Wind-stress feedback amplification of abrupt millennial-scale climate changes     

Olivier Arzel  Matthew H. England 《Climate Dynamics》2013,40(3-4):983-995

The influence of changes in surface wind-stress on the properties (amplitude and period) and domain of existence of thermohaline millennial oscillations is studied by means of a coupled model of intermediate complexity set up in an idealized spherical sector geometry of the Atlantic basin. Using the atmospheric CO₂ concentration as the control parameter, bifurcation diagrams of the model are built to show that the influence of wind-stress changes on glacial abrupt variability is threefold. First, millennial-scale oscillations are significantly amplified through wind-feedback-induced changes in both northern sea ice export and oceanic heat transport. Changes in surface wind-stress more than double the amplitude of the strong warming events that punctuate glacial abrupt variability obtained under prescribed winds in the model. Second, the average duration of both stadials and interstadials is significantly lengthened and the temporal structure of observed variability is better captured under interactive winds. Third, the generation of millennial-scale oscillations is shown to occur for significantly colder climates when wind-stress feedback is enabled. This behaviour results from the strengthening of the negative temperature-advection feedback associated with stronger northward oceanic heat transport under interactive winds.  相似文献   

Towards good governance of urban greening: insights from four initiatives in Melbourne,Australia     

Brian Coffey  Judy Bush  Laura Mumaw  Lisa de Kleyn  Casey Furlong  Raven Cretney 《The Australian geographer》2020,51(2):189-204

ABSTRACT

Urban greening can enhance sustainability and liveability, through conserving biodiversity, mitigating urban heat and enhancing people’s health and wellbeing. However, urban greening is complex, as it occurs in unique ecological settings, with social, cultural and economic factors shaping the forms it takes. This raises questions about the governance of urban greening, including what counts as ‘good governance’. In this paper, we first outline principles of good governance drawn from the natural resource management context. We then present four urban greening initiatives from Melbourne Australia representing different scales, land tenures and organising structures. Following this, we analyse how governance of the four initiatives addresses good governance principles. Our analysis shows that there are diverse ways in which urban greening can be practiced and governed. The importance of more ‘informal’ initiatives should not be discounted relative to formalised initiatives, as a spectrum of approaches can be seen as strength. Further, in determining what constitutes good governance, the standards against which initiatives are assessed should be tailored to their specific circumstances, and consider impacts to the environment itself. These findings point to good urban greening governance being both situated and principled.  相似文献   

The travel time of P seismic waves in Europe and Western Russia     

P. C. England  M. H. Worthington 《Geophysical Journal International》1977,48(1):63-70

  相似文献   

Notes on framboidal pyrite from Allandale New South Wales,Australia     

J. Ostwald  B. M. England 《Mineralium Deposita》1977,12(1):111-116

Pyrite masses composed of compacted pyrite framboids in chalcedony in weathered andesites at Allandale, New South Wales, Australia, show evidence of colloidal origin and contemporaneous deposition of pyrite and silica. Free framboids and framboidal clusters in the chalcedony show indications of crystallization into pyrite polyhedra and pyrite octahedra.  相似文献   

Thermal regimes and regional metamorphism in the vicinity of overthrust faults: an example of shear heating and inverted metamorphic zonation from southern California     

Colin M. Graham  Philip C. England 《Earth and Planetary Science Letters》1976,31(1):142-152

Thermal models are developed and temperature-depth profiles computed to account for the development of sharply inverted metamorphic zonations and estimatedP-T conditions beneath deep-seated thrust faults, with particular reference to the metamorphism of the Pelona Schist-Vincent Thrust system of southern California.Models dependent only upon conductive redistribution of heat from an initially hot upper plate are inadequate to account for the observed temperature distributions and theP-T time constraints can only be satisfied if a total shear heating of 3 hfu or more occurs in the region of the thrusts. These heating rates are consistent with known rates of plate movement, shear stresses along major fault zones, and shear strengths of rocks.Petrological constraints indicate the likelihood of buffering of the maximum temperature attained by shear heating due to marked reduction of shear strengths of rocks upon increase of temperature and release of water during metamorphic dehydration reactions.These models may be of general applicability to inverted metamorphic zonations, notably those beneath obducted Newfoundland ophiolites, and are consistent with our present understanding of the thermal properties of the upper parts of subduction zones.  相似文献   

The magnetic effects of brecciation and shock in meteorites: I. The Ll-chondrites     

Aviva Brecher  Judy Stein  Miriam Fuhrman 《Earth, Moon, and Planets》1977,17(3):205-216

The complex brecciation and shock history of amphoterite (LL-) chondrites is well reflected in their diverse natural magnetic remanence (NRM) behavior: Most LL-chondrites have a multicomponent, undemagnetizable NRM, analogous to that of lunar breccias. Only one meteorite among those studied, namely Dhurmsala (LL6), meets the criteria of NRM stability and directional coherence with progressive AF cleaning, indicative of a useful paleoremanence. Ancient field paleointensity determinations for Dhurmsala (LL6) of 0.03 and 0.1 Oe, agree well with our earlier estimates of 0.01 and 0.08 Oe for the LL6 Jelica and Vavilovka, respectively. In light of their petrographic structure, cooling rates, radiometric ages and shock indicators, it appears likely that the NRM may have been thermally imprinted, during cooling following shock-metamorphism. The closely similar saturation remanence (IRM_s) behavior for LL-chondrites, in contrast to the intragroup scatter in NRM characteristics, implies that - although formed by similar process from the same starting material, - the LL-chondrites have suffered widely different degrees of shock/metamorphic reheating.  相似文献   

On the response of the oceanic wind-driven circulation to atmospheric CO2 increase   总被引：1，自引：0，他引：1  

Oleg A. Saenko  John C. Fyfe  Matthew H. England 《Climate Dynamics》2005,25(4):415-426

A global, flux-corrected climate model is employed to predict the surface wind stress and associated wind-driven oceanic circulation for climate states corresponding to a doubling and quadrupling of the atmospheric CO₂ concentration in a simple 1% per year CO₂ increase scenario. The model indicates that in response to CO₂ increase, the position of zero wind stress curl in the mid-latitudes of the Southern Hemisphere shifts poleward. In addition, the wind stress intensifies significantly in the mid-latitudes of the Southern Hemisphere. As a result, the rate of water circulation in the subpolar meridional overturning cell in the Southern Ocean increases by about 6 Sv (1 Sv=10⁶ m³ s⁻¹) for doubled CO₂ and by 12 Sv for quadrupled CO₂, implying an increase of deep water upwelling south of the circumpolar flow and an increase of Ekman pumping north of it. In addition, the changes in the wind stress and wind stress curl translate into changes in the horizontal mass transport, leading to a poleward expansion of the subtropical gyres in both hemispheres, and to strengthening of the Antarctic Circumpolar Current. Finally, the intensified near-surface winds over the Southern Ocean result in a substantial increase of mechanical energy supply to the ocean general circulation.  相似文献   

Rear-arc vs. arc-front volcanoes in the Katmai reach of the Alaska Peninsula: a critical appraisal of across-arc compositional variation     

Hildreth  Wes  Fierstein  Judy  Siems  David F.  Budahn  James R.  Ruíz  Joaquin 《Contributions to Mineralogy and Petrology》2004,147(3):243-275

Physical and compositional data and K-Ar ages are reported for 14 rear-arc volcanoes that lie 11–22 km behind the narrowly linear volcanic front defined by the Mount Katmai-to-Devils Desk chain on the Alaska Peninsula. One is a 30-km³ stratocone (Mount Griggs; 51–63% SiO₂) active intermittently from 292 ka to Holocene. The others are monogenetic cones, domes, lava flows, plugs, and maars, of which 12 were previously unnamed and unstudied; they include seven basalts (48–52% SiO₂), four mafic andesites (53–55% SiO₂), and three andesite-dacite units. Six erupted in the interval 500–88 ka, one historically in 1977, and five in the interval 3–2 Ma. No migration of the volcanic front is discernible since the late Miocene, so even the older units erupted well behind the front. Discussion explores the significance of the volcanic front and the processes that influence compositional overlaps and differences among mafic products of the rear-arc volcanoes and of the several arc-front edifices nearby. The latter have together erupted a magma volume of about 200 km³, at least four times that of all rear-arc products combined. Correlation of Sr-isotope ratios with indices of fractionation indicates crustal contributions in volcanic-front magmas (0.7033–0.7038), but lack of such trends among the rear-arc units (0.70298–0.70356) suggests weaker and less systematic crustal influence. Slab contributions and mantle partial-melt fractions both appear to decline behind the front, but neither trend is crisp and unambiguous. No intraplate mantle contribution is recognized nor is any systematic across-arc difference in intrinsic mantle-wedge source fertility discerned. Both rear-arc and arc-front basalts apparently issued from fluxing of typically fertile NMORB-source mantle beneath the Peninsular terrane, which docked here in the Mesozoic.Electronic Supplementary Material Supplementary material is available for this article if you access the article at . A link in the frame on the left on that page takes you directly to the supplementary material.Editorial responsibility: T.L. Grove  相似文献   

Diurnal variation of vertical temperature gradients within a field of maize: implications for Satellite microwave radiometry     

Hornbuckle  B.K. England  A.W. 《Geoscience and Remote Sensing Letters, IEEE》2005,2(1):74-77

We present the diurnal variation of vertical temperature differences measured within and beneath a maize canopy over the course of a growing season, and we analyze the implied temperature gradients in the context of microwave radiometry and soil moisture retrieval in particular. We find that the temperature differences can be as large as 9 K in magnitude within the vegetation canopy and as large as 10 K between the soil surface and a depth of 4.5 cm. Satellite overpass times at 1:30 A.M. and 1:30 P.M. occur close to when the magnitude of the temperature differences are largest. For 6 A.M. and 6 P.M. overpass times, temperature differences were smaller in magnitude at 6 P.M. This contradicts the widely held assumption that surface temperature gradients are more uniform at 6 A.M. than at 6 P.M.  相似文献   

The field of crustal velocity in Asia calculated from Quaternary rates of slip on faults   总被引：33，自引：0，他引：33  

Philip England  Peter Molnar 《Geophysical Journal International》1997,130(3):551-582

Rates of Quaternary faulting, when treated as measures of strain rates within regions several times larger than the depths of brittle faulting, yield a velocity field for Asia that matches the average relative velocity between the Indian and Eurasian plates ove the past 2 Myr (NUVEL-1A), and the velocity of Shanghai with respect to Eurasia, measured with Very Long Baseline Interferometry (VLBI). By using rates of slip on discrete surfaces (faults) to define average strain rates, we explicitly assume tha the large-scale deformation can be treated as that of a continuum. Depending on the scales over which strain rates are averaged, 87 to 93 per cent of the assumed strain rates are fit within assigned 1-sigma uncertainties, and 97 to 99 per cent are fit withi 2-sigma. The internal consistency of these data and the agreement with independen rates (NUVEL-1A and VLBI) test the validity of treating large-scale deformation of continents as that of a continuum. In the calculated velocity field, a large fraction, ˜ 85 per cent, of India's convergence with Eurasia is absorbed by crustal, or lithospheric, thickening. Among consistently misfit assumed strain rates are those dominated by high rates of strike-slip faulting. Strain associated with 20-30 mm a^-1 of slip on the Altyn Tagh, Karakax, and Karakorum faults is inconsistent with the distributions of strain in surrounding regions. We conclude that these rates, all of which are based on correlations of ages of offset landforms with changes in global climate, and not on radiometric dating, have been systematically overestimated. Lateral transport out of India's northward path is relatively minor; South China is calculated to move east-southeast at less than 10 mm a^-1.  相似文献