Using satellites to investigate the sensitivity of longwave downward radiation to water vapor at high elevations

Many studies suggest that high-elevation regions may be among the most sensitive to future climate change. However, in situ observations in these often remote locations are too sparse to determine the feedbacks responsible for enhanced warming rates. One of these feedbacks is associated with the sensitivity of longwave downward radiation (LDR) to changes in water vapor, with the sensitivity being particularly large in many high-elevation regions where the average water vapor is often low. We show that satellite retrievals from the Moderate Resolution Imaging Spectroradiometer (MODIS) and Clouds and the Earth’s Radiant Energy System (CERES) can be used to expand the current ground-based observational database and that the monthly averaged clear-sky satellite estimates of humidity and LDR are in good agreement with the well-instrumented Center for Snow and Avalanche Studies ground-based site in the southwestern Colorado Rocky Mountains. The relationship between MODIS-retrieved precipitable water vapor and surface specific humidity across the contiguous United States was found to be similar to that previously found for the Alps. More important, we show that satellites capture the nonlinear relationship between LDR and water vapor and confirm that LDR is especially sensitive to changes in water vapor at high elevations in several midlatitude mountain ranges. Because the global population depends on adequate fresh water, much of which has its source in high mountains, it is critically important to understand how climate will change there. We demonstrate that satellites can be used to investigate these feedbacks in high-elevation regions where the coverage of surface-based observations is insufficient to do so

Iron-Line Emission as a Probe of Bardeen-Petterson Accretion Disks

In this work we show that Bardeen-Petterson accretion disks can exhibit unique, detectable features in relativistically broadened emission line profiles. Some of the unique characteristics include inverted line profiles with sharper red horns and softer blue horns and even profiles with more than 2 horns from a single rest-frame line. We demonstrate these points by constructing a series of synthetic line profiles using simple two-component disk models. We find that the resultant profiles are very sensitive to the two key parameters one would like to constrain, namely the Bardeen-Petterson transition radius r_{BP} and the relative tilt \beta between the two disk components over a range of likely values [10 < r_{BP}/(GM/c^2) < 40 ; 15deg < \beta < 45deg]. We use our findings to show that some of the ``extra'' line features observed in the spectrum of the Seyfert-I galaxy MCG--6-30-15 may be attributable to a Bardeen-Petterson disk structure. Similarly, we apply our findings to two likely Bardeen-Petterson candidate Galactic black holes - GRO J1655-40 and XTE J1550-564. We provide synthetic line profiles of these systems using observationally constrained sets of parameters. Although we do not formally fit the data for any of these systems, we confirm that our synthetic spectra are consistent with current observations.Comment: 13 pages, 11 figures, submitted to Ap

The Formation and Gravitational-Wave Detection of Massive Stellar Black-Hole Binaries

If binaries consisting of two 100 Msun black holes exist they would serve as extraordinarily powerful gravitational-wave sources, detectable to redshifts of z=2 with the advanced LIGO/Virgo ground-based detectors. Large uncertainties about the evolution of massive stars preclude definitive rate predictions for mergers of these massive black holes. We show that rates as high as hundreds of detections per year, or as low as no detections whatsoever, are both possible. It was thought that the only way to produce these massive binaries was via dynamical interactions in dense stellar systems. This view has been challenged by the recent discovery of several stars with mass above 150 Msun in the R136 region of the Large Magellanic Cloud. Current models predict that when stars of this mass leave the main sequence, their expansion is insufficient to allow common envelope evolution to efficiently reduce the orbital separation. The resulting black-hole--black-hole binary remains too wide to be able to coalesce within a Hubble time. If this assessment is correct, isolated very massive binaries do not evolve to be gravitational-wave sources. However, other formation channels exist. For example, the high multiplicity of massive stars, and their common formation in relatively dense stellar associations, opens up dynamical channels for massive black hole mergers (e.g., via Kozai cycles or repeated binary-single interactions). We identify key physical factors that shape the population of very massive black-hole--black-hole binaries. Advanced gravitational-wave detectors will provide important constraints on the formation and evolution of very massive stars.Comment: ApJ accepted, extended description of modelin

Age and geochemistry of Late Neoproterozoic and Early Cambrian igneous rocks in southern New Brunswick: similarities and contrasts

Late Proterozoic to Early Cambrian igneous rocks are major components of the fault-bounded Caledonia, Brookville, and New River terranes of southern New Brunswick. As previously demonstrated, ca. 620 Ma and ca. 560– 550 Ma volcanic and plutonic rocks of the Caledonia terrane are petrologically similar to coeval units elsewhere in the Avalon terrane sensu stricto of the northern Appalachian orogen. In contrast, the Golden Grove Plutonic Suite and volcanic rocks of the Dipper Harbour Formation in the Brookville terrane are mainly younger, ranging in age from ca. 555 Ma to 525 Ma. A new U-Pb (zircon) age reported here confirms that rhyolite in the Dipper Harbour Formation crystallized at 553 ± 3 Ma, like the older units of the Golden Grove Plutonic Suite to which they are chemically similar. However, they differ chemically from felsic units of similar age in the Caledonia terrane, with higher K2O and Rb, lower Na2O, and negative epsilon Nd values, although they also appear to have formed in an extensional setting. The Early Cambrian history of the two terranes is also very different, with clastic sediment deposition dominating in the Caledonia terrane while an active continental margin subduction zone developed on the Brookville terrane. A U-Pb (zircon) age of 539 ± 4 Ma shows that volcanic rocks in the Simpsons Island Formation in the New River terrane are early Cambrian, similar to the ages of some plutons of the Golden Grove Plutonic Suite. More petrological studies of the Simpsons Island Formation are needed to assess it tectonic setting and relationship to the older (ca. 555 Ma) Leavitts Head Formation and Ragged Falls Plutonic Suite. These units are chemically similar to one another, consistent with their inferred comagmatic relationship, and are interpreted to have formed in an extensional setting. They are more similar to ca. 555– 545 Ma volcanic and plutonic rocks of the Brookville terrane than to 560– 550 Ma volcanic and plutonic rocks of the Caledonia terrane, although all of these units apparently formed in extensional settings. Too few data are available from volcanic units in the northeastern part of the New River terrane (Lobster Brook Formation) to compare them to the Leavitts Head Formation or to assess their tectonic setting. A U-Pb age of 622 ± 2 Ma from the Blacks Harbour Granite in the southern part of the New River terrane is similar to previously reported ages from the Lingley Suite in the northeastern part of the terrane. More mapping and sampling are needed to define the extent of these ca. 625 Ma units in the New River terrane and assess their tectonic setting, although a subduction environment is suggested by the available data. RÉSUMÉ Les roches ignées du Protérozoïque tardif au Cambrien précoce constituent des éléments importants des terranes limités par des failles de Caledonia, de Brookville et de New River dans le Sud du Nouveau-Brunswick. Il a déjà été démontré que les roches volcaniques et plutoniques d'environ 620 Ma et de 560 à 550 Ma du terrane de Caledonia sont pétrologiquement semblables aux unités contemporaines ailleurs à l'intérieur du terrane d'Avalon, faisant partie, au sens strict, du nord de l'orogène des Appalaches. Par contraste, le cortège plutonique de Golden Grove et les roches volcaniques de la Formation de Dipper Harbour dans le terrane de Brookville sont essentiellement plus récentes; leurs âges varient entre 755 Ma et 525 Ma. Une nouvelle datation au U-Pb (à partir de zircon) signalée aux présentes confirme que la rhyolite de la Formation de Dipper Harbour s'est cristallisée vers 553±3 Ma, tout comme les unités plus anciennes du cortège plutonique de Golden Grove auxquelles ces roches ressemblent sur le plan chimique. Elles diffèrent toutefois du point de vue chimique des unités felsiques d'âge analogue du terrane de Caledonia, en présentant des concentrations plus élevées de K2O et de Rb, des concentrations inférieures de Na2O, et des valeurs Nd epsilon négatives, même si elles semblent s'être formées dans un cadre d'extension. Le passé des deux terranes au cours du Cambrien précoce est également très différent : un dépôt de sédiments clastiques prédomine dans le terrane de Caledonia, tandis qu'une zone active de subduction de la marge continentale s'est développée dans le terrane de Brookville. Une datation au U-Pb (à partir de zircon) situant les roches volcaniques de la Formation de Simpsons Island dans le terrane de New River à 539 ±4 Ma, révèle qu'elles remontent au Cambrien, ce qui leur confère des âges semblables à certains plutons du cortège plutonique de Golden Grove. Il faudrait réaliser d'autres études pétrologiques de la Formation de Simpsons Island pour évaluer son cadre tectonique et ses rapports avec la Formation plus ancienne (environ 555 Ma) de Leavitts Head et le cortège plutonique de Ragged Falls. Ces unités sont chimiquement semblables les unes aux autres, ce qui correspond à leur présumée relation comagmatique. Elles sont interprétées comme des unités s'étant formées dans un cadre d'extension. Elles ressemblent plus aux roches plutoniques et volcaniques d'environ 555 à 545 Ma du terrane de Brookville qu'aux roches plutoniques et volcaniques de 560 à 550 Ma du terrane de Caledonia, même si ces unités se sont apparemment constituées dans des cadres d'extension. On dispose de trop peu de données des unités volcaniques du nord-est du terrane de New River (Formation de Lobster Brook) pour les comparer à la Formation de Leavitts Head ou pour évaluer leur cadre tectonique. L'âge au U-Pb de 622 ±2 Ma du granite de Blacks Harbour dans le sud du terrane de New River est semblable aux âges précédemment signalés dans le cas du cortège de Lingley dans le nord-est du terrane. D'autres travaux de cartographie et d'échantillonnage s'avèrent nécessaires pour définir l'étendue de ces unités d'environ 625 Ma dans le terrane de New River ainsi que pour évaluer leur cadre tectonique, même si les données dont on dispose laissent supposer un environnement de subduction

Pilot/Controller Coordinated Decision Making in the Next Generation Air Transportation System

Introduction: NextGen technologies promise to provide considerable benefits in terms of enhancing operations and improving safety. However, there needs to be a thorough human factors evaluation of the way these systems will change the way in which pilot and controllers share information. The likely impact of these new technologies on pilot/controller coordinated decision making is considered in this paper using the "operational, informational and evaluative disconnect" framework. Method: Five participant focus groups were held. Participants were four experts in human factors, between x and x research students and a technical expert. The participant focus group evaluated five key NextGen technologies to identify issues that made different disconnects more or less likely. Results: Issues that were identified were: Decision Making will not necessarily improve because pilots and controllers possess the same information; Having a common information source does not mean pilots and controllers are looking at the same information; High levels of automation may lead to disconnects between the technology and pilots/controllers; Common information sources may become the definitive source for information; Overconfidence in the automation may lead to situations where appropriate breakdowns are not initiated. Discussion: The issues that were identified lead to recommendations that need to be considered in the development of NextGen technologies. The current state of development of these technologies provides a good opportunity to utilize recommendations at an early stage so that NextGen technologies do not lead to difficulties in resolving breakdowns in coordinated decision making