What controls equatorial Atlantic winds in boreal spring?

The factors controlling equatorial Atlantic winds in boreal spring are examined using both observations and general circulation model (GCM) simulations from the coupled model intercomparison phase 5. The results show that the prevailing surface easterlies flow against the attendant pressure gradient and must therefore be maintained by other terms in the momentum budget. An important contribution comes from meridional advection of zonal momentum but the dominant contribution is the vertical transport of zonal momentum from the free troposphere to the surface. This implies that surface winds are strongly influenced by conditions in the free troposphere, chiefly pressure gradients and, to a lesser extent, meridional advection. Both factors are linked to the patterns of deep convection. Applying these findings to GCM errors indicates, that, consistent with the results of previous studies, the persistent westerly surface wind bias found in most GCMs is due mostly to precipitation errors, in particular excessive precipitation south of the equator over the ocean and deficient precipitation over equatorial South America. Free tropospheric influences also dominate the interannual variability of surface winds in boreal spring. GCM experiments with prescribed climatological sea-surface temperatures (SSTs) indicate that the free tropospheric influences are mostly associated with internal atmospheric variability. Since the surface wind anomalies in boreal spring are crucial to the development of warm SST events (Atlantic Niños), the results imply that interannual variability in the region may rely far less on coupled air–sea feedbacks than is the case in the tropical Pacific.     

Equatorial Atlantic variability and its relation to mean state biases in CMIP5

Coupled general circulation model (GCM) simulations participating in the Coupled Model Intercomparison Project Phase 5 (CMIP5) are analyzed with respect to their performance in the equatorial Atlantic. In terms of the mean state, 29 out of 33 models examined continue to suffer from serious biases including an annual mean zonal equatorial SST gradient whose sign is opposite to observations. Westerly surface wind biases in boreal spring play an important role in the reversed SST gradient by deepening the thermocline in the eastern equatorial Atlantic and thus reducing upwelling efficiency and SST cooling in the following months. Both magnitude and seasonal evolution of the biases are very similar to what was found previously for CMIP3 models, indicating that improvements have only been modest. The weaker than observed equatorial easterlies are also simulated by atmospheric GCMs forced with observed SST. They are related to both continental convection and the latitudinal position of the intertropical convergence zone (ITCZ). Particularly the latter has a strong influence on equatorial zonal winds in both the seasonal cycle and interannual variability. The dependence of equatorial easterlies on ITCZ latitude shows a marked asymmetry. From the equator to 15°N, the equatorial easterlies intensify approximately linearly with ITCZ latitude. When the ITCZ is south of the equator, on the other hand, the equatorial easterlies are uniformly weak. Despite serious mean state biases, several models are able to capture some aspects of the equatorial mode of interannual SST variability, including amplitude, pattern, phase locking to boreal summer, and duration of events. The latitudinal position of the boreal spring ITCZ, through its influence on equatorial surface winds, appears to play an important role in initiating warm events.     

Diffusion and sorption of Cs, I and HTO in samples of the argillaceous Wakkanai Formation from the Horonobe URL, Japan: Clay-based modeling approach

Diffusion and sorption behaviors of cationic Cs⁺, anionic I⁻ and neutral HTO in samples of the Wakkanai Formation from the Horonobe underground research laboratory (URL), Japan, were investigated as a function of ionic strength (I) of synthetic groundwater by through-diffusion and batch sorption experiments and mechanistic modeling. The effective diffusivities (D_e) measured by through-diffusion experiments showed cation excess and anion exclusion effects, which were strongly dependent on I; D_e for Cs⁺ decreased as I increased, D_e for I⁻ showed the opposite dependency and D_e for HTO showed no dependence. The sorption of Cs⁺ measured by through-diffusion and batch sorption experiments were described by Freundlich isotherms with consistent parameters and decreased with I as a result of competitive ion exchange.Diffusion and sorption behaviors were interpreted by assuming the clay components of illite and smectite control diffusion and sorption mechanisms. The component additive (CA) sorption model, which includes illite and smectite contents and their ion exchange constants, provided a reasonable account of the Cs⁺ sorption trends measured as functions of I and Cs concentration. The diffusion model was developed by coupling the electrical double layer (EDL) model, describing the change of ionic concentrations (cation excess and anion deficit) and viscoelectric effects caused by electrostatic interaction at negatively charged clay surfaces, and a simplified pore model assuming one type of pore shape and includes their size distribution. When averaging the electrostatic effects by using the pore surface area distribution, the model could predict the cation excess and anion exclusion effects, and its dependence on I reasonably well. This result implies the nanoscale pores dominating the pore surface area can strongly impact on ionic diffusion in argillaceous rocks. The clay-based modeling approach described here provides a useful tool to predict ionic diffusion and sorption in argillaceous rocks.     

Secular change in lifetime of granitic crust and the continental growth: A new view from detrital zircon ages of sandstones

U-Pb ages of detrital zircons were newly dated for 4 Archean sandstones from the Pilbara craton in Australia, Wyoming craton in North America, and Kaapvaal craton in Africa. By using the present results with previously published data, we compiled the age spectra of detrital zircons for 2.9, 2.6, 2.3,1.0, and0.6 Ga sandstones and modern river sands in order to document the secular change in age structure of continental crusts through time. The results demonstrated the following episodes in the history of continental crust:(1) low growth rate of the continents due to the short cycle in production/destruction of granitic crust during the Neoarchean to Paleoproterozoic(2.9-23 Ga),(2) net increase in volume of the continents during Paleo-to Mesoproterozoic(2.3-1.0 Ga), and(3) net decrease in volume of the continents during the Neoproterozoic and Phanerozoic(after 1.0 Ga). In the Archean and Paleoproterozoic, the embryonic continents were smaller than the modern continents, probably owing to the relatively rapid production and destruction of continental crust. This is indeed reflected in the heterogeneous crustal age structure of modern continents that usually have relatively small amount of Archean crusts with respect to the post-Archean ones. During the Mesoproterozoic, plural continents amalgamated into larger ones comparable to modern continental blocks in size. Relatively older crusts were preserved in continental interiors, whereas younger crusts were accreted along continental peripheries.In addition to continental arc magmatism, the direct accretion of intra-oceanic island arc around continental peripheries also became important for net continental growth. Since 1.0 Ga, total volume of continents has decreased, and this appears consistent with on-going phenomena along modern active arc-trench system with dominant tectonic erosion and/or arc subduction. Subduction of a huge amount of granitic crusts into the mantle through time is suggested, and this requires re-consideration of the mantle composition and heterogeneity.     

Recent insights into analytical precision and modelling of DDA and NMM for practical problems

This paper discussed the analytical precision on equations of motion in some practical studies that use 2-D DDA, 2D-Coupled analysis of NMM & DDA, and 3D-DDA. We point out the main reason for numerical instability in DDA is loss of the effective digits when superposing the global stiffness matrix under the variable conditions of large and the small blocks. Categories of analyses are distributed in 2D-DDA static masonry structures such as the Great Pyramid and the Pont du Gard, 2D-DDA dynamic rock fall problems and the sensitivity of its analysis on the velocity ratio and the penalty, earthquake response analysis of rock slopes, 2D-NMM, 2D-coupled analysis of DDA and NMM and 3D-DDA rock fall problem. The selected examples on the Great Pyramid, Pont du Gard and Bayon Temple at Angkor Thom are located in Egypt, France and Cambodia respectively as UNESCO world heritages sites. The authors evaluated the applicability of the methods and the reliability of the results by comparing different methods and site observations from the practical problems.     

Trajectories of Moving Objects on a Network: Detection of Similarities,Visualization of Relations,and Classification of Trajectories

Development in techniques of spatial data acquisition enables us to easily record the trajectories of moving objects. Movement of human beings, animals, and birds can be captured by GPS loggers. The obtained data are analyzed by visualization, clustering, and classification to detect patterns frequently or rarely found in trajectories. To extract a wider variety of patterns in analysis, this article proposes a new method for analyzing trajectories on a network space. The method first extracts primary routes as subparts of trajectories. The topological relations among primary routes and trajectories are visualized as both a map and a graph‐based diagram. They permit us to understand the spatial and topological relations among the primary routes and trajectories at both global and local scales. The graph‐based diagram also permits us to classify trajectories. The representativeness of primary routes is evaluated by two numerical measures. The method is applied to the analysis of daily travel behavior of one of the authors. Technical soundness of the method is discussed as well as empirical findings.     

Strength Anisotropy of Compacted Decomposed Granite Soils

In order to investigate the strength and deformation anisotropy of compacted decomposed granite soils, a series of drained triaxial compression tests was performed on unsaturated and saturated decomposed granite soils. The specimens were subjected to compression tests such that the angle δ of the direction of the major principal stress, σ ₁, during triaxial compression relative to the compaction plane (bedding plane) varies, with δ = 0°, 45° and 90°. Test results indicated that the compressive strain of the specimens subjected to isotropic consolidation was influenced strongly by the angle δ. In addition, the effect of the angle δ on the triaxial compressive strength and deformation was more evident in unsaturated specimens than in saturated specimens. Based on the test results, a procedure which can be used to estimate the shear strength of unsaturated soils taking into account various angles δ was proposed.     

Crystallization experiments of intercumulus melts for nakhlites under QFM ± 2 at 1 bar

Abstract— Crystallization of parent melts for nakhlites was experimentally studied under QFM ± 2 at one bar. Isothermal experiments suggest that melts having parent magma composition for nakhlites crystallize both augites and titanomagnetites at liquidus temperatures of 1144–1154 °C. Compositions of the augites are identical to those of phenocrystic core augites (En_36–38Fs_22–25Wo_39–40) in nakhlites. No olivines crystallize from the isothermal runs, and solidus temperature is about 1000 °C. Linear‐cooling experiments were carried out at various cooling rates (1–17 °C/h) ranging from liquidus to solidus temperatures under similar pressure conditions to the isothermal runs. Augites, titanomagnetites, and fayalites crystallized in the cooling runs, but magnesian olivines never crystallized there. Magnesian core augite in the cooling runs has the same composition as those of nakhlites. Rims of augite crystals from the cooling runs of 1–4 °C/h consist of two layers, ferroan augite inner rim and hedenbergite outer rim, which are very similar to those in the Miller Range (MIL) 03346 nakhlite. Small amounts of pyroxferroite crystallized in mesostasis and augite rims from two cooling runs. Titanomagnetites from cooling runs never accompany ilmenite lamellae as seen in nakhlites, suggesting that the subsolidus cooling rate of the cooling runs was much more rapid than those of nakhlite intercumulus melts. The cooling experiments reproduce the crystallization processes of pyroxenes and the compositional change of residual melt for a rapidly cooled magma such as MIL 03346.     

Characteristics of Seismoelectric Wave Fields Associated with Natural Microcracks

Properties of seismoelectric waves in relation to natural earthquakes have been investigated. The electromagnetic disturbances were analyzed to test the hypothesis that pulse-like electric variations are directly related to microcracks as source. Because variation is very difficult to detect, there have been few quantitative field investigations. We used selected events with clear S and P phases from the data catalog obtained before the Tohoku earthquake in 2011. The electric strength of the fast P wave (P_f), S wave (S), and electromagnetic wave (EM) associated with formation of cracks of tensile mode were estimated. The co-seismic electric signal accompanied by the S wave has the largest strength, well above the noise level, and the EM wave has the lowest strength. Analytical estimation of the ratio of the strengths of the P_f and EM phases to that of the S phase by use of Pride’s equations gave results partially in agreement with observation (the order was Ap_f > A_s > A_em). The strength of the observed electromagnetic mode is approximately two orders of magnitude larger than that estimated from the theory. We suggest this greater strength can be attributed to the converted modes at layer contracts or to the effect of the boundary between free atmosphere and crust. Overall agreement between observations and theoretical estimates suggests that electromagnetic anomalies, crustal deformation, and groundwater changes can be investigated on the basis of the unified equations for the coupled electromagnetics, acoustics, and hydrodynamics of porous media.