Climate forcings and climate sensitivities diagnosed from atmospheric global circulation models     

Bruce T. Anderson  Jeff R. Knight  Mark A. Ringer  Clara Deser  Adam S. Phillips  Jin-Ho Yoon  Annalisa Cherchi 《Climate Dynamics》2010,35(7-8):1461-1475

Understanding the historical and future response of the global climate system to anthropogenic emissions of radiatively active atmospheric constituents has become a timely and compelling concern. At present, however, there are uncertainties in: the total radiative forcing associated with changes in the chemical composition of the atmosphere; the effective forcing applied to the climate system resulting from a (temporary) reduction via ocean-heat uptake; and the strength of the climate feedbacks that subsequently modify this forcing. Here a set of analyses derived from atmospheric general circulation model simulations are used to estimate the effective and total radiative forcing of the observed climate system due to anthropogenic emissions over the last 50 years of the twentieth century. They are also used to estimate the sensitivity of the observed climate system to these emissions, as well as the expected change in global surface temperatures once the climate system returns to radiative equilibrium. Results indicate that estimates of the effective radiative forcing and total radiative forcing associated with historical anthropogenic emissions differ across models. In addition estimates of the historical sensitivity of the climate to these emissions differ across models. However, results suggest that the variations in climate sensitivity and total climate forcing are not independent, and that the two vary inversely with respect to one another. As such, expected equilibrium temperature changes, which are given by the product of the total radiative forcing and the climate sensitivity, are relatively constant between models, particularly in comparison to results in which the total radiative forcing is assumed constant. Implications of these results for projected future climate forcings and subsequent responses are also discussed.  相似文献   

Geomorphic controls and transition zones in the lower Sabine River     

Jonathan D. Phillips 《水文研究》2008,22(14):2424-2437

Instream flow science and management requires identification of characteristic hydrological, ecological, and geomorphological attributes of stream reaches. This study approaches this problem by identifying geomorphic transition zones along the lower Sabine River, Texas and Louisiana. Boundaries were delineated along the lower Sabine River valley based on surficial geology, valley width, valley confinement, network characteristics (divergent versus convergent), sinuousity, slope, paleomeanders, and point bars. The coincidence of multiple boundaries reveals five key transition zones separating six reaches of distinct hydrological and geomorphological characteristics. Geologic controls and gross valley morphology play a major role as geomorphic controls, as does an upstream‐to‐downstream gradient in the importance of pulsed dam releases, and a down‐to‐upstream gradient in coastal backwater effects. Geomorphic history, both in the sense of the legacy of Quaternary sea level changes, and the effects of specific events such as avulsions and captures, are also critical. The transition zones delineate reaches with distinct hydrological characteristics in terms of the relative importance of dam releases and coastal backwater effects, single versus multi‐channel flow patterns, frequency of overbank flow, and channel‐floodplain connectivity. The transitional areas also represent sensitive zones which can be expected to be bellwethers in terms of responses to future environmental changes. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

Sedimentation in bottomland hardwoods downstream of an east Texas dam     

J. Phillips 《Environmental Geology》2001,40(7):860-868

Dams and reservoirs are often efficient sediment traps, and conventional wisdom holds that fluvial sediment supplies are reduced well downstream. However, there are reasons to question the extent to which fluvial and alluvial sediment supplies are reduced more than a few kilometers downstream of dams. Sedimentation in bottomlands of Loco Bayou, east Texas, was investigated at a site less than 16 km downstream of Loco Dam and Lake Nacogdoches, which controls 86% of the 265-km² drainage area. Turbidity levels are generally as high or higher than those on Loco Bayou upstream of the lake. Sedimentation rates on the lower floodplain since the dam was completed are 11 mm year^-1 or more. This rate is high enough to suggest that the dam has no effect on sediment supplies 16 km downstream. The spatial pattern of sedimentation and the vegetation distribution suggest that the elevation and frequency of flooding, not fluvial sediment availability, are the critical factors in determining sediment supplies to these floodplains.  相似文献   

Application of Regional Phase Amplitude Tomography to Seismic Verification   总被引：1，自引：0，他引：1  

W. S. Phillips  H. E. Hartse  S. R. Taylor  A. A. Velasco  G. E. Randall 《Pure and Applied Geophysics》2001,158(7):1189-1206

v--vWe have applied tomographic techniques to amplitude data to quantify regional phase path effects for use in source discrimination studies. Tomography complements interpolation (kriging) methods by extending our ability to apply path corrections into regions devoid of calibration events, as well as raising levels of confidence in the corrections because of their more physical basis. Our tomography technique solves for resolvable combinations of attenuation, source-generation, site and spreading terms. First difference regularization is used to remove singularities and reduce noise effects.¶In initial tests the technique was applied to a data set of 1488, 1.0 Hz, P_g/L_g amplitude ratios from 13 stations for paths inside a 30° by 40° box covering western China and surrounding regions. Tomography reduced variance 60%, relative to the power-law distance correction traditionally applied to amplitude ratios. Relative P_g/L_g attenuation varied with geologic region, with low values in Tibet, intermediate values in basins and high values for platforms and older crust. Spatial patterns were consistent with previous path effect studies in Asia, especially local earthquake coda-Q. Relative spreading was consistent with expected values for P_g and L_g. Relative site terms were similar to one another, yet some tradeoff with attenuation was evident.¶Tomography residuals followed systematic trends with distance, which may result from the evolution from direct to coda phases, focusing, model tradeoff or data windowing effects. Examination of the residuals using a kriging interpolator showed coherent geographical variations, indicating unmodeled path effects. The residual patterns often follow geological boundaries, which could result from attenuating zones or minor blockages that are too thin to be resolved, or that have anisotropic effect on regional phases. These results will guide efforts to reparameterize tomography models to more effectively represent regional wave attenuation and blockage. The interpolated residuals also can be combined with predictions of the tomographic model to account for path effects in discrimination studies on a station by station basis.  相似文献   

Shallow Velocity Structure at the Shagan River Test Site in Kazakhstan     

J. L. Bonner  D. C. Pearson  W. S. Phillips  S. R. Taylor 《Pure and Applied Geophysics》2001,158(11):2017-2039

—?During 1997 and 1998, twelve chemical explosions were detonated in boreholes at the former Soviet nuclear test site near the Shagan River (STS) in Kazakhstan. The depths of these explosions ranged from 2.5 to 550 m, while the explosive yield varied from 2 to 25 tons. The purpose of these explosions was for closure of the unused boreholes at STS, and each explosion was recorded at local distances by a network of seismometers operated by Los Alamos National Laboratory and the Institute of Geophysics for the National Nuclear Center (NNC). Short-period, fundamental-mode Rayleigh waves (Rg) were generated by these explosions and recorded at the local stations, resultingly the waves exhibited normal dispersion between 0.2 and 3 seconds. Dispersion curves were generated for each propagation path using the Multiple Filter Analysis and Phase Match Filtering techniques. Tomographic maps of Rg group velocity were constructed and show a zone of relatively high velocities for the southwestern (SW) region of the test site and slow propagation for the northeastern (NE) region. For 0.5?sec Rg, the regions are separated by the 2.1?km/sec contour, as propagation in the SW is greater than 2.1?km/sec and less in the NE region. At 1.0 sec period, the 2.3?km/sec contour separates the two regions. Finally, for 1.5 and 2.0 sec, the separation between the two regions is less distinct as velocities in the NE section begin to approach the SW except for a low velocity region (<2.1?km/sec) near the center of the test site. Local geologic structure may explain the different regions as the SW region is composed predominantly of crystalline intrusive rocks, while the NE region consists of alluvium, tuff deposits, and Paleozoic sedimentary rocks. Low velocities are also observed along the Shagan River as it passes through the SW region of the test site for shorter period Rg (0.5–1.0?sec). Iterative, least-squares inversions of the Rg group velocity dispersion curves show shear-wave velocities for the southwestern section that are on average 0.4?km/sec higher than the NE region. At depths greater than 1.5?km the statistical difference between the models is no longer significant. The observed group velocities and different velocity structures correlate with P-wave complexity and with spatial patterns of magnitude residuals observed from nuclear explosions at STS, and may help to evaluate the mechanisms behind those observations.  相似文献   

A Portable Air-Minipermeameter for Rapid In Situ Field Measurements   总被引：1，自引：1，他引：1  

J. Matthew Davis  John L. Wilson  Fred M. Phillips 《Ground water》1994,32(2):258-266

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Deterministic uncertainty in landscapes     

Jonathan D. Phillips 《地球表面变化过程与地形》1994,19(5):389-401

Deterministic complexity (chaos) may be common in geomorphic systems, but traditional definitions may have limited practical utility for empirical geomorphology. These definitions are based on sensitivity to initial conditions, which in geomorphology are both unknown and unknowable. Further, chaos analysis depends on distinguishing deterministic complexity from stochastic complexity. This is problematic in geomorphology because some stochastic complexity is virtually always present in addition to any chaos that may be present. While it is important to recognize that some complex, apparently random patterns may derive from inherent non-linear system dynamics, this is of limited use in explaining process–response relationships or mechanics of landscape evolution. A more general term, which subsumes chaos, is deterministic uncertainty, i.e. uncertainty associated with an identifiable but unknown or uncertain source. An analysis of landscape entropy shows that such underlying constraints produce spatial patterns which are apparently chaotic. For the case of geologic controls, the apparent contribution of deterministic chaos to the landscape entropy is a direct non-linear function of the extent of geologic constraints. However, the underlying constraints and their contribution to observed spatial patterns can also be interpreted in non-chaotic terms. Examples are given, involving geologic constraints on stream channel networks and parent material control of surface soil textures. Because both randomness and chaos may be more apparent than real, the concept of deterministic uncertainty is more useful in process geomorphology than that of chaos.  相似文献   

Book reviews     

Gaston Fischer  E. Klingelé  P. D. Phillips 《Pure and Applied Geophysics》1980,119(4):888-892

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A population analysis for Be and B oxyanions     

J. L. Schlenker  D. T. Griffen  M. W. Phillips  G. V. Gibbs 《Contributions to Mineralogy and Petrology》1978,65(3):347-350

Mulliken bond overlap populations calculated for beryllium and boron oxyanions isolated from a number of minerals and synthetic compounds correlate with observed bond lengths with shorter bonds tending to involve larger overlap populations. As the populations were calculated assuming constant bond lengths and observed valence angles, the correlations are asserted to reflect the angular geometry impressed on the oxyanions by neighboring cations. Extended Hückel theory shows that the dependence of overlap population upon valence angles is greater for boron than for beryllium oxyanions. This is consistent with the observation that bond length variations in boron oxyanions are greater than those in corresponding beryllium oxyanions. As expected, observed bond lengths correlate with valence angles with the shorter bonds tending to be involved in wider angles.Now at Department of Geophysical Sciences, University of Chicago, Chicago, Illinois 60637, USANow at Geochemistry Branch, Phillips Petroleum Co., Bartlesville, Oklahoma 74004, USANow at Department of Geology, University of Toledo, Toledo, Ohio 43606, USA  相似文献   

The biotite-prehnite association     

Evan R. Phillips  Peter C. Rickwood 《Lithos》1975,8(4):275-281

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