ALBERT

Description: Vladimir Ivanovitch Vernadsky was a Russian mineralogist and crystallographer by training (St. Petersburg Univ.). He was born in St. Petersburg, on the 12th of March 1863, and died on the 6th of January 1945, in Moscow. About 1910, he became a geochemist and later on a founding father of Biogeochemistry, due to his concern with the "questions related to the importance of life on the geological history of the Earth". This new direction was the result of his field observations, of his broad mineralo-geological knowledge, and his studies, from 1917, on the phenomena of life in the biosphere, confirmed by many of his readings, like the book by Clarke (1908), "The Data of Geochemistry", and in particular the "Hydrogéologie" of J. B. Lamarck (1802). From this, and knowing the Lamarck work, and the Suess work and the definition of a biosphere he redefined and worked the biosphere concept in larger biogeochemical terms.

Description: Roe deer Capreolus capreolus has often been mentioned in the literature as a good bioindicator of environmental pollution. To find out the levels of heavy metals (Cd, Pb, Hg, As, Zn) in roe deer tissues, this research project was begun near metallurgic and electricity generating centres of Slovenia in 1997. The results of the first sampling year reveal that metal burdens are the highest in the Koroška region, an industrial area in the northern part of Slovenia with a centuries-old tradition of mining and processing of lead ore. Levels (expressed on a wet weight basis) of Cd (2.91 ± 2.92, 7.13 ± 4.43 and 22.7 ± 8.92 mg kg−1 for fawns, yearlings and adults, respectively), As (0.23 ± 0.03 mg kg−1) and Zn (47.1 ± 8.26 mg kg−1) in kidneys as well as levels of Pb (0.71 ± 0.65 mg kg−1) in liver of animals shot in the Koroška region significantly exceed the levels measured in other Slovenian regions. On the contrary, metal levels in viscera of roe deer from the Šalek Valley (where the major Slovene power plant of Šoštanj is located) are low (0.14 ± 0.01, 38.2 ± 4.39 and 0.02 ± 0.03 mg kg−1 for As, Zn and Hg in kidney; 0.21 ± 0.04 mg kg−1 for Pb in liver, respectively). Relatively high levels of Hg (0.23 ± 0.09 mg kg−1; six- to tenfold higher compared to other areas of interest) in kidneys and Pb (0.55 ± 0.13 mg kg−1) in liver of animals shot in the control area of the Triglav National Park, which represents the area without any local emission sources, demonstrate the possibility that animals are being exposed to contaminants that we would not have expected from other data. Consequently, the value of roe deer as an accumulative bioindicator of environmental pollution with heavy metals is clearly confirmed.

Description: Notes on the adaptation to various habitats, climatic conditions, life-cycles, dispersion as well as on some morpho-physiological ones of the main phytophagous (Tetranychidae and Eriophyidae) and predaceous (Phytoseiidae) mites typical of the Mediterranean area are reported in the present paper.

Description: The concept of scale (in sensu lato) is considered to be very promising as the integrative basis for modern ecology. Nowadays it is not a full-blown theory but rather a flexible and progressively developing methodology to outline future unifying theories. It provides a powerful conceptual framework for generating testable hypotheses and studying a wide range of ecological phenomena related with such themes as heterogeneity, hierarchy and size. Spatio-temporal heterogeneity, organizational hierarchies and body size are the main scaling factors for ecological patterns and processes. Broad comparison of patterns for these three different but interrelated dimensions can reveal some new regularities ("scaling laws") of ecological systems. It also allows us to look at the worlds of different organisms "through their own eyes". Some examples of applying the cross-scaling approach in marine ecology are considered: — Patterns and scales of spatial heterogeneity; — Species-area curves and body size; — Co-occurrence of congeners as scale-dependent phenomenon; — Spatio-temporal ranges of ecological hierarchies.

Description: The age of dispersers is one of the important factors influencing the ecology and evolution of dispersal. Explanations in textbooks assume special social or genetic advantages to predict the dispersing age class. However, recent theoretical results suggest that age specific dispersal can evolve even without special advantages for the dispersing age class. Here we discuss and interpret these results on the basis of the invasion fitness concept and show with general arguments that the evolution of age specific dispersal is possible for purely demographic reasons. This furthers our general understanding of the evolution of age specific dispersal.

Description: Changing temperature regime has an important effect on the respiratory metabolism of Glomeris balcanica. A left skewing response of animals to increasing temperature is revealed and modeled. Acclimation from fluctuating to constant temperatures depresses metabolism through a three-step process. Short-term acclimation results in strongly depressed metabolism, mid-term acclimation induces metabolic recovery, whereas long-term acclimation results in an irreversible decline of metabolic activity. Heavy metal burdens of food do not affect the left skewing thermal response of animals, although they depress metabolic levels at the high temperature range, shorten tolerance ranges by shifting down the upper tolerance threshold, enlarge optimal temperature range (metabolic constancy) and stimulate the faster activation of the metabolic compensatory mechanism. Finally, no effect of short-term fasting on respiration was detected.

Description: The available quantitative information (age, growth, maturation and mortality) for 103 fish stocks in Hellenic Seas was analysed here in the context of life-history theory and compared with similar information from other areas of the world. The results showed that the fish species and stocks inhabiting Hellenic waters are generally small in size, have low longevity, mature at an early age and size, and probably suffer high adult mortality rates. Such a pattern most probably is an adaptation to the synergetic combination of highly oligotrophic conditions and high subtropical temperatures prevailing in Hellenic waters and is consistent with life-history theory. Finally, the auximetric grid was used to compare the growth of four species, each represented by more than six stocks. The results revealed that the growth spaces occupied by the four species reflect their strikingly different feeding habits, especially with respect to the size of prey and the relative importance of fish prey to their diet.

Description: Compositions of oribatid mite communities were compared under five stages of native Scots pine regeneration (spanning 100 yr) within the Abernethy Forest Reserve, U.K. Sampling was conducted during autumn and spring, and oribatid mites identified using the morphospecies technique. Results showed the oribatid mite fauna to be abundant and diverse. Density of mites generally decreased with soil depth, however in the woodland sites the upper 10 cm of soil contained more individuals than the litter layer. Eleven morphospecies showed significant differences (p 〈 0.05) in abundance between sites, with marked preferences shown for either mature woodland or tree-less moorland. During spring, morphospecies richness and mite density were highest at the woodland sites, but during autumn they were greater at the moorland sites. Shannon Wiener diversity indices and measures of evenness, calculated for each site, showed that despite having a high morphospecies richness, sites were often dominated by a few very abundant morphospecies. A greater number of mites were collected during autumn, but only one morphospecies showed significant seasonal differences in numbers. Factors influencing differences in oribatid communities at each site are discussed and the use of morphospecies as an identification tool is also assessed.

Description: Recent studies have shown that wild birds breeding in acidified areas have difficulties with obtaining sufficient calcium for their eggshells, and that the cause of it is the shortage of land snails. Many birds have to search for Ca-rich snail shells on a daily basis during egg production. Molluscs depend on litter calcium, which has decreased due to acidification of the environment. Calcium limitation may be a widespread phenomenon also in non-acidified, naturally Ca-poor areas. The problem is that while in the latter areas the time for development of specific adaptations may have been sufficient, then in acidified areas, on the contrary, calcium shortage is a recent phenomenon. Therefore, since the extent of calcium limitation in non-acidified areas is hard to derive from observational data, experimental approach is needed. We provide experimental evidence that specific calcium deficit does affect reproductive traits also in the birds breeding in naturally base-poor habitats. Our study was conducted in a heterogeneous woodland area in Estonia containing deciduous forest patches as well as base-poor pine forest with low snail abundance. Ca supplementation, using snail shell and chicken eggshell fragments, was carried out for pied flycatchers and great tits. Extra calcium affected positively several reproductive traits like egg volume and eggshell thickness, start of breeding, and fledglings’ parameters. The negative relationship between calcium availability and lay-date suggests that birds adjust their breeding tactics to conditions of Ca deficiency, for example, by postponing laying.

Description: The seed content of soils is often estimated through germination tests, though these methods are always somewhat inaccurate due to the presence of dormant seeds in the samples. The researcher thus faces the question of whether to continue the germination test or to stop it in the search for an accuracy-to-effort balance. In this paper I analyze the accuracy of seed content estimates obtained after a first-year germination test, by comparison to the germination recorded after three-year cultivation, in 48 soil seed bank samples and 389 from herbivore dung. After the first 9-month cultivation, I recorded 85 ± 1% seedlings and 90 ± 1% species in soil samples, while the accuracy in those of dung was significantly lower, 48 ± 1% seedlings and 65 ± 1% species. The accuracy of estimations varied among samples within experiments, with significant differences in the estimation of species richness in both cases. I did not find consistent differences in the accuracy of estimations linked to seedling densities in growing pots, but the taxonomic composition of samples was a major source of bias. Thus, 22% and 36% of the most frequent species showed germinabilities in the first year significantly different from the rest, and some generalities arose, like the high germinability of grasses and the hardseededness of legumes. I would thus recommend the use of at least two germination cycles for seed bank estimations and a cautious approach when comparing samples with very different origin and/or taxonomic composition.

Description: Restoration ecology has often been regarded as a subordinate component of conservation biology and yet the two disciplines differ from each other. Conservation aims at staving off extinction, i.e. preserving ecological structures and services which still exist, however endangered they may be. On the other hand, the principal objective of restoration is re-building ecological structures and services that have been destroyed. The most distinct focus of conservation is on population response to exploitation, whereas restoration is principally concerned with over-exploited sites and landscapes in which communities/ecosystems are to be re-built. Conservation aims at preserving as many species as possible; on the other hand, the biodiversity approach in restoration may be addressed on three levels viz. 1) initial species diversity, 2) post-restoration increase of diversity via spontaneous species immigration, and 3) age-state diversity of developing plant cover. The conceptual framework in conservation biology differs from that in restoration ecology. The two basic paradigms used in conservation biology are 1) small-population paradigm and 2) declining-population paradigm, and one of its useful concepts is population viability assessment (PVA). The two principal paradigms used in restoration ecology are 1) nature-in-balance paradigm and 2) nature-in-flux paradigm. Interfaces between conservation and restoration may be recognized when e.g., recovery strategies for threatened species include habitat/ecosystem restoration, or when population processes in non-threatened species are studied to verify their usefulness as restoration material. Integration of species and ecosystem approaches is already recognizable in ecology. It is to be hoped that in future conservation and restoration become integrated components of ecosystem management, but for the time being they remain two different facets of the same problem which is the negative human impact upon environment.

Description: The concept of the generalized entropy is analyzed, with the particular attention to the definition postulated by Tsallis [J. Stat. Phys. 52, 479 (1988)]. We show that the Tsallis entropy can be rigorously obtained as the solution of a nonlinear functional equation; this equation represents the entropy of a complex system via the partial entropies of the subsystems involved, and includes two principal parts. The first part is linear (additive) and leads to the conventional, Boltzmann, definition of entropy as the logarithm of the statistical weight of the system. The second part is multiplicative and contains all sorts of multilinear products of the partial entropies; inclusion of the multiplicative terms is shown to reproduce the generalized entropy exactly in the Tsallis sense. We speculate that the physical background for considering the multiplicative terms is the role of the long-range correlations supporting the "macroscopic" ordering phenomena (e.g., formation of the "coarse-grained" correlated patterns). We prove that the canonical distribution corresponding to the Tsallis definition of entropy, coincides with the so-called "kappa" redistribution which appears in many physical realizations. This has led us to associate the origin of the "kappa" distributions with the "macroscopic" ordering ("coarse-graining") of the system. Our results indicate that an application of the formalism based on the Tsallis notion of entropy might actually have sense only for the systems whose statistical weights, Ω, are relatively small. (For the "coarse-grained" systems, the weight \omega could be interpreted as the number of the "grains".) For large Ω (i.e., Ω -〉 ∞), the standard statistical mechanical formalism is advocated, which implies the conventional, Boltzmann definition of entropy as ln Ω.

Description: Cellular automaton versions of the Burridge-Knopoff model have been shown to reproduce the power law distribution of event sizes; that is, the Gutenberg-Richter law. However, they have failed to reproduce the occurrence of foreshock and aftershock sequences correlated with large earthquakes. We show that in the case of partial stress recovery due to transient creep occurring subsequently to earthquakes in the crust, such spring-block systems self-organize into a statistically stationary state characterized by a power law distribution of fracture sizes as well as by foreshocks and aftershocks accompanying large events. In particular, the increase of foreshock and the decrease of aftershock activity can be described by, aside from a prefactor, the same Omori law. The exponent of the Omori law depends on the relaxation time and on the spatial scale of transient creep. Further investigations concerning the number of aftershocks, the temporal variation of aftershock magnitudes, and the waiting time distribution support the conclusion that this model, even "more realistic" physics in missed, captures in some ways the origin of the size distribution as well as spatio-temporal clustering of earthquakes.

Description: We study the flow obtained from a three-layer, eddy-resolving quasigeostrophic ocean circulation model subject to an applied wind stress curl. For this model we will consider transport between the northern and southern gyres separated by an eastward jet. We will focus on the use of techniques from dynamical systems theory, particularly lobe dynamics, in the forming of geometric structures that govern transport. By "govern", we mean they can be used to compute Lagrangian transport quantities, such as the flux across the jet. We will consider periodic, quasiperiodic, and chaotic velocity fields, and thus assess the effectiveness of dynamical systems techniques in flows with progressively more spatio-temporal complexity. The numerical methods necessary to implement the dynamical systems techniques and the significance of lobe dynamics as a signature of specific "events", such as rings pinching off from a meandering jet, are also discussed.

Description: Satisfactory method of removing noise from experimental chaotic data is still an open problem. Normally it is necessary to assume certain properties of the noise and dynamics, which one wants to extract, from time series. The wavelet based method of denoising of time series originating from low-dimensional dynamical systems and polluted by the Gaussian white noise is considered. Its efficiency is investigated by comparing the correlation dimension of clean and noisy data generated for some well-known dynamical systems. The wavelet method is contrasted with the singular value decomposition (SVD) and finite impulse response (FIR) filter methods.

Description: Simulations in three dimensions of a Harris current sheet with mass ratio, mi/me = 180, and current sheet thickness, pi/L = 0.5, suggest the existence of a linearly unstable oblique mode, which is independent from either the drift-kink or the tearing instability. The new oblique mode causes reconnection independently from the tearing mode. During the initial linear stage, the system is unstable to the tearing mode and the drift kink mode, with growth rates that are accurately described by existing linear theories. How-ever, oblique modes are also linearly unstable, but with smaller growth rates than either the tearing or the drift-kink mode. The non-linear stage is first reached by the drift-kink mode, which alters the initial equilibrium and leads to a change in the growth rates of the tearing and oblique modes. In the non-linear stage, the resulting changes in magnetic topology are incompatible with a pure tearing mode. The oblique mode is shown to introduce a helical structure into the magnetic field lines.

Description: We have investigated the nonlinear properties of the electromagnetic ion/ion cyclotron instability (EMIIC) by means of hybrid simulations (macroparticle ions, massless electron fluid). The instability is driven by the relative (super-Alfvénic) streaming of two field-aligned ion beams in a low beta plasma (ion thermal pressure to magnetic field pressure) and may be of importance in the plasma sheet boundary layer. As shown in previously reported simulations the waves propagate obliquely to the magnetic field and heat the ions in the perpendicular direction as the relative beam velocity decreases. By running the simulation to large times it can be shown that the large temperature anisotropy leads to the ion cyclotron instability (IC) with parallel propagating Alfvén ion cyclotron waves. This is confirmed by numerically solving the electromagnetic dispersion relation. An application of this property to the plasma sheet boundary layer is discussed.

Description: Thin anisotropic current sheets (CSs) are phenomena of the general occurrence in the magnetospheric tail. We develop an analytical theory of the self-consistent thin CSs. General solitions of the Grad-Shafranov equation are obtained in a quasi-adiabatic approximation which neglects the jumps of the sheet adiabatic invariant Iz This is possible if the anisotropy of the initial distribution function is not too strong. The resulting structure of the thin CSs is interpreted as a sum of negative dia- and positive paramagnetic currents flowing near the neutral plane. In the immediate vicinity of the magnetic field reversal region the paramagnetic current arising from the meandering motion of the ions on Speiser orbits dominates. The maximum CS thick-ness is achieved in the case of weak plasma anisotropy and is of the order of the thermal ion gyroradius outside the sheet. A unified picture of thin CS scalings includes both the quasi-adiabatic regimes of weak and strong anisotropies and the nonadiabatic limit of super-strong anisotropy of the source ion distribution. The later limit corresponds to the case of almost field-aligned initial distribution, when the ratio of the drift velocity outside the CS to the thermal ion velocity exceeds the ratio of the magnetic field outside the CS to its value in-side the CS (vD/vT〉 B0/Bn). In this regime the jumps of Iz, become essential, and the current sheet thickness is approaching to some small but finite value, which depends upon the parameter Bn /B0. Convective electric field increases the effective anisotropy of the source distribution and might produce the essential CS thinning which could have important implications for the sub-storm dynamics.

Description: Magnetic holes (MHs) are depressions of the magnetic field magnitude. Turner et al. (1977) identified the first MHs in the solar wind and determined an occurrence rate of 1.5 MHs/d. Winterhalter et al. (1994) developed an automatic identification criterion to search for MHs in Ulysses data in the solar wind between 1 AU and 5.4 AU. We adopt their criterion to expand the search to the heliocentric distances down to 0.3 AU using data from Helios 1 and 2 and up to 17 AU using data from Voyager 2. We relate our observations to two theoretical approaches which describe the so-called linear MHs in which the magnetic vector varies in magnitude rather than direction. Therefore we focus on such linear MHs with a directional change less than 10º. With our observations of about 850 MHs we present the following results: Approximately 30% of all the identified MHs are linear. The maximum angle between the initial magnetic field vector and any vector inside the MH is 20º in average and shows a weak relation to the depth of the MHs. The angle between the initial magnetic field and the minimum variance direction of those structures is large and very probably close to 90º. The MHs are placed in a high β environment even though the average solar wind shows a smaller β. The widths decrease from about 50 proton inertial length in a region between 0.3 AU and 0.4 AU heliocentric distance to about 15 proton inertial length at distances larger than 10 AU. This quantity is correlated with the β of the MH environments with respect to the heliocentric distance. There is a clear preference for the occurrence of depressions instead of compressions. We discuss these results with regard to the main theories of MHs, the mirror instability and the alternative soliton approach. Although our observational results are more consistent with the soliton theory we favour a combination of both. MHs might be the remnants of initial mirror mode structures which can be described as solitons during the main part of their lifetime.

Description: We investigate trapping of mirror modes in a magnetic slab. This model is a simplification of a real situation in front of the magnetopause where mirror waves may become trapped in a region close to the magnetopause for tangential discontinuity conditions and an unidentified (hypothetical) boundary deeper in the sheath which we, for simplicity, assume to be another tangential discontinuity. Such magnetic slabs may trap mirror modes selecting a particular perpendicular wave lengths which follows from a quantization condition on the perpendicular wavenumber.

Description: The study of the interaction of the solar wind with magnetized and unmagnetized planets forms a central topic of space research. Focussing on planetary magnetosheaths, we review some major developments in this field. Magnetosheath structures depend crucially on the orientation of the interplanetary magnetic field, the solar wind Alfvén Mach number, the shape of the obstacle (axisymmetric/non-axisymmetric, etc.), the boundary conditions at the magnetopause (low/high magnetic shear), and the degree of thermal anisotropy of the plasma. We illustrate the cases of Earth, Jupiter and Venus. The terrestrial magnetosphere is axisymmetric and has been probed in-situ by many spacecraft. Jupiter's magnetosphere is highly non-axisymmetric. Furthermore, we study magnetohydrodynamic effects in the Venus magnetosheath.

Description: Well-defined ring-like backstreaming ion distributions have been recently reported from observations made by the 3DP/PESA-High analyzer onboard the WIND spacecraft in the Earth's foreshock at large distances from the bow shock, which suggests a local production mechanism. The maximum phase space density for these distributions remains localized at a nearly constant pitch-angle value for a large number of gyroperiods while the shape of the distribution remains very steady. These distributions are also observed in association with quasi-monochromatic low frequency (~ 50 mHz) waves with substantial amplitude (δB/B〉0.2). The analysis of the magnetic field data has shown that the waves are propagating parallel to the background field in the right-hand mode. Parallel ion beams are also often observed in the same region before the observation of both the ring-like distributions and the waves. The waves appear in cyclotron resonance with the ion parallel beams. We investigate first the possibility that the ion beams could provide the free energy source for driving an ion/ion instability responsible for the ULF wave occurrence. For that, we solve the wave dispersion relation with the observed parameters. Second, we show that the ring-like distributions could then be produced by a coherent nonlinear wave-particle interaction. It tends to trap the ions into narrow cells in velocity space centered on a well-defined pitch-angle, directly related to the saturation wave amplitude in the analytical theory. The theoretical predictions are in good quantitative agreement with the observations

Description: We describe an effect of phase-locking catastrophe arising in an ensemble of a great number of oscillators interacting by means of their emitting waves. These waves can be either pulsatile, that is, soliton-like, or continuous stationary waves generated by the oscillators considered as resonators. Each one of these waves will introduce certain perturbations among the phases of the oscillators of the ensemble in such a way that it is possible to follow in time the distribution of these phases. In fact, we deduce the p.d.e's governing the evolution in time of this distribution, which displays a tendency of accumulating around certain of its values (phase-locking), and also of sudden increasing of the intensity of the physical effect (a "phase transition").

Description: The dynamic evolution of laboratory water surface waves has been studied within the framework of dynamical systems with the aim to identify stochastic or deterministic nonlinear features. Three different regimes are considered: pure wind waves, pure mechanical waves and mixed (wind and mechanical) waves. These three regimes show different dynamics. The results on wind waves do not clearly support the recently proposed idea that a deterministic Stokes-like component dominate the evolution of such waves; they are more appropriately described by a similarity-like approach that includes a random character. Cubic resonant interactions are clearly identified in pure mechanical waves using tricoherence functions. However, detailed aspects of the interactions do not fully agree with existing theoretical models. Finally, a deterministic motion is observed in mixed waves, which therefore are best described by a low dimensional nonlinear deterministic process.

Description: The interaction between sea waves and a deformable sea-bed is studied with a simple two-layer model in which the upper-layer fluid is inviscid and the lower-layer fluid is bi-viscous to account for non-Newtonian behaviour of sand and sediments. The nonlinear response of the system to periodic forcing by an external surface pressure is determined. It is shown that a simple bi-viscous rheology allows small wavelength morphology in the lower layer to be generated from large wavelength surface waves in the upper inviscid layer, although the morphology is not permanent. For a bi-viscous rheology with a pressure-dependent yield stress (which accounts for the fact that sand yields less readily under loading than unloading), however, small wavelength and permanent features are formed in the seabed.

Description: The work is concerned with the results of theoretical and laboratory modelling the processes of the large-scale structure generation under turbulent convection in the rotating-plane horizontal layer of an incompressible fluid with unstable stratification. The theoretical model describes three alternative ways of creating unstable stratification: a layer heating from below, a volumetric heating of a fluid with internal heat sources and combination of both factors. The analysis of the model equations show that under conditions of high intensity of the small-scale convection and low level of heat loss through the horizontal layer boundaries a long wave instability may arise. The condition for the existence of an instability and criterion identifying the threshold of its initiation have been determined. The principle of action of the discovered instability mechanism has been described. Theoretical predictions have been verified by a series of experiments on a laboratory model. The horizontal dimensions of the experimentally-obtained long-lived vortices are 4÷6 times larger than the thickness of the fluid layer. This work presents a description of the laboratory setup and experimental procedure. From the geophysical viewpoint the examined mechanism of the long wave instability is supposed to be adequate to allow a description of the initial step in the evolution of such large-scale vortices as tropical cyclones - a transition form the small-scale cumulus clouds to the state of the atmosphere involving cloud clusters (the stage of initial tropical perturbation).

Description: We investigate the coupling between current and tearing instability modes of a thin current sheet using the particle code GISMO. We identify pure tearing modes (kx≠ 0), instabilities in the current flow direction (ky≠ 0) and general 3D reconnection modes (kx≠ 0 and ky≠ 0). Our results give evidence that the coupling between tearing modes and current instabilities plays an important role for spontaneous magnetic reconnection. These modes give a substantial contribution to magnetic reconnection, additional to the well known 2D tearing mode. When allowing reconnection to occur in three spatial dimensions, a configuration, which was initially invariant in the current How direction, develops into a configuration with no invariant direction.

Description: In a system with at least one ignorable spatial dimension charged particles moving in fluctuating fields are tied to the magnetic field lines. Thus, in one-and two-dimensional simulations cross-field diffusion is inhibited and important physics may be lost. We have investigated cross-field diffusion in self-consistent 3-D magnetic turbulence by fully 3-dimensional hybrid simulation (macro-particle ions, massless electron fluid). The turbulence is generated by the electromagnetic ion/ion beam instability. A cold, low density, ion beam with a high velocity stream relative to the background plasma excites the right-hand resonant instability. Such ion beams may be important in the region of the Earth's foreshock. The field turbulence scatters the beam ions parallel as well as perpendicular to the magnetic field. We have determined the parallel and perpendicular diffusion coefficient for the beam ions in the turbulent wave field. The result compares favourably well (within a factor 2) with hard-sphere scattering theory for the cross-field diffusion coefficient. The cross-field diffusion coefficient is larger than that obtained in a static field with a Kolmogorov type spectrum and similar total fluctuation power. This is attributed to the resonant behaviour of the particles in the fluctuating field.

Description: In the mathematical modelling of sediment compaction and porous media flow, the rheological behaviour of sediments is typically modelled in terms of a nonlinear relationship between effective pressure pe and porosity Φ, that is pe = pe (Φ). The compaction law is essentially a poroelastic one. However, viscous compaction due to pressure solution becomes important at larger depths and causes this relationship to become more akin to a viscous rheology. A generalised viscoelastic compaction model of Maxwell type is formulated, and different styles of nonlinear behaviour are asymptotically analysed and compared in this paper.

Description: Several technical suggestions to construct a high-resolution spectral model on a sphere (the T682 barotropic model) are presented and their implementation of FORTRAN77 libraries is provided as a free software package ISPACK (http://www.gfd-dennou.org/arch/ispack/). A test experiment on decaying turbulence is conducted to demonstrate the ability of the model.

Description: It is well known that lithospheric seismic processes are characterized by self-similarity or scale invariance in terms of earthquake-size, time, space and space-time distributions, although precise details of underlying dynamics are not clear. In this study we apply nonlinear dynamics theory tools, such as a correlation dimension, "surrogate" data analysis and positive Lyapunov exponent calculation, to investigate dynamical characteristics of seismicity in the Caucasian region. Interevent time intervals and magnitude sequences are considered for different area and magnitude windows. We find significant evidence of a low dimensional nonlinear structure of earthquake time distribution, obtained by consideration of time interval sequences between all events encountered, above some threshold magnitude, in the original catalogue. However nonlinear structure is absent in artificially generated sequences of time intervals between independent events as well as time intervals between aftershocks. It seems that this kind of filtration of the original catalogue destroys the existing temporal structure of considered lithospheric processes. Unlike artificial inter-aftershock time interval sequences, obtained by removing independent events from the original series, the time interval sequence between the Racha earthquake aftershocks reveals clear evidence of nonlinear structure. Earthquake magnitude dynamics. for all considered regions and magnitude windows, reveal high dimensional nonlinearity.

Description: The methods of nonlinear dynamics are used to reveal the origin of complicated dynamic behaviour (CDB) of a dynamic model of the mesospheric photochemical system (PCS) perturbed by diurnal variations in photolysis rates. We found that CDB appearance during the multi-day evolution is unambiguously determined by two peculiarities in the model behaviour during its 24-hours evolution. These peculiarities are the presence of a stage of abrupt changes in reagent concentrations and the "humped" dependence of the end-night atomic hydrogen concentrations on those at the beginning of the night. Using a successive analysis we found that these two peculiarities are, in turn, conditioned by the specific features of the chemical processes involved in the model, namely, by the catalytic cycle whose net rate is independent of the concentration of the destroyed species (here, it is atomic oxygen). We believe that similar peculiarities inherent in other atmospheric PCSs indicate that under appropriate conditions they may also demonstrate CDB. We identified the mechanism of the CDB appearance and described it in two ways. The first one reveals a sequence of the processes causing the exponential (on the average) growth of a perturbation of the solution with time. In particular, we found that the behaviour of small perturbations of an arbitrary solution of model equations is identical to the behaviour of a linear oscillator excited parametrically. The second way shows the mechanism of CDB appearance by means of 1-dimensional mapping, which is, basically, the same as the well-known Feigenbaum mappings.

Description: The ion dynamics in the distant Earth's magnetotail is studied in the case that a cross tail electric field and reconnection parity magnetic turbulence are present in the neutral sheet. A test particle simulation is performed for the ions, and moments of the ion distribution function are obtained as a function of the magnetic fluctuation level, δB/B0, and of the value of the cross tail electric field, Ey. It is found that magnetic turbulence can split the current carrying region into a double current sheet, in agreement with inferences from observations in the distant magnetotail. The problem of ion conductivity is addressed by varying the value of the cross tail electric field from zero to the observed one: we find that Ohm's law is not enforced, and that a non local, system dependent conductivity is necessary to describe the ion response to the electric field. Also, it appears that the relation between current and electric field may be nonlinear.

Description: Runoff generation in a forested catchment (0.18 km2) was simulated using a quasi-three-dimensional rainfall-runoff model. The model was formulated over a finite grid where water movement was assumed to be dominantly vertical in the unsaturated soil zone and horizontal in the saturated soil. The vertical soil moisture distribution at each grid cell was calculated using a conceptual approximation to the one-dimensional Richards equation. The approximation allowed the use of a simple soil surface boundary condition and an efficient solution to the water table elevation over the finite grid. The approximation was coupled with a two-dimensional ground water model to calculate lateral soil water movement between the grid cells and exfiltration over saturated areas, where runoff was produced by the saturation-excess mechanism. Runoff was an input to a channel network, which was modelled as a nonlinear reservoir. The proposed approximation for the vertical soil moisture distribution in unsaturated soil compared well to a numerical solution of the Richards equation during shallow water table conditions, but was less satisfactory during prolonged dry periods. The simulation of daily catchment outflow was successful with the exception of underprediction of extremely high peak flows. The calculated water table depth compared satisfactorily with the measurements. An overall comparison with the earlier results of tracer studies indicated that the modelled contribution of direct rainfall/snowmelt in streamflow was higher than the isotopically traced fraction of event-water in runoff. The seasonal variation in the modelled runoff-contributing areas was similar to that in the event-water-contributing areas from the tracer analysis.

Description: Dense raingauge experiments in the past have experienced difficulties in the automated recording of rainfall amount and timing which with the benefit of modern instrument technology are now less problematic. The HYdrological Radar EXperiment, HYREX, provided a timely opportunity to design and implement a dense raingauge network in support of rainfall measurement and modelling research studies concerned with the use of weather radar in hydrology. The principles and random function theory underlying the design of this raingauge network over the Brue catchment in south-west England are detailed in this paper. Keywords: raingauge, design, network, rainfall, flood, spatial correlation

Description: A continuous simulation methodology, which incorporates the quantification of modelling uncertainties, is used for flood frequency estimation. The methodology utilises the rainfall-runoff model TOPMODEL within the uncertainty framework of GLUE. Long return period estimates are obtained through the coupling of a stochastic rainfall generator with TOPMODEL. Examples of applications to four gauged UK catchments are provided. A comparison with a traditional statistical approach indicates the suitability of the methodology as an alternative technique for flood frequency estimation. It is suggested that, given an appropriate choice of rainfall-runoff model and stochastic rainstorm generator, the basic methodology can be adapted for use in many other regions of the world. Keywords: Floods; Frequency; TOPMODEL; Rainfall-runoff modelling

Description: The need for the development of a method for generating an ensemble of rainfall scenarios, which are conditioned on the observed rainfall, and its place in the HYREX programme is discussed. A review of stochastic models for rainfall, and rainfall forecasting techniques, is followed by a justification for the choice of the Modified Turning Bands (MTB) model in this context. This is a stochastic model of rainfall which is continuous over space and time, and which reproduces features of real rainfall fields at four distinct scales: raincells, cluster potential regions, rainbands and the overall outline of a storm at the synoptic scale. The model can be used to produce synthetic data sets, in the same format as data from a radar. An inversion procedure for inferring a construction of the MTB model which generates a given sequence of radar images is described. This procedure is used to generate an ensemble of future rainfall scenarios which are consistent with a currently observed storm. The combination of deterministic modelling at the large scales and stochastic modelling at smaller scales, within the MTB model, makes the system particularly suitable for short-term forecasts. As the lead time increases, so too does the variability across the set of generated scenarios. Keywords: MTB model, space-time rainfall field model, rainfall radar, HYREX, real-time flow forecasting

Description: The sensitivity analysis described in Hashemi et al. (2000) is based on one-at-a-time perturbations to the model parameters. This type of analysis cannot highlight the presence of parameter interactions which might indeed affect the characteristics of the flood frequency curve (ffc) even more than the individual parameters. For this reason, the effects of the parameters of the rainfall, rainfall runoff models and of the potential evapotranspiration demand on the ffc are investigated here through an analysis of the results obtained from a factorial experimental design, where all the parameters are allowed to vary simultaneously. This latter, more complex, analysis confirms the results obtained in Hashemi et al. (2000) thus making the conclusions drawn there of wider validity and not related strictly to the reference set selected. However, it is shown that two-factor interactions are present not only between different pairs of parameters of an individual model, but also between pairs of parameters of different models, such as rainfall and rainfall-runoff models, thus demonstrating the complex interaction between climate and basin characteristics affecting the ffc and in particular its curvature. Furthermore, the wider range of climatic regime behaviour produced within the factorial experimental design shows that the probability distribution of soil moisture content at the storm arrival time is no longer sufficient to explain the link between the perturbations to the parameters and their effects on the ffc, as was suggested in Hashemi et al. (2000). Other factors have to be considered, such as the probability distribution of the soil moisture capacity, and the rainfall regime, expressed through the annual maximum rainfalls over different durations. Keywords: Monte Carlo simulation; factorial experimental design; analysis of variance (ANOVA)

Description: Since the mid 1980s, changes in political imperatives plus technological changes in computer hardware and software have heightened the awareness of the economic value and importance of quality datasets to scientific research. The Natural Environment Research Council’s (NERC) interdisciplinary Thematic and Special Topic Programmes have highlighted the need for a coherent data management policy to provide and preserve these quality datasets for posterity. The Hydrological Radar EXperiment (HYREX) Special Topic Programme brought together multi-disciplinary researchers from UK public sector laboratories and universities. In this paper, the HYREX data management strategy, its problems and its solutions are discussed. The HYREX data archive, situated at NERC’s British Atmospheric Data Centre, is described. Keywords: radar, data, archive, web, storm, flood

Description: The modification of raindrops by the canopy of olive trees increases the kinetic energy of the rain per unit area. The kinetic energy computed from the measured drop size distribution under the tree canopy in simulated rainfall experiments is greater than that received in the open, 17.1 J mm-1, as against 15.7 J mm-1 . This causes higher soil detachment and loss than that observed outside the canopy. Tillage treatments of the soil modify its erodibility, accelerate soil detachment and reduce, simultaneously, the velocity of runoff. Both effects reduce the amount of sediment compared to that observed in the non-tilled soil. The average values of soil lost per unit of rain depth and unit area were 5.81 g mm-1 m-2 (conventional tillage) and 4.02 g mm-1 m-2 (zero tillage) under the canopy compared to 0.89 g mm-1 m-2 (conventional tillage) and 0.95 g mm-1 m-2 (zero tillage) in the open.

Description: The HYREX experiment has provided a data set unique in the UK, with a dense network of raingauges available for studying the rainfall at a fine local scale and a network of radar stations allowing detailed examination of the spatial and temporal structure of rainfall at larger scales. In this paper, the properties and characteristics of the rainfall process, as measured by the HYREX recording network of rainguages and radars, are studied from a statistical perspective. The results of these analyses are used to develop various models of the rainfall process, for use in hydrological applications. Some typical results of these various modelling exercises are presented. Keywords: Rainfall statistics, rainfall models, hydrological design

Description: An analysis of riverine outflow into the Baltic Sea is presented for the years 1901 – 1990. The monthly outflows were calculated from the measurements in a number of representative rivers. The analysis included estimation of seasonal and multi-year characteristics of riverine outflows and periodic structure, as well as stochastic and statistical indicators characterising the influence of riverine water on the variability of the sea level and water volume in the basin. The article presents prognostic characteristics determined using analysis of parametric stochastic processes. The results obtained are related to oceanographic characteristics of the Baltic Sea. Keywords: Baltic volume; Baltic balance; river outflow; river seasonality

Description: The classification of river waves as gravity, diffusion or kinematic waves, corresponds to different forms of the momentum equation in the Saint-Venant system. This paper aims to define approximation zones of the Saint-Venant equations for flood routing in natural channels with overbank flow in the flooded area. Using linear perturbation theory, the different terms in the Saint-equations were analysed as a function of the balance between friction and inertia. Then, using non-dimensionalised variables, flood waves were expressed as a function of three parameters: the Froude number of the steady uniform flow, a dimensionless wave, number of the unsteady component of the motion and the ratio between the flooded area zone width and the main channel width. Finally, different theoretical cases, corresponding to different flooded area zone widths were analysed and compared. Results show that, when the width of the flooded area increases, the domain of application of the diffusive wave and the inematic wave models is restricted. Keywords: Saint-Venant equations; river waves; overbank flow

Description: Runoff generation in a forested catchment (0.18 km2) was simulated using a quasi-three-dimensional rainfall-runoff model. The model was formulated over a finite grid where water movement was assumed to be dominantly vertical in the unsaturated soil zone and horizontal in the saturated soil. The vertical soil moisture distribution at each grid cell was calculated using a conceptual approximation to the one-dimensional Richards equation. The approximation allowed the use of a simple soil surface boundary condition and an efficient solution to the water table elevation over the finite grid. The approximation was coupled with a two-dimensional ground water model to calculate lateral soil water movement between the grid cells and exfiltration over saturated areas, where runoff was produced by the saturation-excess mechanism. Runoff was an input to a channel network, which was modelled as a nonlinear reservoir. The proposed approximation for the vertical soil moisture distribution in unsaturated soil compared well to a numerical solution of the Richards equation during shallow water table conditions, but was less satisfactory during prolonged dry periods. The simulation of daily catchment outflow was successful with the exception of underprediction of extremely high peak flows. The calculated water table depth compared satisfactorily with the measurements. An overall comparison with the earlier results of tracer studies indicated that the modelled contribution of direct rainfall/snowmelt in streamflow was higher than the isotopically traced fraction of event-water in runoff. The seasonal variation in the modelled runoff-contributing areas was similar to that in the event-water-contributing areas from the tracer analysis.

Description: Recently, changing land-use practices in the uplands of Scotland have resulted in increased re-colonisation of wet heath moorland by natural Scots pine (Pinus sylvestris) woodland. The simple semi-empirical water use model, HYLUC, was used to determine the change in water balance with increasing natural pine colonisation. The model worked well for 1996. However, values of soil moisture deficit simulated by HYLUC diverged significantly from measurements in 1997 when rainfall quantity and intensities were less. Measured interception by the forest canopy (interception by the undergrowth was not measured) was very different from HYLUC simulated values. By changing interception parameters to those optimised against measured canopy interception, HYLUC simulated changing soil moisture deficits better and gave more confidence in the resulting transpiration values. The results showed that natural pine woodland interception may be similar to plantation stands although the physical structure of the natural and plantation forests are different. Though having fewer storage sites for interception in the canopy, the natural pine woodland had greater ventilation and so evaporation of intercepted rainfall was enhanced, especially during low intensity rainfall. To understand the hydrological changes that would result with changing land-use (an expansion of natural forests into the wet heath land), the modelled outputs of the wet heath and mature forest sites were compared. Evaporation, a combination of transpiration and interception, was 41% greater for the forest site than for the wet heath moorland. This may have significant consequences for the rainfall-runoff relationship and consequently for the hydrological response of the catchment as the natural woodland cover increases Keywords: Evaporation; interception; transpiration; water balance; Scots pine; forest

Description: The approximate travel times for suspended sediment transport through two multi-channel networks are estimated using flow modelling. The focus is on the movement of high sediment concentrations that travel rapidly downstream. Since suspended sediment transport through river confluences and bifurcation movement is poorly understood, it is assumed that the sediment moves at approximately the average channel velocity during periods of high sediment load movement. Calibration of the flow model is discussed, with an emphasis on the incorporation of cross-section data, that are not referenced to a datum, using a continuous water surface profile. Various flow regimes are examined for the Mackenzie and the Slave River Deltas in the Northwest Territories, Canada, and a significant variation in travel times is illustrated. One set of continuous daily sediment measurements throughout the Mackenzie Delta is used to demonstrate that the travel time estimates are reasonable. Keywords: suspended sediment; multi-channel river systems; flow modelling; sediment transport

Description: The synthetic generation of random fields with specified probability distribution, correlation structure and probability of no-rain areas is used as the basis for the formulation of a stochastic space-time rainfall model conditional on rain gauge observations. A new procedure for conditioning while preserving intermittence is developed to provide constraints to Monte Carlo realisations of possible rainfall scenarios. The method addresses the properties of the convolution operator involved in generating random field realisations and is actually independent of the numerical algorithm used for unconditional simulation. It requires only the solution of a linear system of algebraic equations the order of which is given by the number of the conditioning nodes. Applications of the methodology are expected in rainfall field reconstruction from sparse rain gauge data and in rainfall downscaling from the large scale information that may be provided by remote sensing devices or numerical weather prediction models. Keywords: Space-time rainfall; Conditioning; Stochastic models

Description: A numerical multifractal analysis was performed for five river networks extracted from Calabrian natural basins represented on 1:25000 topographic sheets. The spectrum of generalised fractal dimensions, D(q), and the sequence of mass exponents, τ(q), were obtained using an efficient generalised box-counting algorithm. The multi-fractal spectrum, f(α), was deduced with a Legendre transform. Results show that the nature of the river networks analysed is multifractal, with support dimensions, D(0), ranging between 1.76 and 1.89. The importance of the specific number of digitised points is underlined, in order to accurately define, the geometry of river networks through a direct generalised box-counting measure that is not influenced by their topology. The algorithm was also applied to a square portion of the Trionto river network to investigate border effects. Results confirm the multifractal behaviour, but with D(0) = 2. Finally, some open mathematical problems related to the assessment of the box-counting dimension are discussed. Keywords: River networks; measures; multifractal spectrum

Description: Five stalagmite drip-waters in the Grotte de Villars, Dordogne, have been monitored from early 1997 to early 1998, for variations in discharge, major inorganic species and dissolved luminescent organic matter. When compared to surface precipitation, each drip-water has a subtly different response, both in terms of discharge variability and lag time between surface precipitation and drip rate response. Calculated water excess is shown to be important in determining drip-water discharge; during periods of soil moisture deficit, drip-waters either show no response to surface precipitation, or in the case of one sample station, respond only to high intensity and/or high quantity precipitation events. All drip-waters have a large storage component to their flow. Four sample stations have a similar hydrochemical and luminescence response, although the precise timing and magnitude of the responses may vary between drip sources that are

Description: The dense network of 49 raingauges over the 135 km2 Brue catchment in Somerset, England is used to examine the accuracy of rainfall estimates obtained from raingauges and from weather radar. Methods for data quality control and classification of precipitation types are first described. A super-dense network comprising eight gauges within a 2 km grid square is employed to obtain a "true value" of rainfall against which the 2 km radar grid and a single "typical gauge" estimate can be compared. Accuracy is assessed as a function of rainfall intensity, for different periods of time-integration (15 minutes, 1 hour and 1 day) and for two 8-gauge networks in areas of low and high relief. In a similar way, the catchment gauge network is used to provide the "true catchment rainfall" and the accuracy of a radar estimate (an area-weighted average of radar pixel values) and a single "typical gauge" estimate of catchment rainfall evaluated as a function of rainfall intensity. A single gauge gives a standard error of estimate for rainfall in a 2 km square and over the catchment of 33% and 65% respectively, at rain rates of 4 mm in 15 minutes. Radar data at 2 km resolution give corresponding errors of 50% and 55%. This illustrates the benefit of using radar when estimating catchment scale rainfall. A companion paper (Wood et al., 2000) considers the accuracy of rainfall estimates obtained using raingauge and radar in combination. Keywords: rainfall, accuracy, raingauge, radar

Description: An Aggregated Dead Zone (ADZ) model is presented for longitudinal dispersion of tracer in river channels, in which the channel cross-section is divided into two parallel regions: the bulk flow and dead zone storage. Tracer particles in the bulk flow are assumed to obey plug-flow advection at the discharge velocity U without any mixing effects. The dispersive properties of the model are completely embodied in the residence time for tracer storage in the dead zone. The model provides an excellent description and prediction of empirical concentration-time distributions, for times t 〈 x/U. Its physical realism is demonstrated by using it to describe the evolution of a tracer cloud in the River Severn, U.K., and by comparing it with a more complex model which incorporates the additional effects of shear flow dispersion within the bulk flow. The ADZ model is a potentially useful tool for practical prediction of dispersion in natural channels. Keywords: Channels; dispersion; dead zones; tracers; River Severn

Description: Physically based distributed models are rarely calibrated and validated thoroughly because of lack of data. In practice, validation is limited to comparison of simulated and predicted discharges in a catchment, or of simulated and observed piezometric levels in some calibrated wells. Rarely, internal noncalibrated wells or discharge stations are included in model evaluation. In this study, the fully distributed physically based MIKE SHE model was applied to the 600-km2 catchment of the Grote and the Kleine Gete, Belgium. Firstly, the MIKE SHE model was calibrated against both daily discharge measurements and observed water levels and then validated using a simple split-sample test. The observed discharges were simulated successfully in both the calibration and the validation period, while results for the piezometric levels differed considerably among the wells. In addition, a multi-site validation test for 2 internal discharge stations and 6 observation wells showed inferior results for the discharge stations and comparable results for the water table wells. As in the calibration and the split-sample test validation, water table fluctuations were predicted well in some wells, but with little agreement in others. This may be due to scale effects and to the poor quality of the data in certain areas of the catchment. Mainly, the lack of data made it difficult to simulate time series of internal catchment variables with acceptable accuracy so that even the calibrated and validated model could not provide reliable predictions of the water table over the entire catchment. Keywords: integral hydrological modelling; distributed code; MIKE-SHE; model performance; model calibration; model validation

Description: The physically-based soil-vegetation-atmosphere-transfer model PROMET (PRocess-Oriented Model for Evapo Transpiration) developed at the Institute of Geography, University of Munich, is applied to the Ammer basin (approx. 600 km2 ) in the alpine foreland of Germany. The hourly actual evapotranspiration rate is calculated for a 14-year time series. A rainfall-runoff model, based on an enhanced distributed TOPMODEL structure, is linked to the SVAT-model in order to provide a hydrological model covering the water-cycle at the basin scale in a 30m-resolution. The model is driven with meteorological data taken from regular synoptic stations of the German Weather Service. Soil physical and plant physiological parameters for the SVAT model were either measured at the test site or taken from literature. The topographical parameters were derived from detailed digital terrain analysis. The study intends to combine, within a GIS-based model framework, the understanding and application of physical processes inherent in the basin such as the spatial distribution and temporal evolution of evapotranspiration and runoff patterns. The influence of an evapotranspiration coefficient ETcoeff, implemented in the formulation of the soil-topographic-index, to account for seasonal dynamics in distributed runoff formation due to the annual course of vegetation activity is investigated. The SVAT model shows convincing results in the long-term water balance description with a mean annual deviation of less then 6% over a fourteen year time period. Introducing the evapotranspiration-soil-topographic-index αET leads to a considerable improvement; the runoff model component simulating the daily runoff over the year reaches an efficiency of ε = 0.92. Keywords: Water cycle; Geographic Information System; SVAT; TOPMODEL

Description: : A tracer experiment using Rhodamine WT dye was carried out to measure longitudinal dispersion in a 14-km reach of the River Severn in Wales, U.K. The river’s discharge was measured at six points and the depth, width and cross-sectional area were measured at 86 points along the test reach. The channel geometry was close to being statistically uniform. Discharge and velocity were both nearly constant. Dye concentrations were recorded at stations between 210 and 13775 m downstream of injection. Dye was injected over a short interval as a near-uniform line source across the channel. These conditions make the data useful for testing mathematical theories of dispersion. They are presented in full. Keywords: Channels; dispersion; tracers; River Severn

Description: A stochastic model is developed for the synthesis of daily precipitation using conditioning by weather types. Daily precipitation statistics at multiple sites within the region of Yorkshire, UK, are linked to objective Lamb weather types (LWTs) and used to split the region into three distinct precipitation sub-regions. Using a variance minimisation criterion, the 27 LWTs are clustered into three physically realistic groups or ‘states'. A semi-Markov chain model is used to synthesise long sequences of weather states, maintaining the observed persistence and transition probabilities. The Neyman-Scott Rectangular Pulses (NSRP) model is then fitted for each weather state, using a defined summer and winter period. The combined model reproduces key aspects of the historic precipitation regime at temporal resolutions down to the hourly level. Long synthetic precipitation series are useful in the sensitivity analysis of water resource systems under current and changed climatic conditions. This methodology enables investigation of the impact of variations in weather type persistence or frequency. In addition, rainfall model statistics can be altered to simulate instances of increased intensity or proportion of dry days for example, for individual weather groups. The input of such data into a water resource model, simulating potential atmospheric circulation changes, will provide a valuable tool for future planning of water resource systems. The ability of the model to operate at an hourly level also allows its use in a wider range of hydrological impact studies, e.g. variations in river flows, flood risk estimation etc. Keywords: water resources; climate change; impacts; stochastic rainfall model; Lamb weather types

Description: The objective of the present study is to test the performance of the ECMWF land surface module (LSM) developed by Viterbo and Beljaars (1995) and to identify primary future adjustments, focusing on the hydrological components. This was achieved by comparing off-line simulations against observations and a detailed state-of-the-art model over a range of experimental conditions. Results showed that the standard LSM, which uses fixed vegetation and soil parameter values, systematically underestimated evapotranspiration, partly due to underestimating bare soil evaporation, which appeared to be a conceptual problem. In dry summer conditions, transpiration was seriously underestimated. The bias in surface runoff and percolation was not of the same sign for all three locations. A sensitivity analysis, set up to explore the impact of using standard parameter values, found that implementing specific soil hydraulic properties had a significant effect on runoff and percolation at all three sites. Evapotranspiration, however affected only slightly at the temperate humid climate sites. Under semi-arid conditions, introducing site specific soil hydraulic properties plus a realistic rooting depth improved simulation results considerably. Future adjustments to the standard LSM should focus on parameter values of soil hydraulic functions and rooting depths and, conceptually, on the bare soil evaporation parameterisation and the soil bottom boundary condition. Implications of changing soil hydraulic properties for future large-simulations were explored briefly. For Europe, soil data requirements can be fulfilled partly by the recent data base HYPRES. Sandy and loamy sand soils will then cover about 65% of Europe, whereas in the present model 100% of the area is loam. Keywords: land surface model; soil hydraulic properties; water balance simulation

Description: As part of the national monitoring programme for long-range transported air pollutants, four groundwater aquifers in southern Norway were monitored for acidification trends during the period 1980 – 1995. For the monitoring station, Langvasslia in south eastern Norway, sampling continued until the end of 1999. This groundwater aquifer is about 3 km north east of the calibrated catchment Lake Langtjern. The catchment of the groundwater aquifer, covered completely by Norway spruce, was clear-cut in September 1986 and was treated with glyphosate in the summer, 1991. The chemical effects on the chemistry of the groundwater are generally similar to those observed in stream-water from clear-cut areas: increases in water runoff, water temperature, concentrations of K, NO3, and organic carbon (TOC), and decrease in SO4 concentration. In the groundwater aquifer, inorganic Al and ANC increased more than would have been expected without clear-cutting. By 1999 NO3 concentrations were nearly the same as prior to clear-cutting, whereas K still was elevated. Keywords: Groundwater; clear-cutting; water chemistry; monitoring.

Description: The HYREX dense raingauge network over the Brue catchment in Somerset, England is used to explore the accuracy of calibrated (raingauge-adjusted) weather radar data. Calibration is restricted to the use of any single gauge within the catchment so as to simulate the conditions in a typical rainfall monitoring network. Combination of a single gauge and a radar estimate is used to obtain calibrated radar estimates, with the "calibration factor" varying dynamically from one time-frame to the next. Comparing this dynamic calibration with a static (long-term) calibration factor indicates the distance from a gauge over which the dynamic calibration is useful. A tapered calibration factor is implemented which behaves in the same way as the raw dynamic calibration at short distances, tending towards the static calibration factor at larger distances. This hybrid approach outperforms raingauge, uncalibrated radar, and statically-calibrated radar estimates of rainfall for the majority of raingauges in the catchment. The results provide valuable guidance on the density of raingauge network to employ in combination with a weather radar for flood estimation and forecasting. Keywords: radar, raingauge, calibration, rainfall, accuracy

Description: The effects of the early growth of plantation forestry on the biogeochemical cycling of potassium, calcium and magnesium have been investigated in a stand of 12 year old Sitka spruce and adjacent moorland growing on acid peaty podzol soils in mid Wales. Element budgets have been calculated for both systems using measurements of soil and vegetation base cation pools and fluxes. In the moorland, the magnesium budget is approximately at steady-state with no net change to the soil store whilst the soil is accumulating potassium. The calcium budget is approximately balanced but contains significant uncertainties due to between plot variability in calcium leaching losses. Afforestation has greatly increased the above-ground living biomass which holds 7 to 15 times more nutrients compared to the living aerial biomass in the moorland. With the exception of magnesium, the base cation stores within the forest soil are being depleted as the increase in atmospheric deposition due to the forest canopy provides only a small offset to the much larger accumulation of base cations within the trees. The current net rate of change in the soil store of calcium is sustainable for only 65 years. However, as the trees mature, their demand for calcium will be reduced and they should be able to ‘tap' deeper sources of calcium in the soil profile as well as in the drift and regolith material. Keywords: Forestry, base cations, element cycling, calcium, magnesium, potassium

Description: It is widely recognised that topography plays an important role in the generation of runoff. The scale of a digital elevation model has been found to have some impacts on the results of hydrological modelling in several studies. In particular it has been shown that the representation of the statistical distribution of the topographic index used by TOPMODEL is sensitive to the scale of the digital terrain model. The objectives of this study are to develop an analysis of the topography and scale effects for the Haute-Mentue catchment and to test the role of different spatial resolution on parameter calibration. The major result is that the spatial scale is important for the parameter values, but not determinant for the modelling results if a pertinent methodology is adopted for the determination of digital watershed representation. Keywords: digital elevation model, topographic index, scale problems, TOPMODEL

Description: A simple two-dimensional rainfall model, based on advection and conservation of mass in a vertical cloud column, is investigated for use in short-term rainfall and flood forecasting at the catchment scale under UK conditions. The model is capable of assimilating weather radar, satellite infra-red and surface weather observations, together with forecasts from a mesoscale numerical weather prediction model, to obtain frequently updated forecasts of rainfall fields. Such data assimilation helps compensate for the simplified model dynamics and, taken together, provides a practical real-time forecasting scheme for catchment scale applications. Various ways are explored for using information from a numerical weather prediction model (16.8 km grid) within the higher resolution model (5 km grid). A number of model variants is considered, ranging from simple persistence and advection methods used as a baseline, to different forms of the dynamic rainfall model. Model performance is assessed using data from the Wardon Hill radar in Dorset for two convective events, on 10 June 1993 and 16 July 1995, when thunderstorms occurred over southern Britain. The results show that (i) a simple advection-type forecast may be improved upon by using multiscan radar data in place of data from the lowest scan, and (ii) advected, steady-state predictions from the dynamic model, using "inferred updraughts", provides the best performance overall. Updraught velocity is inferred at the forecast origin from the last two radar fields, using the mass-balance equation and associated data and is held constant over the forecast period. This inference model proves superior to the buoyancy parameterisation of updraught employed in the original formulation. A selection of the different rainfall forecasts is used as input to a catchment flow forecasting model, the IH PDM (Probability Distributed Moisture) model, to assess their effect on flow forecast accuracy for the 135 km2 Brue catchment in Somerset. Keywords: rainfall forecasting, flood forecasting, weather radar, satellite, storm model

Description: A Vertically Pointing Radar (VPR) has been commissioned and deployed at a number of sites in southern England, to investigate numerically spatial and temporal variations in the vertical reflectivity profile (Zvp); particularly those associated with the intersection by the radar beam of a melting layer – the bright band. Comparisons with data from other instrumentation, notably with the S-band research radar at Chilbolton, but also with disdrometer data and rainfall measurements from a number of sophisticated rain gauges, show that VPR scans of the atmosphere provide detailed and reliable quantitative measurements of the Zvp. Analysis of a three year archive of Zvp data for Manchester has shown a bright band to be present in over 80% of rainfall events, highlighting the extent of the problem of bright band errors in scanning weather radar data. The primary characteristics of the bright band such as the height and magnitude (in dBZ) of the top, bottom and peak are identified objectively from VPR Zvp data by an automatic bright band recognition algorithm. It is envisaged that this approach could form the basis of an objective, automatic real time correction procedure for scanning weather radars. Keywords: Vertically Pointing Radar, weather radar, hydrometeorology, bright-band, melting-layer, vertical radar reflectivity

Description: In northern Vietnam, exposed carbonate rock formations cover an area of more than 50,000 km2 .Their accumulated thickness from the Cambrian to the Triassic is in some places as much as 3000 m. Numerous thermal waters (springs and wells) occur in these strongly karstified carbonate massifs. This is the result of significant ancient and present orogenic activity, as the region demonstrates by its strong seismic activity. These karstic formations are water-bearing and strongly recharged by rainfall of between 1600 mm and 2000 mm per year in 90% of the area concerned. In view of the average annual air temperatures (17°C-25°C according to the region), 23 sample springs or wells were chosen with water temperatures of between 29°C and 68°C. Hydrochemical characteristics of these thermal waters emerging in different carbonate-rock units were examined by chemical analyses of major ions. In this large region, thermal waters are divided into four hydrochemical types: the Na-Cl type resulting from the intrusion of sea water for distances of up to several kilometres inland and depths of 1000 m, the Ca-SO4 type, probably resulting from the leaching of deposits of metallic sulphides that are widely distributed in these carbonate-rock units, and finally the Ca-HCO3 and Mg-HCO3 types which are chemically similar to fresh karstic waters in limestones and dolostones. The occurrence of these thermal groundwaters as well as their chemical characteristics seem to indicate the existence of large-scale deepseated groundwater flow systems in the karstic aquifers. Keywords: Vietnam; thermal waters; karst; hydrochemistry

Description: By both tradition and purpose, the land parameterization schemes of hydrological and meteorological models differ greatly. Meteorologists are concerned primarily with solving the energy balance, whereas hydrologists are most interested in the water balance. Meteorological climate models typically have multi-layered soil parameterisation that solves temperature fluxes numerically with diffusive equations. The same approach is carried over to a similar treatment of water transport. Hydrological models are not usually so interested in soil temperatures, but must provide a reasonable representation of soil moisture to get runoff right. To treat the heterogeneity of the soil, many hydrological models use only one layer with a statistical representation of soil variability. Such a hydrological model can be used on large scales while taking subgrid variability into account. Hydrological models also include lateral transport of water – an imperative if' river discharge is to be estimated. The concept of a complexity chain for coupled modelling systems is introduced, together with considerations for mixing model components. Under BALTEX (Baltic Sea Experiment) and SWECLIM (Swedish Regional Climate Modelling Programme), a large-scale hydrological model of runoff in the Baltic Basin is used to review atmospheric climate model simulations. This incorporates both the runoff record and hydrological modelling experience into atmospheric model development. Results from two models are shown. A conclusion is that the key to improved models may be less complexity. Perhaps the meteorological models should keep their multi-layered approach for modelling soil temperature, but add a simpler, yet physically consistent, hydrological approach for modelling snow processes and water transport in the soil. Keywords: land surface modelling; hydrological modelling; atmospheric climate models; subgrid variability; Baltic Basin

Description: The critical loads approach is widely used within Europe to assess the impacts of acid deposition on terrestrial and freshwater ecosystems. Recent work in Great Britain has focused on the national application of the First-order Acidity Balance (FAB) model to a freshwaters dataset of 1470 lake and stream water chemistry samples from sites across Britain which were selected to represent the most sensitive water bodies in their corresponding 10 km grid square. A ``Critical Load Function" generated for each site is compared with the deposition load of S and N at the time of water chemistry sampling. The model predicts that when catchment processes reach steady-state with these deposition levels, increases in nitrate leaching will depress acid neutralizing capacity (ANC) below the critical threshold of 0 μeql-1 at more than a quarter of the sites sampled, i.e. the critical load of acid deposition is exceeded at these sites. The critical load exceedances are generally found in upland regions of high deposition where acidification has been previously recognised, but critical loads in large areas of western Scotland are also exceeded where little biological evidence of acidification has yet been found. There is a regional variation in the deposition reduction requirements for protection of the sampled sites. The FAB model indicates that in Scotland, most of the sampled sites could be protected by sufficiently large reductions in S deposition alone. In the English and Welsh uplands, both S and N deposition must be reduced to protect the sites. Current international commitments to reduce S deposition throughout Europe will therefore be insufficient to protect the most sensitive freshwaters in England and Wales. Keywords: critical loads; acidification; nitrate; FAB model; acid deposition

Description: A methodology is presented for the disaggregation of numerical model fields of convective rainfall using a physically based procedure. The scheme uses surface sensible heat flux values derived from high-resolution multichannel satellite radiometer observations. The sensible heat flux values initialise a simple convective model to calculate the convective disaggregation parameter (CDP), which is theoretically proportional to the convective rainfall rate. The CDP diagnostic parameter can be derived as a one-time field if the surface characteristics are invariant, as a seasonal value may be, or it may be evaluated on a case by case basis. Once found, the CDP can be used to disaggregate numerical weather prediction (NWP) convective rainfall fields for as far ahead as such fields are produced.

Description: This article compares the results of three different models, namely empirical, geomorphoclimatic and stochastic, proposed in the literature for synthesising the reduction curve of average river discharges, of given frequency, over different durations. The analysis used observed reduction ratios inferred for twelve recording gauge stations with known rating curves, situated on central Italian watercourses all of which flow into the Adriatic sea. Particular emphasis was laid on the difficulties encountered in the parameterisation of the models, on the relations between the different formulations and on the existence of a link between the model parameters and the characteristic response times of the basins.

Description: The sensitivity of catchment runoff models to rainfall is investigated at a variety of spatial scales using data from a dense raingauge network and weather radar. These data form part of the HYREX (HYdrological Radar EXperiment) dataset. They encompass records from 49 raingauges over the 135 km2 Brue catchment in south-west England together with 2 and 5 km grid-square radar data. Separate rainfall time-series for the radar and raingauge data are constructed on 2, 5 and 10 km grids, and as catchment average values, at a 15 minute time-step. The sensitivity of the catchment runoff models to these grid scales of input data is evaluated on selected convective and stratiform rainfall events. Each rainfall time-series is used to produce an ensemble of modelled hydrographs in order to investigate this sensitivity. The distributed model is shown to be sensitive to the locations of the raingauges within the catchment and hence to the spatial variability of rainfall over the catchment. Runoff sensitivity is strongest during convective rainfall when a broader spread of modelled hydrographs results, with twice the variability of that arising from stratiform rain. Sensitivity to rainfall data and model resolution is explored and, surprisingly, best performance is obtained using a lower resolution of rainfall data and model. Results from the distributed catchment model, the Simple Grid Model, are compared with those obtained from a lumped model, the PDM. Performance from the distributed model is found to be only marginally better during stratiform rain (R2 of 0.922 compared to 0.911) but significantly better during convective rain (R2 of 0.953 compared to 0.909). The improved performance from the distributed model can, in part, be accredited to the excellence of the dense raingauge network which would not be the norm for operational flood warning systems. In the final part of the paper, the effect of rainfall resolution on the performance of the 2 km distributed model is explored. The need to recalibrate the model for use with rainfall data of a given resolution, particularly for periods of convective rain, is highlighted. Again, best performance is obtained using lower resolution rainfall data. This is interpreted as evidence for the need to improve the distributed model structure to make better use of the higher resolution information on rainfall and topographic controls on runoff. Degrading the resolution of rainfall data, model or both to achieve the smoothing apparently needed is not seen as wholly appropriate. Keywords: rainfall, runoff, sensitivity, scale, model, flood

Description: Predictions of average surface temperature of a sparsely vegetated West-African savannah by both single and dual source models of surface energy partitioning are compared. Within the single source model, the ``excess resistance" to heat transfer away from the canopy (compared to momentum absorption) is characterised by parameter kB-1, where k is the von Kármán constant and B is the Stanton number. Two values of this parameter are used; first kB-1 = 2 (a value often used within surface energy balance models but primarily applicable to permeable vegetation types) and then 12.4 (a value applicable to the savannah in question, which consists more of bluff roughness elements). As expected, the latter parameterisation generates better predictions of surface temperature. To make accurate predictions of surface temperature using a dual source model, then that model’s in-canopy aerodynamic resistance must be increased. Information on this increase is found through direct model intercomparison with the single source model parameterised with kB-1 = 12.4. Keywords: Penman-Monteith equation; Surface temperature; Canopy resistance; Savannah; Dual-Source model

Description: A quasi three-dimensional model is developed to simulate the behaviour of the aquifer system which is the resource of drinkable water for the town of Milano (Italy). Non continuous semipermeable layers locally separate permeable levels in a multilayered system, consisting of a phreatic and three confined aquifers. The numerical model is a conservative finite difference scheme based on the discretisation of the water balance equation for stationary flow. The grid spacing is 500 m and has been chosen, taking into account the distribution of the data in an area of about 400 km2. The model has been calibrated with a "trial and error" procedure, by comparison of the results of the model with the observations for three years (1950, 1974 and 1982) which correspond to different flow situations. Once calibrated, the model has been used as a predictive tool, to forecast the behaviour of the aquifer system for other years of the 20th century; the comparison between the model forecasts and observations is good. The model is capable of describing both the strong drawdown of the water table in the 1970s, when the water demand for domestic and industrial needs was very high, and the rise of the water table in the 1990s, when water extraction decreased. The results of the model confirm that the phreatic level is controlled largely by the local extraction of water; moreover, the aquifer system reacts to an increasing water demand with a small increase of the inflow and with a strong decrease of the outflow from its boundaries.

Description: A deterministic forecast of surface precipitation involves solving a time-dependent moisture balance equation satisfying conservation of total water substance. A realistic solution needs to take into account feedback between atmospheric dynamics and the diabatic sources of heat energy associated with phase changes, as well as complex microphysical processes controlling the conversion between cloud water (or ice) and precipitation. Such processes are taken into account either explicitly or via physical parameterisation schemes in many operational numerical weather prediction models; these can therefore generate precipitation forecasts which are fully consistent with the predicted evolution of the atmospheric state as measured by observations of temperature, wind, pressure and humidity. This paper reviews briefly the atmospheric moisture balance equation and how it may be solved in practice. Solutions are obtained using the Meteorological Office Mesoscale version of its operational Unified Numerical Weather Prediction (NWP) model; they verify predicted precipitation rates against catchment-scale values based on observations collected during an Intensive Observation Period (IOP) of HYREX. Results highlight some limitations of an operational NWP forecast in providing adequate time and space resolution, and its sensitivity to initial conditions. The large-scale model forecast can, nevertheless, provide important information about the moist dynamical environment which could be incorporated usefully into a higher resolution, ‘storm-resolving’ prediction scheme. Keywords: Precipitation forecasting; moisture budget; numerical weather prediction

Description: Three hours of high frequency vertical windspeed and carbon dioxide concentration data recorded over tropical forest in Brazil are presented and discussed in relation to various detrending techniques used in eddy correlation analysis. Running means with time constants 100, 1000 and 1875s and a 30 minute linear detrend, as commonly used to determine fluxes, have been calculated for each case study and are presented. It is shown that, for different trends in the background concentration of carbon dioxide, the different methods can lead to the calculation of radically different fluxes over an hourly period. The examples emphasise the need for caution when interpreting eddy correlation derived fluxes especially for short term process studies. Keywords: Eddy covariance; detrending; running mean; carbon dioxide; tropical forest

Description: Variations in sodium and chloride in atmospheric inputs (rainfall and mist), stream runoff and groundwater stores are documented for the upper Severn River (Afon Hafren and Afon Hore catchments), Plynlimon, mid-Wales. The results show five salient features. Sodium and chloride concentrations are highly variable and highly correlated in rainfall and mist. The sodium-chloride relationship in rainfall has a slope close to the sodium/chloride ratio in sea-water, and an intercept that is not significantly different from zero. This indicates that sea-salt is the dominant source of both sodium and chloride in rainfall, which would be expected given the maritime nature of the metrology. For mist, there is also a straight line with near-zero intercept, but with a slightly higher gradient than the sea-salt ratio, presumably due to small additional sodium inputs from other sources. There is an approximate input-output balance for both sodium and chloride, with the exception of one groundwater well, in which high chemical weathering results in an anomalous high Na/Cl ratio. Thus, atmospheric deposition is the dominant source of both sodium and chloride in groundwater and streamflow. The fluctuations in sodium and chloride concentrations in the streams and groundwaters are strongly damped compared to those in the rain and the mist, reflecting the storage and mixing of waters in the subsurface. On all timescales, from weeks to years, sodium fluctuations are more strongly damped than chloride fluctuations in streamflow. The additional damping of sodium is consistent with ion exchange buffering of sodium in the catchment soils.  Sodium and chloride concentrations are linearly correlated in the streams and groundwaters, but the slope is almost universally less than the sea-salt ratio and there is a non-zero intercept. The Na/Cl ratio in streamflow and groundwater is higher than the sea-salt ratio when salinity is low and lower than the sea-salt ratio when salinity is high. This pattern of behaviour is again consistent with ion exchange buffering of sodium in the catchment soils. The core features of this study are two fold. Firstly, sodium and chloride concentrations are highly damped within the streams and groundwaters relative to the atmospheric input. Secondly, streamflow sodium and chloride respond in similar ways across the catchments, except for the added cation exchange damping of the sodium signal. These findings are remarkable given the heterogeneous nature of the catchments and the complexity of the chemical time series signals in the streams. Keywords: Sodium; chloride; rainfall; mist; stream water; groundwater; Plynlimon; Hafren; Hore; Tanllwyth; moorland; Sitka spruce; forest; cation exchange; fractal

Description: Regionalized and at-site flood frequency curves exhibit considerable variability in their shapes, but the factors controlling the variability (other than sampling effects) are not well understood. An application of the Monte Carlo simulation-based derived distribution approach is presented in this two-part paper to explore the influence of climate, described by simulated rainfall and evapotranspiration time series, and basin factors on the flood frequency curve (ffc). The sensitivity analysis conducted in the paper should not be interpreted as reflecting possible climate changes, but the results can provide an indication of the changes to which the flood frequency curve might be sensitive. A single site Neyman Scott point process model of rainfall, with convective and stratiform cells (Cowpertwait, 1994; 1995), has been employed to generate synthetic rainfall inputs to a rainfall runoff model. The time series of the potential evapotranspiration (ETp) demand has been represented through an AR(n) model with seasonal component, while a simplified version of the ARNO rainfall-runoff model (Todini, 1996) has been employed to simulate the continuous discharge time series. All these models have been parameterised in a realistic manner using observed data and results from previous applications, to obtain ‘reference’ parameter sets for a synthetic case study. Subsequently, perturbations to the model parameters have been made one-at-a-time and the sensitivities of the generated annual maximum rainfall and flood frequency curves (unstandardised, and standardised by the mean) have been assessed. Overall, the sensitivity analysis described in this paper suggests that the soil moisture regime, and, in particular, the probability distribution of soil moisture content at the storm arrival time, can be considered as a unifying link between the perturbations to the several parameters and their effects on the standardised and unstandardised ffcs, thus revealing the physical mechanism through which their influence is exercised. However, perturbations to the parameters of the linear routing component affect only the unstandardised ffc. In Franchini et al. (2000), the sensitivity analysis of the model parameters has been assessed through an analysis of variance (ANOVA) of the results obtained from a formal experimental design, where all the parameters are allowed to vary simultaneously, thus providing deeper insight into the interactions between the different factors. This approach allows a wider range of climatic and basin conditions to be analysed and reinforces the results presented in this paper, which provide valuable new insight into the climatic and basin factors controlling the ffc. Keywords: stochastic rainfall model; rainfall runoff model; simulation; derived distribution; flood frequency; sensitivity analysis

Description: : Calibration of a model against more than one output variable is important for reliable simulations of internal processes. In this study, a genetic algorithm combined with local optimisation was proposed for automatic single- and multi-criteria calibration of the HBV model, a conceptual runoff model. The model and the optimisation algorithm were applied in two catchments with different geology where, in addition to observed runoff, time series of groundwater level data were available. For a theoretical, error-free test case with synthetic data, the optimisation algorithm was usually able to find the true parameter values. For the real-world case, parameter values varied considerably when calibrating against runoff only. However, parameter values were constrained significantly when calibrating against both runoff and groundwater levels. Furthermore, for one of the catchments, the results of the multi-criteria calibration motivated a modification of the model structure. Keywords: Multi-criteria calibration; genetic algorithm; parameter uncertainty; conceptual runoff models; HBV model; groundwater levels

Description: The fractionation in chemical elements for UK river waters is described relative to the continental crust based on data collected within studies of upland acidic catchments in mid-Wales and major eastern-UK rivers. Four types of river are examined (upland, rural, agricultural and industrial/urban) together with an average for the UK based on a "river enrichment factor", REF. Here, the REF is defined as the ratio of the median river water concentration to the average abundance for the upper continental crust for each element. For this purpose, graphical representations of the logarithm of the REF are presented sequentially in increasing order of magnitude. The results demonstrate vividly the high fractionating of the more volatile, anionic and ‘sea-salt' elements to the aqueous phase and the retention of transition elements of high charge due to solubility controls with intermediate controls for the divalent base cations of intermediate solubility. They also show the increasing significance of pollutants in the agriculturally and industrially/ urban impacted environments. Keywords: Elements; major elements; trace elements; nutrients; river; hydrochemistry; enrichment factor; river enrichment factor; LOIS; Plynlimon; River Severn; Afon Hafren; River Tweed; River Aire; River Thames

Description: Errors arise when using conventional radar reflectivity, Z, to estimate rainfall rate, R, and these can be particularly severe during severe convective storms; the very events when accurate estimates are needed so that action can be taken to mitigate the effects of flooding. Concentration is on three problems associated with heavy rainfall: hail, attenuation and absolute calibration of the radar, and consider how polarisation radar parameters, differential reflectivity, ZDR, and specific differential phase shift KDP, might lead to their alleviation. It is essential to consider the fundamental limits to the accuracy with which these parameters can be estimated. If ZDR can be measured to an accuracy of 0.2 dB, then it provides a measure of mean raindrop shape which is sufficiently precise to improve rainrate estimates. This can be achieved at S-band (10 cm), but seems very difficult for operational C-band (5 cm) radars; differential attenuation by the heavy rain introduces a negative bias into ZDR which increases with range. However, the magnitude of this bias at C-band can then be used to correct for the total attenuation of Z. Differential phase, KDP has the advantage that it is a phase measurement and so is unaffected by attenuation. It only responds to the rainfall and is unaffected by the hail, but KDP is a noisy parameter and is only useful for heavy rainfall above 30 – 60 mm hr-1. Fortuitously, KDP and ZDR are not independent and one use of KDP and ZDR may well be to exploit this redundancy to identify rain areas as opposed to hail, and in rainfall to use the redundancy to provide an automatic calibration of the absolute reflectivity, Z, to 0.5 dB (12%). Finally, the noisy character of both ZDR and KDP together with the low level of the co-polar correlation coefficient provide the first reliable means of detecting and removing anomalous propagation which is a major operational problem for all weather radars. Keywords: polarisation radar, rainfall calibration, attenuation, hail, anomalous propagation

Description: This paper explores the potential for assessing the impacts of climate change upon flood frequency for the gauged, upland Wye catchment at Plynlimon, Wales, UK, while taking account of uncertainty in modelling rainfall-runoff processes under current conditions. A continuous simulation methodology which uses a stochastic rainfall model to drive the rainfall-runoff model TOPMODEL is utilised. Behavioural parameter sets for both the rainfall model and TOPMODEL are identified prior to the climate change runs using the Generalised Likelihood Uncertainty Estimation (GLUE) methodology. The "medium-high" UKCIP98 climate change scenario, obtained from the HadCM2 GCM simulations, is used as a starting point for a variety of different scenarios at the catchment scale. It is demonstrated that while the scenarios have only a small impact upon the likelihood weighted flood frequency uncertainty bounds in comparison with the current condition scenario, the risk of a given discharge as an element in the distribution of T year floods is changed. This underlines the need to account explicitly for uncertainty within hydrological modelling, especially in estimating the impacts of climate change. Keywords: Climate change; Floods; Frequency; TOPMODEL

Description: This paper addresses the problem of uniqueness of catchment areas in relation to model representations of flow processes. The uniqueness of field measurements as a limitation on model representations is discussed. The treatment of uniqueness as a residual from a modelled relationship may conceal information about the uniqueness of catchments, while the treatment of uniqueness as a set of parameter values within a particular model structure is problematic due to the equifinality of model structures and parameter sets. The analysis suggests that a fully reductionist approach to describe the uniqueness of individual catchment areas by the aggregation of descriptions of small scale behaviour will be impossible given current measurement technologies. A suggested strategy for the representation of uniqueness of place as a fuzzy mapping of the landscape into a model space is suggested. This will lead to a quantification of the uncertainty in predictions of any particular location in a way that allows a conditioning of the mapping on the basis of the available data. This process can incorporate a hypothesis testing approach to model evaluation but the problem of multiple behavioural models may provide an ultimate limitation on the realism of process representations: not on the principle of realism but on the possibility of unambiguous process representations.

Description: Key issues involved in converting MTB ensemble forecasts of rainfall into ensemble forecasts of runoff are addressed. The physically-based distributed modelling system, SHETRAN, is parameterised for the Brue catchment, and used to assess the impact of averaging spatially variable MTB rainfall inputs on the accuracy of simulated runoff response. Averaging is found to have little impact for wet antecedent conditions and to lead to some underestimation of peak discharge under dry catchment conditions. The simpler ARNO modelling system is also parameterised for the Brue and SHETRAN and ARNO calibration and validation results are found to be similar. Ensemble forecasts of runoff generated using both SHETRAN and the simpler ARNO modelling system are compared. The ensemble is more spread out with the SHETRAN model, and a likely explanation is that the ARNO model introduces too much smoothing. Nevertheless, the forecasting performance of the simpler model could be adequate for flood warning purposes. Keywords: SHETRAN, ARNO, HYREX, rainfall-runoff model, Brue, real-time flow forecasting

Description: The classical one-dimensional advection-diffusion equation (ADE) gives an inadequate description of tracer cloud evolution in the River Severn, U.K. A solute transport model incorporating the effects of tracer storage in dead zones is presented in which the channel is conceived as being divided into two parallel regions. The bulk flow region occurs in the central part. Its longitudinal dispersive properties are described by the ADE. Adjacent to this, an additional cross-sectional area is defined in which tracer can be stored temporarily in regions of slowly moving water called dead zones. Exchange between the two regions follows a first order rate equation. Applying the model to the River Severn shows that a dispersing cloud’s evolution occurs in two distinct stages with a rapid transitional phase. Initially, shear-dispersion is dominant while the tracer particles mix fully over the bulk flow. Once this has occurred, dead zone storage accounts well for the non-Fickian evolution of the cloud. After the transitional phase the dead zone storage mechanism clearly dominates over shear-dispersion. Overall, the combined shear flow dispersion – dead zone model (D-DZM) provides a much better, physically consistent description of the tracer cloud’s evolution than the simple classical ADE approach can do alone. Keywords: Channels; dispersion; dead zones; tracers; River Severn

Description: Sivakumar et al. (2000a), by employing the correlation dimension method, provided preliminary evidence of the existence of chaos in the monthly rainfall-runoff process at the Gota basin in Sweden. The present study verifies and supports the earlier results and strengthens such evidence. The study analyses the monthly rainfall, runoff and runoff coefficient series using the nonlinear prediction method, and the presence of chaos is investigated through an inverse approach, i.e. identifying chaos from the results of the prediction. The presence of an optimal embedding dimension (the embedding dimension with the best prediction accuracy) for each of the three series indicates the existence of chaos in the rainfall-runoff process, providing additional support to the results obtained using the correlation dimension method. The reasonably good predictions achieved, particularly for the runoff series, suggest that the dynamics of the rainfall-runoff process could be understood from a chaotic perspective. The predictions are also consistent with the correlation dimension results obtained in the earlier study, i.e. higher prediction accuracy for series with a lower dimension and vice-versa, so that the correlation dimension method can indeed be used as a preliminary indicator of chaos. However, the optimal embedding dimensions obtained from the prediction method are considerably less than the minimum dimensions essential to embed the attractor, as obtained by the correlation dimension method. A possible explanation for this could be the presence of noise in the series, since the effects of noise at higher embedding dimensions could be significantly greater than that at lower embedding dimensions. Keywords: Rainfall-runoff; runoff coefficient; chaos; phase-space; correlation dimension; nonlinear prediction; noise

Description: An experimental short-term acidification with HCl at a first-order stream in central Maine, USA was used to study processes controlling the changes in stream chemistry and to assess the ability of stream substrate to buffer pH. The streambed exerted a strong buffering capacity against pH change by ion exchange during the 6-hour acidification. Streambed substrates had substantial cation and anion exchange capacity in the pH range of 4.1 to 6.5. The ion exchange for cations and SO42- were rapid and reversible. The speed of release of cations from stream substrates was Na1+〉 Ca2+ 〉 Mg2+ 〉 Aln+ 〉 Be2+, perhaps relating to charge density of these cations. Ca2+ desorption dominated neutralisation of excess H+ for the first 2 hr. As the reservoir of exchangeable Ca diminished, desorption (and possibly dissolution) of Al3+ became the dominant neutralising mechanism. The exchangeable (and possibly soluble) reservoir of Al was not depleted during the 6-hour acidification. Sulphate adsorption during the acidification reduced the concentration of SO42- in stream water by as much as 20 μeq L-1 (from 70 μeq L-1). Desorption of SO42- and adsorption of base cations after the artificial acidification resulted in a prolongation of the pH depression. The streambed had the capacity to buffer stream water chemistry significantly during an acidifying event affecting the entire upstream catchment. Keywords: stream acidification; ion exchange; sediment; sulfate exchange; aluminium; beryllium

Description: Hourly stream temperatures monitored over 28 months, which spanned a 3 month period of environmentally sensitive plot-scale harvesting of 20 ha. (20%) of the Nant Tanllwyth catchment (0.89 km2) on the south side of the main stream in early 1996, resulted in a 0.58°C (p〈 0.001) increase in monthly mean stream temperature. Over the same 28 month experimental period, there was no significant increase in the monthly mean air temperature recorded at a nearby automatic weather station. Monthly mean temperatures are highest in July and August in the year before and the year after the clearfelling, and one of the main effects of the clearfelling was to decrease the difference between the monthly mean stream and air temperatures. Despite the air temperatures being cooler in the post-clearfelling year, the stream temperatures still showed an increase in the summer months. Monthly mean maximum stream temperatures, also highest in July and August in the year before and the year after the clearfelling, showed a marked increase of 7.0°C: in July and 5.3°C in August from the pre- to the post-clearfelling years, while monthly mean minimum air temperatures actually showed a slight decrease for the same months. The likely effects on stream fauna are discussed, as are suggestions for, and likely effects of, buffer strips alongside the streams. Keywords: stream temperature; air temperature; ground surface temperature; clearfelling; Plynlimon

Description: A procedure for the parameterisation of drain flow hydrographs is proposed. This involves the derivation of empirical linear response functions, which are themselves parameterised. The parameters are the time and height of the peak, and the recession characteristics. The recession limb of the hydrograph can be approximated best by the Youngs (1985) analysis, which requires two parameters. The merit of this method is illustrated by an analysis of data from a drainage experiment at North Wyke, Devon, UK; this shows that the model fits the data very well. Keywords: Drainflow hydrographs; response functions

Description: Information on the magnitude and variability of low river flows at the river reach scale is central to most aspects of water resource and water quality management. Within the UK, river stretches with permanent gauging stations represent less than one percent of the total number of river stretches mapped at a scale of 1:50,000 and fewer that 20% of gauged catchments can be regarded as having natural flow regimes. This has led to the development of simple, multivariate models for predicting average annual natural flow duration statistics through relationships with catchment characteristics. One assumption within these models is that low flows occur at the same time at all points within a catchment, irrespective of the hydrogeological nature and climatic condition of the catchment. This paper discusses the implications of spatial variations in the timing of low flow events for this type of model. Differences in the timing of the mean day of occurrence of the annual Q95 flow in UK catchments can be identified with low flows occurring earlier in the year within impermeable dry catchments and later in the year for wet permeable catchments. However, any differences in the mean day of occurrence between different catchments are generally masked by the magnitude of the inter-year variability in the day of occurrence. From analysis of linear combinations of flow statistics from nearest-neighbour gauged catchments, the paper demonstrates that the assumption of temporal coherence of low flows will generally result in an under-estimate of Q95; these underestimates are more significant for pairs of impermeable catchments than for combinations of permeable catchments and impermeable-permeable catchments.

Description: Tarawa Atoll, Gilbert Islands (1° 30′N, 173° 00′E) is an isolated place, comparatively recently emergent – 2500 years bp and 2 – 3 m above present sea-level (Marshall & Jacobson, 1985). During the course of a study of the marine ostracods (Eagar, in press) it was noted that there are relatively few places where freshwater is visible on the surface of the atoll. This is not unusual, given the low precipitation (154 mm a−1) and the daytime temperatures of Tarawa (27–30°C). Five freshwater ponds on South Tarawa (Fig. 1) were examined and two species of Ostracoda were found: Cyprinotus cingalensis Brady, 1886 and Limnocythere notodonta Vávra, 1906. At Bairiki (locality A), a pond adjacent to the causeway linking Bairiki with Betio was sampled and yielded abundant Cyprinotus cingalensis. Other ponds were found at Ambo (Locality B) and Temaiku Bight (Localities C and D with two ponds). Only the pond (Locality B), an established babai pit (taro; Cyrtosperma chamissonis), adjacent to the roadside at Ambo yielded further specimens of the ostracod Limnocythere notodonta, although in low numbers.The question of how these species were introduced onto Tarawa Atoll is intriguing. C. cingalensis is known from Ceylon (Brady, 1886), Hawaii and the Sandwich Islands. The record by Vávra (1906) from Australia may be incorrect. Limnocythere notodonta was previously recorded only from Java (Vávra, 1906). Both species may have been distributed in the same way that Sars (e.g., Sars, 1896) transported species from different parts of the world to Norway to describe . . .

Description: Assemblages of Middle Devonian (Givetian) phytoplankton from the Holy Cross Mountains include sphaeromorphs possessing blister-like ornamentation typical of the genus Tapajonites Sommer & van Boekel, 1963. Study of the sculptural elements under high magnification indicates the presence of patterns resembling impressions of pyrite crystals. It is suggested that ornamentation in Tapajonites, or at least in some sphaeromorphs assignable to that genus, is of a secondary nature.

Description: The genus Aubignyna Margerel, 1970 (type A. mariei) was originally described from the upper Pliocene of NW France. Examination and re-illustration of topotypes of A. mariei Margerel, 1970, the holotype of Buccella planidorso Atkinson, 1969 (from the Recent of Cardigan Bay, Wales) and syntypes of Rotalia perlucida Heron-Allen & Earland, 1913 (from the Clare Island Survey, western Ireland) shows them to be conspecific. Consequently, the type species of Aubignyna becomes R. perlucida, for which a lectotype is chosen. A new species of microforaminifera formally described here is assigned to Aubignyna and shown to occur in a wide range of intertidal–shallow subtidal, brackish–normal marine estuaries and lagoons in Europe and North America.

Description: Continental slopes are presumed key areas for deposition of organic carbon exported from the shelf. Analysis of across-slope differences in diatom and silicoflagellate fluxes recorded in bottom sediments of the Goban Spur margin, a typical North Atlantic slope environment, was carried out to test if they can provide information on the magnitude of advection of material from the shelf into deeper waters. Total diatom and silicoflagellate accumulation rates showed strong across-slope differences. Minimum values are recorded at the shelf break where maximum surface productivity conditions occur while the deeper sampling stations record fluxes as high as 183×106 valves cm–2 ka–1. While high diatom fluxes show a clear correspondence with the activity of a permanent bottom nepheloid layer operating in the region, they do not correlate with productivity patterns observed in the water column. Diatom assemblages are mainly composed of Chaetoceros resting spores and Thalassionema nitzschioides (Grunow) Grunow ex Hustedt, typical indicators of spring bloom conditions in the area. The absence of clear across-slope trends in the diatom assemblages is interpreted as the effect of random mixing driven by the strong hydrodynamic regime provoked by the activity of the bottom nepheloid layer. The dominance of Chaetoceros resting spores across the slope is related to important exportation of shelf-derived production. However, due to the broad ecological tolerances of the main taxa composing the diatom assemblages, they do not allow precise estimations on the magnitude of the primary vertical flux vs. the secondary lateral flux in this slope environment. Use of the tychoplanktonic and benthic diatoms, which are restricted to the neritic realm, allows only the estimation of the minimum amount of shelf-derived diatoms reaching the slope sediments (at least 13% of the total diatom assemblage for the upper slope area of the Goban Spur). This study shows that major limitations exist for the use of diatoms preserved in surface sediments of this area as tracers of shelf-derived production transported to the continental slope.

Description: Ynezidinium malloyi gen. nov., sp. nov. shows paratabulation details that indicate it belongs to the Family Gonyaulacaceae, subfamily Leptodiniodeae, but which, in combination, distinguish it from previously described genera. The paratabulation details include: (1) pentagonal sixth precingular (li) in contact with both fourth and first apicals (A and lu); (2) elongate and subparallel fourth and first apicals; (3) straight to slightly sigmoidal sulcal region; (4) lack of small intercalary (K) paraplates; and (5) Q/B preapical arrangement. Other species herein assigned to Ynezidinium include: Ynezidinium brevisulcatum (Michoux, 1985) comb. nov., Y. latolineatum (Yun, 1981) comb. nov., Y. pentahedrias (Damassa, 1979) comb. nov. and Y. waipawaense (Wilson, 1988) comb. nov.

Description: The ostracod Kinnekullea comma occurs in the upper part of the Cautley Mudstone Formation (Ashgill Series) in the Cautley district of northern England, thus geographically extending the stratigraphical value of K. comma as a locum for the Dicellograptus anceps graptolite Biozone in Ordovician shelly marine facies of Britain and Ireland. Its occurrence, in Scotland and England, confirms it as one of the earliest trans-Iapetus Ocean ostracod species.

Description: The recent description of Umbriadinium mediterraneense Bucefalo Palliani & Riding 1997 from the Early Jurassic of central Italy and Greece has provided new information on the phylogeny of the dinoflagellate cyst Family Suessiaceae. On the basis of the morphology of the five suessiacean genera, a subdivision of the family into two new subfamilies is proposed. These are the Late Triassic Suessioideae and the Early Jurassic Umbriadinoideae. The evolution of the Family Suessiaceae is related to the evolution of scleractinian corals, largely on the basis of the similarity of their evolutionary patterns and geographical palaeodistributions.

Description: Organic microfossils of regular dodecahedral shape are found in the Palaeogene (Lower Oligocene) of the central and northern parts of the Norwegian North Sea. The shape and structure of these fossils are very similar to coccospheres of the calcareous nannoplankton genus Braarudosphaera. The individual pentagonal plates show the same morphological features as replicas of the inner surface of pentaliths forming calcareous coccospheres. It is the first evidence that a representative of calcareous nannoplankton (Haptophyta, Coccolithophorales) is found to produce acid-resistant organic microfossils. The organic remains might have been produced by an undescribed species of the genus Braarudosphaera or represent an unknown stage in the life cycle of species which normally produce calcareous plates.

Description: INTRODUCTIONThe Reverend Henry Eley ma was a little-known Victorian cleric who wrote a delightful book entitled Geology in the Garden in 1859. In it are described and illustrated many foraminifera preserved in flint, which are some of the first recorded Upper Cretaceous foraminifera from south east England. Jones & Parker thought well enough of his work to review Eley’s material in 1872. Eley’s collection is preserved in The Natural History Museum, London.BACKGROUNDWhilst undertaking an investigation into the life and work of Professor Thomas Rupert Jones, I came across an old collection of foraminifera in The Natural History Museum (registration numbers 54916–54944) attributed to a Rev. H. Eley. This, Jones had not only recorded in his Catalogue (1882: p. 14) but earlier in 1872 (with W. K. Parker) had thought worthy of revision – much as they had done with other more famous collections during the 1860s in their series On the Nomenclature of the Foraminifera. Why they should choose such an apparently obscure collection was unclear until I had chance to read a letter in the Museum’s archive, which Jones (1882) had previously mentioned. The letter was written by Eley to Jones on the 23 February 1872 from 5 Bloomsbury Place, Brighton. This indicates that Jones knew Eley and his whereabouts, since the former writes that he was going to read the March 1872 issue of the Geological Magazine with interest, because he remembered that ... ‘the note at the foot of page 195 of the Geology . . .

Description: Since the publication of An Atlas of British Recent Foraminiferids (Murray, 1971) there have been many taxonomic changes. Some result from the revised generic classification summarized by Loeblich & Tappan (1987), some from later taxonomic revision, while others are corrections. In the following list, the name used in 1971 is followed by the revised name. Where the generic assignment is after Loeblich & Tappan (1987) the new name is listed without a reference. OD stands for original designation, i.e. the species is type of the genus. Brief explanations are given as appropriate.Pl. 1: Reophax scottii Chaster = Leptohalysis scottii (Chaster); thin, delicate and flexible test.Pl. 4: Cribrostomoides jeffreysii (Williamson) = Veleroninoides jeffreysii (Williamson); evolute planispiral test with interio-areal aperture (Jones et al., 1993)Pl. 8: Textularia sagittula Defrance group: as was noted on p. 31, this is a complex of variable forms. It includes Textularia bocki Höglund, Spirorutilis wrighti (Silvestri), and Textularia spp. 1–3 of Banner & Pereira (1981).Pl. 9: Textularia earlandi Parker = Morulaeplecta bulbosa Höglund; streptospiral initial end.Pl. 10: Trochammina globigeriniformis (Parker & Jones) var. pygmaea Höglund = Portatrochammina murrayi Brönnimann & Zaninetti, 1984; distinguished from T. g. var. pygmaea (apertural slit without a lip) by having a slit-shaped aperture ‘which extends below the border of the umbilical flap from the first chamber of the final whorl to the penultimate chamber’.Pl. 11: Trochammina ochracea (Williamson) = Lepidodeuterammina ochracea (Williamson); OD.Pl. 12: Trochammina rotaliformis Heron-Allen & Earland = Deuterammina sp.; according to Brönnimann . . .

Description: In the course of studies on Devonian radiolarian faunas from Nanning, Guangxi, SW China (Luo et al., 1997), numerous smooth siliceous microspheres (Fig. 1) are encountered together with abundant spherical entactiniid radiolarians. The present investigation reveals that these microspheres are siliceous casts formed through precipitation of silica between the medullary and cortical shells of entactiniid radiolarians. As these microspheres are commonly the most abundant particles encountered in some Devonian samples, an understanding of their origins is desirable.Examined material is from two bedded chert samples collected from the upper part of the Tanhe Formation at Wuxiangling, 5 km SE of Nanning, Guangxi Province, SW China. Tanhe Formation consists of thin dark grey, brown grey cherty rock and cherty mudstone containing abundant radiolarians (entactiniids, ceratoikiscids and palaeoscenidiids) and tentaculitids. Based on zonation of tentaculitid faunas this formation is Lower to Middle Devonian (Upper Emsian – Lower Givetian) (Zhong et al., 1992; Kuang et al., 1996). A standard method (Pessagno & Newport, 1972) for extraction of radiolarians from cherts using hydroflouric acid was applied.Free microspheres are the most common individuals (Pl. 1, figs 1, 8). All have smooth surfaces and possess some relatively larger holes or pores. Average microsphere diameter (20 specimens) is 92 μm. Hole shapes vary from three-bladed to round with spines rarely seen penetrating the microspheres (Pl. 1, figs 7, 10). A full range of material from microsphere-bearing entactiniids in which there are remnants of the original spongy radiolarian shells (Pl. 1, figs 5–7, 9) to solitary microspheres . . .