Preferred structures in large-scale circulation and the effect of doubling greenhouse gas concentration in HadCM3

Preferred structures in the surface pressure variability are investigated in and compared between two 100-year simulations of the Hadley Centre climate model HadCM3. In the first (control) simulation, the model is forced with pre-industrial carbon dioxide concentration (1×CO2) and in the second simulation the model is forced with doubled CO2 concentration (2×CO2). Daily winter (December-January-February) surface pressures over the Northern Hemisphere are analysed. The identification of preferred patterns is addressed using multivariate mixture models. For the control simulation, two significant flow regimes are obtained at 5% and 2.5% significance levels within the state space spanned by the leading two principal components. They show a high pressure centre over the North Pacific/Aleutian Islands associated with a low pressure centre over the North Atlantic, and its reverse. For the 2×CO2 simulation, no such behaviour is obtained. At higher-dimensional state space, flow patterns are obtained from both simulations. They are found to be significant at the 1% level for the control simulation and at the 2.5% level for the 2×CO2 simulation. Hence under CO2 doubling, regime behaviour in the large-scale wave dynamics weakens. Doubling greenhouse gas concentration affects both the frequency of occurrence of regimes and also the pattern structures. The less frequent regime becomes amplified and the more frequent regime weakens. The largest change is observed over the Pacific where a significant deepening of the Aleutian low is obtained under CO2 doubling

On the existence of young embedded clusters at high Galactic latitude

Careful analyses of photometric and star count data available for the nine putative young clusters identified by Camargo et al. (2015, 2016) at high Galactic latitudes reveal that none of the groups contain early-type stars, and most are not significant density enhancements above field level. 2MASS colours for stars in the groups match those of unreddened late-type dwarfs and giants, as expected for contamination by (mostly) thin disk objects. A simulation of one such field using only typical high latitude foreground stars yields a colour-magnitude diagram that is very similar to those constructed by Camargo et al. (2015, 2016) as evidence for their young groups as well as the means of deriving their reddenings and distances. Although some of the fields are coincident with clusters of galaxies, one must conclude that there is no evidence that the putative clusters are extremely young stellar groups.Comment: Accepted for publication (MNRAS

Taking the C out of CVMFS

The Cern Virtual Machine File System is most well known as a distribution mechanism for the WLCG VOs@@ experiment software; as a result, almost all the existing expertise is in installing clients mount the central Cern repositories. We report the results of an initial experiment in using the cvmfs server packages to provide Glasgow-based repository aimed at software provisioning for small UK-local VOs. In general, although the documentation is sparse, server configuration is reasonably easy, with some experimentation. We discuss the advantages of local CVMFS repositories for sites, with some examples from our test VOs, vo.optics.ac.uk and neiss.org.uk

Xenon isotopes in nanodiamonds and other presolar grains

pdf freely available cb 18/07/0

QSO's from Galaxy Collisions with Naked Black Holes

In the now well established conventional view (see Rees [1] and references therein), quasi-stellar objects (QSOs) and related active galactic nuclei (AGN) phenomena are explained as the result of accretion of plasma onto giant black holes which are postulated to form via gravitational collapse of the high density regions in the centers of massive host galaxies. This model is supported by a wide variety of indirect evidence and seems quite likely to apply at least to some observed AGN phenomena. However, one surprising set of new Hubble Space Telescope (HST) observations [2-4] directly challenges the conventional model, and the well known evolution of the QSO population raises some additional, though not widely recognized, difficulties. We propose here an alternative possibility: the Universe contains a substantial independent population of super-massive black holes, and QSO's are a phenomenon that occurs due to their collisions with galaxies or gas clouds in the intergalactic medium (IGM). This hypothesis would naturally explain why the QSO population declines very rapidly towards low redshift, as well as the new HST data.Comment: plain TeX file, no figures, submitted to Natur