The impact of organic pollution on the macrobenthic fauna of Dubai Creek (UAE)

Dubai Creek is a tidal marine intrusion bisecting Dubai within the United Arab Emirates (UAE). The creek extends 14km inland from its opening into the Arabian Gulf, with a narrow lower creek channel leading to a lagoon section in the upper creek. The creek contains numerous sources of organic pollution including sewage outlet flows and boat waste. A survey of the creek was performed, assessing organic pollution, water properties, and the benthic macrofaunal community. The upper creek was heavily polluted with macrofauna communities commonly associated with organic pollution and eutrophication, while the lower creek contained low pollution and relatively healthy macrofauna communities. There is little net tidal flow of water within the creek and residence time in the lagoon is high, which may account for the high organic pollution levels. However, some evidence of the pollution effect moving into the lower creek was found. The results are considered in light of current and historic organic loading within the creek and future developments in the area.     

A laboratory study of meteor smoke analogues: Composition, optical properties and growth kinetics

Meteoric smoke forms in the mesosphere from the recondensation of the metallic species and silica produced by meteoric ablation. A photochemical flow reactor was used to generate meteoric smoke mimics using appropriate photolytic precursors of Fe and Si atoms in an excess of oxidant. The following systems were studied: (i) Fe+O₃/O₂, (ii) Fe+O₃/O₂+H₂O, (iii) Fe+Si/SiO+O₃/O₂ and (iv) Si/SiO+O₃/O₂. The resulting nano-particles were captured for imaging by transmission electron microscopy, combined with elemental analysis using X-ray (EDX) and electron energy loss (EELS) techniques. These systems generated particle compositions consistent with: (i) Fe₂O₃ (hematite), (ii) FeOOH (goethite), (iii) Fe₂SiO₄ (fayalite) and (iv) SiO₂ (silica). Electron diffraction revealed that the Fe-containing particles were entirely amorphous, while the SiO₂ particles displayed some degree of crystallinity. The Fe-containing particles formed fractal aggregates with chain-like morphologies, whereas the SiO₂ particles were predominantly spherical and compact in appearance. The optical extinction spectra of the Fe-containing particles were measured from 300 nm<λ<650 nm. Excellent agreement was found with the extinction calculated from Mie theory using the refractive indices for the bulk compounds, and assuming that the fractal aggregates are composed of poly-disperse distributions of constituent particles with radii ranging from 5 to 100 nm. These sizes were confirmed from measurements of the particle size distributions and microscopic imaging. Finally, the particle growth kinetics of the Fe-containing systems exhibit unexpectedly rapid agglomerative coagulation. This was modelled by assuming an initial period of coalescent particle growth resulting from diffusional (Brownian) coagulation to form primary particles; further growth of these particles is then dominated by long-range magnetic dipole–dipole interactions, leading to the fractal aggregates observed. The atmospheric implications of this work are then discussed.     

RoboNet‐II: Follow‐up observations of microlensing events with a robotic network of telescopes

RoboNet‐II uses a global network of robotic telescopes to perform follow‐up observations of microlensing events in the Galactic Bulge. The current network consists of three 2 m telescopes located in Hawaii and Australia (owned by Las Cumbres Observatory) and the Canary Islands (owned by Liverpool John Moores University). In future years the network will be expanded by deploying clusters of 1 m telescopes in other suitable locations. A principal scientific aim of the RoboNet‐II project is the detection of cool extra‐solar planets by the method of gravitational microlensing. These detections will provide crucial constraints to models of planetary formation and orbital migration. RoboNet‐II acts in coordination with the PLANET microlensing follow‐up network and uses an optimization algorithm (“web‐PLOP”) to select the targets and a distributed scheduling paradigm (eSTAR) to execute the observations. Continuous automated assessment of the observations and anomaly detection is provided by the ARTEMiS system (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Bayesian modelling of clusters of galaxies from multifrequency-pointed Sunyaev–Zel'dovich observations

We present a Bayesian approach to modelling galaxy clusters using multi-frequency pointed observations from telescopes that exploit the Sunyaev–Zel'dovich effect. We use the recently developed multinest technique to explore the high-dimensional parameter spaces and also to calculate the Bayesian evidence. This permits robust parameter estimation as well as model comparison. Tests on simulated Arcminute Microkelvin Imager observations of a cluster, in the presence of primary CMB signal, radio point sources (detected as well as an unresolved background) and receiver noise, show that our algorithm is able to analyse jointly the data from six frequency channels, sample the posterior space of the model and calculate the Bayesian evidence very efficiently on a single processor. We also illustrate the robustness of our detection process by applying it to a field with radio sources and primordial CMB but no cluster, and show that indeed no cluster is identified. The extension of our methodology to the detection and modelling of multiple clusters in multi-frequency SZ survey data will be described in a future work.     

Radio source calibration for the Very Small Array and other cosmic microwave background instruments at around 30 GHz

Accurate calibration of data is essential for the current generation of cosmic microwave background (CMB) experiments. Using data from the Very Small Array (VSA), we describe procedures which will lead to an accuracy of 1 per cent or better for experiments such as the VSA and CBI. Particular attention is paid to the stability of the receiver systems, the quality of the site and frequent observations of reference sources. At 30 GHz the careful correction for atmospheric emission and absorption is shown to be essential for achieving 1 per cent precision.
The sources for which a 1 per cent relative flux density calibration was achieved included Cas A, Cyg A, Tau A and NGC 7027 and the planets Venus, Jupiter and Saturn. A flux density, or brightness temperature in the case of the planets, was derived at 33 GHz relative to Jupiter which was adopted as the fundamental calibrator. A spectral index at ∼30 GHz is given for each.
Cas A, Tau A, NGC 7027 and Venus were examined for variability. Cas A was found to be decreasing at 0.394 ± 0.019 per cent yr⁻¹ over the period 2001 March to 2004 August. In the same period Tau A was decreasing at 0.22 ± 0.07 per cent yr⁻¹. A survey of the published data showed that the planetary nebula NGC 7027 decreased at 0.16 ± 0.04 per cent yr⁻¹ over the period 1967–2003. Venus showed an insignificant (1.5 ± 1.3 per cent) variation with Venusian illumination. The integrated polarization of Tau A at 33 GHz was found to be 7.8 ± 0.6 per cent at position angle =148°± 3°.     

Autonomous software: Myth or magic?

We discuss work by the eSTAR project which demonstrates a fully closed loop autonomous system for the follow up of possible micro‐lensing anomalies. Not only are the initial micro‐lensing detections followed up in real time, but ongoing events are prioritised and continually monitored, with the returned data being analysed automatically. If the “smart software” running the observing campaign detects a planet‐like anomaly, further follow‐up will be scheduled autonomously and other telescopes and telescope networks alerted to the possible planetary detection.We further discuss the implications of this, and how such projects can be used to build more general autonomous observing and control systems. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

On Precipitation and Virga over Three Locations during the 1999–2004 Canadian Prairie Drought

The recent 1999–2004 drought, and especially the period from 2001 to 2002, had major impacts across Canada and in the western Canadian Prairie region in particular. This study characterizes the recent drought with respect to precipitation on a small scale at three sites: Calgary, Edmonton and Saskatoon. Climatologically, precipitation events of low daily accumulation (≤0 mm) account for the majority of the total accumulation (up to 58%) at all study locations. During the recent drought, these events contributed a higher proportion of the total precipitation (up to 63%) because of a lack of heavy precipitation events. Using radar data at these locations, precipitation events were also classified into three categories: convective, stratiform and virga. There was wide variation in the relative importance of stratiform and convective precipitation at the sites with, for example, some drought periods being dominated by convective and others by stratiform events. Virga was also present with an average cloud base temperature <0°C which would have led to efficient sublimational loss contributing to the reduction of precipitation at the surface. Any understanding of drought must take into account such precipitation issues.

R ésumé ?[Traduit par la rédaction] La récente sécheresse de 1999–2004, et plus spécialement la période de 2001 à 2002, a eu des répercussions majeures au Canada en général et dans la région des Prairies canadiennes en particulier. La présente étude caractérise cette sécheresse récente en fonction des précipitation à petite échelle à trois sites : Calgary, Edmonton et Saskatoon. D'un point de vue climatologique, les événements de précipitations de faible accumulation journalière (≤10 mm) comptent pour la majorité de l'accumulation totale (jusqu'à 58 %) à tous les endroits étudiés. Durant la récente sécheresse, ces événements ont constitué une plus grande proportion des précipitations totales (jusqu'à 63 %) à cause du faible nombre d'événements de fortes précipitations. À l'aide des données radar à ces endroits, les événements de précipitation ont aussi été classifiées en trois catégories : convective, stratiforme et virga. Il y a eu une grande variation de l'importance relative des précipitations stratiformes et convectives à ces sites avec, par exemple, certaines périodes de sécheresse dominées par des événements convectifs et d'autres par des événements stratiformes. Il y a eu aussi des virgas avec une température moyenne de la base des nuages <0°C, ce qui aurait causé des pertes par sublimation contribuant à la réduction des précipitations à la surface. Pour comprendre toute sécheresse on doit prendre en compte ce genre de facteurs liés aux précipitations.     

Seasonal Neutron-Flux Variations in the Polar Caps of Mars as Revealed by the Russian HEND Instrument Onboard the NASA 2001 Mars Odyssey Spacecraft

We analyze the flux of epithermal neutrons from the Martian surface recorded by the Russian High-Energy Neutron Detector (HEND) from February 19 through December 19, 2002. The HEND was installed onboard the NASA 2001 Mars Odyssey spacecraft and is designed to measure neutron fluxes with energies above 1 eV. Over the period of observations, statistically significant variations in the flux of epithermal (10–100 keV) neutrons were found in the northern and southern polar caps. The largest neutron-flux variations were found at subpolar latitudes, where the relative difference between the summer and winter values can reach severalfold. This correlation becomes weaker with increasing distance from the poles. Thus, the relative change in the neutron flux near the 60° parallel is slightly more than 10%. We assume that the detected variations result from the global circulation of atmospheric carbon dioxide in subpolar Martian regions. To additionally test this assumption, we compared the HEND neutron measurements onboard 2001 Mars Odyssey and the seasonal variations in the CO₂-layer thickness as observed by the Mars Orbital Laser Altimeter (MOLA) onboard Mars Global Surveyor (MGS).