Improving the assessment and valuation of climate change impacts for policy and regulatory analysis     

Alex L. Marten  Robert E. Kopp  Kate C. Shouse  Charles W. Griffiths  Elke L. Hodson  Elizabeth Kopits  Bryan K. Mignone  Chris Moore  Steve C. Newbold  Stephanie Waldhoff  Ann Wolverton 《Climatic change》2013,117(3):433-438

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Figure rotation of dark haloes in cold dark matter simulations     

S. E. Bryan  C. M. Cress 《Monthly notices of the Royal Astronomical Society》2007,380(2):657-664

We investigate the figure rotation of dark matter haloes identified in Λ cold dark matter (CDM) simulations. We find that when strict criteria are used to select suitable haloes for study, five of the 222 haloes identified in our   z = 0  simulation output undergo coherent figure rotation over a  5 h ⁻¹ Gyr  period. We discuss the effects of varying the selection criteria and find that pattern speeds for a much larger fraction of the haloes can be measured when the criteria are relaxed. Pattern speeds measured over a  1 h ⁻¹ Gyr  period follow a lognormal distribution, centred at  Ω_p= 0.2 h rad Gyr⁻¹  with a maximum value of 0.94 h rad Gyr⁻¹. Over a  5 h ⁻¹ Gyr  period, the average pattern speed of a halo is about  0.1 h rad Gyr⁻¹  and the largest pattern speed found is  0.24 h rad Gyr⁻¹  . Less than half of the selected haloes showed alignment between their figure rotation axis and minor axis, the exact fraction being somewhat dependent on how one defines a halo. While the pattern speeds observed are lower than those generally thought capable of causing spiral structure, we note that coherent figure rotation is found over very long periods and argue that further simulations would be required before strong conclusions about spiral structure in all galaxies could be drawn. We find no correlation between halo properties such as total mass and the pattern speed.  相似文献   

Towards simulating star formation in the interstellar medium     

Adrianne D. Slyz  Julien E. G. Devriendt  Greg Bryan  Joseph Silk 《Monthly notices of the Royal Astronomical Society》2005,356(2):737-752

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Elevated stream trace and minor element concentrations in the foreland of receding tropical glaciers   总被引：1，自引：0，他引：1  

Sarah K. Fortner  Bryan G. MarkJeffrey M. McKenzie  Jeffrey BuryAnnette Trierweiler  Michel BaraerPatrick J. Burns  LeeAnn Munk 《Applied Geochemistry》2011,26(11):1792-1801

Globally, the ongoing retreat of mountain glaciers will ultimately diminish fresh water supplies. This has already begun in watersheds with greatly reduced glacial coverage. Still unknown are the affects of glacial retreat on downstream water quality, including the threats to human and ecosystem health. In the Cordillera Blanca, retreating glaciers have exposed sulfide-rich rock outcrops, negatively affecting the quality of the glacial meltwater. This study has evaluated glacial melt stream hydrogeochemistry in the sulfide-bearing Rio Quilcay watershed (∼9°27′S, ∼77°22′W) during the 2008 dry season. Surface water samples were collected from the upper 12 km of the watershed during the 2008 dry season. Dissolved (0.4 μm) and unfiltered acidified (pH < 2) Al, Co, Cu, Fe, Ni, Mn, Pb, Zn and dissolved major ions and organic C (DOC) concentrations were quantified and pH and temperature were measured in the field. Twenty of 22 stream samples had pH values below 4, generating significantly (p < 0.01, α = 0.05) greater cation denudation normalized to discharge than other worldwide glacier-fed streams. Additionally, dissolved trace and minor element concentrations were comparable to acid mine drainage. Non-conservative dissolved element behaviors resulted from adsorption/desorption reactions in tributary mixing zones. At low pH values, hydrous Fe oxides acted as the dominant sorption surfaces. The poor water quality observed in Cordillera Blanca headwaters coupled with the likely exposure of additional sulfide-rich outcrops from ongoing glacial retreat may pose water quality challenges.  相似文献   

Cyclic sedimentation in the Permian coal measures of New South Wales     

S. E. Bryan  R. J. Holcombe  C. R. Fielding 《Australian Journal of Earth Sciences》2013,60(2):293-316

Statistical analysis of borehole sections through the Illawarra and Newcastle Coal Measures of the Sydney Basin shows that cyclic sedimentation is present. The composite sequence for the Southern Coalfield (Illawarra Coal Measures) is (in ascending order): sandstone—sandstone/siltstone alternations—shale—coal, whereas that for the Newcastle Coalfield is: shale—sandstone/siltstone alternations—sandstone, often conglomeratic, or conglomerate—sandstone/siltstone alternations—shale —coal.

The environment of deposition is discussed. It is suggested that in the Southern Coalfield cyclicity is due to sedimentational processes inherent in the deltaic and alluvial conditions envisaged during Permian times. Periodic influxes of glacial meltwaters, although not essential, are not ruled out.

In the Newcastle Coalfield, however, the composite sequence does not match easily the ideal cycles expected in deltaic and/or alluvial regimes. Contemporary volcanism and tectonism complicated matters and lack of sedimentological details makes it impossible at present to give preference to any one mechanism of cycle formation.  相似文献   

Contact metamorphism of pelitic,psammitic and calcareous sediments in the Southern Highlands of New South Wales     

Bryan E. Chenhall  Brian G. Jones  Paul F. Carr 《Australian Journal of Earth Sciences》2013,60(3):389-401

Contact metamorphism has been recognized along a 4 km wide belt adjacent to the shallow‐dipping eastern margin of the Arthursleigh Tonalite, an Early Devonian pluton of the Marulan Batholith, eastern New South Wales. In Ordovician psammitic and pelitic rocks three zones of progressive contact metamorphism range from muscovite + biotite + chlorite assemblages in the outer zone to K‐feldspar + cordierite assemblages adjacent to the pluton and in metasedimentary xenoliths. Retrograde phenomena include extensive replacement of metamorphic minerals by ‘sericite’ and chlorite. Calcareous metasediments adjacent to the tonalite typically contain assemblages of quartz + calcic plagioclase + ferrosalite + sphene, or wollastonite + calcite + diopside with minor grossularite and vesuvianite. Thermal effects in volcanic rocks along the western margin of the pluton are confined to recrystallization of the groundmass.

The regional geology indicates confining pressures of approximately 1 kbar at the time of emplacement of the tonalite. Contact metamorphic temperatures were estimated from two‐feldspar geothermometry to attain a maximum of approximately 590°C for rocks in the innermost zone of the aureole and 700°C for the xenoliths. Fluid compositions attending progressive contact metamorphism were water‐rich (Xco₂<0.2) and, during cooling, these fluids probably account for the extensive retrograde hydration observed in the aureole.  相似文献   

Calibrating a neural network‐based urban change model for two metropolitan areas of the Upper Midwest of the United States     

Bryan C. Pijanowski Corresponding author  Snehal Pithadia  Bradley A. Shellito  Konstantinos Alexandridis 《International journal of geographical information science》2013,27(2):197-215

We parameterized neural net‐based models for the Detroit and Twin Cities metropolitan areas in the US and attempted to test whether they were transferable across both metropolitan areas. Three different types of models were developed. First, we trained and tested the neural nets within each region and compared them against observed change. Second, we used the training weights from one area and applied them to the other. Third, we selected a small subset (～1%) of the Twin Cities area where a lot of urban change occurred. Four model performance metrics are reported: (1) Kappa; (2) the scale which correct and paired omission/commission errors exceed 50%; (3) landscape pattern metrics; and (4) percentage of cells in agreement between model simulations. We found that the neural net model in most cases performed well on pattern but not location using Kappa. The model performed well only in one case where the neural net weights from one area were used to simulate the other. We suggest that landscape metrics are good to judge model performance of land use change models but that Kappa might not be reliable for situations where a small percentage of urban areas change.  相似文献   

Constrained age of Glacial Lake Narragansett and the deglacial chronology of the Laurentide Ice Sheet in southeastern New England     

Bryan A. Oakley  Jon C. Boothroyd 《Journal of Paleolimnology》2013,50(3):305-317

The lack of radiocarbon ages and correlated varve sequences in southeastern New England has left the deglacial chronology of the region poorly constrained. A 265-year varve series from Glacial Lake Narragansett was constructed from eight continuous sediment cores collected from the Providence River, Narragansett Bay, Rhode Island. This varve series could not be correlated with either the North American Varve Chronology or other varve sequences from southern New England or southeastern New York. The uncorrelated varve sequences presented here represent the minimum time of deposition within the northern segment of Glacial Lake Narragansett. These sequences, used in conjunction with the calibrated North American Varve Chronology and cosmogenic exposure ages from recessional end moraines, provide minimum (>19,400 cal BP) and maximum (<20,500 cal BP) ages for Glacial Lake Narragansett. Correlations with the updated Greenland (NGRIP and GRIP) ice core records suggest that cold periods associated with moraine formation are 200–250 years older than the cosmogenic exposure ages. Whereas many studies refer to the last glacial maximum occurring from 20,000 to 18,000 cal BP, the constrained age of Glacial Lake Narragansett suggests that at least for the southeastern portion of the Laurentide Ice Sheet, deglaciation was well underway by this time.  相似文献   

Leveraging ensemble meteorological forcing data to improve parameter estimation of hydrologic models     

Hongli Liu  Bryan A. Tolson  Andrew J. Newman  Andrew W. Wood 《水文研究》2021,35(11):e14410

As continental to global scale high-resolution meteorological datasets continue to be developed, there are sufficient meteorological datasets available now for modellers to construct a historical forcing ensemble. The forcing ensemble can be a collection of multiple deterministic meteorological datasets or come from an ensemble meteorological dataset. In hydrological model calibration, the forcing ensemble can be used to represent forcing data uncertainty. This study examines the potential of using the forcing ensemble to identify more robust parameters through model calibration. Specifically, we compare an ensemble forcing-based calibration with two deterministic forcing-based calibrations and investigate their flow simulation and parameter estimation properties and the ability to resist poor-quality forcings. The comparison experiment is conducted with a six-parameter hydrological model for 30 synthetic studies and 20 real data studies to provide a better assessment of the average performance of the deterministic and ensemble forcing-based calibrations. Results show that the ensemble forcing-based calibration generates parameter estimates that are less biased and have higher frequency of covering the true parameter values than the deterministic forcing-based calibration does. Using a forcing ensemble in model calibration reduces the risk of inaccurate flow simulation caused by poor-quality meteorological inputs, and improves the reliability and overall simulation skill of ensemble simulation results. The poor-quality meteorological inputs can be effectively filtered out via our ensemble forcing-based calibration methodology and thus discarded in any post-calibration model applications. The proposed ensemble forcing-based calibration method can be considered as a more generalized framework to include parameter and forcing uncertainties in model calibration.  相似文献   

Local variability in temperature, humidity and radiation in the BaekduDaegan Mountain protected area of Korea   总被引：1，自引：1，他引：0  

CHAE Heemun  LEE Hyunju  LEE Sangsin  CHEONG Yukyong  UM Gijeung  MARK Bryan  PATRICK Nathan 《山地科学学报》2012,9(5):613-627

A novel embedded sensor network records changes in key climatic-environmental variables over a range of altitude in the BaekduDaegan Mountain (BDM) of Gangwon Province in Korea, a protected mountain region with unique biodiversity undergoing climate change research. The investigated area is subdivided into three horizontal north-south study areas. Three variables, temperature (T, ℃), relative humidity (RH, %), and light intensity (LI, lumens m -2 , or lux, lx), have been continuously measured at hourly intervals from June, 2010 to September, 2011 using HOBO H8 devices at 10 fixed study sites. These hourly observations are aggregated to monthly, seasonal and annual mean values, and results are summarized to inaugurate a long-term climate change investigation. A region wide T difference in accordance with altitude, or lapse rate, over the interval is calculated as 0.4℃100 m -1 . T lapse rates change seasonally, with winter lapse rates being greater than those of summer. RH is elevated in summer compared to other seasons. LI within forestland is lower during summer and higher during other seasons. The obtained results could closely relate to the vegetation type and structure and the terrain state since data loggers were located in forestland.  相似文献