Atlantic Forcing of Persistent Drought in West Africa Shanahan, T.M; Overpeck, J.T; Anchukaitis, K.J ...
Science (American Association for the Advancement of Science),
04/2009, Letnik:
324, Številka:
5925
Journal Article
Recenzirano
Although persistent drought in West Africa is well documented from the instrumental record and has been primarily attributed to changing Atlantic sea surface temperatures, little is known about the ...length, severity, and origin of drought before the 20th century. We combined geomorphic, isotopic, and geochemical evidence from the sediments of Lake Bosumtwi, Ghana, to reconstruct natural variability in the African monsoon over the past three millennia. We find that intervals of severe drought lasting for periods ranging from decades to centuries are characteristic of the monsoon and are linked to natural variations in Atlantic temperatures. Thus the severe drought of recent decades is not anomalous in the context of the past three millennia, indicating that the monsoon is capable of longer and more severe future droughts.
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.
Recent projections of climatic change have focused a great deal of scientific and public attention on patterns of carbon (C) cycling as well as its controls, particularly the factors that determine ...whether an ecosystem is a net source or sink of atmospheric carbon dioxide (CO₂). Net ecosystem production (NEP), a central concept in C-cycling research, has been used by scientists to represent two different concepts. We propose that NEP be restricted to just one of its two original definitions-the imbalance between gross primary production (GPP) and ecosystem respiration (ER). We further propose that a new term-net ecosystem carbon balance (NECB)-be applied to the net rate of C accumulation in (or loss from negative sign) ecosystems. Net ecosystem carbon balance differs from NEP when C fluxes other than C fixation and respiration occur, or when inorganic C enters or leaves in dissolved form. These fluxes include the leaching loss or lateral transfer of C from the ecosystem; the emission of volatile organic C, methane, and carbon monoxide; and the release of soot and CO₂ from fire. Carbon fluxes in addition to NEP are particularly important determinants of NECB over long time scales. However, even over short time scales, they are important in ecosystems such as streams, estuaries, wetlands, and cities. Recent technological advances have led to a diversity of approaches to the measurement of C fluxes at different temporal and spatial scales. These approaches frequently capture different components of NEP or NECB and can therefore be compared across scales only by carefully specifying the fluxes included in the measurements. By explicitly identifying the fluxes that comprise NECB and other components of the C cycle, such as net ecosystem exchange (NEE) and net biome production (NBP), we can provide a less ambiguous framework for understanding and communicating recent changes in the global C cycle.
Genomic selection increases accuracy and decreases generation interval, accelerating genetic changes in populations. Assumptions of genetic improvement must be addressed to quantify the magnitude and ...direction of change. Genetic trends of US dairy cattle breeds were examined to determine the genetic gain since the implementation of genomic evaluations in 2009. Inbreeding levels and generation intervals were also investigated. Breeds included Ayrshire, Brown Swiss, Guernsey, Holstein (HO), and Jersey (JE), which were characterized by the evaluation breed the animal received. Mean genomic predicted breeding values (PBV¯) were analyzed per year to calculate genetic trends for bulls and cows. The data set contained 154,008 bulls and 33,022,242 cows born since 1975. Breakpoints were estimated using linear regression, and nonlinear regression was used to fit the piecewise model for the small sample number in some years. Generation intervals and inbreeding levels were also investigated since 1975. Milk, fat, and protein yields, somatic cell score, productive life, daughter pregnancy rate, and livability PBV¯ were documented. In 2017, 100% of bulls in this data set were genotyped. The percentage of genotyped cows has increased 23 percentage points since 2010. Overall, production traits have increased steadily over time, as expected. The HO and JE breeds have benefited most from genomics, with up to 192% increase in genetic gain since 2009. Due to the low number of observations, trends for Ayrshire, Brown Swiss, and Guernsey are difficult to infer from. Trends in fertility are most substantial; particularly, most breeds are trending downwards and daughter pregnancy rate for JE has been decreasing steadily since 1975 for bulls and cows. Levels of genomic inbreeding are increasing in HO bulls and cows. In 2017, genomic inbreeding levels were 12.7% for bulls and 7.9% for cows. A suggestion to control this is to include the genomic inbreeding coefficient with a negative weight to the selection index of bulls with high future genomic inbreeding levels. For sires of bulls, the current generation intervals are 2.2 yr in HO, 3.2 in JE, 4.4 in Brown Swiss, 5.1 in Ayrshire, and 4.3 in Guernsey. The number of colored breed bulls in the United States is currently at an extremely low level, and this number will only increase with a market incentive or additional breed association involvement. Increased education and extension could be beneficial to increase knowledge about inbreeding levels, use of genomics and genetic improvement, and genetic diversity in the genomic selection era.
Valid and reliable ischemic stroke subtype determination is crucial for well-powered multicenter studies. The Causative Classification of Stroke System (CCS, available at http://ccs.mgh.harvard.edu) ...is a computerized, evidence-based algorithm that provides both causative and phenotypic stroke subtypes in a rule-based manner. We determined whether CCS demonstrates high interrater reliability in order to be useful for international multicenter studies.
Twenty members of the International Stroke Genetics Consortium from 13 centers in 8 countries, who were not involved in the design and development of the CCS, independently assessed the same 50 consecutive patients with acute ischemic stroke through reviews of abstracted case summaries. Agreement among ratings was measured by kappa statistic.
The κ value for causative classification was 0.80 (95% confidence interval CI 0.78-0.81) for the 5-subtype, 0.79 (95% CI 0.77-0.80) for the 8-subtype, and 0.70 (95% CI 0.69-0.71) for the 16-subtype CCS. Correction of a software-related factor that generated ambiguity improved agreement: κ = 0.81 (95% CI 0.79-0.82) for the 5-subtype, 0.79 (95% CI 0.77-0.80) for the 8-subtype, and 0.79 (95% CI 0.78-0.80) for the 16-subtype CCS. The κ value for phenotypic classification was 0.79 (95% CI 0.77-0.82) for supra-aortic large artery atherosclerosis, 0.95 (95% CI 0.93-0.98) for cardioembolism, 0.88 (95% CI 0.85-0.91) for small artery occlusion, and 0.79 (0.76-0.82) for other uncommon causes.
CCS allows classification of stroke subtypes by multiple investigators with high reliability, supporting its potential for improving stroke classification in multicenter studies and ensuring accurate means of communication among different researchers, institutions, and eras.
COVID-19 is causing a major once-in-a-century global pandemic. The scientific and clinical community is in a race to define and develop effective preventions and treatments. The major features of ...disease are described but clinical trials have been hampered by competing interests, small scale, lack of defined patient cohorts and defined readouts. What is needed now is head-to-head comparison of existing drugs, testing of safety including in the background of predisposing chronic diseases, and the development of new and targeted preventions and treatments. This is most efficiently achieved using representative animal models of primary infection including in the background of chronic disease with validation of findings in primary human cells and tissues. We explore and discuss the diverse animal, cell and tissue models that are being used and developed and collectively recapitulate many critical aspects of disease manifestation in humans to develop and test new preventions and treatments.
To obtain accurate mass measurements for cold planets discovered by microlensing, it is usually necessary to combine light curve modeling with at least two lens mass-distance relations. The physical ...parameters of the planetary system OGLE-2014-BLG-0124L have been constrained thanks to accurate parallax effect between ground-based and simultaneous space-based Spitzer observations. Here, we resolved the source+lens star from sub-arcsecond blends in H-band using adaptive optics (AO) observations with NIRC2 mounted on Keck II telescope. We identify additional flux, coincident with the source to within 160 mas. We estimate the potential contributions to this blended light (chance-aligned star, additional companion to the lens or to the source) and find that 85% of the NIR flux is due to the lens star at HL = 16.63 0.06 and KL = 16.44 0.06. We combined the parallax constraint and the AO constraint to derive the physical parameters of the system. The lensing system is composed of a mid-late type G main sequence star of ML = 0.9 0.05 M located at DL = 3.5 0.2 kpc in the Galactic disk. Taking the mass ratio and projected separation from the original study leads to a planet of Mp = 0.65 0.044 MJupiter at 3.48 0.22 au. Excellent parallax measurements from simultaneous ground-space observations have been obtained on the microlensing event OGLE-2014-BLG-0124, but it is only when they are combined with ∼30 minutes of Keck II AO observations that the physical parameters of the host star are well measured.
Tephra fall from the August 1991 eruption of Volcán Hudson affected some 100,000 km
2
of Patagonia and was almost immediately reworked by strong winds, creating billowing clouds of remobilised ash, ...or ‘ash storms’. The immediate impacts on agriculture and rural communities were severe, but were then greatly exacerbated by continuing ash storms. This paper describes the findings of a 3-week study tour of the diverse environments of southern Patagonia affected by ash storms, with an emphasis on determining the impacts of repeated ash storms on agriculture and local practices that were developed in an attempt to mitigate these impacts. Ash storms produce similar effects to initial tephra eruptions, prolonged for considerable periods. These have included the burial of farmland under dune deposits, abrasion of vegetation and contamination of feed supplies with fine ash. These impacts can then cause problems for grazing animals such as starvation, severe tooth abrasion, gastrointestinal problems, corneal abrasion and blindness, and exhaustion if sheep fleeces become laden with ash. In addition, ash storms have led to exacerbated soil erosion, human health impacts, increased cleanup requirements, sedimentation in irrigation canals, and disruption of aviation and land transport. Ash deposits were naturally stabilised most rapidly in areas with high rainfall (>1,500 mm/year) through compaction and enhanced vegetation growth. Stabilisation was slowest in windy, semi-arid regions. Destruction of vegetation and suppression of regrowth by heavy tephra fall (>100 mm) hindered the stabilisation of deposits for years, and reduced the surface friction which increased wind erosivity. Stabilisation of tephra deposits was improved by intensive tillage, use of windbreaks and where there was dense and taller vegetative cover. Long-term drought and the impracticality of mixing ash deposits with soil by tillage on large farms was a barrier to stabilising deposits and, in turn, agricultural recovery. The continuing ash storms motivated the partial evacuation of small rural towns such as Chile Chico (Chile) and Los Antiguos (Argentina) in September–December 1991, after the primary tephra fall in August 1991. Greatly increased municipal cleanup efforts had to be sustained beyond the initial tephra fall to cope with the ongoing impacts of ash storms. Throughout the 1990s, ash storms contributed to continued population migration out of the affected area, leaving hundreds of farms abandoned on the Argentine steppe. The major lesson from our study is the importance of stabilisation of ash deposits as soon as possible after the initial eruption, particularly in windy, arid climates. Suggested mitigation measures include deep cultivation of the ash into the soil and erecting windbreaks.
Effective natural hazard risk assessment requires the characterisation of both hazards and vulnerabilities of exposed elements. Volcanic hazard assessment is at an advanced state and is a ...considerable focus of volcanic scientific inquiry, whereas comprehensive vulnerability assessment is lacking. Cataloguing and analysing volcanic impacts provide insight on likely societal and physical vulnerabilities during future eruptions. This paper reviews documented disruption and physical damage of critical infrastructure elements resulting from four volcanic hazards (tephra fall, pyroclastic density currents, lava flows and lahars) of eruptions in the last 100years. We define critical infrastructure as including energy sector infrastructure, water supply and wastewater networks, transportation routes, communications, and critical components. Common trends of impacts and vulnerabilities are summarised, which can be used to assess and reduce volcanic risk for future eruptions. In general, tephra falls cause disruption to these infrastructure sectors, reducing their functionality, whilst flow hazards (pyroclastic density currents, lava flows and lahars) are more destructive causing considerable permanent damage. Volcanic risk assessment should include quantification of vulnerabilities and we challenge the volcanology community to address this through the implementation of a standardised vulnerability assessment methodology and the development and use of fragility functions, as has been successfully implemented in other natural hazard fields.
•Volcanic risk reduction is a primary goal of research in applied volcanology.•Important to move towards quantitative vulnerability assessment in volcanology.•Review common and reoccurring critical infrastructure impacts from volcanic hazards.•Infrastructure disruption and damage occur across a range of volcanic hazard intensities.•Infrastructure impact severity strongly related to infrastructure design and configuration.
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