41 research outputs found
Opportunistic experiments to constrain aerosol effective radiative forcing
Aerosol–cloud interactions (ACIs) are considered to be the most uncertain driver of present-day radiative forcing due to human activities. The nonlinearity of cloud-state changes to aerosol perturbations make it challenging to attribute causality in observed relationships of aerosol radiative forcing. Using correlations to infer causality can be challenging when meteorological variability also drives both aerosol and cloud changes independently. Natural and anthropogenic aerosol perturbations from well-defined sources provide “opportunistic experiments” (also known as natural experiments) to investigate ACI in cases where causality may be more confidently inferred. These perturbations cover a wide range of locations and spatiotemporal scales, including point sources such as volcanic eruptions or industrial sources, plumes from biomass burning or forest fires, and tracks from individual ships or shipping corridors. We review the different experimental conditions and conduct a synthesis of the available satellite datasets and field campaigns to place these opportunistic experiments on a common footing, facilitating new insights and a clearer understanding of key uncertainties in aerosol radiative forcing. Cloud albedo perturbations are strongly sensitive to background meteorological conditions. Strong liquid water path increases due to aerosol perturbations are largely ruled out by averaging across experiments. Opportunistic experiments have significantly improved process-level understanding of ACI, but it remains unclear how reliably the relationships found can be scaled to the global level, thus demonstrating a need for deeper investigation in order to improve assessments of aerosol radiative forcing and climate change
The Structure of the Oligomerization Domain of Lsr2 from Mycobacterium tuberculosis Reveals a Mechanism for Chromosome Organization and Protection
Lsr2 is a small DNA-binding protein present in mycobacteria and related actinobacteria that regulates gene expression and influences the organization of bacterial chromatin. Lsr2 is a dimer that binds to AT-rich regions of chromosomal DNA and physically protects DNA from damage by reactive oxygen intermediates (ROI). A recent structure of the C-terminal DNA-binding domain of Lsr2 provides a rationale for its interaction with the minor groove of DNA, its preference for AT-rich tracts, and its similarity to other bacterial nucleoid-associated DNA-binding domains. In contrast, the details of Lsr2 dimerization (and oligomerization) via its N-terminal domain, and the mechanism of Lsr2-mediated chromosomal cross-linking and protection is unknown. We have solved the structure of the N-terminal domain of Lsr2 (N-Lsr2) at 1.73 Å resolution using crystallographic ab initio approaches. The structure shows an intimate dimer of two ß–ß–a motifs with no close homologues in the structural databases. The organization of individual N-Lsr2 dimers in the crystal also reveals a mechanism for oligomerization. Proteolytic removal of three N-terminal residues from Lsr2 results in the formation of an anti-parallel β-sheet between neighboring molecules and the formation of linear chains of N-Lsr2. Oligomerization can be artificially induced using low concentrations of trypsin and the arrangement of N-Lsr2 into long chains is observed in both monoclinic and hexagonal crystallographic space groups. In solution, oligomerization of N-Lsr2 is also observed following treatment with trypsin. A change in chromosomal topology after the addition of trypsin to full-length Lsr2-DNA complexes and protection of DNA towards DNAse digestion can be observed using electron microscopy and electrophoresis. These results suggest a mechanism for oligomerization of Lsr2 via protease-activation leading to chromosome compaction and protection, and concomitant down-regulation of large numbers of genes. This mechanism is likely to be relevant under conditions of stress where cellular proteases are known to be upregulated
The hemispheric contrast in cloud microphysical properties constrains aerosol forcing
The change in planetary albedo due to aerosol−cloud interactions during the industrial era is the leading source of uncertainty in inferring Earth’s climate sensitivity to increased greenhouse gases from the historical record. The variable that controls aerosol−cloud interactions in warm clouds is droplet number concentration. Global climate models demonstrate that the present-day hemispheric contrast in cloud droplet number concentration between the pristine Southern Hemisphere and the polluted Northern Hemisphere oceans can be used as a proxy for anthropogenically driven change in cloud droplet number concentration. Remotely sensed estimates constrain this change in droplet number concentration to be between 8 cm−3 and 24 cm−3. By extension, the radiative forcing since 1850 from aerosol−cloud interactions is constrained to be −1.2 W⋅m−2 to −0.6 W⋅m−2. The robustness of this constraint depends upon the assumption that pristine Southern Ocean droplet number concentration is a suitable proxy for preindustrial concentrations. Droplet number concentrations calculated from satellite data over the Southern Ocean are high in austral summer. Near Antarctica, they reach values typical of Northern Hemisphere polluted outflows. These concentrations are found to agree with several in situ datasets. In contrast, climate models show systematic underpredictions of cloud droplet number concentration across the Southern Ocean. Near Antarctica, where precipitation sinks of aerosol are small, the underestimation by climate models is particularly large. This motivates the need for detailed process studies of aerosol production and aerosol−cloud interactions in pristine environments. The hemispheric difference in satellite estimated cloud droplet number concentration implies preindustrial aerosol concentrations were higher than estimated by most models
City of Hitchcock Comprehensive Plan 2020-2040
Hitchcock is a small town located in Galveston
County (Figure 1.1), nestled up on the Texas Gulf
Coast. It lies about 40 miles south-east of Houston.
The boundaries of the city encloses an area of
land of 60.46 sq. miles, an area of water of 31.64
sq. miles at an elevation just 16 feet above sea level.
Hitchcock has more undeveloped land (~90% of
total area) than the county combined. Its strategic
location gives it a driving force of opportunities in
the Houston-Galveston Region.The guiding principles for this planning process were Hitchcock’s vision statement and its corresponding goals, which were crafted by the
task force. The goals focus on factors of growth and development including public participation, development considerations,
transportation, community facilities, economic development, parks, and housing and social vulnerabilityTexas Target Communitie
The genetic architecture of the human cerebral cortex
The cerebral cortex underlies our complex cognitive capabilities, yet little is known about the specific genetic loci that influence human cortical structure. To identify genetic variants that affect cortical structure, we conducted a genome-wide association meta-analysis of brain magnetic resonance imaging data from 51,665 individuals. We analyzed the surface area and average thickness of the whole cortex and 34 regions with known functional specializations. We identified 199 significant loci and found significant enrichment for loci influencing total surface area within regulatory elements that are active during prenatal cortical development, supporting the radial unit hypothesis. Loci that affect regional surface area cluster near genes in Wnt signaling pathways, which influence progenitor expansion and areal identity. Variation in cortical structure is genetically correlated with cognitive function, Parkinson's disease, insomnia, depression, neuroticism, and attention deficit hyperactivity disorder
The CCP4 suite : integrative software for macromolecular crystallography
The Collaborative Computational Project No. 4 (CCP4) is a UK-led international collective with a mission to develop, test, distribute and promote software for macromolecular crystallography. The CCP4 suite is a multiplatform collection of programs brought together by familiar execution routines, a set of common libraries and graphical interfaces. The CCP4 suite has experienced several considerable changes since its last reference article, involving new infrastructure, original programs and graphical interfaces. This article, which is intended as a general literature citation for the use of the CCP4 software suite in structure determination, will guide the reader through such transformations, offering a general overview of the new features and outlining future developments. As such, it aims to highlight the individual programs that comprise the suite and to provide the latest references to them for perusal by crystallographers around the world
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Wind, Rain, and the Closed to Open Cell Transition in Subtropical Marine Stratocumulus
Lagrangian transitions in mesoscale cellular convective (MCC) clouds beginning as closed cell MCC and transitioning to open cells or disorganized but cellular MCC are explored on timescales from 12 to 72 hr. Potential drivers of MCC transitions are shown to act on multiple timescales. Closed-to-open MCC cloud transitions are preceded by strong surface winds and large moisture fluxes at lead times of up to 72 hr; and by high cloud water content, reduced cloud drop concentrations, and intense rain rates at lead times of 12-36 hr. The relationship between intense rain and the formation of open cells is consistent with a cold pool convergence mechanism. A Lagrangian analysis shows that anomalously strong surface winds are associated with higher rain rates as well as subsequent increases in rain rates through modifications to moisture flux and content in the boundary layer. The closed-open MCC transition contrasts with the closed-to-disorganized transition which at long lead times is associated with warm sea surface temperature and at diurnal-scale lead times is associated with variables related to cloud top entrainment drying such as a deepening boundary layer, weakening subsidence and inversion strength, and a drier free troposphere. A conceptual model is proposed where excess boundary layer moisture associated with wind breaks up stratocumulus through the closed-to-open transition, while excess dry-air entrainment at cloud top breaks up stratocumulus through the closed-to-disorganized transition
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Absorbing Aerosol Choices Influences Precipitation Changes Across Future Scenarios
Future precipitation changes are controlled by the atmospheric energy budget, with temperature, water vapor, and absorbing aerosols playing dominant roles in driving radiative changes. Atmospheric energy budgets are calculated for different Shared Socioeconomic Pathways using ScenarioMIP projections from Phase 6 of the Climate Model Intercomparison Project and are used to quantify the influence of 21st century aerosol cleanup on precipitation. Absorbing aerosol influences on shortwave absorption are isolated from the effects of water vapor. Apparent hydrologic sensitivity is ∼40% higher for the Middle of the Road (SSP2‐4.5) scenario with aerosol cleanup than for the Regional Rivalry (SSP3‐7.0) scenario that maintains aerosol. Regionally, cleanup‐induced changes in the atmospheric energy budget are of a similar magnitude to the precipitation increases themselves and are larger than the influence of changes in atmospheric circulation. Policy choices about future absorbing aerosol emissions will therefore have major impacts on global and regional precipitation changes.Plain Language SummaryPrecipitation changes will have a temperature‐dependent and a temperature‐independent part of their response to climate change. Water vapor contributes primarily to the former while well‐mixed greenhouse gases will influence both. The temperature‐independent response will be impacted by absorbing aerosol emissions. This is examined through an atmospheric energy budget where precipitation (i.e., latent heat) balances other energy sources and sinks in the atmosphere (i.e., sensible heat and shortwave and longwave radiation). We utilize a novel set of global climate model simulations that incorporate varied socioeconomic choices over the 21st century to study real‐world implications of future aerosol policies on precipitation. Reductions in absorbing aerosol amount help precipitation to increase because less shortwave absorption will occur in the atmosphere and, on average, other energy contributions do not change per degree warming. Global precipitation change per degree of global warming is ∼40% higher for socioeconomic pathways where aerosol cleanup occurs. Regional precipitation changes associated with regional aerosol changes are larger than those associated with changes in atmospheric circulation. Policy choices for aerosol emissions will thus have a critical impact on the future availability of water, both globally and regionally.Key PointsAtmospheric energy budgets are used to constrain absorbing aerosol influences on 21st century precipitation in ScenarioMIP projectionsShared Socioeconomic Pathways with aerosol cleanup policies can significantly augment 21st century global precipitationImpacts of regional aerosol changes on precipitation are equal or larger than the influence from atmospheric circulation change