Multi-year predictability in a coupled general circulation model   总被引：1，自引：0，他引：1  

Scott Power  Rob Colman 《Climate Dynamics》2006,26(2-3):247-272

Multi-year to decadal variability in a 100-year integration of a BMRC coupled atmosphere-ocean general circulation model (CGCM) is examined. The fractional contribution made by the decadal component generally increases with depth and latitude away from surface waters in the equatorial Indo-Pacific Ocean. The relative importance of decadal variability is enhanced in off-equatorial “wings” in the subtropical eastern Pacific. The model and observations exhibit “ENSO-like” decadal patterns. Analytic results are derived, which show that the patterns can, in theory, occur in the absence of any predictability beyond ENSO time-scales. In practice, however, modification to this stochastic view is needed to account for robust differences between ENSO-like decadal patterns and their interannual counterparts. An analysis of variability in the CGCM, a wind-forced shallow water model, and a simple mixed layer model together with existing and new theoretical results are used to improve upon this stochastic paradigm and to provide a new theory for the origin of decadal ENSO-like patterns like the Interdecadal Pacific Oscillation and Pacific Decadal Oscillation. In this theory, ENSO-driven wind-stress variability forces internal equatorially-trapped Kelvin waves that propagate towards the eastern boundary. Kelvin waves can excite reflected internal westward propagating equatorially-trapped Rossby waves (RWs) and coastally-trapped waves (CTWs). CTWs have no impact on the off-equatorial sub-surface ocean outside the coastal wave guide, whereas the RWs do. If the frequency of the incident wave is too high, then only CTWs are excited. At lower frequencies, both CTWs and RWs can be excited. The lower the frequency, the greater the fraction of energy transmitted to RWs. This lowers the characteristic frequency (reddens the spectrum) of variability off the equator relative to its equatorial counterpart. At low frequencies, dissipation acts as an additional low pass filter that becomes more effective, as latitude increases. At the same time, ENSO-driven off-equatorial surface heating anomalies drive mixed layer temperature responses in both hemispheres. Both the eastern boundary interactions and the accumulation of surface heat fluxes by the surface mixed layer act to low pass filter the ENSO-forcing. The resulting off-equatorial variability is therefore more coherent with low pass filtered (decadal) ENSO indices [e.g. NINO3 sea-surface temperature (SST)] than with unfiltered ENSO indices. Consequently large correlations between variability and NINO3 extend further poleward on decadal time-scales than they do on interannual time-scales. This explains why decadal ENSO-like patterns have a broader meridional structure than their interannual counterparts. This difference in appearance can occur even if ENSO indices do not have any predictability beyond interannual time-scales. The wings around 15–20°S, and sub-surface variability at many other locations are predictable on interannual and multi-year time-scales. This includes westward propagating internal RWs within about 25° of the equator. The slowest of these take up to 4 years to reach the western boundary. This sub-surface predictability has significant oceanographic interest. However, it is linked to only low levels of SST variability. Consequently, extrapolation of delayed action oscillator theory to decadal time-scales might not be justified.  相似文献   

Corrigendum to “Radiocarbon dating, chronologic framework, and changes in accumulation rates of Holocene estuarine sediments from Chesapeake Bay” [Quaternary Research 57 (2002) 58-70]     

Steven M. Colman  Pattie C. Baucom  Thomas M. Cronin  Debra Willard  Peter R. Vogt 《Quaternary Research》2004,61(2):241

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A long-term nearshore wave hindcast for Ireland: Atlantic and Irish Sea coasts (1979–2012)     

Sarah Gallagher  Roxana Tiron  Frédéric Dias 《Ocean Dynamics》2014,64(8):1163-1180

The Northeast Atlantic possesses some of the highest wave energy levels in the world. The recent years have witnessed a renewed interest in harnessing this vast energy potential. Due to the complicated geomorphology of the Irish coast, there can be a significant variation in both the wave and wind climate. Long-term hindcasts with high spatial resolution, properly calibrated against available measurements, provide vital information for future deployments of ocean renewable energy installations. These can aid in the selection of adequate locations for potential deployment and for the planning and design of those marine operations. A 34-year (from 1979 to 2012), high-resolution wave hindcast was performed for Ireland including both the Atlantic and Irish Sea coasts, with a particular focus on the wave energy resource. The wave climate was estimated using the third-generation spectral wave model WAVEWATCH III®; version 4.11, the unstructured grid formulation. The wave model was forced with directional wave spectral data and 10-m winds from the European Centre for Medium Range Weather Forecasts (ECMWF) ERA-Interim reanalysis, which is available from 1979 to the present. The model was validated against available observed satellite altimeter and buoy data, particularly in the nearshore, and was found to be excellent. A strong spatial and seasonal variability was found for both significant wave heights, and the wave energy flux, particularly on the north and west coasts. A strong correlation between the North Atlantic Oscillation (NAO) teleconnection pattern and wave heights, wave periods, and peak direction in winter and also, to a lesser extent, in spring was identified.  相似文献   

Biostratigraphy,microfacies and depositional environments of upper Viséan limestones from the Burren region,County Clare,Ireland     

S.J. Gallagher  C.V. MacDermot  I.D. Somerville  M. Pracht  A.G. Sleeman 《Geological Journal》2006,41(1):61-91

The Burren region in western Ireland contains an almost continuous record of Viséan (Middle Mississippian) carbonate deposition extending from Chadian to Brigantian times, represented by three formations: the Chadian to Holkerian Tubber Formation, the Asbian Burren Formation and the Brigantian Slievenaglasha Formation. The upper Viséan (Holkerian–Brigantian) platform carbonate succession of the Burren can be subdivided into six distinct depositional units outlined below. (1) An Holkerian to lower Asbian unit of skeletal peloidal and bryozoan bedded limestone. (2) Lower Asbian unit of massive light grey Koninckopora‐rich limestone, representing a shallower marine facies. (3) Upper Asbian terraced limestone unit with minor shallowing‐upward cycles of poorly bedded Kamaenella‐rich limestone with shell bands and palaeokarst features. This unit is very similar to other cyclic sequences of late Asbian age in southern Ireland and western Europe, suggesting a glacio‐eustatic origin for this fourth‐order cyclicity. (4) Lower Brigantian unit with cyclic alternations of crinoidal/bryozoan limestone and peloidal limestone with coral thickets. These cycles lack evidence of subaerial exposure. (5) Lower Brigantian bedded cherty dark grey limestone unit, deposited during the maximum transgressive phase of the Brigantian. (6) Lower to upper Brigantian unit mostly comprising cyclic bryozoan/crinoidal cherty limestone. In most areas this youngest unit is truncated and unconformably overlain by Serpukhovian siliciclastic rocks. Deepening enhanced by platform‐wide subsidence strongly influenced later Brigantian cycle development in Ireland, but localized rapid shallowing led to emergence at the end of the Brigantian. A Cf5 Zone (Holkerian) assemblage of microfossils is recorded from the Tubber Formation at Black Head, but in the Ballard Bridge section the top of the formation has Cf6 Zone (Asbian) foraminiferans. A typical upper Asbian Rugose Coral Assemblage G near the top of the Burren Formation is replaced by a lower Brigantian Rugose Coral Assemblage H in the Slievenaglasha Formation. A similar change in the foraminiferans and calcareous algae at this Asbian–Brigantian formation boundary is recognized by the presence of upper Asbian Cf6γ Subzone taxa in the Burren Formation including Cribrostomum lecomptei, Koskinobigenerina sp., Bradyina rotula and Howchinia bradyana, and in the Slievenaglasha Formation abundant Asteroarchaediscus spp., Neoarchaediscus spp. and Fasciella crustosa of the Brigantian Cf6δ Subzone. The uppermost beds of the Slievenaglasha Formation contain a rare and unusual foraminiferal assemblage containing evolved archaediscids close to tenuis stage indicating a late Brigantian age. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

Empirically Derived California Vapor Intrusion Attenuation Factors     

Rafat Abbasi  William Bosan  Dan Gallagher 《Ground Water Monitoring & Remediation》2023,43(1):60-68

The California Department of Toxic Substances Control (DTSC) gathered empirical data from sites contaminated with chlorinated volatile organic compounds and generated a vapor intrusion database. The database includes 52 sites across California with 213 buildings, of which, 53% are residential, and 47% are commercial/industrial (nonresidential). DTSC's objective is to improve its knowledge and understanding of vapor intrusion and derive empirical attenuation factors that are representative of the climatic conditions and types of buildings commonly found in the state. Filtering was applied to remove data of suspect quality that were potentially affected by background sources. After filtering to 600 pairs from 32 sites across California, a subslab attenuation factor (AF) was calculated yielding a 95th percentile of 0.005. After filtering to 2926 paired measurements from 39 sites across California, a soil vapor AF was calculated yielding a 95th percentile of 0.0009. The groundwater data was not analyzed due to the small size of the dataset. The AFs from this study are similar to AFs in a California-specific study by Lahvis and Ettinger (2021). Accordingly, converging lines of evidence suggest that vapor attenuation in California is different from what is observed nationwide by the United States Environmental Protection Agency (USEPA), where an AF of 0.03 was empirically derived and later recommended for initial screening of buildings for potential vapor intrusion exposure (USEPA, 2015).  相似文献   

Discriminating between the roles of late Pleistocene palaeodischarge and geological‐topographic inheritance in fluvial longitudinal profile and channel development          下载免费PDF全文

Colman Gallagher  Matthew Balme  Nicholas Clifford 《地球表面变化过程与地形》2018,43(2):444-462

This paper investigates the influences of palaeohydrology and geological‐topographic inheritance in shaping the channel of the lower River Suir, southeast Ireland. Results of acoustic surveys of the lower River Suir and Waterford Harbour reveal two scales of pseudo‐cyclic river bedforms. Longitudinal elevation profiles of the geological topography (undulating bedrock and till‐mantled bedrock) bounding the present floodplain swath reveal pseudo‐cyclicity in that terrain too. Spectral and statistical analyses are used to quantify the cyclicity of the long profile and geological‐topographic series. These methods show that the dominant cyclicity of the long profile reflects autocorrelation more than inheritance of cyclicity from the bounding geological topography. The cyclicity of the long profile mainly reflects a hydraulic control on pool‐spacing, although some cyclicity probably has been inherited from the geological‐topography. Channel‐forming palaeodischarge is estimated based on the dominant pool‐spacing revealed by spectral analysis, validated using relationships between meander wavelength, channel cross‐sectional geometry and hydraulically‐informed discharge reconstruction. The palaeodischarge estimates are in close agreement and are two orders of magnitude greater than present flood maxima. Significantly, these palaeodischarge estimates also agree closely with palaeodischarge calculated for the submerged Pleistocene palaeochannel that extends across the near‐shore continental shelf from Waterford Harbour. The pool‐sequence of the lower Suir and the submerged palaeochannel represent a former land‐system that was active during a period of low relative sea level during the last glacial. More broadly, the paper offers insights into the landscape evolution of formerly glaciated regions that experienced very wide discharge variability during and after the transition from glacial to interglacial regimes, in a context of complex relative sea level change. Copyright © 2017 John Wiley & Sons, Ltd.  相似文献   

Estimating uncertainties on net erosion from well-log porosity data     

A. Licciardi  K. Gallagher  S. A. Clark 《Basin Research》2020,32(1):51-67

Estimating the amount of erosion experienced by a sedimentary basin during its geological history plays a key role in basin modelling. In this paper, we present a novel probabilistic approach to estimate net erosion from porosity–depth data from a single well. Our approach uses a Markov chain Monte Carlo algorithm which readily allows us to deal with imprecise knowledge of the lithology-dependent compaction parameters in a joint inversion scheme using multiple lithologies. The results using synthetic data highlight the advantages of our approach over conventional techniques for net erosion estimation: (a) uncertainties on compaction parameters can be effectively mapped into a probabilistic solution for net erosion; (b) posterior uncertainties are easy to quantify; (c) the joint inversion scheme can automatically reconcile porosity data from different lithologies. Our results also underscore the critical role of prior assumptions on controlling the retrieved estimates for net erosion. Using real data from a well in the Barents Sea, we simulate three possible scenarios of variable prior assumptions on compaction parameters to demonstrate the general applicability of our approach. Strong prior assumptions on the compaction parameters led to unrealistic estimates of net erosion for the target well, indicating the assumptions are probably inappropriate. Our preferred strategy for this dataset is to include additional data to constrain the normal compaction trend of the sediments. This provides a net erosion estimate for the target well of about 2300 m with a standard deviation of 140 m which is in line with previous studies. Finally, we discuss potential guidelines to deal with real applications in which data from normally compacted sediments are not available. One is to use our algorithm as a hypothesis-testing tool to evaluate the results under a large set of assumed compaction parameters. A second is to infer compaction parameters and net erosion simultaneously from the target well porosity data. Although appealing and successful with synthetic data, this strategy provides results which are strongly dependent on the calibration data and the geological history of the sediments sampled by the target well.  相似文献   

Late‐Quaternary history of ‘great lakes’ on the Tibetan Plateau and palaeoclimatic implications – A review     

Shi‐Yong Yu  Steven M. Colman  Zhong‐Ping Lai 《Boreas: An International Journal of Quaternary Research》2019,48(1):1-19

Geomorphic evidence suggests that shorelines of 100–200 m above the modern lake levels were common across the Tibetan Plateau during late Marine Isotope Stage (MIS) 3. The timing of this lake‐level highstand is mainly based on radiocarbon ages. Problems surrounding the ages of lacustrine sediments at or beyond the limit of the radiocarbon‐dating method have created a need for alternative geochronometers. Chronological advances during the last decade have renewed interest in the timing of events beyond the limit of radiocarbon dating. Here, we synthesize published data for elevated lacustrine landforms of 48 lakes on the Tibetan Plateau, in order to provide a thorough perspective on the timing and pattern of lake‐level changes in this alpine area during the late Quaternary. The ages of these elevated shore features reveal a long‐term trend of relative lake‐level fall from at least MIS 5, instead of a peak in MIS 3, as previously thought. Dating lacustrine terrace sequences reveals that the rate of lake‐level fall ranged from ~1 to 3 mm a^?1, comparable with that of related river downcutting across the plateau. Palaeoclimatic proxy records point to a sustained drying since the Last Interglacial, suggesting that long‐term aridification might be the culprit for this widespread and progressive lake‐level fall.  相似文献   

Swept up lives? Re‐envisioning the homeless city – By Paul Cloke,Jon May and Sarah Johnsen     

Aisling Gallagher 《New Zealand geographer》2012,68(1):70-71

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Star formation in the Small Magellanic Cloud: the youngest star clusters     

E. Sabbi  A. Nota  J. S. Gallagher  M. Tosi  L. R. Carlson  M. Sirianni  M. Meixner  L. J. Smith  M. S. Oey  R. Walterbos  A. Pasquali  L. Angeretti 《Astrophysics and Space Science》2009,324(2-4):101-107

We combined optical Hubble Space Telescope ACS images with mid-infrared Spitzer data of the two young star clusters NGC346 and NGC602 in the Small Magellanic Cloud, to study how local and global conditions may affect the process of star formation. We found that, while general conditions such as metallicity, or the mass or morphological type of the parent galaxy do not strongly affect the process of star formation, local conditions such as the gas and stellar density can affect both how star formation occurs and propagates, and also the evolution of a star cluster from early times.  相似文献