Global distribution,seasonal, and inter-annual variations of mesospheric semidiurnal tide observed by TIMED TIDI

Based on TIDI mesospheric wind observations, we analyzed the semidiurnal tide westward zonal wavenumber 1 and 2 (SW1 and SW2) component seasonal, inter-annual variations, and possible sudden stratospheric warming (SSW) related changes. Major findings are as follows: (1) The SW1 has a peak near the South Pole during the December solstice and near the North Pole during the March equinox. (2) The SW2 peaks at 60S and 60N mostly during winter solstices. The SW2 also peaks during late summer and early fall in the northern hemisphere. (3) The QBO effect on the semidiurnal tide is much weaker than that on the diurnal tide. The March equinox northern SW1 zonal amplitude appears to be stronger during the westward phase of the QBO, which is opposite of migrating diurnal tide QBO response. (4) Possible SSW event related changes in the semidiurnal tide are significant but not always consistent. Enhancements in the mid-latitude SW2 component during SSWs are observed, which may be related to the increase of total ozone at mid and high latitudes during SSW events. TIDI observations also show a decrease in the SW2 in the opposite hemisphere during a southern SSW event in 2002. Small increases in the high latitude SW1 in both hemispheres during the 2002 southern SSW event were recorded.     

Metallic mineral deposits

Except for the fringing reef, the limestones of Christmas Island in the Indian Ocean are of Late Eocene (Tertiary “b") and Early Miocene (Tertiary “e” to “f") age. The Upper Eocene limestone is an algal limestone containing Discocyclina, Nummulites, and Heterostegina. The Lower Miocene limestone is an algal limestone containing in its lower part species of Lepidocyclina (Eulepidina) followed by Miogypsinoides dehaarti. Miogypsinoides dehaarti extends into the zone of Flosculinella bontangensis. No rocks younger than Burdigalian were identified other than on the fringing reef which contains an assemblage of Pliocene‐Pleistocene Foraminifera.     

Evaluation of In Situ Heterogeneity of Elements in Solids: Implications for Analytical Geochemistry

A general method for the evaluation of in situ heterogeneity of geochemical materials is described and the significance of the results discussed, by using three case studies and earlier data sets. The heterogeneity of Pb in soil (expressed as RSD due to sampling, RSD_samp) varies from < 5 to > 100% between different sites, in a way that relates to the mode of deposition of the element. The heterogeneity of an element also varies systematically as a function of the distance scale at some sites. This variation can be modelled using linear regression, accounting for over 90% of the experimental variance, at seven scales over three orders of magnitude. Variation in heterogeneity between elements at the same site, seems to be somewhat diagnostic of the origin of the element, lithogenic being less than anthropogenic, although the later is also being modified by the mode of deposition. Where the heterogeneity is large (RSD > 30%), it is proposed that it can be expressed more accurately as a heterogeneity factor (10^GSDsamp), to reflect its frequency distribution, which is positively skewed towards higher concentration values.     

Climate,conflict, and social stability: what does the evidence say?

Are violent conflict and socio-political stability associated with changes in climatological variables? We examine 50 rigorous quantitative studies on this question and find consistent support for a causal association between climatological changes and various conflict outcomes, at spatial scales ranging from individual buildings to the entire globe and at temporal scales ranging from an anomalous hour to an anomalous millennium. Multiple mechanisms that could explain this association have been proposed and are sometimes supported by findings, but the literature is currently unable to decisively exclude any proposed pathway. Several mechanisms likely contribute to the outcomes that we observe.     

A three-dimensional discontinuous Galerkin model applied to the baroclinic simulation of Corpus Christi Bay

In this work, we present results of a numerical study of Corpus Christi Bay, Texas and surrounding regions and compare simulated model results to recorded data. The validation data for the year 2000 include the water elevation, velocity, and salinity at selected locations. The baroclinic computations were performed using the University of Texas Bays and Estuaries 3D (UTBEST3D) simulator based on a discontinuous Galerkin finite element method for unstructured prismatic meshes. We also detail some recent advances in the modeling capabilities of UTBEST3D, such as a novel turbulence scheme and the support for local vertical discretization on parts of the computational domain. All runs were conducted on parallel clusters; an evaluation of parallel performance of UTBEST3D is included.     

Loss estimation for non‐ductile reinforced concrete building in Victoria,British Columbia,Canada: effects of mega‐thrust Mw9‐class subduction earthquakes and aftershocks

This paper presents, within the performance‐based earthquake engineering framework, a comprehensive probabilistic seismic loss estimation method that accounts for main sources of uncertainty related to hazard, vulnerability, and loss. The loss assessment rigorously integrates multiple engineering demand parameters (maximum and residual inter‐story drift ratio and peak floor acceleration) with consideration of mainshock–aftershock sequences. A 4‐story non‐ductile reinforced concrete building located in Victoria, British Colombia, Canada, is considered as a case study. For 100 mainshock and mainshock–aftershock earthquake records, incremental dynamic analysis is performed, and the three engineering demand parameters are fitted with a probability distribution and corresponding dependence computed. Finally, with consideration of different demolition limit states, loss assessment is performed. From the results, it can be shown that when seismic vulnerability models are integrated with seismic hazard, the aftershock effects are relatively minor in terms of overall seismic loss (1–4% increase). Moreover, demolition limit state parameters, uncertainties of collapse fragility, and non‐collapse seismic demand prediction models have showed significant contribution to the loss assessment. The seismic loss curves for the reference case and for cases with the varied parameters can differ by as large as about 150%. Copyright © 2015 John Wiley & Sons, Ltd.     

Identification and measurement of neutron-absorbing elements on Mercury’s surface

MESSENGER Neutron Spectrometer (NS) observations of cosmic-ray-generated thermal neutrons provide the first direct measurements of Mercury’s surface elemental composition. Specifically, we show that Mercury’s surface is enriched in neutron-absorbing elements and has a measured macroscopic neutron-absorption cross section of 45-81 × 10⁻⁴ cm²/g, a range similar to the neutron absorption of lunar basalts from Mare Crisium. The expected neutron-absorbing elements are Fe and Ti, with possible trace amounts of Gd and Sm. Fe and Ti, in particular, are important for understanding Mercury’s formation and how its surface may have changed over time through magmatic processes. With neutron Doppler filtering - a neutron energy separation technique based on spacecraft velocity - we demonstrate that Mercury’s surface composition cannot be matched by prior models, which have characteristically low abundances of Fe, Ti, Gd, and Sm. While neutron spectroscopy alone cannot separate the relative contributions of individual neutron-absorbing elements, these results provide strong new constraints on the nature of Mercury’s surface materials. For example, if all the measured neutron absorption were due to the presence of an Fe-Ti oxide and that oxide were ilmenite, then Mercury’s surface would have an ilmenite content of 7-18 wt.%. This result is in general agreement with the inference from color imaging and visible-near-infrared spectroscopy that Mercury’s overall low reflectance is consistent with a surface composition that is enriched in Fe-Ti oxides. The incorporation of substantial Fe and Ti in oxides would imply that the oxygen fugacity of basalts on Mercury is at the upper range of oxygen fugacities inferred for basalts on the Moon.     

Limitations of single-basket trading: lessons from the Montreal Protocol for climate policy

Numerous policy options exist to reduce future greenhouse gas emissions. A single-basket approach, which controls aggregate emissions, was adopted by the Kyoto Protocol. Such an approach allows emissions reductions of one gas to be traded with those of other gases in the “basket”, with the trade “price” determined by some weighting metric like the Global Warming Potential. To reduce stratospheric ozone depletion, the Montreal Protocol also dealt with controlling many compounds, but did so employing an alternative, multi-basket scheme. Trading was allowed within each basket, but not among baskets. While the Montreal Protocol has been highly successful using this approach, we show that if a single-basket approach had been adopted the short-term success could have been at risk due to the non-unique relationship between controls and environmental impacts when using a single basket. Using climate policy as an example, and without considering technological and economic constraints, we further show that the magnitude of the ambiguities in impacts associated with a single-basket approach depends on the rapidity of the emission phaseout. Fast phaseouts lead to less ambiguity than do slow ones. These results suggest that for each set of greenhouse gas control policies considered, the benefit of additional flexibility associated with a single-basket approach should be weighed against the associated increased uncertainties in the impacts to ascertain whether a single- or a multi-basket approach has the greater chance of successfully mitigating climate change.     

Oxygen, hydrogen, and helium isotopes for investigating groundwater systems of the Cape Verde Islands, West Africa

Stable isotopes (δ¹⁸O, δ²H), tritium (³H), and helium isotopes (³He, ⁴He) were used for evaluating groundwater recharge sources, flow paths, and residence times of three watersheds in the Cape Verde Islands (West Africa). Stable isotopes indicate the predominance of high-elevation precipitation that undergoes little evaporation prior to groundwater recharge. In contrast to other active oceanic hotspots, environmental tracers show that deep geothermal circulation does not strongly affect groundwater. Low tritium concentrations at seven groundwater sites indicate groundwater residence times of more than 50 years. Higher tritium values at other sites suggest some recent recharge. High ⁴He and ³He/⁴He ratios precluded ³H/³He dating at six sites. These high ³He/⁴He ratios (R/R_a values of up to 8.3) are consistent with reported mantle derived helium of oceanic island basalts in Cape Verde and provided end-member constraints for improved dating at seven other locations. Tritium and ³H/³He dating shows that São Nicolau Island’s Ribeira Fajã Basin has groundwater residence times of more than 50 years, whereas Fogo Island’s Mosteiros Basin and Santo Antão Island’s Ribeira Paul Basin contain a mixture of young and old groundwater. Young ages at selected sites within these two basins indicate local recharge and potential groundwater susceptibility to surface contamination and/or salt-water intrusion.     

On the interpretation of seasonal variations of stratospheric ozone

Insight into the causes of the annual and semi-annual ozone oscillations may be gained from the analysis of photochemical model behavior. In this paper, the monthly variations of the ozone mixing ratio computed by the two-dimensional photochemical model of Garcia and Solomon (1983, J. geophys. Res. 88, 1379) are Fourier-analyzed and compared with SBUV observations of ozone mixing ratio. Remarkably good qualitative agreement between the model calculations and the observations is found. Analysis of computed transport and chemical production and destruction rates reveals the causes of the modelled seasonal ozone variations.

It will be shown that at high latitudes and low altitudes, modelled ozone abundances increase in the winter due to transport and decrease in the summer due to chemical destruction. In the middle stratosphere, the calculated annual ozone variation is largely due to the annual variation in the odd-oxygen production rate, and in the upper stratosphere, the computed annual ozone variation is caused by the large calculated annual oscillation in temperature. Comparison between the model and observations suggests that the equatorial semi-annual oscillation above 10 mb is caused mainly by the semi-annual temperature and wind oscillation (SAO). Below 10 mb the computed equatorial ozone variation is caused by the increased rates of odd-oxygen production associated with the semi-annual zenith crossings of the Sun. Finally, the calculated polar semi-annual ozone oscillations are found to be caused by modulation of the radiatively driven middle-stratospheric ozone variation by temperature dependent chemical destruction processes.