U.K. HiGEM Shaffrey, L. C.; Stevens, I.; Norton, W. A. ...
Journal of climate,
04/2009, Letnik:
22, Številka:
8
Journal Article
Recenzirano
Odprti dostop
This article describes the development and evaluation of the U.K.’s new High-Resolution Global Environmental Model (HiGEM), which is based on the latest climate configuration of the Met Office ...Unified Model, known as the Hadley Centre Global Environmental Model, version 1 (HadGEM1). In HiGEM, the horizontal resolution has been increased to 0.83° latitude × 1.25° longitude for the atmosphere, and 1/3° × 1/3° globally for the ocean. Multidecadal integrations of HiGEM, and the lower-resolution HadGEM, are used to explore the impact of resolution on the fidelity of climate simulations.
Generally, SST errors are reduced in HiGEM. Cold SST errors associated with the path of the North Atlantic drift improve, and warm SST errors are reduced in upwelling stratocumulus regions where the simulation of low-level cloud is better at higher resolution. The ocean model in HiGEM allows ocean eddies to be partially resolved, which dramatically improves the representation of sea surface height variability. In the Southern Ocean, most of the heat transports in HiGEM is achieved by resolved eddy motions, which replaces the parameterized eddy heat transport in the lower-resolution model. HiGEM is also able to more realistically simulate small-scale features in the wind stress curl around islands and oceanic SST fronts, which may have implications for oceanic upwelling and ocean biology.
Higher resolution in both the atmosphere and the ocean allows coupling to occur on small spatial scales. In particular, the small-scale interaction recently seen in satellite imagery between the atmosphere and tropical instability waves in the tropical Pacific Ocean is realistically captured in HiGEM. Tropical instability waves play a role in improving the simulation of the mean state of the tropical Pacific, which has important implications for climate variability. In particular, all aspects of the simulation of ENSO (spatial patterns, the time scales at which ENSO occurs, and global teleconnections) are much improved in HiGEM.
The atmospheric response to a localized distribution of tropical heating is examined in terms of the stationary waves excited and how these impact the mean flow near the tropical tropopause. This is ...done by examining nonlinear simulations of the Gill model with a primitive equation model that extends from the surface up into the stratosphere. The model produces strong cooling of zonal mean temperatures near the tropical tropopause when the heating is on the equator but weaker cooling with the heating at 15'N. The model shows that equatorial Rossby waves that penetrate the lower stratosphere and changes in EP flux divergence that correspond to the observed changes between December and August. It is suggested that ascent in the upper tropical troposphere is driven by vorticity advection or equivalently potential vorticity fluxes due to these equatorial Rossby waves, particularly when the heating is close to the equator. The model results provide support to the hypothesis that the annual cycle in tropical tropopause temperatures is a result of the annual variation in latitude of tropical heating and that equatorial Rossby waves are key in producing the response in the upper troposphere and lower stratosphere.
Countryside Survey is a unique large scale long-term monitoring programme investigating stock and change of habitats, landscape features, vegetation, soil and freshwaters of Great Britain. Repeat ...field surveys combine policy and scientific objectives to provide evidence on how multiple aspects of the environment are changing over time, a key goal of international science in the face of profound human impacts on ecosystems. Countryside Survey 2007 (CS2007), the fifth survey since 1978, retained consistency with previous surveys, whilst evolving in line with technological and conceptual advances in the collection and integration of data to understand landscape change. This paper outlines approaches taken in the 2007 survey and its subsequent analysis and presents some of the headline results of the survey and their relevance for national and international policy objectives.
Key changes between 1998 and 2007 included: a) significant shifts in agricultural land cover from arable to grassland, accompanied by increases in the area of broadleaved woodland, b) decreases in the length of managed hedges associated with agricultural land, as a proportion deteriorated to lines of trees and c) increases in the areas and numbers of wet habitats (standing open water, ponds) and species preferring wetter conditions (1998–2007 and 1978–2007). Despite international policy directed at maintaining and enhancing biodiversity, there were widespread decreases in species richness in all linear and area habitats, except on arable land, consistent with an increase in competitive and late successional species between 1998 and 2007 and 1978 and 2007. Late successional and competitive species: Stinging nettle (Urtica dioica), Hawthorn (Cratageous monogyna) and Bramble (Rubus fruticosus), in the top ten recorded species recorded in 2007, all increased between 1998 and 2007. The most commonly recorded species in CS (1990, 1998 and 2007) was agricultural Ryegrass (Lolium perenne).
Increases in both water quality and soil pH were in line with policy aimed at addressing previous deterioration of both. Headwater streams broadly showed continued improvements in biological quality from 1998 to 2007, continuing trends seen since 1990. In soils, there were significant increases in soil pH between 1998 and 2007 consistent with recovery from acidification.
► We report on the approaches to, and results from, CS2007. ► Between 1998 and 2007 there were significant shifts in land cover. ► Plant species richness decreased between 1998 and 2007 and between 1978 and 2007. ► Headwater streams continued to improve between 1998 and 2007. ► Soil pH changes indicated continued recovery from acidification.
A quantitative examination of the annual cycle in the tropical tropopause temperatures, tropical ascent, momentum balance, and wave driving is performed using ECMWF analyses to determine how the ...annual cycle in tropical tropopause temperatures arises. Results show that the annual cycle in tropical tropopause temperatures is driven by the annual variation in ascent and consequent dynamical (adiabatic) cooling at the tropical tropopause. Mass divergence local to the tropical tropopause has the dominant contribution to ascent near the tropical tropopause. The annual cycle in mass divergence, and the associated meridional flow, near the tropical tropopause is driven by Eliassen-Palm (EP) flux divergence, that is, wave dissipation. The EP flux divergence near the tropical tropopause is dominated by stationary waves with both the horizontal and vertical components of the EP flux contributing. However, the largest annual cycle is in the divergence of the vertical EP flux and in particular from the contribution in the vertical flux of zonal momentum. These results do not match the existing theory that the annual cycle is driven by the wave dissipation in the extratropical stratosphere, that is, the stratospheric pump. It is suggested that the annual cycle is linked to equatorial Rossby waves forced by convective heating in the tropical troposphere.
A sensitivity experiment has been performed with a stratosphere‐resolving GCM where the mean state and variability of the stratosphere have been altered. It is shown that this has a significant ...effect on the mean and variability of wintertime northern hemisphere surface climate. In particular it is shown that the stratosphere strongly contributes to the persistence of the surface Arctic Oscillation at lags of 10–25 days. This confirms the importance of the stratosphere on surface climate that has been inferred by recent studies examining the Arctic Oscillation in reanalysis datasets.
Background
Vascular surgical care has changed dramatically in recent years with little knowledge of the impact of system failures on patient safety. The primary aim of this multicentre observational ...study was to define the landscape of surgical system failures, errors and inefficiency (collectively termed failures) in aortic surgery. Secondary aims were to investigate determinants of these failures and their relationship with patient outcomes.
Methods
Twenty vascular teams at ten English hospitals trained in structured self‐reporting of intraoperative failures (phase I). Failures occurring in open and endovascular aortic procedures were reported in phase II. Failure details (category, delay, consequence), demographic information (patient, procedure, team experience) and outcomes were reported.
Results
There were strong correlations between the trainer and teams for the number and type of failures recorded during 88 procedures in phase I. In 185 aortic procedures, teams reported a median of 3 (i.q.r. 2–6) failures per procedure. Most frequent failures related to equipment (unavailability, failure, configuration, desterilization). Most major failures related to communication. Fourteen failures directly harmed 12 patients. Significant predictors of an increased failure rate were: endovascular compared with open repair (incidence rate ratio (IRR) for open repair 0·71, 95 per cent c.i. 0·57 to 0·88; P = 0·002), thoracic aneurysms compared with other aortic pathologies (IRR 2·07, 1·39 to 3·08; P < 0·001) and unfamiliarity with equipment (IRR 1·52, 1·20 to 1·91; P < 0·001). The major failure total was associated with reoperation (P = 0·011), major complications (P = 0·029) and death (P = 0·027).
Conclusion
Failure in aortic procedures is frequently caused by issues with team‐working and equipment, and is associated with patient harm. Multidisciplinary team training, effective use of technology and new‐device accreditation may improve patient outcomes.
Towards safer surgery
The effect of various HF‐based etching processes on the laser damage resistance of scratched fused silica surfaces has been investigated. Conventionally polished and subsequently scratched fused ...silica plates were treated by submerging in various HF‐based etchants (HF or NH4F:HF at various ratios and concentrations) under different process conditions (e.g., agitation frequencies, etch times, rinse conditions, and environmental cleanliness). Subsequently, the laser damage resistance (at 351 or 355 nm) of the treated surface was measured. The laser damage resistance was found to be strongly process dependent and scaled inversely with scratch width. The etching process was optimized to remove or prevent the presence of identified precursors (chemical impurities, fracture surfaces, and silica‐based redeposit) known to lead to laser damage initiation. The redeposit precursor was reduced (and hence the damage threshold was increased) by: (1) increasing the SiF62− solubility through reduction in the NH4F concentration and impurity cation impurities, and (2) improving the mass transport of reaction product (SiF62−) (using high‐frequency ultrasonic agitation and excessive spray rinsing) away from the etched surface. A 2D finite element crack‐etching and rinsing mass transport model (incorporating diffusion and advection) was used to predict reaction product concentration. The predictions are consistent with the experimentally observed process trends. The laser damage thresholds also increased with etched amount (up to ∼30 μm), which has been attributed to: (1) etching through lateral cracks where there is poor acid penetration, and (2) increasing the crack opening resulting in increased mass transport rates. With the optimized etch process, laser damage resistance increased dramatically; the average threshold fluence for damage initiation for 30 μm wide scratches increased from 7 to 41 J/cm2, and the statistical probability of damage initiation at 12 J/cm2 of an ensemble of scratches decreased from ∼100 mm−1 of scratch length to ∼0.001 mm−1.
The ultimate limitations of the balance, slow-manifold, and potential vorticity inversion concepts are investigated. These limitations are associated with the weak but nonvanishing ...spontaneous-adjustment emission, or Lighthill radiation, of inertia-gravity waves by unsteady, two-dimensional or layerwise-two-dimensional vortical flow (the wave emission mechanism sometimes being called "geostrophic" adjustment even though it need not take the flow toward geostrophic balance).
Vascular malformations and tumors, also known as "vascular anomalies", comprise an extensive variety of lesions involving all parts of the body. Knowledge of their classification and imaging ...characteristics is paramount. Whereas hemangiomas are benign vascular tumors, characterized by cellular proliferation and hyperplasia; vascular malformations are not real tumors and characteristically exhibit normal endothelial turnover. Vascular malformations are classified according to the predominant vascular channel as arterial, capillary, venous, lymphatic, or mixed. Ultrasound and MRI are the main imaging modalities used in the diagnosis and classification of the vascular anomalies. In this series of two articles we review the classification of vascular anomalies, describe the role of imaging, summarize their distinctive histopathogenic, clinical and imaging features, and discuss the treatment options. On the first article we discuss the high-flow lesions, whereas the slow-flow lesions will be reviewed on the second. Complex syndromes with associated vascular tumors and malformations will be also presented.
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