15 research outputs found
Climate dynamics and fluid mechanics: Natural variability and related uncertainties
The purpose of this review-and-research paper is twofold: (i) to review the
role played in climate dynamics by fluid-dynamical models; and (ii) to
contribute to the understanding and reduction of the uncertainties in future
climate-change projections. To illustrate the first point, we focus on the
large-scale, wind-driven flow of the mid-latitude oceans which contribute in a
crucial way to Earth's climate, and to changes therein. We study the
low-frequency variability (LFV) of the wind-driven, double-gyre circulation in
mid-latitude ocean basins, via the bifurcation sequence that leads from steady
states through periodic solutions and on to the chaotic, irregular flows
documented in the observations. This sequence involves local, pitchfork and
Hopf bifurcations, as well as global, homoclinic ones. The natural climate
variability induced by the LFV of the ocean circulation is but one of the
causes of uncertainties in climate projections. Another major cause of such
uncertainties could reside in the structural instability in the topological
sense, of the equations governing climate dynamics, including but not
restricted to those of atmospheric and ocean dynamics. We propose a novel
approach to understand, and possibly reduce, these uncertainties, based on the
concepts and methods of random dynamical systems theory. As a very first step,
we study the effect of noise on the topological classes of the Arnol'd family
of circle maps, a paradigmatic model of frequency locking as occurring in the
nonlinear interactions between the El Nino-Southern Oscillations (ENSO) and the
seasonal cycle. It is shown that the maps' fine-grained resonant landscape is
smoothed by the noise, thus permitting their coarse-grained classification.
This result is consistent with stabilizing effects of stochastic
parametrization obtained in modeling of ENSO phenomenon via some general
circulation models.Comment: Invited survey paper for Special Issue on The Euler Equations: 250
Years On, in Physica D: Nonlinear phenomen
Considerations for application of benchmark dose modeling in radiation research: workshop highlights
publishedVersio
Combining biomarker and bulk compositional gradient analysis to assess reservoir connectivity
Author Posting. © The Author(s), 2010. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Organic Geochemistry 41 (2010): 812-821, doi:10.1016/j.orggeochem.2010.05.003.Hydraulic connectivity of petroleum reservoirs represents one of the biggest uncertainties for
both oil production and petroleum system studies. Here, a geochemical analysis involving bulk and
detailed measures of crude oil composition is shown to constrain connectivity more tightly than is
possible with conventional methods. Three crude oils collected from different depths in a single well
exhibit large gradients in viscosity, density, and asphaltene content. Crude oil samples are collected
with a wireline sampling tool providing samples from well‐defined locations and relatively free of
contamination by drilling fluids; the known provenance of these samples minimizes uncertainties in the
subsequent analysis. The detailed chemical composition of almost the entire crude oil is determined by
use of comprehensive two‐dimensional gas chromatography (GC×GC) to interrogate the nonpolar
fraction and negative ion electrospray ionization Fourier transform ion cyclotron resonance mass
spectrometry (ESI FT‐ICR MS) to interrogate the polar fraction. The simultaneous presence of 25‐
norhopanes and mildly altered normal and isoprenoid alkanes is detected, suggesting that the reservoir
has experienced multiple charges and contains a mixture of oils biodegraded to different extents. The
gradient in asphaltene concentration is explained by an equilibrium model considering only gravitational
segregation of asphaltene nanoaggregates; this grading can be responsible for the observed variation in
viscosity. Combining these analyses yields a consistent picture of a connected reservoir in which the
observed viscosity variation originates from gravitational segregation of asphaltene nanoaggregates in a
crude oil with high asphaltene concentration resulting from multiple charges, including one charge that
suffered severe biodegradation. Observation of these gradients having appropriate magnitudes
suggests good reservoir connectivity with greater confidence than is possible with traditional techniques
alone.The mass spectrometry work was
supported by the NSF Division of Materials Research through DMR‐06‐54118, and the State of Florida
Storylines: an alternative approach to representing uncertainty in physical aspects of climate change
As climate change research becomes increasingly applied, the need for actionable information is growing rapidly. A key aspect of this requirement is the representation of uncertainties. The conventional approach to representing uncertainty in physical aspects of climate change is probabilistic, based on ensembles of climate model simulations. In the face of deep uncertainties, the known limitations of this approach are becoming increasingly apparent. An alternative is thus emerging which may be called a ‘storyline’ approach. We define a storyline as a physically self-consistent unfolding of past events, or of plausible future events or pathways. No a priori probability of the storyline is assessed; emphasis is placed instead on understanding the driving factors involved, and the plausibility of those factors. We introduce a typology of four reasons for using storylines to represent uncertainty in physical aspects of climate change: (i) improving risk awareness by framing risk in an event-oriented rather than a probabilistic manner, which corresponds more directly to how people perceive and respond to risk; (ii) strengthening decision-making by allowing one to work backward from a particular vulnerability or decision point, combining climate change information with other relevant factors to address compound risk and develop appropriate stress tests; (iii) providing a physical basis for partitioning uncertainty, thereby allowing the use of more credible regional models in a conditioned manner and (iv) exploring the boundaries of plausibility, thereby guarding against false precision and surprise. Storylines also offer a powerful way of linking physical with human aspects of climate change
Home-based narrowband UVB, topical corticosteroid or combination for children and adults with vitiligo: HI-Light Vitiligo three-arm RCT
BACKGROUND: Systematic reviews suggest that narrowband ultraviolet B light combined with treatments such as topical corticosteroids may be more effective than monotherapy for vitiligo. OBJECTIVE: To explore the clinical effectiveness and cost-effectiveness of topical corticosteroid monotherapy compared with (1) hand-held narrowband ultraviolet B light monotherapy and (2) hand-held narrowband ultraviolet B light/topical corticosteroid combination treatment for localised vitiligo. DESIGN: Pragmatic, three-arm, randomised controlled trial with 9 months of treatment and a 12-month follow-up. SETTING: Sixteen UK hospitals - participants were recruited from primary and secondary care and the community. PARTICIPANTS: Adults and children (aged ≥ 5 years) with active non-segmental vitiligo affecting ≤ 10% of their body area. INTERVENTIONS: Topical corticosteroids [mometasone furoate 0.1% (Elocon®, Merck Sharp & Dohme Corp., Merck & Co., Inc., Whitehouse Station, NJ, USA) plus dummy narrowband ultraviolet B light]; narrowband ultraviolet B light (narrowband ultraviolet B light plus placebo topical corticosteroids); or combination (topical corticosteroids plus narrowband ultraviolet B light). Topical corticosteroids were applied once daily on alternate weeks and narrowband ultraviolet B light was administered every other day in escalating doses, with a dose adjustment for erythema. All treatments were home based. MAIN OUTCOME MEASURES: The primary outcome was self-assessed treatment success for a chosen target patch after 9 months of treatment ('a lot less noticeable' or 'no longer noticeable' on the Vitiligo Noticeability Scale). Secondary outcomes included blinded assessment of primary outcome and percentage repigmentation, onset and maintenance of treatment response, quality of life, side effects, treatment burden and cost-effectiveness (cost per additional successful treatment). RESULTS: In total, 517 participants were randomised (adults, n = 398; and children, n = 119; 52% male; 57% paler skin types I-III, 43% darker skin types IV-VI). At the end of 9 months of treatment, 370 (72%) participants provided primary outcome data. The median percentage of narrowband ultraviolet B light treatment-days (actual/allocated) was 81% for topical corticosteroids, 77% for narrowband ultraviolet B light and 74% for combination groups; and for ointment was 79% for topical corticosteroids, 83% for narrowband ultraviolet B light and 77% for combination. Target patch location was head and neck (31%), hands and feet (32%), and rest of the body (37%). Target patch treatment 'success' was 20 out of 119 (17%) for topical corticosteroids, 27 out of 123 (22%) for narrowband ultraviolet B light and 34 out of 128 (27%) for combination. Combination treatment was superior to topical corticosteroids (adjusted risk difference 10.9%, 95% confidence interval 1.0% to 20.9%; p = 0.032; number needed to treat = 10). Narrowband ultraviolet B light was not superior to topical corticosteroids (adjusted risk difference 5.2%, 95% confidence interval -4.4% to 14.9%; p = 0.290; number needed to treat = 19). The secondary outcomes supported the primary analysis. Quality of life did not differ between the groups. Participants who adhered to the interventions for > 75% of the expected treatment protocol were more likely to achieve treatment success. Over 40% of participants had lost treatment response after 1 year with no treatment. Grade 3 or 4 erythema was experienced by 62 participants (12%) (three of whom were using the dummy) and transient skin thinning by 13 participants (2.5%) (two of whom were using the placebo). We observed no serious adverse treatment effects. For combination treatment compared with topical corticosteroids, the unadjusted incremental cost-effectiveness ratio was £2328.56 (adjusted £1932) per additional successful treatment (from an NHS perspective). LIMITATIONS: Relatively high loss to follow-up limits the interpretation of the trial findings, especially during the post-intervention follow-up phase. CONCLUSION: Hand-held narrowband ultraviolet B light plus topical corticosteroid combination treatment is superior to topical corticosteroids alone for treatment of localised vitiligo. Combination treatment was relatively safe and well tolerated, but was effective in around one-quarter of participants only. Whether or not combination treatment is cost-effective depends on how much decision-makers are willing to pay for the benefits observed. FUTURE WORK: Development and testing of new vitiligo treatments with a greater treatment response and longer-lasting effects are needed. TRIAL REGISTRATION: Current Controlled Trials ISRCTN17160087. FUNDING: This project was funded by the National Institute for Health Research (NIHR) Health Technology Assessment programme and will be published in full in Health Technology Assessment; Vol. 24, No. 64. See the NIHR Journals Library website for further project information
Validation and forecasting accuracy in models of climate change
Forecasting researchers, with few exceptions, have ignored the current major forecasting controversy: global warming and the role of climate modelling in resolving this challenging topic. In this paper, we take a forecaster’s perspective in reviewing established principles for validating the atmospheric-ocean general circulation models (AOGCMs) used in most climateforecasting, and in particular by the Intergovernmental Panel on ClimateChange (IPCC). Such models should reproduce the behaviours characterising key model outputs, such as global and regional temperature changes. We develop various time series models and compare them with forecasts based on one well-established AOGCM from the UK Hadley Centre. Time series models perform strongly, and structural deficiencies in the AOGCM forecasts are identified using encompassing tests. Regional forecasts from various GCMs had even more deficiencies. We conclude that combining standard time series methods with the structure of AOGCMs may result in a higher forecastingaccuracy. The methodology described here has implications for improving AOGCMs and for the effectiveness of environmental control policies which are focussed on carbon dioxide emissions alone. Critically, the forecast accuracy in decadal prediction has important consequences for environmental planning, so its improvement through this multiple modelling approach should be a priority