Climatic and environmental reconstructions based on fossil assemblages from middle devensian (Weichselian) deposits of the river Thames at south kensington, central London, UK

Fossiliferous silts within the Late Pleistocene Kempton Park Gravel, of the River Thames Valley, were exposed in 1980 during foundation works for the Ismaili Centre in South Kensington, London. The results of a multidisciplinary study of the geomorphology, sediments, fossil plants, vertebrates, molluscs, ostracods and insects are reported. The silts were deposited under two distinct climatic regimes; a lower unit accumulated when the climate was arctic and an upper when the temperatures were at least as warm as those of the present day. Both these units occupy the same channel system and are separated from one another by less than a metre of sediment, implying that the climatic change was probably sudden and intense. The strongest evidence for this climatic difference comes from a study of the Coleoptera, which show an almost complete replacement of the arctic element in the fauna by a suite of temperate species. Palaeotemperature reconstructions using the Mutual Climatic Range method, based on the coleopteran assemblages from the lower unit, suggest that the mean temperature of the warmest month was 9±2 °C and that of the coldest month −22±10 °C. For the upper unit the mean temperature of the warmest month had risen to about 17 °C and that of the coldest month to about −4 °C. The episode represented by the lower unit, with its arctic climate, had not previously been recognized in the Thames Valley. The fauna from the upper, temperate, unit is very similar to that from other sites in the Kempton Park Gravel, such as that from Isleworth, 10 km upriver, which, like the upper unit at the Ismaili Centre, was characterized by the virtual absence of trees. It would appear that in such cases this treelessness does not indicate cold conditions, equivalent to those of the modern tundra, but may instead result from a combination of ecological and temporal factors. The value of multidisciplinary studies in reaching such conclusions is emphasized.The temperate episode described here is correlated with the thermal maximum at the early part of the Upton Warren Interstadial Complex. An earlier suggestion, based on amino acid epimerization ratios, that the Upton Warren Interstadial correlates with Oxygen Isotope Sub-stage 5a is not supported by the data, which show no evidence of the forested environments that characterized this period in both Britain and the adjacent Continent. It is thought that the temperate deposits at the Ismaili Centre belong to the Middle (Pleniglacial), rather than the Early, Devensian (Weichselian) and are equivalent to Oxygen Isotope Stage 3.     

Control‐volume mixed finite element methods

A key ingredient in simulation of flow in porous media is accurate determination of the velocities that drive the flow. Large‐scale irregularities of the geology (faults, fractures, and layers) suggest the use of irregular grids in simulation. This paper presents a control‐volume mixed finite element method that provides a simple, systematic, easily implemented procedure for obtaining accurate velocity approximations on irregular (i.e., distorted logically rectangular) block‐centered quadrilateral grids. The control‐volume formulation of Darcy’s law can be viewed as a discretization into element‐sized “tanks” with imposed pressures at the ends, giving a local discrete Darcy law analogous to the block‐by‐block conservation in the usual mixed discretization of the mass‐conservation equation. Numerical results in two dimensions show second‐order convergence in the velocity, even with discontinuous anisotropic permeability on an irregular grid. The method extends readily to three dimensions.     

Harmonic Analysis of Sedimentary Cyclic Sequences in Kansas, Midcontinent, USA

Several stratigraphic sequences in the Upper Carboniferous (Pennsylvanian) in Kansas (Midcontinent, USA) were analyzed quantitatively for periodic repetitions. The sequences were coded by lithologic type into strings of datasets. The strings then were analyzed by an adaptation of a one-dimensional Fourier transform analysis and examined for evidence of periodicity. The method was tested using different states in coding to determine the robustness of the method and data. The most persistent response is in multiples of 8–10 ft (2.5–3.0 m) and probably is dependent on the depositional thickness of the original lithologic units. Other cyclicities occurred in multiples of the basic frequency of 8–10 with persistent ones at 22 and 30 feet (6.5–9.0 m) and large ones at 80 and 160 feet (25–50 m). These levels of thickness relate well to the basic cyclothem and megacyclothem as measured on outcrop. We propose that this approach is a suitable one for analyzing cyclic events in the stratigraphic record.     

March 1990 Hailstorm Damage in Sydney,Australia

On 18 March 1990, an intense hailstorm in Sydney, New South Wales, Australia caused insured damage valued at A$million – the third most expensive loss event in Australian insurance history.While damage was widespread with claims for buildings spread across more than 130 postcodes, 20% of the claims came from just two postcodes. The proportion of dwellings of brick construction that made a claim was significantly less than the proportion of policies for this type of construction. Fibro (fibre-cement), timber and aluminium-clad dwellings are more likely to sustain damage than brick buildings in this type of storm.Hail caused the majority of damage to exterior building items while water damage more commonly affected interior building items and contents. While the repair of Interior building items such as ceilings and walls cost more than contents damage on average, the repair/replacement costs of contents contributed more to the total costs. Damage to window glass and roofs together made up more than 50% of the total claim.     

High spatial and temporal resolution observations of an impulse-driven field line resonance in radar backscatter artificially generated with the Tromsø heater

The CUTLASS Finland HF radar has been operated in conjunction with the EISCAT Tromsø RF ionospheric heater facility to examine a ULF wave characteristic of the development of a field line resonance (FLR) driven by a cavity mode caused by a magnetospheric impulse. When the heater is on, striating the ionosphere with field-aligned ionospheric electron density irregularities, a large enough radar target is generated to allow post-integration over only 1 second. When combined with 15 km range gates, this gives radar measurements of a naturally occurring ULF wave at a far better temporal and spatial resolution than has been achieved previously. The time-dependent signature of the ULF wave has been examined as it evolves from a large-scale cavity resonance, through a transient where the wave period was latitude-dependent and the oscillation had the characteristics of freely ringing field lines, and finally to a very narrow, small-scale local field line resonance. The resonance width of the FLR is only 60 km and this is compared with previous observations and theory. The FLR wave signature is strongly attenuated in the ground magnetometer data. The characterisation of the impulse driven FLR was only achieved very crudely with the ground magnetometer data and, in fact, an accurate determination of the properties of the cavity and field line resonant systems challenges the currently available limitations of ionospheric radar techniques. The combination of the latest ionospheric radars and facilities such as the Tromsø ionospheric heater can result in a powerful new tool for geophysical research.     

Study of sporadic-E clouds by backscatter radar

It is shown that swept-frequency backscatter ionograms covering a range of azimuths can be used to study the dynamics of sporadic-E clouds. A simple technique based on analytic ray tracing can be used to simulate the observed narrow traces associated with E_s patches. This enables the location and extent of the sporadic-E clouds to be determined. The motion of clouds can then be determined from a time sequence of records. In order to demonstrate the method, results are presented from an initial study of 5 days of backscatter ionograms from the Jindalee Stage B data base obtained during March-April 1990. Usually 2–3 clouds were observed each day, mainly during the evening and up to midnight. The clouds lasted from 1–4 h and extended between 30°–80° in azimuth and 150–800 km in range. The clouds were mostly stationary or drifted generally westward with velocities of up to 80 ms^–1. Only one cloud was observed moving eastward.     

Simulation of normal distributed smooth fields by Karhunen-Loéve expansion in combination with kriging

Simulation of multigaussian stochastic fields can be made after a Karhunen-Loéve expansion of a given covariance function. This method is also called simulation by Empirical Orthogonal Functions. The simulations are made by drawing stochastic coefficients from a random generator. These numbers are multiplied with eigenfunctions and eigenvalues derived from the predefined covariance model. The number of eigenfunctions necessary to reproduce the stochastic process within a predefined variance error, turns out to be a cardinal question. Some ordinary analytical covariance functions are used to evaluate how quickly the series of eigenfunctions can be truncated. This analysis demonstrates extremely quick convergence to 99.5% of total variance for the 2nd order exponential (‘gaussian’) covariance function, while the opposite is true for the 1st order exponential covariance function. Due to these convergence characteristics, the Karhunen-Loéve method is most suitable for simulating smooth fields with ‘gaussian’ shaped covariance functions. Practical applications of Karhunen-Loéve simulations can be improved by spatial interpolation of the eigenfunctions. In this paper, we suggest interpolation by kriging and limits for reproduction of the predefined covariance functions are evaluated.