated. The exact timing of these events remains unclear. In this study, Ni isotopic compositions and Fe/Ni elemental ratios are presented for two non-cumulate eucrites, Bouvante and Juvinas, including mineral separates from the latter. The samples are characterized by variable, well-resolved ⁶⁰Ni-excesses consistent with the former presence of live ⁶⁰Fe (t_1/2 = 2.62 Ma) at the time of eucrite crystallization. A significant fraction of Ni with a terrestrial-like composition appears to be surface correlated. This Ni may be the product of terrestrial contamination or was introduced by a chondritic impactor during brecciation. Altogether, the data provide evidence for a complex and probably multi-stage history of Fe and/or Ni redistribution, which impedes the interpretation of the chronological data.     

Die Kreide in der Zentralkordillere östlich von Lima (Peru,Südamerika)

Lower and Upper Cretaceous sediments were investigated in the Peruvian Central Cordillera. As in the western facies of Central and Northern Peru, the Goyllarisquisga Group is subdivided into several lithologically different formations, in which sediments were transported from east to west. The area of investigation is situated west of the facies boundary between Marañon geanticline and West Peruvian trough; this indicates that the boundary continues south and does not follow the line Celendin-Rio Palanga as suggested byWilson. The limestones and dolomites of the Santa Formation were deposited in shallow water, possibly with intermittent subaerial exposure. The sandstone of the Farrat Formation are interpreted to be sediments of a west-east transgression; vertically they grade into the limestones of the Pariahuanca-Formation. Facies and thickness of the Chulec and Pariahuanca-Formation are little different from those in neighbouring areas. During deposition of the thick Jumasha Formation, the differences are much more significant, and only comparison with Northwest Peru shows some agreement.