Evaluating the S-isotope fractionation associated with Phanerozoic pyrite burial     

Nanping Wu  Harald Strauss  Donald E. Canfield 《Geochimica et cosmochimica acta》2010,74(7):2053-1124

This study examines the sulfur isotope record of seawater sulfate proxies using δ³⁴S and Δ³³S to place constraints on the average global fractionation (Δ³⁴S_py) associated with pyrite formation and burial and the exponent λ that relates variations of the ³⁴S/³²S to variations of the ³³S/³²S. The results presented here use an analysis of the sulfur isotope record from seawater sulfate proxies and sedimentary sulfide to extract this quantity as the arithmetic difference between δ³⁴S of seawater sulfate and contemporaneous sulfide. It also uses an independent method that draws on inferences about the Δ³³S evolution of seawater sulfate to evaluate this further. These two methods yield similar results suggesting that Δ³⁴S_py and λ changed over the course of the Phanerozoic from slightly lower values of Δ³⁴S_py (lower values of λ) in the early Phanerozoic (Cambrian-Permian) to higher values of Δ³⁴S_py (higher values of λ) starting in the Triassic. This change of Δ³⁴S_py and the exponent λ is interpreted to reflect a change in the proportion of sulfide that was reoxidized and processed by bacterial disproportionation on a global scale. The revised record of Δ³⁴S_py also yields model pyrite burial curves making them more closely resemble model evolution curves for other element systems and global sea level curves. It is suggested that possible links to sea level may occur via changes in the area of submerged continental shelves which would provide additional loci for pyrite burial.The slightly different constraints used by the two approaches to calculate this fractionation may allow for additional information to be obtained about the sulfur cycle with future studies. For instance, the correspondence of these results suggests that the inferred variation of ³⁴S/³²S of pyrite is real, and that there is no significant missing sink of fractionated sulfur at the resolution of the present study (such as might be associated with organic sulfur). Burial of organic sulfur may, however, have been important at some times in the Phanerozoic and shorter timescale deviations between results provided by these methods may be observed with higher resolution sampling. If observed, this would suggest either that the record for pyrite (or less likely sulfate) is biased, or that another sink (possibly as organic sulfur) was important during these times in the Phanerozoic.  相似文献   

The photochemical model of Titan’s atmosphere and ionosphere: A version without hydrodynamic escape     

Vladimir A. Krasnopolsky 《Planetary and Space Science》2010,58(12):1507-1515

There are observational and theoretical evidences both in favor of and against hydrodynamic escape (HDE) on Titan, and the problem remains unsolved. A test presented here for a static thermosphere does not support HDE on Titan and Triton but favors HDE on Pluto. Cooling of the atmosphere by the HCN rotational lines is limited by rotational relaxation above 1100 km and self-absorption below 900 km on Titan. HDE can affect the structure and composition of the atmosphere and its evolution. Hydrocarbon, nitrile, and ion chemistries are strongly coupled on Titan, and attempts to calculate them separately may result in significant errors. Here we apply our photochemical model of Titan’s atmosphere and ionosphere to the case of no hydrodynamic escape. Our model is still the only after-Cassini self-consistent model of coupled neutral and ion chemistry. The lack of HDE is a distinct possibility, and comparing models with and without HDE is of practical interest. The mean difference between the models and the neutral and ion compositions observed by INMS are somewhat better for the model with HDE. A reaction of NH₂ with H₂CN suggested by Yelle et al. (2009) reduces but does not remove a significant difference between the ammonia abundances in the models and INMS observations. Losses of methane and nitrogen and production and deposition to the surface of hydrocarbons and nitriles are evaluated in the model, along with lifetimes and evolutionary aspects.  相似文献   

New evidence of orographic precipitation suppression by aerosols in central China   总被引：1，自引：0，他引：1  

Xin Yang  Marion Ferrat  Zhanqing Li 《Meteorology and Atmospheric Physics》2013,119(1-2):17-29

The correlation between light precipitation events and visibility at Mt. Hua, (Shannxi Province, China) and at the surrounding plains stations was analyzed. Trends and changes in visibility, precipitation, the precipitation difference between Mt. Hua and the plains stations (De) and wind speed over the study area during the years 1980–2009 were also investigated. The significant positive correlation between visibility and light precipitation throughout the study period indicates that light precipitation events, notably orographic precipitation, are suppressed by aerosol pollution in this region. The trend of increasing air pollution aerosols since 1980, represented by visibility at Mt. Hua, ended in 2002 with a decreasing trend observed in more recent years. These changes were mirrored by corresponding changes in De. However, the total precipitation trends at Mt. Hua and the plains stations are consistent in both frequency and amount during the two periods, suggesting that the suppressive effect of pollution aerosols on light and moderate precipitation is the most likely cause for the changes in orographic precipitation at Mt. Hua during this time. The analysis of wind strength suggests that the increase in winds at Mt. Hua is highly related to the aerosol radiative effects; this increase of mountain winds is therefore a potential cause for the reduction in precipitation at Mt. Hua. This research provides further support for the hypothesis that aerosol microphysical effects can reduce orographic precipitation and suggests that aerosol radiative effects might act to suppress orographic precipitation through changes in wind speed.  相似文献   

Cloud-Aerosol-Radiation (CAR) ensemble modeling system: Overall accuracy and efficiency     

曾庆存 《大气科学进展》2013,30(4):955-973

The Cloud-Aerosol-Radiation (CAR) ensemble modeling system has recently been built to better understand cloud/aerosol/radiation processes and determine the uncertainties caused by different treatments of cloud/aerosol/radiation in climate models. The CAR system comprises a large scheme collection of cloud, aerosol, and radiation processes available in the literature, including those commonly used by the world's leading GCMs. In this study, detailed analyses of the overall accuracy and efficiency of the CAR system were performed. Despite the different observations used, the overall accuracies of the CAR ensemble means were found to be very good for both shortwave (SW) and longwave (LW) radiation calculations. Taking the percentage errors for July 2004 compared to ISCCP (International Satellite Cloud Climatology Project) data over (60°N, 60°S) as an example, even among the 448 CAR members selected here, those errors of the CAR ensemble means were only about-0.67% (-0.6 W m-2 ) and-0.82% (-2.0 W m-2 ) for SW and LW upward fluxes at the top of atmosphere, and 0.06% (0.1 W m-2 ) and -2.12% (-7.8 W m-2 ) for SW and LW downward fluxes at the surface, respectively. Furthermore, model SW frequency distributions in July 2004 covered the observational ranges entirely, with ensemble means located in the middle of the ranges. Moreover, it was found that the accuracy of radiative transfer calculations can be significantly enhanced by using certain combinations of cloud schemes for the cloud cover fraction, particle effective size, water path, and optical properties, along with better explicit treatments for unresolved cloud structures.  相似文献   

The impact of the MJO on clusters of wintertime circulation anomalies over the North American region   总被引：3，自引：2，他引：1  

Emily E. Riddle  Marshall B. Stoner  Nathaniel C. Johnson  Michelle L. L’Heureux  Dan C. Collins  Steven B. Feldstein 《Climate Dynamics》2013,40(7-8):1749-1766

Recent studies have shown that the Madden–Julian Oscillation (MJO) impacts the leading modes of intraseasonal variability in the northern hemisphere extratropics, providing a possible source of predictive skill over North America at intraseasonal timescales. We find that a k-means cluster analysis of mid-level geopotential height anomalies over the North American region identifies several wintertime cluster patterns whose probabilities are strongly modulated during and after MJO events, particularly during certain phases of the El Niño-Southern Oscillation (ENSO). We use a simple new optimization method for determining the number of clusters, k, and show that it results in a set of clusters which are robust to changes in the domain or time period examined. Several of the resulting cluster patterns resemble linear combinations of the Arctic Oscillation (AO) and the Pacific/North American (PNA) teleconnection pattern, but show even stronger responses to the MJO and ENSO than clusters based on the AO and PNA alone. A cluster resembling the positive (negative) PNA has elevated probabilities approximately 8–14 days following phase 6 (phase 3) of the MJO, while a negative AO-like cluster has elevated probabilities 10–20 days following phase 7 of the MJO. The observed relationships are relatively well reproduced in the 11-year daily reforecast dataset from the National Centers for Environmental Prediction (NCEP) Climate Forecast System version 2 (CFSv2). This study statistically links MJO activity in the tropics to common intraseasonal circulation anomalies over the North American sector, establishing a framework that may be useful for improving extended range forecasts over this region.  相似文献   

EU 20-20-20 energy policy as a model for global climate mitigation     

Katherine Calvin  Bjorn Bakken  Marshall Wise  Sonny Kim  Patrick Luckow 《Climate Policy》2013,13(5):581-598

The EU has established an aggressive portfolio with explicit near-term targets for 2020 – to reduce GHG emissions by 20%, rising to 30% if the conditions are right, to increase the share of renewable energy to 20%, and to make a 20% improvement in energy efficiency – intended to be the first step in a long-term strategy to limit climate forcing. The effectiveness and cost of extending these measures in time are considered along with the ambition and propagation to the rest of the world. Numerical results are reported and analysed for the contribution of the portfolio's various elements through a set of sensitivity experiments. It is found that the hypothetical programme leads to very substantial reductions in GHG emissions, dramatic increases in use of electricity, and substantial changes in land-use including reduced deforestation, but at the expense of higher food prices. The GHG emissions reductions are driven primarily by the direct limits. Although the carbon price is lower under the hypothetical protocol than it would be under the emissions cap alone, the economic cost of the portfolio is higher, between 13% and 22%.  相似文献   

2015—2017年夏季南京雨滴谱特征          下载免费PDF全文

梅海霞  梁信忠  曾明剑  李力  祖繁  李玉涛 《应用气象学报》2020,31(1):117-128

利用2015—2017年夏季南京地区的雨滴谱数据,对南京在梅雨开始前、梅雨期及梅雨结束后3个不同时段降水的宏微观特征进行分析发现:梅雨开始前对流活动强度偏弱,但对流降水的雨滴平均质量加权直径、分钟级强降水频率和逐小时累积短时强降水的频率为3个时段中最高;天气尺度强迫提供的有利于降水的持续性条件、弱对流强度下充分的凝结过程及微物理相关过程对云粒子的损耗偏弱,是有利于该时段大雨滴形成和降水效率提高的重要因素。梅雨结束后,高温高湿环境易产生剧烈对流活动,导致对流降水的大尺度雨滴样本比例及分钟级极端降水发生频率位于3个时段的首位。层云降水时,梅雨期降水频率、降水率及雨滴尺度平均值均位于首位,小尺度雨滴样本比例最低;有利天气尺度强迫条件下的充分碰并作用是主要原因之一。不同时段雨滴谱谱形参数（μ）与斜率（Λ）之间的二项式关系式的差异与μ的取值有关。  相似文献   

通过影响高度多路径质量控制改进热带对流层低层GPS掩星资料同化效果          下载免费PDF全文

邹晓蕾  刘辉 《大气科学学报》2020,43(1):116-127

与观测气象、电离层和气候的GPS卫星计划COSMIC-1相比,COSMIC-2有更大功率的GPS接收天线,高2倍的采样率(100 Hz),小3倍的轨道倾角(24°)。因此,COSMIC-2和未来小卫星将为热带地区提供前所未有的大量无线电掩星观测资料。因为热带对流层低层水汽含量高,折射率有局地大梯度,违背大气球对称性假定,造成影响多路径现象,所以热带地区的掩星资料同化具有较大挑战性。本文首先利用之前研究中提出的影响参数多路径质量控制方法,去除热带对流层低层弯角模拟中出现影响参数多路径现象的资料,然后使用有限射线长度二维(2D)路径追踪观测算子和一维(1D)Abel变换观测算子,进行GPS弯角资料同化。结果表明,如果射线路径限制在离近地面点±300~400 km的水平距离以内,有限射线长度2D路径追踪观测算子得到的弯角模拟与2D射线追踪观测算子得到的弯角廓线之差不仅无偏,而且其标准差远比1D Abel的弯角模拟精度高。此外,无论采用1D Abel变换还是有限射线长度2D路径追踪观测算子来模拟弯角,影响参数多路径质量控制方案都能进一步改进GPS掩星弯角资料同化和预报精度。  相似文献   

Satellite altimeter observations of nonlinear Rossby eddy–Kuroshio interaction at the Luzon Strait     

Quanan Zheng  Chang-Kuo Tai  Jianyu Hu  Hongyang Lin  Rong-Hua Zhang  Feng-Chun Su  Xiaofeng Yang 《Journal of Oceanography》2011,67(4):365-376

Satellite altimeter sea level data from 1993 to 2008 are used to analyze the interaction of nonlinear Rossby eddies with the Kuroshio at the Luzon Strait (LS). The sea level anomaly data show that the west Pacific (WP) is a source of nonlinear Rossby eddies, and the South China Sea (SCS) is a sink. The LS serves as a gateway between the two. The scale analysis indicates that eddies with a radius larger than 150 km are strong enough to significantly alter the Kuroshio and are able to modify the local circulation pattern. Statistical analysis indicates that the probability for eddies to penetrate through the Kuroshio may reach at least 60%. A case study of an anticyclonic mesoscale eddy passing through the LS in June–July 2004 indicates that the Kuroshio behaves as an unsteady flow with its stream path frequently modified, in a way of cutting off, meandering and branching during its interaction with the eddy. We therefore suggest that nonlinear Rossby eddies may play a significant role in modification of the local circulation system near the LS and in exchanges of the mass, momentum and energy between the WP and the SCS.  相似文献   

Binary near-Earth asteroid formation: Rubble pile model of tidal disruptions     

Kevin J. Walsh  Derek C. Richardson 《Icarus》2006,180(1):201-216

We present numerical simulations of near-Earth asteroid (NEA) tidal disruption resulting in bound, mutually orbiting systems. Using a rubble pile model we have constrained the relative likelihoods for possible physical and dynamical properties of the binaries created. Overall 110,500 simulations were run, with each body consisting of ∼1000 particles. The encounter parameters of close approach distance and velocity were varied, as were the bodies' spin, elongation and spin axis direction. The binary production rate increases for closer encounters, at lower speeds, for more elongated bodies, and for bodies with greater spin. The semimajor axes for resultant binaries are peaked between 5 to 20 primary radii, and there is an overall trend for high eccentricity, with 97% of binaries having e > 0.1. The secondary-to-primary size ratios of the simulated binaries are peaked between 0.1 and 0.2, similar to trends among observed asteroid binaries. The spin rates of the primary bodies are narrowly distributed between 3.5- and 6-h periods, whereas the secondaries' periods are more evenly distributed and can exceed 15-h periods. The spin axes of the primary bodies are very closely aligned with the angular momenta of the binary orbits, whereas the secondary spin axes are nearly random. The shapes of the primaries show a large distribution of axis ratios, where those with low elongation (ratio of long and short axis) are both oblate and prolate, and nearly all with large elongation are prolate. This work presents results that suggest tidal disruption of gravitational aggregates can make binaries physically similar to those currently observed in the NEA population. As well, tidal disruption may create an equal number of binaries with qualities different from those observed, mostly binaries with large separation and with elongated primaries.  相似文献