A poincaré model for the earth's fluid core

Abstract

The superconducting-gravimeter data of Melchior and Ducarme (1986) has been interpreted as internal motion in the Earth's core by Aldridge and Lumb (1987) using a Poincaré model. Several low-order modes with periods of 13–16 hours have been tentatively identified in the core which is taken to be an incompressible, homogeneous fluid within a rigid, rotating container. The identification is based on asymptotic values of the frequencies which change slowly with time while the modes decay with an e-folding time of about 280 days. The slow change in frequency with time implies a small temporal variation in the rotation rate of the core. This mean flow is a nonlinear effect often observed in laboratory experiments designed to excite Poincaré modes. Interaction among modes during free ringdown is also observed in those experiments and apparently in the data of Melchior et al. (1988) as well. Laboratory work thus provides the link to extend the Poincaré model to include viscous and nonlinear effects in order to interpret the gravimetric observations as core modes.     

Leveraging modern climatology to increase adaptive capacity across protected area networks

Human-driven changes in the global environment pose an increasingly urgent challenge for the management of ecosystems that is made all the more difficult by the uncertain future of both environmental conditions and ecological responses. Land managers need strategies to increase regional adaptive capacity, but relevant and rapid assessment approaches are lacking. To address this need, we developed a method to assess regional protected area networks across biophysically important climatic gradients often linked to biodiversity and ecosystem function. We plot the land of the southwestern United States across axes of historical climate space, and identify landscapes that may serve as strategic additions to current protected area portfolios. Considering climate space is straightforward, and it can be applied using a variety of relevant climate parameters across differing levels of land protection status. The resulting maps identify lands that are climatically distinct from existing protected areas, and may be utilized in combination with other ecological and socio-economic information essential to collaborative landscape-scale decision-making. Alongside other strategies intended to protect species of special concern, natural resources, and other ecosystem services, the methods presented herein provide another important hedging strategy intended to increase the adaptive capacity of protected area networks.     

The influence of slope orientation upon the soil moisture regime,and its hydrogeomorphological significance

Slope insolation provides a basis for the differentiation of micro-environments, within which various soil moisture regimes control differences in soil behaviour. Limiting factors, however, regulate evapotranspiration losses so that, cumulatively, spatial inequalities are diminutive. Nevertheless, seasonal divergence of soil and soil moisture conditions is sufficient to effect within-catchment differences in water disposition.     

Managing private and public adaptation to climate change

Adaptation to climate change is already being delivered by public and private actors, yet there has been little analysis of the relationships between the providers and beneficiaries of adaptation. This paper reviews the type of actors that are supplying adaptation services and their motivations. We then focus on a specific, under-explored case of adaptation: that of privately provided adaptation public goods and services, the realization of which is contingent on the individual management of private goods and private risks. Following the work of Olson (1965) we find that the benefits of the privately provided adaptation public good do not necessarily accrue back to the (same) individuals who are the providers. The characteristics of this particular form of public good pose specific institutional challenges. In this paper we: 1) explore the characteristics and defining features of these privately provided adaptation public goods; 2) argue that this form of adaptation provisioning is increasingly recognised as a feature in climate change adaptation (and/or social transformation) problems; 3) review existing cases of effective/ineffective management of these public goods; and 4) outline the institutions that may be required to facilitate the management of these public goods for adaptation.     

The nature and environments of compact steep spectrum radio sources from studies of their angular sizes

The angular sizes of compact steep spectrum sources in the Peacock and Wall sample were found to decrease steeply with redshift, similar to the angular size-redshift variation for extended sources. This, however, could be an artefact if the compact sources are not all of the same nature.Models such as those of Subramanian and Swarup with a beam power of 10³⁷ W were found to be compatible with compact sources being either young sources at an early stage of development or relatively weak sources in dense, active media where star formation is continuing.     

Wavelength Dependence of the Orbital Variability of the Eclipsing Nova-Like Object Dw Uma

Results of three-colour VRI CCD photometry are presented obtained during 11 nights in 2001. Twelve new minima timings are derived. The eclipse depth decreases with wavelength, being equal to 1.28, 1.13 and 1.02 for V, R and I, respectively. The instrumental magnitudes and colours are tabulated for the mid-eclipse, out-of-eclipse part and the eclipsed component. The V−R colour of the eclipsed component of emission is by 0.22 mag bluer than that for mid-eclipse, indicating a much higher temperature of the eclipsed region.     

Book reviews

Climate change in contrasting river basins: adaptation strategies for water, food and environment. Edited by J Aerts and P Droogers. Published in 2004 by CABI Publishing, 288 p., hardcover. ISBN: 0–85199–835–6. Price: US$100 (orders: services@dadirect.com.au).

Australian water bugs. Their biology and identification (Hemiptera‐Heteroptera, Gerromorpha &; Nepomorpha). By Nils M Andersen? and Tom A Weir. Published in 2004 by CSIRO Publishing/Apollo Books, P.O. Box 1139, Collingwood, VIC 3066, Australia. 344 p., hardcover. ISBN: 0–643–090517. Price: AU$135.00 (orders: publishing.sales@csiro.au).

The Lakes Handbook. Volume I: Limnology and Limnetic Ecology. Volume II: Lake restoration and rehabilitation. Edited by Patrick O'Sullivan and Colin Reynolds. Published by Blackwell Publishing Ltd., 109 Cowley Road, Oxford OX4 1JF, United Kingdom (http//www.blackwellpublishing.com). Volume I (published in 2003) 712 p., hardcover. ISBN: 0632047976. Price: £125. Volume II (published in 2004) 568 p., hardcover. ISBN: 063204795X. Price: £125.     

Tsunamis generated by landslides at the coast of conical islands: experimental benchmark dataset for mathematical model validation

This paper presents a new experimental campaign aimed at reproducing tsunamis generated by landslides at the flank of conical islands. In order to describe in high details the wave field around the island a special acquisition system, which consists of both fixed and movable wave gauges, has been employed. Indeed, each experiment has been repeated several times by changing the configuration of the movable gauges, then obtaining a single virtual experiment with high spatial resolution measurements. Fixed run-up gauges measure the waves at fixed locations to statistically quantify the repeatability of the experiments. Selected experimental results are illustrated within the paper that is mainly aimed at defining a benchmark dataset, available on request, for the development/calibration/validation of analytical and numerical models of tsunamis generated by landslides.