An AOGCM simulation of the climate response to a volcanic super-eruption   总被引：1，自引：0，他引：1  

Gareth S. Jones  Jonathan M. Gregory  Peter A. Stott  Simon F. B. Tett  Robert B. Thorpe 《Climate Dynamics》2005,25(7-8):725-738

Volcanic ‘super-eruptions’ have been suggested to have significantly influenced the Earth’s climate, perhaps causing glaciations and impacting on the human population. Climatic changes following a hypothetical ‘super-eruption’ are simulated using a coupled atmosphere ocean general circulation model, incorporating scaled volcanic stratospheric aerosols. Assumptions are made about the stratospheric sulphate aerosol loading, size distribution, lifetime, chemical make up and spatial distribution. As this study is concentrating on the physical climatological impacts over long timescales, microphysics and chemical interactive processes are not simulated. Near-surface temperatures fall by as much as 10 K globally for a few months and a considerable deviation from normal temperatures continues for several decades. A warming pattern is evident over northern land masses during the winter due to increased longwave forcing and a positive AO mode. The overturning rate of the North Atlantic thermohaline circulation doubles in intensity. Snow and ice increases in extent to a maximum coverage of 35% of the Earth. Despite these and other impacts longer term climatic changes that could lead to a transition to a glaciation do not occur, for present day boundary conditions and one possible plausible aerosol loading.  相似文献   

Real-Time River Level Monitoring Using GPS Heighting     

Terry Moore  Kefei Zhang  Gareth Close  Roger Moore 《GPS Solutions》2000,4(2):63-67

This paper presents the current progress of the River Level Monitoring using GPS Heighting (RiGHt) project. The aim of the project is to develop an integrated system to allow the continuous monitoring of river heights using a buoy equipped with Global Positioning System (GPS) and satellite communications and using Geographical Information System (GIS) techniques. ? 2000 John Wiley & Sons, Inc.  相似文献   

Response to Gardner et al.     

Gareth J. Williams  Ingrid S. Knapp  James E. Maragos  Simon K. Davy 《Marine pollution bulletin》2011,62(12):2878-2879

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The effect of impact obliquity on shock heating in planetesimal collisions     

Thomas M. Davison  Fred J. Ciesla  Gareth S. Collins  Dirk Elbeshausen 《Meteoritics & planetary science》2014,49(12):2252-2265

Collisions between planetesimals in the early solar system were a common and fundamental process. Most collisions occurred at an oblique incidence angle, yet the influence of impact angle on heating in collisions is not fully understood. We have conducted a series of shock physics simulations to quantify oblique heating processes, and find that both impact angle and target curvature are important in quantifying the amount of heating in a collision. We find an expression to estimate the heating in an oblique collision compared to that in a vertical incidence collision. We have used this expression to quantify heating in the Rhealsilvia‐forming impact on Vesta, and find that there is slightly more heating in a 45° impact than in a vertical impact. Finally, we apply these results to Monte Carlo simulations of collisional processes in the early solar system, and determine the overall effect of impact obliquity from the range of impacts that occurred on a meteorite parent body. For those bodies that survived 100 Myr without disruption, it is not necessary to account for the natural variation in impact angle, as the amount of heating was well approximated by a fixed impact angle of 45°. However, for disruptive impacts, this natural variation in impact angle should be accounted for, as around a quarter of bodies were globally heated by at least 100 K in a variable‐angle model, an order of magnitude higher than under an assumption of a fixed angle of 45°.  相似文献   

Hydrocode modeling of the Sierra Madera impact structure     

Tamara J. Goldin  Kai Wünnemann  H. Jay Melosh  Gareth S. Collins 《Meteoritics & planetary science》2006,41(12):1947-1958

Abstract— We present the first hydrocode simulations of the formation of the Sierra Madera structure (west Texas, USA), which was caused by an impact into a thick sedimentary target sequence. We modeled Sierra Madera using the iSALE hydrocode, and here we present two best‐fit models: 1) a crater with a rim (final crater) diameter of ?12 km, in agreement with previous authors' interpretations of the original structure, and 2) a crater ?16 km in diameter with increased postimpact erosion. Both models fit some of the geologic observational data, but discrepancies with estimates of peak shock pressure, extent of deformation, and stratigraphic displacement remain. This study suggests that Sierra Madera may be a larger crater than previously reported and illustrates some of the challenges in simulating impact deformation of sedimentary lithologies. As many terrestrial craters possess some amount of sedimentary rocks in the target sequence, numerical models of impacts into sedimentary targets are essential to our understanding of target rock deformation and the mechanics of crater formation.  相似文献   

Knowledge gaps in our perceptual model of Great Britain's hydrology     

Thorsten Wagener  Simon J. Dadson  David M. Hannah  Gemma Coxon  Keith Beven  John P. Bloomfield  Wouter Buytaert  Hannah Cloke  Paul Bates  Joseph Holden  Louise Parry  Rob Lamb  Nick A. Chappell  Matthew Fry  Gareth Old 《水文研究》2021,35(7):e14288

There is a no lack of significant open questions in the field of hydrology. How will hydrological connectivity between freshwater bodies be altered by future human alterations to the hydrological cycle? Where does water go when it rains? Or what is the future space–time variability of flood and drought events? However, the answers to these questions will vary with location due to the specific and often poorly understood local boundary conditions and system properties that control the functional behaviour of a catchment or any other hydrologic control volume. We suggest that an open, shared and evolving perceptual model of a region's hydrology is critical to tailor our science questions, as it would be for any other study domain from the plot to the continental scale. In this opinion piece, we begin to discuss the elements of and point out some knowledge gaps in the perceptual model of the terrestrial water cycle of Great Britain. We discuss six major knowledge gaps and propose four key ways to reduce them. While the specific knowledge gaps in our perceptual model do not necessarily transfer to other places, we believe that the development of such perceptual models should be at the core of the debate for all hydrologic communities, and we encourage others to have a similar debate for their hydrologic domain.  相似文献   

Thermal consequences of impacts in the early solar system     

Fred J. Ciesla  Thomas M. Davison  Gareth S. Collins  David P. O'Brien 《Meteoritics & planetary science》2013,48(12):2559-2576

Collisions between planetesimals were common during the first approximately 100 Myr of solar system formation. Such collisions have been suggested to be responsible for thermal processing seen in some meteorites, although previous work has demonstrated that such events could not be responsible for the global thermal evolution of a meteorite parent body. At this early epoch in solar system history, however, meteorite parent bodies would have been heated or retained heat from the decay of short‐lived radionuclides, most notably ²⁶Al. The postimpact structure of an impacted body is shown here to be a strong function of the internal temperature structure of the target body. We calculate the temperature–time history of all mass in these impacted bodies, accounting for their heating in an onion‐shell–structured body prior to the collision event and then allowing for the postimpact thermal evolution as heat from both radioactivities and the impact is diffused through the resulting planetesimal and radiated to space. The thermal histories of materials in these bodies are compared with what they would be in an unimpacted, onion‐shell body. We find that while collisions in the early solar system led to the heating of a target body around the point of impact, a greater amount of mass had its cooling rates accelerated as a result of the flow of heated materials to the surface during the cratering event.  相似文献   

Numerical modeling of asteroid survivability and possible scenarios for the Morokweng crater‐forming impact     

Ross W. K. Potter  Gareth S. Collins 《Meteoritics & planetary science》2013,48(5):744-757

The fate of the impactor is an important aspect of the impact‐cratering process. Defining impactor material as surviving if it remains solid (i.e., does not melt or vaporize) during crater formation, previous numerical modeling and experiments have shown that survivability decreases with increasing impact velocity, impact angle (with respect to the horizontal), and target density. Here, we show that in addition to these, impactor survivability depends on the porosity and shape of the impactor. Increasing impactor porosity decreases impactor survivability, while prolate‐shaped (polar axis > equatorial axis) impactors survive impact more so than spherical and oblate‐shaped (polar axis < equatorial axis) impactors. These results are used to produce a relatively simple equation, which can be used to estimate the impactor fraction shocked to a given pressure as a function of these parameters. By applying our findings to the Morokweng crater‐forming impact, we suggest impact scenarios that explain the high meteoritic content and presence of unmolten fossil meteorites within the Morokweng crater. In addition to previous suggestions of a low‐velocity and/or high‐angled impact, this work suggests that an elongated and/or low porosity impactor may also help explain the anomalously high survivability of the Morokweng impactor.  相似文献   

Ganymede crater dimensions – Implications for central peak and central pit formation and development     

Veronica J. Bray  Paul M. Schenk  H. Jay Melosh  Joanna V. Morgan  Gareth S. Collins 《Icarus》2012,217(1):115-129

The morphology of impact craters on the icy Galilean satellites differs from craters on rocky bodies. The differences are thought due to the relative weakness of ice and the possible presence of sub-surface water layers. Digital elevation models constructed from Galileo images were used to measure a range of dimensions of craters on the dark and bright terrains of Ganymede. Measurements were made from multiple profiles across each crater, so that natural variation in crater dimensions could be assessed and averaged scaling trends constructed. The additional depth, slope and volume information reported in this work has enabled study of central peak formation and development, and allowed a quantitative assessment of the various theories for central pit formation. We note a possible difference in the size-morphology progression between small craters on icy and silicate bodies, where central peaks occur in small craters before there is any slumping of the crater rim, which is the opposite to the observed sequence on the Moon. Conversely, our crater dimension analyses suggest that the size-morphology progression of large lunar craters from central peak to peak-ring is mirrored on Ganymede, but that the peak-ring is subsequently modified to a central pit morphology. Pit formation may occur via the collapse of surface material into a void left by the gradual release of impact-induced volatiles or the drainage of impact melt into sub-crater fractures.  相似文献   

Managing Urban Futures: Sustainability and Urban Growth in Developing Countries – By M. Keiner, M. Koll-Schretzenmayr and W. A. Schmid     

Gareth A. Jones 《Singapore journal of tropical geography》2008,29(1):104-106

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