Modeling the time-dependent response of the Asian summer monsoon to obliquity forcing in a coupled GCM: a PHASEMAP sensitivity experiment   总被引：1，自引：0，他引：1  

Guang-Shan Chen  Zhengyu Liu  Steven C. Clemens  Warren L. Prell  Xiaodong Liu 《Climate Dynamics》2011,36(3-4):695-710

To study the time-dependent response of the Asian summer monsoon to obliquity forcing, we analyze a 284,000-year long transient simulation produced by a fully coupled global climate model (GCM) using a new phase mapping (PHASEMAP) approach. Here we focus on understanding the phase response of monsoonal circulation to insolation forcing at the Earth-orbital obliquity band (41 Kyr). Our results show that the East Asian summer monsoon (EASM) can be divided into two geographic regions: the North East Asian summer monsoon (NEASM) and the South East Asian summer monsoon (SEASM). The Indian summer monsoon (ISM) and the SEASM are in phase at the obliquity band, strengthened with an increase in obliquity from Obliquity minima (Omin) to Obliquity maxima (Omax). The NEASM is out of phase with the ISM and SEASM, weakened with an increase in obliquity from Omin to Omax. We hypothesize that the inverse phase between the NEASM and the ISM at the obliquity band results from an ISM–NEASM teleconnection linked to the formation mechanism of the Bonin High.  相似文献   

Consistent scale-dependency of future increases in hourly extreme precipitation in two convection-permitting climate models     

Helsen  Samuel  van Lipzig  Nicole P. M.  Demuzere  Matthias  Vanden Broucke  Sam  Caluwaerts  Steven  De Cruz  Lesley  De Troch  Rozemien  Hamdi  Rafiq  Termonia  Piet  Van Schaeybroeck  Bert  Wouters  Hendrik 《Climate Dynamics》2020,54(3):1267-1280

Climate Dynamics - Convection-permitting models (CPMs) have been proven successful in simulating extreme precipitation statistics. However, when such models are used to study climate change,...  相似文献   

Modeling Use of Space from Social Media Data Using a Biased Random Walker     

Steven D. Prager  R. Paul Wiegand 《Transactions in GIS》2014,18(6):817-833

Individuals and other entities move through space as a function of local characteristics of place, their internal behavioral models, and the topological structure of the underlying space. When a collection of locations (i.e. geotagged photos or other geotagged social media information) from a large number of individuals is assembled, it becomes possible to understand the interrelationship between the individuals and the space they occupy. This research systematically considers this interrelationship through an examination of the effect of the intersection of behavioral and spatial characteristics on individuals moving on street networks. The research illustrates how social media data, in combination with a biased random walker, can be used to understand and model the interaction of spatial structure and social‐environmental factors on influencing individuals' use of their environment. The biased walker offers a flexible approach to incorporate consideration of both social‐environmental and structural factors into a model and we demonstrate this through a case study wherein we are able to use the random walker to model the characteristics of Flickr users in New York City.  相似文献   

Spring-summer temperatures since AD 1780 reconstructed from stable oxygen isotope ratios in white spruce tree-rings from the Mackenzie Delta,northwestern Canada     

Trevor J. Porter  Michael F. J. Pisaric  Robert D. Field  Steven V. Kokelj  Thomas W. D. Edwards  Peter deMontigny  Richard Healy  Allegra N. LeGrande 《Climate Dynamics》2014,42(3-4):771-785

High-latitude δ¹⁸O archives deriving from meteoric water (e.g., tree-rings and ice-cores) can provide valuable information on past temperature variability, but stationarity of temperature signals in these archives depends on the stability of moisture source/trajectory and precipitation seasonality, both of which can be affected by atmospheric circulation changes. A tree-ring δ¹⁸O record (AD 1780–2003) from the Mackenzie Delta is evaluated as a temperature proxy based on linear regression diagnostics. The primary source of moisture for this region is the North Pacific and, thus, North Pacific atmospheric circulation variability could potentially affect the tree-ring δ¹⁸O-temperature signal. Over the instrumental period (AD 1892–2003), tree-ring δ¹⁸O explained 29 % of interannual variability in April–July minimum temperatures, and the explained variability increases substantially at lower-frequencies. A split-period calibration/verification analysis found the δ¹⁸O-temperature relation was time-stable, which supported a temperature reconstruction back to AD 1780. The stability of the δ¹⁸O-temperature signal indirectly implies the study region is insensitive to North Pacific circulation effects, since North Pacific circulation was not constant over the calibration period. Simulations from the NASA-GISS ModelE isotope-enabled general circulation model confirm that meteoric δ¹⁸O and precipitation seasonality in the study region are likely insensitive to North Pacific circulation effects, highlighting the paleoclimatic value of tree-ring and possibly other δ¹⁸O records from this region. Our δ¹⁸O-based temperature reconstruction is the first of its kind in northwestern North America, and one of few worldwide, and provides a long-term context for evaluating recent climate warming in the Mackenzie Delta region.  相似文献   

Analysis of the present and future winter Pacific-North American teleconnection in the ECHAM5 global and RegCM3 regional climate models     

Andrea M. Allan  Steven W. Hostetler  Jay R. Alder 《Climate Dynamics》2014,42(5-6):1671-1682

We use the NCEP/NCAR Reanalysis (NCEP) and the MPI/ECHAM5 general circulation model to drive the RegCM3 regional climate model to assess the ability of the models to reproduce the spatiotemporal aspects of the Pacific-North American teleconnection (PNA) pattern. Composite anomalies of the NCEP-driven RegCM3 simulations for 1982–2000 indicate that the regional model is capable of accurately simulating the key features (500-hPa heights, surface temperature, and precipitation) of the positive and negative phases of the PNA with little loss of information in the downscaling process. The basic structure of the PNA is captured in both the ECHAM5 global and ECHAM5-driven RegCM3 simulations. The 1950–2000 ECHAM5 simulation displays similar temporal and spatial variability in the PNA index as that of NCEP; however, the magnitudes of the positive and negative phases are weaker than those of NCEP. The RegCM3 simulations clearly differentiate the climatology and associated anomalies of snow water equivalent and soil moisture of the positive and negative PNA phases. In the RegCM3 simulations of the future (2050–2100), changes in the location and extent of the Aleutian low and the continental high over North America alter the dominant flow patterns associated with positive and negative PNA modes. The future projections display a shift in the patterns of the relationship between the PNA and surface climate variables, which suggest the potential for changes in the PNA-related surface hydrology of North America.  相似文献   

A reconstruction of extratropical Indo-Pacific sea-level pressure patterns during the Medieval Climate Anomaly     

Ian D. Goodwin  Stuart Browning  Andrew M. Lorrey  Paul A. Mayewski  Steven J. Phipps  Nancy A. N. Bertler  Ross P. Edwards  Tim J. Cohen  Tas van Ommen  Mark Curran  Cameron Barr  J. Curt Stager 《Climate Dynamics》2014,43(5-6):1197-1219

Subtropical and extratropical proxy records of wind field, sea level pressure (SLP), temperature and hydrological anomalies from South Africa, Australia/New Zealand, Patagonian South America and Antarctica were used to reconstruct the Indo-Pacific extratropical southern hemisphere sea-level pressure anomaly (SLPa) fields for the Medieval Climate Anomaly (MCA ~700–1350 CE) and transition to the Little Ice Age (LIA 1350–1450 CE). The multivariate array of proxy data were simultaneously evaluated against global climate model output in order to identify climate state analogues that are most consistent with the majority of proxy data. The mean SLP and SLP anomaly patterns derived from these analogues illustrate the evolution of low frequency changes in the extratropics. The Indo-Pacific extratropical mean climate state was dominated by a strong tropical interaction with Antarctica emanating from: (1) the eastern Indian and south-west Pacific regions prior to 1100 CE, then, (2) the eastern Pacific evolving to the central Pacific La Niña-like pattern interacting with a +ve SAM to 1300 CE. A relatively abrupt shift to –ve SAM and the central Pacific El Niño-like pattern occurred at ~1300. A poleward (equatorward) shift in the subtropical ridge occurred during the MCA (MCA–LIA transition). The Hadley Cell expansion in the Australian and Southwest Pacific, region together with the poleward shift of the zonal westerlies is contemporaneous with previously reported Hadley Cell expansion in the North Pacific and Atlantic regions, and suggests that bipolar climate symmetry was a feature of the MCA.  相似文献   

Petrochemistry and hydrothermal alteration within the Tyrone Igneous Complex,Northern Ireland: implications for VMS mineralization in the British and Irish Caledonides     

Steven P. Hollis  Stephen Roberts  Garth Earls  Richard Herrington  Mark R. Cooper  Stephen J. Piercey  Sandy M. Archibald  Martin Moloney 《Mineralium Deposita》2014,49(5):575-593

Although volcanogenic massive sulfide (VMS) deposits can form within a wide variety of rift-related tectonic environments, most are preserved within suprasubduction affinity crust related to ocean closure. In stark contrast to the VMS-rich Appalachian sector of the Grampian-Taconic orogeny, VMS mineralization is rare in the peri-Laurentian British and Irish Caledonides. Economic peri-Gondwanan affinity deposits are limited to Avoca and Parys Mountain. The Tyrone Igneous Complex of Northern Ireland represents a ca. 484–464 Ma peri-Laurentian affinity arc–ophiolite complex and a possible broad correlative of the Buchans-Robert’s Arm belt of Newfoundland, host to some of the most metal-rich VMS deposits globally. Stratigraphic horizons prospective for VMS mineralization in the Tyrone Igneous Complex are associated with rift-related magmatism, hydrothermal alteration, synvolcanic faults, and high-level subvolcanic intrusions (gabbro, diorite, and/or tonalite). Locally intense hydrothermal alteration is characterized by Na-depletion, elevated SiO₂, MgO, Ba/Sr, Bi, Sb, chlorite–carbonate–pyrite alteration index (CCPI) and Hashimoto alteration index (AI) values. Rift-related mafic lavas typically occur in the hanging wall sequences to base and precious metal mineralization, closely associated with ironstones and/or argillaceous sedimentary rocks representing low temperature hydrothermal venting and volcanic quiescence. In the ca. 475 Ma pre-collisional, calc-alkaline lower Tyrone Volcanic Group rift-related magmatism is characterized by abundant non-arc type Fe-Ti-rich eMORB, island-arc tholeiite, and low-Zr tholeiitic rhyolite breccias. These petrochemical characteristics are typical of units associated with VMS mineralization in bimodal mafic, primitive post-Archean arc terranes. Following arc-accretion at ca. 470 Ma, late rifting in the ensialic upper Tyrone Volcanic Group is dominated by OIB-like, subalkaline to alkali basalt and A-type, high-Zr rhyolites. These units are petrochemically favorable for Kuroko-type VMS mineralization in bimodal-felsic evolved arc terranes. The scarcity of discovered peri-Laurentian VMS mineralization in the British and Irish Caledonides is due to a combination of minimal exploration, poor-preservation of upper ophiolite sequences, and limited rifting in the Lough Nafooey arc of western Ireland. The geological and geochemical characteristics of the Tyrone Volcanic Group of Northern Ireland and peri-Gondwanan affinity arc/backarc sequences of Ireland and northwest Wales represent the most prospective sequences in the British and Irish Caledonides for VMS mineralization.  相似文献   

A methodology to constrain the parameters of a hydrogeological discrete fracture network model for sparsely fractured crystalline rock,exemplified by data from the proposed high-level nuclear waste repository site at Forsmark,Sweden   总被引：3，自引：1，他引：2  

Sven Follin  Lee Hartley  Ingvar Rhén  Peter Jackson  Steven Joyce  David Roberts  Ben Swift 《Hydrogeology Journal》2014,22(2):313-331

The large-scale geological structure of the crystalline rock at the proposed high-level nuclear waste repository site at Forsmark, Sweden, has been classified in terms of deformation zones of elevated fracture frequency. The rock between deformation zones was divided into fracture domains according to fracture frequency. A methodology to constrain the geometric and hydraulic parameters that define a discrete fracture network (DFN) model for each fracture domain is presented. The methodology is based on flow logging and down-hole imaging in cored boreholes in combination with DFN realizations, fracture connectivity analysis and pumping test simulations. The simulations suggest that a good match could be obtained for a power law size distribution where the value of the location parameter equals the borehole radius but with different values for the shape parameter, depending on fracture domain and fracture set. Fractures around 10–100 m in size are the ones that typically form the connected network, giving inflows in the simulations. The report also addresses the issue of up-scaling of DFN properties to equivalent continuous porous medium (ECPM) bulk flow properties. Comparisons with double-packer injection tests provide confidence that the derived DFN formulation of detailed flows within individual fractures is also suited to simulating mean bulk flow properties and their spatial variability.  相似文献   

A polyphase glacitectonic model for ice-marginal retreat and terminal moraine development: the Middle Pleistocene British Ice Sheet,northern Norfolk,UK     

Jonathan R. Lee  Emrys Phillips  Stephen J. Booth  James Rose  Hannah M. Jordan  Steven M. Pawley  Martin Warren  Russell S. Lawley 《Proceedings of the Geologists' Association. Geologists' Association》2013

Recent investigations from modern environments demonstrate that many terminal moraines do not simply record a single glacial maximum, but instead reveal a complex oscillatory pattern of ice-marginal behaviour including polyphase retreat. Within this study, we examine the geomorphology, geology and internal structure of a terminal moraine complex – the ‘Cromer Ridge’ in north Norfolk to reconstruct patterns of ice-marginal behaviour. Previously, this landform was interpreted as the limit of a southern extension of the British Ice Sheet during a Middle Pleistocene glaciation. Evidence presented here reveals a more complicated pattern of ice-marginal behaviour with the ‘Cromer Ridge’ reinterpreted as a ‘complex’ comprising several ridge elements. We propose that the maximum ice extent lay further to the south, with the size and morphology of the largest ridge element (the ‘Cromer Ridge’ as previously defined) a facet of thrust-stacking at an ice-marginal still-stand. We recognise multiple oscillations of the ice-front recorded against a twelve-stage model for the decay of the southern margins of a fast-flowing lobe of North Sea ice. Changes in ice-marginal dynamics are identified by the superimposition and lateral and vertical evolution of glacitectonic styles. Differences between these various states, and switches between ‘shallow’ and ‘deep’ thin-skinned glacitectonics, are strongly influenced by sub-marginal and proglacial water availability. Examination of the evidence for the morphostratigraphic proposals for the glacitectonic assemblage, within the context of the above interpretation, suggests that many of the ‘glacigenic landforms’ are erosional and a MIS 12 age of formation is favoured although several anomalies remain to be explained.  相似文献   

Phase Mixing in Unperturbed and Perturbed Hamiltonian Systems     

Henry E. Kandrup  Steven J. Novotny 《Celestial Mechanics and Dynamical Astronomy》2004,88(1):1-35

This paper summarises a numerical investigation of phase mixing in time-independent Hamiltonian systems that admit a coexistence of regular and chaotic phase space regions, allowing also for low amplitude perturbations idealised as periodic driving, friction, and/or white and coloured noise. The evolution of initially localised ensembles of orbits was probed through lower order moments and coarse-grained distribution functions. In the absence of time-dependent perturbations, regular ensembles disperse initially as a power law in time and only exhibit a coarse-grained approach towards an invariant equilibrium over comparatively long times. Chaotic ensembles generally diverge exponentially fast on a time scale related to a typical finite time Lyapunov exponent, but can exhibit complex behaviour if they are impacted by the effects of cantori or the Arnold web. Viewed over somewhat longer times, chaotic ensembles typical converge exponentially towards an invariant or near-invariant equilibrium. This, however, need not correspond to a true equilibrium, which may only be approached over very long time scales. Time-dependent perturbations can dramatically increase the efficiency of phase mixing, both by accelerating the approach towards a near-equilibrium and by facilitating diffusion through cantori or along the Arnold web so as to accelerate the approach towards a true equilibrium. The efficacy of such perturbations typically scales logarithmically in amplitude, but is comparatively insensitive to most other details, a conclusion which reinforces the interpretation that the perturbations act via a resonant coupling.  相似文献