Activity-composition relations in the system CaCO₃-MgCO₃ predicted from static structure energy calculations and Monte Carlo simulations     

Victor L. Vinograd  Benjamin P. Burton  Neil L. Allan 《Geochimica et cosmochimica acta》2007,71(4):974-983

Thermodynamic mixing properties and subsolidus phase relations of the rhombohedral carbonate system, (1 − x) · CaCO₃ − x · MgCO₃, were modelled in the temperature range of 623-2023 K with static structure energy calculations based on well-parameterised empirical interatomic potentials. Relaxed static structure energies of a large set of randomly varied structures in a 4 × 4 × 1 supercell of calcite (a = 19.952 Å, c = 17.061 Å) were calculated with the General Utility Lattice Program (GULP). These energies were cluster expanded in a basis set of 12 pair-wise effective interactions. Temperature-dependent enthalpies of mixing were calculated by the Monte Carlo method. Free energies of mixing were obtained by thermodynamic integration of the Monte Carlo results. The calculated phase diagram is in good agreement with experimental phase boundaries.  相似文献   

Simulated effects of land immersion on regional arid climate: a case study of the pre-Saharan playa of Chott el-Jerid (south of Tunisia)     

Bilel Fathalli  Thierry Castel  Benjamin Pohl 《Theoretical and Applied Climatology》2020,140(1):231-250

The potential effects on the regional climate induced by partially immersing the arid pre-Saharan playa basin of Chott el-Jerid (south of Tunisia) are investigated by comparing two multi-year (1991–2011) sets of numerical simulations each consisting of ten-member ensemble and performed using the WRF regional climate model. The first WRF ensemble is performed under current land use and land cover, while the second is carried out after introducing a virtual large and shallow surface water reservoir (a lake) in Chott el-Jerid. The most pronounced effects generated by the artificial lake are circumscribed over its surface and slightly spread downwind to the other parts of the Chott. The lake has a clear moderating effect on near-surface air temperatures by increasing (decreasing) the wintertime (summertime) air temperatures. Sensible heat fluxes are remarkably increased in winter and decreased in summer over the lake following the temperature gradient between the lake surface and the overlying atmosphere. Latent heat fluxes, moisture convergence, and water vapor mixing ratio are increased over the lake throughout the year, especially in winter. The lake also induces domain-wide decreased (increased) surface pressures and land (lake) breeze circulation in winter (summer). Simulated rainfall amounts are most increased over the lake in winter likely because of an enhanced atmospheric instability, while they slightly decrease in summer.  相似文献   

Correction to: Simulated effects of land immersion on regional arid climate: a case study of the pre-Saharan playa of Chott el-Jerid (South of Tunisia)     

Fathalli  Bilel  Castel  Thierry  Pohl  Benjamin 《Theoretical and Applied Climatology》2020,140(1):251-251

Theoretical and Applied Climatology - In the original article, the last panel of Fig. 10 should be labeled “h”. Also some data and Table 2 caption were unfortunately incorrect.  相似文献   

Hiatus of wetland methane emissions associated with recent La Niña episodes in the Asian monsoon region     

Xiaoyan Zhang  Xiyan Xu  Gensuo Jia  Benjamin Poulter  Zhen Zhang 《Climate Dynamics》2020,54(9):4095-4107

The variability of methane emissions from wetlands in the tropics and northern temperate regions can explain more than 70% of the interannual variation in global wetland methane emissions, which are largely driven by climate variability. We use climate reanalysis, remote sensing wetland area dataset and simulations from 11 land models contributing to Global Methane Budget to investigate the interannual variation and anomalies of wetland methane emissions in the Asian Monsoon region. Methane emissions in this region steadily increased over 2000–2012. However, abnormally low methane emissions were found in equatorial fully humid (Af), warm temperate winter dry (Cw), and warm temperate fully humid (Cf) Asian Monsoon climate sub-regions in 2008, 2009 and 2011, respectively. These spatially-shifting low emissions occurred simultaneously with observed wetland area shrinkage due to abnormally low precipitation. Interannual variability of wetland methane emissions in Asian Monsoon region are primarily driven by South Asian Monsoon system. However, the abnormally low emissions are related to strong La Niña events, and its accompanying effect of weakened East Asian Monsoon system and eastward Western Pacific subtropical high, which drives the shifting pattern of rainfall, and thus the spatial pattern of methane emission anomalies.  相似文献   

Downscaling large-scale climate variability using a regional climate model: the case of ENSO over Southern Africa   总被引：1，自引：1，他引：0  

Damien Boulard  Benjamin Pohl  Julien Crétat  Nicolas Vigaud  Thanh Pham-Xuan 《Climate Dynamics》2013,40(5-6):1141-1168

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Heat waves in the United States: definitions, patterns and trends   总被引：3，自引：0，他引：3  

Tiffany T. Smith  Benjamin F. Zaitchik  Julia M. Gohlke 《Climatic change》2013,118(3-4):811-825

High temperatures and heat waves are related but not synonymous concepts. Heat waves, generally understood to be acute periods of extreme warmth, are relevant to a wide range of stakeholders because of the impacts that these events have on human health and activities and on natural environments. Perhaps because of the diversity of communities engaged in heat wave monitoring and research, there is no single, standard definition of a heat wave. Experts differ in which threshold values (absolute versus relative), duration and ancillary variables to incorporate into heat wave definitions. While there is value in this diversity of perspectives, the lack of a unified index can cause confusion when discussing patterns, trends, and impacts. Here, we use data from the North American Land Data Assimilation System to examine patterns and trends in 15 previously published heat wave indices for the period 1979–2011 across the Continental United States. Over this period the Southeast region saw the highest number of heat wave days for the majority of indices considered. Positive trends (increases in number of heat wave days per year) were greatest in the Southeast and Great Plains regions, where more than 12 % of the land area experienced significant increases in the number of heat wave days per year for the majority of heat wave indices. Significant negative trends were relatively rare, but were found in portions of the Southwest, Northwest, and Great Plains.  相似文献   

Globalization,Pacific Islands,and the paradox of resilience   总被引：1，自引：0，他引：1  

Matthew Lauer  Simon Albert  Shankar Aswani  Benjamin S. Halpern  Luke Campanella  Douglas La Rose 《Global Environmental Change》2013,23(1):40-50

On April 2nd, 2007 a 12 m tsunami struck Simbo, a relatively remote island in Western Province, Solomon Islands. Although Simbo's population continues to depend on their own food production and small-scale governance regimes regulate access to resources, the island's way of life over the last century has increasingly been affected by processes associated with globalization. In this context of a rapidly globalizing world, this article examines the island's resilience and vulnerability to the tsunami and the adaptive capacities that enabled the response and recovery. The tsunami completely destroyed two villages and damaged fringing coral reefs, but casualties were low and social–ecological rebound relatively brisk. By combining social science methods (household surveys, focus group and ethnographic interviews) and underwater reef surveys we identify a number of countervailing challenges and opportunities presented by globalization that both nurture and suppress the island's resilience to high amplitude, low-frequency disturbances like tsunamis. Analysis suggests that certain adaptive capacities that sustain general system resilience come at the cost of more vulnerability to low-probability hazards. We discuss how communities undergoing increasingly complex processes of change must negotiate these kinds of trade-offs as they manage resilience at multiple spatial and temporal scales. Understanding the shifting dynamics of resilience may be critical for Pacific Island communities who seek to leverage globalization in their favor as they adapt to current social–ecological change and prepare for future large-scale ecological disturbances.  相似文献   

Is the Highest Cosmic-Ray Flux Yet to Come?     

R. D. Strauss  M. S. Potgieter 《Solar physics》2014,289(8):3197-3205

The recent 2009 solar-minimum period was characterized by a record-setting high Galactic cosmic-ray flux observed at Earth. This, along with the unexpected low heliospheric magnetic-field magnitude, caused this period to be characterized as unusual compared with previous minimum epochs. In this work, selected solar-activity proxies and corresponding cosmic-ray observations for the past five solar cycles are compared with each other, and we identify those that showed unusual behaviour during the 2009 solar-minimum modulation period. Using a state-of-the-art numerical-modulation model, the proton-intensity spectra for the past solar minima are reproduced to establish which of the transport processes might be considered the main cause of this unusually high cosmic-ray flux. It is found that diffusion was more prominent during 2009 so that drift effects on the modulation of cosmic rays in the heliosphere were less evident than during previous solar-polarity epochs. However, particle drifts still occurred and because of these drift effects, the proton spectrum is predicted to be even higher during the coming A>0 solar-minimum period.  相似文献   

First‐order exchange coefficient coupling for simulating surface water–groundwater interactions: parameter sensitivity and consistency with a physics‐based approach     

Brian A. Ebel  Benjamin B. Mirus  Christopher S. Heppner  Joel E. VanderKwaak  Keith Loague 《水文研究》2009,23(13):1949-1959

Distributed hydrologic models capable of simulating fully‐coupled surface water and groundwater flow are increasingly used to examine problems in the hydrologic sciences. Several techniques are currently available to couple the surface and subsurface; the two most frequently employed approaches are first‐order exchange coefficients (a.k.a., the surface conductance method) and enforced continuity of pressure and flux at the surface‐subsurface boundary condition. The effort reported here examines the parameter sensitivity of simulated hydrologic response for the first‐order exchange coefficients at a well‐characterized field site using the fully coupled Integrated Hydrology Model (InHM). This investigation demonstrates that the first‐order exchange coefficients can be selected such that the simulated hydrologic response is insensitive to the parameter choice, while simulation time is considerably reduced. Alternatively, the ability to choose a first‐order exchange coefficient that intentionally decouples the surface and subsurface facilitates concept‐development simulations to examine real‐world situations where the surface‐subsurface exchange is impaired. While the parameters comprising the first‐order exchange coefficient cannot be directly estimated or measured, the insensitivity of the simulated flow system to these parameters (when chosen appropriately) combined with the ability to mimic actual physical processes suggests that the first‐order exchange coefficient approach can be consistent with a physics‐based framework. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

Gaussianity of cosmic velocity fields and linearity of the velocity–gravity relation     

Pawe&#; Cieciel&#;g  Micha&#; J. Chodorowski  Marcin Kiraga  Michael A. Strauss  rzej Kudlicki  François R. Bouchet 《Monthly notices of the Royal Astronomical Society》2003,339(3):641-651

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