Determining the optimal soil temperature scheme for atmospheric modelling applications

The treatment of the land surface can have a significant impact on the performance of atmospheric models, influencing the surface energy balance and near surface atmospheric variables. In numerical weather prediction models it is especially important to reproduce the observed diurnal cycle in screen-level temperature, which requires an accurate representation of the surface temperature, and therefore an accurate and computationally efficient representation of soil heat storage and transfer. We present a technique for analysing the accuracy of numerical soil temperature schemes, and a methodology for choosing the optimal layer thicknesses for schemes with a given number of layers. Furthermore, the analysis suggests that first generation land surface schemes, which typically used a layer-average surface temperature, may be more accurate in this respect than the latest land surface schemes, which tend to use a skin surface temperature boundary condition.The British Crowns right to retain a non-exclusive royalty-free license in and to any copyright is acknowledged.     

Responses of foraminiferal isotopic variations at ODP Site 1143 in the southern South China Sea to orbital forcing

1 Astronomical theory One of the greatest achievements of the EarthSciences in the 20th century is the establishment of theMilankovitch theory or the astronomical theory[1]. AsImbrie pointed out[2], the astronomical theory can bedescribed as a simple system model. The input to thesystem can be defined as changes in the geometry ofthe Earth’s orbit or the seasonal and latitudinal distri-bution of incoming solar radiation, whereas the outputto the system can be defined as one or more calc…     

Metamorphic zircon from Xindian eclogite,Dabie Terrain: U-Pb age and oxygen isotope composition

~~Metamorphic zircon from Xindian eclogite,Dabie Terrain: U-Pb age and oxygen isotope composition@E. Deloule$CRPG-CNRS Nancy,54501,France1. Vavra, G, Gebauer. D., Schmid. R. et al., Multiple zircon growth and recrystallization during polyphase Late Carboniferous to Tri-assic metamorphism in granulites of the Ivrea Zone (Southern Alps): an ion microprobe (SHRIMP) study, Contrib. Mineral Petrol., 1996, 122:337-358 2. Vavra, G, Schmid, R., Gebauer, D., Internal morphology, ha…     

镀镍碳为还原剂在线高温裂解法测定硫酸钡中氧同位素组成

测定矿物或水中硫酸根的氧同位素组成(δ18O)能够识别物质来源及转化过程,常用的方法是将硫酸根转化为硫酸钡再用离线或在线法测试其δ18O值。目前普遍采用1420℃在线测试硫酸钡的氧同位素组成,该方法极易缩短反应炉的寿命,通过添加还原剂碳可以降低反应温度,但是已有报道对于添加还原剂后的反应温度讨论较少。本文选择镀镍碳(Ni-C)作为还原剂,将样品经Ni-C高温处理后进行一系列条件实验,确认了采用元素分析仪-稳定同位素质谱仪(EA-IRMS)测定硫酸钡中氧同位素组成的分析方法的关键技术参数:硫酸钡在线反应温度为1350℃; Ni-C与硫酸钡样品量的质量比范围选择0. 73～2. 15;为了获得更加精确的数据,硫酸钡与Ni-C用量都控制在700±100μg。在以上实验条件下,EA/HT-IRMS测定硫酸钡δ18O值的精密度为±0. 12‰～±0. 26‰,优于在线法已报道的精密度±0. 20‰～±0. 50‰。本方法在满足测试精密度的前提下,通过添加Ni-C降低了硫酸钡在线反应温度,延长了反应炉使用寿命。     

广西沿海全新世以来气候变化

本文根据孢粉分析，有孔虫氧同位素分析，历史记载及现代气温观测资料，综合资料广西沿海全新世以来的气候变化，经过研究，初步划分了本区全新世以来的７个气候期，在晚全新世内，进一步划分了７个气候亚期，早全新世，中全新的气候变化具有１５００－２０００ａ周期，晚全新世界的气候变化具有５００－１０００ａ周期，晚全新世中－晚期的气候变化具２００ａ周期，２００ａ来的气候变化呈冷，热交替出现，具有１０－２０ａ或３０－     

广西拉么Zn—Cu矿床中夕卡岩的主要矿物特点与Ca—Fe—Si—C—O体系T—lgfO2图解

用电子探针数据研究了该矿床中主要夕卡岩矿物特点及其变化规律。采用理想结晶溶液固溶体位置混合模式,计算了石榴子石和辉石矿物对中钙铁榴石和钙铁辉石的摩尔分数。在计算纯固相和流体相参加的反应抵达平衡时的边界方程中,加上理想结晶固溶体中端元组分摩尔分数的修正项后,我们便可以计算出有纯固相、流体相和理想结晶溶液固溶体参加反应的在给定T、P条件下的lgfo_2值。计算结果表明:无变度点4周围的Hed+And+Wol组合对本矿区具有重要的地质地球化学意义。     

Properties of fluids attending variable recrystallization of quartzite during contact metamorphism in the White‐Inyo Range,California

Fluid inclusions in the metamorphic aureole of the Eureka Valley‐Joshua Flat‐Beer Creek (EJB) pluton in the White‐Inyo Range, California, reveal the compositions and origin of fluids that were present during variable recrystallization of quartzite with sedimentary grain shapes to metaquartzite with granoblastic texture. Metamorphosed sedimentary formations, including quartzites, marbles, calcsilicates and schists, became ductile and strongly attenuated in the aureole during growth of the magma chamber. The microstructures of quartzites have an unusual distribution in that within ~250 m from the pluton, where temperatures exceeded 650 °C, they exhibit relict sedimentary grain shapes, only small amount of grain boundary migration (GBM), and crystallographic preferred orientations (CPOs) dominated by <a> slip. At distances >250 m, quartzites were completely recrystallized by GBM and CPOs are indicative of prism [c] slip, characteristics that are typically associated with H₂O‐assisted, high‐T recrystallization. The lack of extensive GBM in the inner aureole can be attributed to rapid replacement of H₂O by CO₂ produced by reaction of quartz grains with calcite cement that also produced interstitial wollastonite. Fluid inclusions in the inner aureole generally occur in margins of quartz grains and are either wholly aqueous (Type 1) or also contain H₂S, CO₂ and CH₄ (Type 2). Type 2 inclusions occur only in some stratigraphic layers. In both inclusion types, NaCl and CaCl₂, in variable proportions, dominate the solutes in the aqueous phase, whereas FeCl₂ and KCl are less abundant solutes. The solutes indicate attainment of a degree of equilibrium with carbonates and schists that are interbedded with the quartzites. Some Types 1 and 2 inclusions in the inner aureole show evidence of decrepitation due to high amounts of strain and/or heating suffered by the host rocks, which suggests that they represent pore fluids that existed in the rocks prior to contact metamorphism. In addition to Type 1 inclusions, outer aureole quartzites also contain inclusions that contain CO₂ vapour bubbles in addition to aqueous phase (Type 3). These inclusions only occur in interiors of granoblastic quartz that was produced by large amounts of GBM. The aqueous phase has identical ranges of first melting and final ice melting temperatures as Type 1 inclusions, suggesting that they have the same solute compositions. These inclusions are thought to represent the interstitial pore H₂O that promoted recrystallization of quartz and reacted with graphite to produce CO₂. Absence of significant amounts of CH₄ in Type 3 inclusions is attributed to elevated fO₂ that was buffered by mineral assemblages in interbedded schists. As opposed to the large amount of CO₂ that was produced by the wollastonite‐forming reaction in the inner aureole to inhibit GBM, the amount of CO₂ produced in the outer aureole by reaction between H₂O and graphite was apparently insufficient to inhibit recrystallization of quartz.     

Evaluation of various relationships of reaeration rate coefficient for modeling dissolved oxygen in a river with extreme flow variations in Pakistan

Mathematical relationships have been developed for reaeration rate coefficient (K_a) by various researchers. These relationships have a number of variables such as depth, velocity, width, slope, Froud number, molecular diffusion coefficient, kinematic viscosity and the gas‐transfer Reynolds number. From these variables, 29 relations have been developed and divided into four groups. To evaluate their predictive capability for highly variable flow rivers receiving high pollution loads form large cities, these relationships have been used to model dissolved oxygen (DO) in the River Ravi. Such rivers are either saturated with DO during high flows or anaerobic during critical low‐flow conditions. The evaluation is based on the agreement between model DO values calculated using K_a obtained from the available equations and the measured DO concentrations in the river samples in terms of sum of square of residuals (SSR) and coefficient of determination (R²). It has been found that in general, the group of equations containing depth and velocity as the only two variables affecting K_a performed better than the equations in other groups as reflected by lower SSR and higher R² values. The study results also reveal that the turbulence‐based reaeration rate coefficient equation containing additional variables also resulted in close agreement between DO model results and the measured values. The study results identify the most important parameters affecting the reaeration rate coefficient and the suitability of various K_a relationships as well for rivers with highly variable flows. Copyright © 2012 John Wiley & Sons, Ltd.     

Precipitation stable isotope variability and subcloud evaporation processes in a semi‐arid region

The stable isotopic (²H/¹H and ¹⁸O/¹⁶O) composition of precipitation has been used for a variety of hydrological and paleoclimate studies, a starting point for which is the behaviour of stable isotopes in modern precipitation. To this end, daily precipitation samples were collected over a 7‐year period (2008–2014) at a semi‐arid site located at the Macquarie Marshes, New South Wales (Australia). The samples were analysed for stable isotope composition, and factors affecting the isotopic variability were investigated. The best correlation between δ ¹⁸O of precipitation was with local surface relative humidity. The reduced major axis precipitation weighted local meteoric water line was δ ²H = 7.20 δ ¹⁸O + 9.1. The lower slope and intercept (when compared with the Global Meteoric Water Line) are typical for a warm dry climate, where subcloud evaporation of raindrops is experienced. A previously published model to estimate the degree of subcloud evaporation and the subsequent isotopic modification of raindrops was enhanced to include the vertical temperature and humidity profile. The modelled results for raindrops of 1.0 mm radius showed that on average, the measured D‐excess (=δ ²H ? 8 δ ¹⁸O) was 19.8‰ lower than that at the base of the cloud, and 18% of the moisture was evaporated before ground level (smaller effects were modelled for larger raindrops). After estimating the isotopic signature at the base of the cloud, a number of data points still plotted below the global meteoric water line, suggesting that some of the moisture was sourced from previously evaporated water. Back trajectory analysis estimated that 38% of the moisture was sourced over land. Precipitation samples for which a larger proportion of the moisture was sourced over land were ¹⁸O and ²H‐enriched in comparison to samples for which the majority of the moisture was sourced over the ocean. The most common weather systems resulting in precipitation were inland trough systems; however, only East Coast Lows contributed to a significant difference in the isotopic values. Copyright © 2016 Australian Nuclear Science and Technology Organisation. Hydrological Processes. © 2016 John Wiley & Sons, Ltd.