Multidecadal signals in the interannual variability of atmospheric angular momentum

To assess whether trends in the troposphere's circulation have occurred this century in concert with changes at the surface, we consider the low-frequency behavior in the global angular momentum of the atmosphere. Values of this index have been computed each month since 1870 from model experiments conducted by the UK Hadley Centre for Climate Prediction and Research, in which the model atmosphere is driven by prescribed boundary forcings, most especially sea surface temperature (SST) fields. The interannual variability of the model's atmospheric angular momentum compares favorably with that derived from the NCEP/NCAR reanalysis for the period of overlap (the second half of the twentieth century). Evidence is found for a notable increase in interannual variability since around 1970, but this recent high level of variability may not be significantly greater than that during 1900–1920. This latter result is strongly dependent on the character of the SST field used in an experiment, because low-frequency signals in atmospheric momentum are closely linked to those in the El Niño/Southern Oscillation. Large differences exist, however, among SST estimates in the tropical Pacific for the early part of the century.     

A benthic index of biological integrity for assessing habitat quality in estuaries of the southeastern USA

A benthic index of biotic integrity was developed for use in estuaries of the southeastern USA (Cape Henry, VA; St. Lucie Inlet, FL) using a modification of the method developed by Weisberg et al. (1997. An estuarine benthic index of biotic integrity (B-IBI) for Chesapeake Bay. Estuaries, 20 (1), 149–158). Data from non-degraded stations sampled in 1993 and 1994 were analyzed using classification analysis of species composition to define major habitat types relative to selected physical parameters. Various benthic metrics were then tested on a larger 1994 data set for each major habitat to determine those that discriminated between non-degraded and degraded sites classified on the basis of dissolved oxygen, sediment chemistry, and sediment toxicity results. Scoring criteria for each metric were developed based on the distribution of values at non-degraded sites. Average scores from different combinations of the most sensitive metrics were compared to derive the final index, which integrates the average scores of four metrics (number of taxa, abundance, dominance, and percent sensitive taxa). An independent data set representing sites sampled in 1993 and 1995 was used to validate the index. The final combined index correctly classified 93% of stations province-wide in the developmental data set and 75% of stations in the validation data set. Comparison of the index results with those of individual benthic measures and sediment bioassays from stations sampled in 1993 and 1995 showed that the index detected a higher percentage of samples where bioeffects were expected (based on sediment chemistry) than did any of these other measures individually.     

Hydrodynamic simulations of rotating molecular jets

Molecular outflows and the jets which may drive them can be expected to display signatures associated with rotation if they are the channels through which angular momentum is extracted from material accreting on to protostars. Here, we determine some basic signatures of rapidly rotating flows through three-dimensional numerical simulations of hydrodynamic jets with molecular cooling and chemistry. We find that these rotating jets generate a broad advancing interface which is unstable and develops into a large swarm of small bow features. In comparison to precessing jets, there is no stagnation point along the axis. The greater the rotation rate, the greater the instability. On the other hand, velocity signatures are only significant close to the jet inlet since jet expansion rapidly reduces the rotation speed. We present predictions for atomic, H₂ and CO submillimetre images and spectroscopy including velocity channel maps and position–velocity diagrams. We also include simulated images corresponding to Spitzer IRAC band images and CO emission, relevant for APEX and eventual ALMA observations. We conclude that protostellar jets often show signs of slow precession but only a few sources display properties which could indicate jet rotation.     

On the possibility of a convective vortex sheet in a fluid heated from below

Summary A theoretical explanation for equatorial accelerations is briefly reviewed. A simple laboratory dishpan experiment is suggested to explore the possibility of the formation in a fluid of what may be termed aconvective vortex sheet, characterized by a sharp zone of horizontal shear in the mean motion field and whose dynamics should tend to produce an equatorial acceleration.     

Experiments to Study Radiation Transport in Clumpy Media

Clumpiness of the interstellar medium may play an important role in the transfer of infrared continuum radiation in star forming regions (Boisse, 1990). For example, in homogeneous models, C II emission should be confined to the cloud edge (Viala, 1986). However, in star formation regions (such as M17SW, M17 and W51), it is observed to extend deep into the molecular cloud (Stutzki et al., 1988; Keene et al., 1985). One plausible interpretation of these observations is that, due to their clumpiness, the clouds are penetrated by UV radiation far deeper than expected from simple homogeneous models. The interaction of H II regions around young massive stars with a clumpy medium is another area of interest. Molecular clouds are well established to be clumpy on length scales down to the limits of observational resolution. Clumps can act as localized reservoirs of gas which can be injected into the surroundings by photoionization and/or hydrodynamic ablation (Dyson et al., 1995; Mathis et al., 1998). The calculation of radiation transport in hot, clumpy materials is a challenging problem. Approximate, statistical treatments of this problem have been developed by several workers, but their application has not been tested in detail. We describe laboratory experiments, using the Omega laser to test modelling of radiation transport through clumpy media in the form of inhomogeneous plasmas.     

Statistical algorithms for identification of astronomical X‐ray sources

Observations of present and future X‐ray telescopes include a large number of ipitous sources of unknown types. They are a rich source of knowledge about X‐ray dominated astronomical objects, their distribution, and their evolution. The large number of these sources does not permit their individual spectroscopical follow‐up and classification. Here we use Chandra Multi‐Wavelength public data to investigate a number of statistical algorithms for classification of X‐ray sources with optical imaging follow‐up. We show that up to statistical uncertainties, each class of X‐ray sources has specific photometric characteristics that can be used for its classification. We assess the relative and absolute performance of classification methods and measured features by comparing the behaviour of physical quantities for statistically classified objects with what is obtained from spectroscopy. We find that among methods we have studied, multi‐dimensional probability distribution is the best for both classifying source type and redshift, but it needs a sufficiently large input (learning) data set. In absence of such data, a mixture of various methods can give a better final result.We discuss some of potential applications of the statistical classification and the enhancement of information obtained in this way. We also assess the effect of classification methods and input data set on the astronomical conclusions such as distribution and properties of X‐ray selected sources. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Governing large-scale marine commons: Contextual challenges in the Coral Triangle

Environment and development agendas are increasingly being characterised by regional-scale initiatives. This trend is in part motivated by recognition of the need to account for global drivers of change (e.g., climate change, migration, and globalisation), the aspirations of achieving large-scale ecological goals (such as maintaining ecosystem processes), and reconciling potentially conflicting priorities in multi-use planning. However, regional-scale governance is challenging and there is little theoretical guidance or empirical evidence to suggest how it can be achieved. This paper uses the Institutional Analysis and Development framework to highlight the diverse contextual factors that challenge governance of a large-scale marine common, using an example of the Coral Triangle Initiative. The analysis points to the need for a critical, reflexive approach to the Coral Triangle Initiative if it is to effectively navigate diverse contexts and reconcile multiple objectives in the region. Recognising the heterogeneous, multi-scale and interlinked nature of large-scale marine systems is critical. Coping with contextual complexity will require innovative approaches that strive to be inclusive of varied perspectives and actors, enable and support effective collective-choice arrangements at lower levels of organisation, and organise and link diverse institutional arrangements at multiple scales. Large-scale marine governance will also involve a great deal of experimentation and regular adjustments to governance arrangements to account for the dynamic nature of regional commons.     

Hydrogen and helium abundances in neutron-star atmospheres

An analysis is presented of the burning and diffusion of hydrogen and helium in a neutron-star atmosphere. An initial two-component atmosphere of hydrogen and carbon and of helium and carbon is examined utilizing various photospheric temperatures. The hydrogen burns through the proton-proton reaction and the CN-cycle and the helium by the triple-alpha process and alpha capture on carbon. It is found that only a negligible proportion of hydrogen or helium can exist after a few years in the neutron-star atmosphere.