Detecting trends that are nonlinear and asymmetric on diurnal and seasonal time scales

Trends in climate time series are often nonlinear and temporally-asymmetric, i.e. the trend is different for different seasons and/or hours of the day. Here a method is developed that allows the nonlinearity and temporal asymmetry of a trend to be investigated simultaneously. First, nonlinear trend components are extracted from a univariate time series, by adapting a nonparametric dimension-reduction method. Then, the nonlinear trend components are substituted into a regression model in which the periodic mean component and the periodic variation in the amplitude of the nonlinear trend are modeled using harmonic functions of the seasonal and diurnal periods. Third, trend patterns in the positive and negative anomalies are investigated, by extending the nonlinear trend model using indicator variables. Fourth, a non-local inferential test is developed to test the statistical significance of the trend patterns. The nonlinear trend model is applied to a simulated time series, as well as to long-term high-resolution temperature records from five Southern Hemisphere sites: Lucas Heights, Sydney Airport, Cape Grim, Macquarie Island and Law Dome. Our method should be generally useful for identifying the effect of both climate-related factors and observation/site-related factors on seasonal and diurnal trends in meteorological data series.     

Modeling the Transient Response of Saline Intrusion to Rising Sea‐Levels

Sea levels are expected to rise as a result of global temperature increases, one implication of which is the potential exacerbation of sea water intrusion into coastal aquifers. Given that approximately 70% of the world's population resides in coastal regions, it is imperative to understand the interaction between fresh groundwater and sea water intrusion in order to best manage available resources. For this study, controlled investigation has been carried out concerning the temporal variation in sea water intrusion as a result of rising sea levels. A series of fixed inland head two‐dimensional sea water intrusion models were developed with SEAWAT in order to assess the impact of rising sea levels on the transient migration of saline intrusion in coastal aquifers under a range of hydrogeological property conditions. A wide range of responses were observed for typical hydrogeological parameter values. Systems with a high ratio of hydraulic conductivity to recharge and high effective porosity lagged behind the equilibrium sea water toe positions during sea‐level rise, often by many hundreds of meters, and frequently taking several centuries to equilibrate following a cease in sea‐level rise. Systems with a low ratio of hydraulic conductivity to recharge and low effective porosity did not develop such a large degree of disequilibrium and generally stabilized within decades following a cease in sea‐level rise. This study provides qualitative initial estimates for the expected rate of intrusion and predicted degree of disequilibrium generated by sea‐level rise for a range of hydrogeological parameter values.     

Temporal and life history related trends of perfluorochemicals in harbor porpoises from the Danish North Sea

Eighty-five stranded or bycaught harbor porpoises collected from the Danish North Sea between 1980 and 2005 were analyzed for perfluorochemicals in the liver. PFOS was the predominant compound, making up on average 88.9% of the ∑PFC, followed by PFOSA (7.8%). PFUnA (1.9%) and PFDA (1.2%) were detected in most samples. PFHxS, PFNA and PFOA were only found in a minority of the samples. We found substantial differences in PFC concentrations among life history stages, the highest concentrations were found in neonates, suckling juveniles and lactating females. Such differences should be considered when PFC levels in wildlife are evaluated. The high concentrations found in young porpoises are of concern as PFCs have known toxic effects on the development of the central nervous system and reproductive organs. Despite efforts to reduce PFC emissions, a decreasing temporal trend of concentrations was not detected for any compound. PFCA concentrations were found to be increasing.     

A Review of Higher Order Ionospheric Refraction Effects on Dual Frequency GPS

Higher order ionospheric effects are increasingly relevant as precision requirements on GPS data and products increase. The refractive index of the ionosphere is affected by its electron content and the magnetic field of the Earth, so the carrier phase of the GPS L1 and L2 signals is advanced and the modulated code delayed. Due to system design the polarisation is unaffected. Most of the effect is removed by expanding the refractive index as a series and eliminating the first term with a linear combination of the two signals. However, the higher order terms remain. Furthermore, transiting gradients in refractive index at a non-perpendicular angle causes signal bending. In addition to the initial geometric bending term, another term allows for the difference that the curvature makes in electron content along each signal. Varying approximations have been made for practical implementation, mainly to avoid the need for a vertical profile of electron density. The magnetic field may be modelled as a tilted co-centric dipole, or using more realistic models such as the International Geomagnetic Reference Field. The largest effect is from the second term in the expansion of the refractive index. Up to several cm on L2, it particularly affects z-translation, and satellite orbits and clocks in a global network of GPS stations. The third term is at the level of the errors in modelling the second order term, while the bending terms appear to be absorbed by tropospheric parameters. Modelling improvements are possible, and three frequency transmissions will allow new possibilities.     

Thallium isotopes in early diagenetic pyrite - A paleoredox proxy?

This paper presents the first study of Tl isotopes in early diagenetic pyrite. Measurements from two sections deposited during the Toarcian Ocean Anoxic Event (T-OAE, ∼183 Ma) are compared with data from Late Neogene (<10 Ma) pyrite samples from ODP legs 165 and 167 that were deposited in relatively oxic marine environments. The Tl isotope compositions of Late Neogene pyrites are all significantly heavier than seawater, which most likely indicates that Tl in diagenetic pyrite is partially sourced from ferromanganese oxy-hydroxides that are known to display relatively heavy Tl isotope signatures. One of the T-OAE sections from Peniche in Portugal displays pyrite thallium isotope compositions indistinguishable from Late Neogene samples, whereas samples from Yorkshire in the UK are depleted in the heavy isotope of Tl. These lighter compositions are best explained by the lack of ferromanganese precipitation at the sediment-water interface due to the sulfidic (euxinic) conditions thought to be prevalent in the Cleveland Basin where the Yorkshire section was deposited. The heavier signatures in the Peniche samples appear to result from an oxic water column that enabled precipitation of ferromanganese oxy-hydroxides at the sediment-water interface.The Tl isotope profile from Yorkshire is also compared with previously published molybdenum isotope ratios determined on the same sedimentary succession. There is a suggestion of an anti-correlation between these two isotope systems, which is consistent with the expected isotope shifts that occur in seawater when marine oxic (ferromanganese minerals) fluxes fluctuate.The results outlined here represent the first evidence that Tl isotopes in early diagenetic pyrite have potential to reveal variations in past ocean oxygenation on a local scale and potentially also for global oceans. However, much more information about Tl isotopes in different marine environments, especially in anoxic/euxinic basins, is needed before Tl isotopes can be confidently utilized as a paleo-redox tracer.     

BeppoSAX observations of GRS 1915+105

The galactic superluminal source GRS 1915+105 was observed byBeppoSAX at several occasions from October 1996 to April 2000. In April 1999 the 2–10 keV light curve showed a long series of quasi regular pulses with a recurrence time of about 50 s. Some preliminary results of a spectral analysis are presented.     

X-ray Spectroscopy of the Scattered Emission in NGC 1068

We discuss the iron K line complex in NGC 1068. The line complex basically consists of three components, as previously reported. A new analysis of the ASCA data shows that cold reflection appears to dominate the observed X-ray emission above 4 keV based on the detection of ‘Compton shoulder’, a weak red wing of the 6.4 keV fluorescence iron K line, and a very flat continuum. The other two weaker lines at higher energies can be identified with FeXXV and FeXXVI and suggest an highly ionized X-ray mirror as well, although the line energies are systematically lower than those expected from the resonant lines, consistent with a redshift by 1.5%. This revised version was published online in July 2006 with corrections to the Cover Date.     

UVES Abundances of Stars in Nearby Dwarf Spheroidal Galaxies

It is a truth universally acknowledged, that a galaxy in possession of a good quantity of gas must want to form stars. It is the details of how and why that baffle us all. The simplest theories either would have this process a carefully self-regulated affair, or one that goes completely out of control and is capable of wrecking the galaxy which hosts it. Of course the majority of galaxies seem to amble along somewhere between these two extremes, and the mean properties tend to favour a quiescent self-regulated evolutionary scenario. But there area variety of observations which require us to invoke transitory ‘bursts’ of star-formation at one time or another in most galaxy types. Several nearby dwarf spheroidal galaxies have clearly determined star-formation histories with apparent periods of zero star formation followed by periods of fairly active star formation. If we are able to understand what separated these bursts we would understand several important phenomena in galaxy evolution. Were these galaxies able to clear out their gas reservoir in a burst of star formation? How did this gas return? or did it? Have these galaxies receieved gas from the IGM instead? Could stars from these types of galaxy contribute significantly to the halo population in our Galaxy? To answer these questions we need to combine accurate stellar photometry and Colour-Magnitude Diagram interpretation with detailed metal abundances to combine a star-formation rate versus time with a range of element abundances with time. Different elements trace different evolutionary process (e.g., relative contributions of type I and II supernovae). We often aren't even sure of the abundance spread in these galaxies. We have collected detailed high resolution UVES spectra of four nearby dwarf spheroidal galaxies (Sculptor, Fornax, Leo I &; Carina) to begin to answer these questions. This is a precursor study to a more complete study with FLAMES. We presented at this meeting the initial results for the Sculptor and Fornax dwarf spheroidal galaxies which have been previously had single element (low resolution) calcium abundance studies (Tolstoy et al., 2001). See Figures 1 and 2.     

The iron Kα Compton shoulder in transmitted and reflected spectra

We calculate the equivalent width of the core, and the centroid energy and relative flux of the first-order Compton shoulder of the iron Kα emission line from neutral matter. The calculations are performed with Monte Carlo simulations. We explore a large range of column densities for both transmitted and reflected spectra, and study the dependence on the iron abundance. The Compton shoulder is now becoming observable in many objects thanks to the improved sensitivity and/or energy resolution of the XMM – Newton and Chandra satellites, and the present work aims to provide a tool to derive information on the geometry and element abundances of the line-emitting matter from Compton shoulder measurements.