Spatial pattern of photospheric granules in a sunspot neighborhood

Based on high-resolution (0.3 arcsec) observations, we studied the behavior of solar granulation in the neighborhood of a sunspot. The bright granules’ spatial distribution and the granules’ surface density as a function of distance from the center of the sunspot umbra were determined.Bright granules distribute delimiting cells of dimensions in the mesogranular scale. The mean diameter of these cells does not show significant variation with the variation of the magnetic field of the sunspot. The granules’ surface density does not show significant variation with distance to the sunspot umbra. Both results point to a very weak, if any, influence of the sunspot magnetic field at distances greater than 20 arcsec.     

Fire and vegetation history during the last 3800 years in northwestern Montana

Foy Lake in northwestern Montana provides a record of annual-to-decadal-scale landscape change. Sedimentary charcoal and pollen analyses were used to document fire and vegetation changes over the last 3800 years, which were then compared to similar records from AD 1880 to 2000. The long-term record at Foy Lake suggests shifts between forest and steppe as well as changes in fire regime that are likely the result of climate change. Fire activity (inferred from the frequency of charcoal peaks) averaged 18 fire episodes/1000 years from 3800 to 2125 cal year BP, and increased from 16 fire episodes/1000 years at 2125 cal year BP to 22 episodes/1000 years at 750 cal year BP, a period when the pollen data suggest that steppe vegetation yielded to increasing patches of forest cover. Between 2125 and 750 cal year BP, increased forest cover produced more background charcoal than before and after this period, when vegetation was dominated by steppe. Between 750 and 75 cal year BP steppe has expanded and fire episode frequency averaged 33 episodes/1000 years, increasing to a maximum of 40 episodes/1000 years at ca. 300 cal year BP and then decreasing to present levels. Since AD 1880, the pollen record indicates an increase in shrubs and grasses from AD 1895 to 1960 as a result of vegetation changes associated with timber harvesting and livestock grazing. No fires have been documented in the Foy Lake watershed since AD 1880. Charcoal from the extralocal fires of AD 1910, burning over 4,111,249 ha in Idaho, Montana, and Wyoming, however, is present in Foy Lake. Between AD 1970 and 2000, increased arboreal pollen in the record is consistent with observations that the forest has become more closed. The activities of Euro–Americans have led to a decline in forest cover between AD 1880 and 1970, followed by a recent increase as trees are now growing in areas previously occupied by steppe. Euro–Americans are likely the cause of a reduction in fire activity in watershed since AD 1880.     

Structure in fluctuations of large-scale soil moisture climate due to external random forcing and internal feedbacks

Large-scale fields of soil moisture are forced by atmospheric precipitation and radiative forcing. When these forcing factors are themselves influenced by surface and soil moisture processes, the result is a nonlinear land-atmosphere system with inherent feedback mechanisms that may strongly modulate variability in climate. Given such feedbacks, simple randomness in the forcing factors may be manifested as a complex statistical signature in the surface hydrology. In this paper, we investigate the impacts of non-Gaussian and colored-noise on the probability distribution of soil moisture resulting from the statistical-dynamical land-atmosphere interaction model of Rodriguez-Iturbe et al. (1991). Persistence of hydroclimatologic anomalies as characterized by the correlation time scale of soil moisture is discussed.     

Solubility behavior of alkali aluminosilicate components in aqueous fluids and silicate melts at high pressure and temperature

The solubility behavior of K₂O, Na₂O, Al₂O₃, and SiO₂ in silicate-saturated aqueous fluid and coexisting H₂O-saturated silicate melts in the systems K₂O-Al₂O₃-SiO₂-H₂O and Na₂O-Al₂O₃-SiO₂-H₂O has been examined in the 1- to 2-GPa pressure range at 1100°C. Glasses of Na- and K-tetrasilicate compositions with 0, 3, and 6 mol% Al₂O₃ were used as starting materials. In both systems, the oxides dissolve incongruently in aqueous fluid and silicate melt. When recalculated to an anhydrous basis, the aqueous fluids are enriched in alkalis and depleted in silica and alumina relative to their proportions in the starting materials. The extent of incongruency is more pronounced in the Na₂O-Al₂O₃-SiO₂-H₂O system than in the K₂O-Al₂O₃-SiO₂-H₂O system.The partition coefficients of the oxides, D_oxide^fluid/melt, are linear and positive functions of the oxide concentration in the fluid for each composition. There is a slight dependence of the partition coefficients on bulk composition. No effect of pressure could be discerned. For alkali metals, the fluid/melt partition coefficients range from 0.06 to 0.8. For Al₂O₃ this range is 0.01 to 0.2, and for SiO₂, it is 0.01 to 0.32. For all compositions, D_K2O^fluid/melt∼D_Na2O^fluid/melt>D_SiO2^fluid/melt>D_Al2O3^fluid/melt for the same oxide concentration in the fluid. D_K2O^fluid/melt, D_Na2O^fluid/melt, and D_SiO2^fluid/melt correlate negatively with the Al₂O₃ content of the systems. This correlation is consistent with a solubility model of alkalis that involve associated KOH°, NaOH°, silicate, and aluminate complexes.     

Inelastic response of one-storey asymmetric-plan systems subjected to bi-directional earthquake motions

The inelastic response of one-storey systems with one axis of asymmetry subjected to bi-directional base motion is studied in this paper. The effect of the system parameters on response is also evaluated: uncoupled torsional-to-lateral frequency ratio, stiffness eccentricity, and yield strength of the lateral resisting elements. The ensemble of earthquake records used consists of 15 two-component strong ground motions. The response to uni-directional excitation is considered first to examine the influence of the system parameters and to serve as a basis to examine the results of the bi-directional case, which are presented in terms of average spectra for bi- over uni-directional lateral-deformation ratios. It is shown that the effect of inelastic behaviour is, on the average, noteworthy for stiff structures, in turn, the same structures are the most affected by the action of bi-directional ground motions. The effect of the relative intensity of the two orthogonal ground motion components is also studied. Copyright © 1999 John Wiley & Sons, Ltd.     

On the influence of reflection over a rhythmic swash zone on surf zone dynamics

The reflection of incident gravity waves over an irregular swash zone morphology and the resulting influence on surf zone dynamics remains mostly unexplored. The wave-phase resolving SWASH model is applied to investigate this feedback using realistic low-tide terraced beach morphology with well-developed beach cusps. The rhythmic reflection generates a standing wave that mimics a subharmonic edge wave, from the superimposition of incident and two-dimensional reflected waves. This mechanism is enhanced by shore-normal, narrow-banded waves in both direction and frequency. Our study suggests that wave reflection over steep beaches could be a mechanism for the development of rhythmic morphological features such as beach cusps and rip currents.     

How does anisotropy in bedrock river granitic outcrops influence pothole genesis and development?

Pothole formation and development may be influenced by joint sets and other heterogeneities within bedrock, as well as by hydraulics. Previous research indicates that most potholes found in rivers of the mountainous Spanish Central System exhibit preferred orientations associated with dominant joints and correlate more strongly with variations in substrate resistance than with hydraulics. Weathering and erosion weaken rock surfaces, which leads to decreased mechanical resistance. We start from the hypothesis that different mechanisms of pothole formation may create around the pothole a distinctive signature in terms of ultrasound pulse velocity and surface hardness. We develop a conceptual model and test it using potholes for which we know the mechanism of formation, demonstrating that the spatial and statistical distributions of dynamical mechanical properties and surface hardness of a pothole may provide insight into its genesis. Copyright © 2016 John Wiley & Sons, Ltd.     

Towards the representation of groundwater in the Joint UK Land Environment Simulator

Groundwater is an important component of the hydrological cycle with significant interactions with soil hydrological processes. Recent studies have demonstrated that incorporating groundwater hydrology in land surface models (LSMs) considerably improves the prediction of the partitioning of water components (e.g., runoff and evapotranspiration) at the land surface. However, the Joint UK Land Environment Simulator (JULES), an LSM developed in the United Kingdom, does not yet have an explicit representation of groundwater. We propose an implementation of a simplified groundwater flow boundary parameterization (JULES-GFB), which replaces the original free drainage assumption in the default model (JULES-FD). We tested the two approaches under a controlled environment for various soil types using two synthetic experiments: (1) single-column and (2) tilted-V catchment, using a three-dimensional (3-D) hydrological model (ParFlow) as a benchmark for JULES’ performance. In addition, we applied our new JULES-GFB model to a regional domain in the UK, where groundwater is the key element for runoff generation. In the single-column infiltration experiment, JULES-GFB showed improved soil moisture dynamics in comparison with JULES-FD, for almost all soil types (except coarse soils) under a variety of initial water table depths. In the tilted-V catchment experiment, JULES-GFB successfully represented the dynamics and the magnitude of saturated and unsaturated storage against the benchmark. The lateral water flow produced by JULES-GFB was about 50% of what was produced by the benchmark, while JULES-FD completely ignores this process. In the regional domain application, the Kling-Gupta efficiency (KGE) for the total runoff simulation showed an average improvement from 0.25 for JULES-FD to 0.75 for JULES-GFB. The mean bias of actual evapotranspiration relative to the Global Land Evaporation Amsterdam Model (GLEAM) product was improved from −0.22 to −0.01 mm day⁻¹. Our new JULES-GFB implementation provides an opportunity to better understand the interactions between the subsurface and land surface processes that are dominated by groundwater hydrology.     

A hybrid deterministic and stochastic approach for tsunami hazard assessment in Iquique,Chile

Natural Hazards - This paper presents an investigation of the collapse of a 325-year-old multi-tiered heritage temple during the 2015 Gorkha earthquake in Kathmandu, Nepal. The research comprises a...     

Strategic priorities for assessing ecological impacts of marine renewable energy devices in the Pentland Firth (Scotland,UK)

The Pentland Firth, located between the north coast of mainland Scotland (UK) and the Orkney Islands, is recognised as an excellent location for the utilisation of tidal stream technology. Potential ecological impacts associated with tidal stream technology may ultimately depend on device design, array size and deployment location. Available ecological data for the Pentland Firth is summarised and strategic priorities for assessing ecological impacts are provided. Baseline data on marine species and habitats in the Pentland Firth is severely lacking and consequently the integrity of any environmental impact assessment could be compromised by this lack of data.