ALBERT

Description: A wind-driven numerical model of the Indian Ocean is used to examine the horizontal statistics of hundreds of passive tracers spread evenly over the model domain. The distribution covers several dynamically distinct regions, revealing a variety of Lagrangian behaviours associated with different geographic locations. In particular, a cluster of trajectories with scaling dimension as large as 1.3 exists throughout the equatorial zone. Spectral analysis of trajectory displacements indicates mixed Rossby-gravity waves are involved in the production of some fractal trajectories.

Description: In this paper we present a review of advances made and problems still existing in the application of the theory of chaos and dynamical systems to time series. In particular we discuss issues pertaining the estimation of dimensions, Lyapunov exponents and nonlinear prediction from an observable. We analyze the problems and discuss proper ways to deal with them.

Description: A novel application of a technique developed from chaos theory is used in describing seasonal to interannual climate predictability over the Northern Hemisphere (NH). The technique is based on an empirical forecast scheme - local approximation in a reconstructed phase space - for time-series data. Data are monthly 500 hPa heights on a latitude-longitude grid covering the NH from 20° N to the equator. Predictability is estimated based on the linear correlation between actual and predicted heights averaged over a forecast range of one- to twelve.month lead. The method is capable of extracting the major climate signals on this time scale including ENSO and the North Atlantic Oscillation.

Description: Our intention in this work is to show, by using two different methods, that magnetospheric dynamics reveal low dimensional chaos. In the first method we extend the chaotic analysis for the AE index time series by including singular value decomposition (SVD) analysis in combination with Theiler's test in order to discriminate dynamical chaos from self-affinity or "crinkliness". The estimated fractality of the AE index time series which is obtained belongs to a strange attractor structure with close returns in the reconstructed phase space. In the second method we extend the linear equivalent magnetospheric electric circuit to a nonlinear one, the arithmetic solution of which reveals low dimensional chaotic dynamics. Both methods strongly support the existence of low dimensional magnetospheric chaos.

Description: Due to the local and global impacts of algae blooms and patchiness on water quality, carbon cycling and climate, models of plankton dynamics are of current interest. In this paper, the temporal and spatial patterns in natural plankton communities are interpreted as transient and stationary nonequilibrium solutions of dynamical nonlinear interaction-diffusion-advection systems. A simple model of phytoplankton-zooplankton dynamics (Scheffer, 1991) is presented in space and time. After summarizing the local properties as multiple stability and oscillations, the emergence of spatial and spatio- temporal patterns is considered, accounting also for diffusion and weak advection. In order to study the emergence and stability of these structures under hydrodynamic forcing, the interaction- diffusion-advection model is coupled to the hydrodynamic equations. It is shown, that the formation of nonequilibrium spatio-temporal density patterns due to the interplay of the deterministic nonlinear biological interactions and physical processes is a rare occurrence in rapidly flowing waters. The two-timing perturbation technique is applied to problems with very rapid single-directed steady flows. A channel under tidal forcing serves as and example for a system with a relatively high detention time of matter. Generally, due to the different time and length scales of planktic interactions, diffusion and transport, initial nonequilibrium plankton patches are simply moved through the system unless the strong hydrodynamic forces do not destroy them before.

Description: A two dimensional system of autonomous nonlinear ordinary differential equations models glacier growth and temperature changes on an idealized planet. We apply standard perturbative techniques from dynamical systems theory to study small amplitude periodic orbits about a constant equilibrium. The equations are put in cononical form and the local phase space topology is examined. Maximum and minimum periods of oscillation are obtained and related to the radius of the orbit. An adjacent equilibrium is shown to have saddle character and the inflowing and outflowing manifolds of this saddle are studied using numerical integration. The inflowing manifolds show the region of attraction for the periodic orbit. As the frequency gets small, the adjacent (saddle) equilibrium approaches the radius of the periodic orbit. The bifurcation of the periodic orbit to a stable homoclinic orbit is observed when an inflowing manifold and an outflowing manifold of the adjacent equilibrium cross.

Description: Fractal and occasionally multifractal behaviour has been invoked to characterize (independently of their magnitude) the spatial distribution of seismic epicenters, whereas more recently, the frequency distribution of magnitudes (irrespective of their spatial location) has been considered as a manifestation of Self-Organized Criticality (SOC). In this paper we relate these two aspects on rather general grounds, (i.e. in a model independent way), and further show that this involves a non-classical SOC. We consider the multifractal characteristics of the projection of the space-time seismic process onto the horizontal plane whose values are defined by the measured ground displacements, we show that it satisfies the requirements for a first order multifractal phase transition and by implication for a non-classical SOC. We emphasize the important consequences of the stochastic alternative to the classical (deterministic) SOC.

Description: A detailed nonlinear time series analysis has been made of two daytime geomagnetic pulsation events being recorded at L'Aquila (Italy, L ≈ 1.6) and Niemegk (Germany, L ≈ 2.3). Grassberger and Procaccia algorithm has been used to investigate the dimensionality of physical processes. Surrogate data test and self affinity (fractal) test have been used to exclude coloured noise with power law spectra. Largest Lyapunow exponents have been estimated using the methods of Wolf et al. The problems of embedding, stability of estimations, spurious correlations and nonlinear noise reduction have also been discussed. The main conclusions of this work, which include some new results on the geomagnetic pulsations, are (1) that the April 26, 1991 event, represented by two observatory time series LAQ1 and NGK1 is probably due to incoherent waves; no finite correlation dimension was found in this case, and (2) that the June 18, 1991 event represented by observatory time series LAQ2 and NGK2, is due to low dimensional nonlinear dynamics, which include deterministic chaos with correlation dimension D2(NGK2) = 2.25 ± 0.05 and D2(NDK2) = 2.02 ± 0.03, and with positive Lyapunov exponents λmax (LAQ2) = 0.055 ± 0.003 bits/s and λmax (NGK2) = 0.052 ± 0.003 bits/s; the predictability time in both cases is ≈ 13 s.

Description: If climate models produced clouds having liquid water amounts close to those observed, they would compute a mean albedo that is often much too large, due to the treatment of clouds as plane-parallel. An approximate lower-bound for this "plane-parallel albedo bias" may be obtained from a fractal model having a range of optical thicknesses similar to those observed in marine stratocumulus, since they are more nearly plane-parallel than most other cloud types. We review and extend results from a model which produces a distribution of liquid water path having a lognormal-like probability density and a power-law wavenumber spectrum, with parameters determined by stratocumulus observations. As the spectral exponent approaches -1, the simulated cloud approaches a well-known multifractal, referred to as the "singular model", but when the exponent is -5/3, similar to what is observed, the cloud exhibits qualitatively different scaling properties, the socalled "bounded model". The mean albedo for bounded cascade clouds is a function of a fractal parameter, 0

Description: We study atmospheric wind turbulence in the framework of universal multifractals, using several medium resolution (10 Hz) time series. We cut these original time series into 704 scale invariant realizations. We then compute the moment scaling exponent of the energy flux K(q) for 4 and 704 realizations, in order to study qualitative difference between strong and weak events associated with multifractal phase transitions. We detect a first order multifractal phase transition of the energy flux at statistical moment of order qD ≈ 2.4 ± 0.2: this means that when the number of realizations increases, moments order q ≥; qD diverge. These results are confirmed by the study of probability distributions, and wind structure functions. A consequence of these findings is that it is no use to compare different cascade models in turbulence by using the high order wind structure functions, because a linear part will always be encountered for high enough order moments. Another important implication for multifractal studies of turbulence is that the asymptotic slope of the scaling moment function is purely a function of sample size and diverges with it; it implies the same for D∞, which has often be considered as finite.

Description: Shear flow in a stable stratification provides a waveguide for internal gravity waves. In the inviscid approximation, internal gravity waves are known to be unstable below a threshold in Richardson number. However, in a viscous fluid, at low enough Reynolds number, this threshold recedes to Ri = 0. Nevertheless, even the slightest viscosity strongly damps internal gravity waves when the Richardson number is small (shear forces dominate buoyant forces). In this paper we address the dynamics that approximately govern wave propagation when the Richardson number is small and the fluid is viscous. When Ri

Description: We present a numerical study of the generation and evolution of a mixed layer in a stably stratified layer of Boussinesq fluid. We use an external forcing in the equation of motion to model the experimental situation where the mechanical energy input is due to an oscillating grid. The results of 2D and 3D numerical simulations indicate that the basic mechanism for the entrainment is the advection of the temperature field. This advection tends to produce horizontally thin regions of small temperature vertical gradients (jets) where the hydrodynamics forces are nearly zero. At the bottom of these structures, the buoyancy brakes the vertical motions. The jets are also characterized by the presence of very short horizontal scales where the thermal diffusion time turn out to be comparable with the dynamics time. As a result, the temperature field is well mixed in a few dynamics times. This process stops when the mechanical energy injected becomes comparable with the energy dissipated by viscosity.

Description: In addition to the bispectral coherence method, phase/time analysis of analytic signals is another promising avenue for the investigation of phase effects in wind waves. Frequency spectra of phase fluctuations obtained from both sea and laboratory experiments follow an F-β power law over several decades, suggesting that a fractal description is appropriate. However, many similar natural phenomena have been shown to be multifractal. Universal multifractals are quantified by two additional parameters: the Lévy index 0 〈 α 〈 2 for the type of multifractal and the co-dimension 0 〈 C1 〈 1 for intermittence. The three parameters are a full statistical measure the nonlinear dynamics. Analysis of laboratory flume data is reported here and the results indicate that the phase fluctuations are 'hard multifractal' (α 〉 1). The actual estimate is close to the limiting value α = 2,  which is consistent with Kolmogorov's lognormal model for turbulent fluctuations. Implications for radar and sonar backscattering from the sea surface are briefly considered.

Description: The radiocarbon record that has been extended from 7199 BC to 1891 AD is of fundamental importance to understand century-scale variations of solar activity. We have, therefore, studied how to extract information from dynamic reconstructions of this observational record. Using some rather unusual methods of nonlinear dynamics, we have found that the data are significantly different from linear coloured noise and that there is some evidence of nonlinear behaviour. The method of recurrence plots exhibits that the grand minima of solar activity are quite different in their recurrence. Most remarkably, it suggests that the recent epoch seems to be similar to the Medieval maximum.

Description: We empirically investigate the scaling behaviour of the horizontal wind along the vertical direction using 287 radiosonde soundings with a resolution of 50 m. We compare the results obtained with those of the horizontal temporal behaviour in the framework of Generalized Scaling Invariance and the unified Scaling model of atmospheric dynamics. We find the scaling to be very well respected over the range 50 m - 13 km (nearly the entire troposphere) and we estimate the universal multifractal indices which characterize the statistics in the vertical. By comparing our result with those obtained in the horizontal we show that the degree of stratification is different for mean and extreme structures. Finally, we theoretically discuss the necessary improvements to the Unified Multifractal model needed to account for them.

Description: Theoretical calculations, simulations and measurements of rotation of earthquake focal mechanisms suggest that the stress in earthquake focal zones follows the Cauchy distribution which is one of the stable probability distributions (with the value of the exponent α equal to 1). We review the properties of the stable distributions and show that the Cauchy distribution is expected to approximate the stress caused by earthquakes occurring over geologically long intervals of a fault zone development. However, the stress caused by recent earthquakes recorded in instrumental catalogues, should follow symmetric stable distributions with the value of α significantly less than one. This is explained by a fractal distribution of earthquake hypocentres: the dimension of a hypocentre set, δ, is close to zero for short-term earthquake catalogues and asymptotically approaches 2¼ for long-time intervals. We use the Harvard catalogue of seismic moment tensor solutions to investigate the distribution of incremental static stress caused by earthquakes. The stress measured in the focal zone of each event is approximated by stable distributions. In agreement with theoretical considerations, the exponent value of the distribution approaches zero as the time span of an earthquake catalogue (ΔT) decreases. For large stress values α increases. We surmise that it is caused by the δ increase for small inter-earthquake distances due to location errors.

Description: There is considerable evidence in support of Milankovic's theory that variations in high-latitude summer insolation caused by Earth orbital variations are the cause of the Pleistocene ice cycles. The enigmatic discrepancy between the spectra of Milankovic forcing and of Pleistocene climate variations is believed to be resolved by the slow, nonlinear response of ice sheets to changes in solar seasonality. An experiment with a preliminary version of a 14-region atmosphere/snow/upper ocean climate model demonstrates that the response of the ocean-atmosphere system alone to Milankovic forcing is capable of driving ice cycles with the observed spectrum. This occurs because of the highly nonlinear response of both the thermal seasons and the annual mean temperature to solar seasons, which is caused in turn by the highly nonlinear feedback between temperature and snow and sea ice.

Description: This is the first issue of a new scientific publication of the European Geophysical Society, which will serve as the official organ of the Section on Nonlinear Processes in Geophysics. At the General Assembly in Strasbourg, 1987, this Section started with a special Joint Symposium on "Computer Simulations in Fluid Dynamics - Earth, Atmosphere and Space Plasmas" with 8 contributions. This was followed, a year later in Bologna, by a Joint Symposium entitled "Chaos and Turbulence in Geophysics" with 20 contributions. Since then the group of "nonlinear" scientists within the EGS has grown rapidly in size and in the quality of its contributions presented at the General Assemblies of the Society. Nowadays the programme of this Section normally includes 10 or more independent sessions with a total of some 250-300 papers. This development encouraged the officers and the members of the Section to search for a journal of their own, rather than to distribute their papers in the "classical" journals ranging from solid Earth geophysics to planetary and space sciences. Originally, the Society was asked to join an already existing publication in the field of nonlinear sciences. After almost two years of negotiations with the editors and the publishers of the most accepted journals in the field, the Section members decided differently; namely to launch their own journal, preferentially with a well known European publisher. However, in view of the general decrease in financial support for science and the generally increasing overheads of the publishers, it was decided that the new journal should be published by the Society itself, as an independent publication owned and run only by the EGS. The Society and the editors of this new journal are pleased to offer a modern, international, interdisciplinary and refereed publication to a young and growing generation of geophysicists with no page charges and fast publication on a "first come - first published" basis. The subscription rates are modest both for libraries and for members of the Society. We hope that scientists from other disciplines will also enjoy reading this journal and that publishing in it will be rewarding for the authors. With best wishes, Dr. Arne K. Richter Executive Secretary

Description: The equations describing the interaction of long inertio-gravity (IG) waves with the Rossby waves are derived. Due to remarkable cancellations, the interaction is shown to be anomalously weak. As a result, an inverse cascade of turbulence produces wave condensate of large amplitude so that wave breaking with front creation can occur.

Description: We consider Hamiltonian description of weakly nonlinear wave dynamics in unstable and nonequilibrium media. We construct the appropriate canonical variables in the whole wavenumber space. The essentially new element is the construction of canonical variables in a vicinity of marginally stable points where two normal modes coalesce. The commonly used normal variables are not appropriate in this domain. The mater is that the approximation of weak nonlinearity breaks down when the dynamical system is written in terms of these variables. In this case we introduce the canonical variables based on the linear combination of modes belonging to the two different branches of dispersion curve. As an example of one of the possible applications of presented results the evolution equations for weakly nonlinear wave packets in the marginally stable area are derived. These equations cannot be derived if we deal with the commonly used normal variables.

Description: Using finite data sets and limited size of study volumes may result in significant spurious effects when estimating the scaling properties of various physical processes. These effects are examined with an example featuring the spatial distribution of induced seismic activity in Creighton Mine (northern Ontario, Canada). The events studied in the present work occurred during a three-month period, March-May 1992, within a volume of approximate size 400 x 400 x 180 m3. Two sets of microearthquake locations are studied: Data Set 1 (14,338 events) and Data Set 2 (1654 events). Data Set 1 includes the more accurately located events and amounts to about 30 per cent of all recorded data. Data Set 2 represents a portion of the first data set that is formed by the most accurately located and the strongest microearthquakes. The spatial distribution of events in the two data sets is examined for scaling behaviour using the method of generalized correlation integrals featuring various moments q. From these, generalized correlation dimensions are estimated using the slope method. Similar estimates are made for randomly generated point sets using the same numbers of events and the same study volumes as for the real data. Uniform and monofractal random distributions are used for these simulations. In addition, samples from the real data are randomly extracted and the dimension spectra for these are examined as well. The spectra for the uniform and monofractal random generations show spurious multifractality due only to the use of finite numbers of data points and limited size of study volume. Comparing these with the spectra of dimensions for Data Set 1 and Data Set 2 allows us to estimate the bias likely to be present in the estimates for the real data. The strong multifractality suggested by the spectrum for Data Set 2 appears to be largely spurious; the spatial distribution, while different from uniform, could originate from a monofractal process. The spatial distribution of microearthquakes in Data Set 1 is either monofractal as well, or only weakly multifractal. In all similar studies, comparisons of result from real data and simulated point sets may help distinguish between genuine and artificial multifractality, without necessarily resorting to large number of data.

Description: Assuming that the behaviour of a nonlinear stochastic system can be described by a Markovian diffusion approximation and that the evolution equations can be reduced to a system of ordinary differential equations, a method for the calculation of prediction time is developed. In this approach, the prediction time depends upon the accuracy of prediction, the intensity of turbulence, the accuracy of the initial conditions, the physics contained in the mathematical model, the measurement errors, and the number of prediction variables. A numerical application to zonal channel flow illustrates the theory. Some possible generalizations of the theory are also discussed.

Description: A unique set of coutemporaneous satellite-tracked drifters and five-day composite Advanced Very High Resolution Radionmeter (AVHRR) satellite imagery of the North Atlantic has been analyzed to examine the surface flow structure of the Gulf Stream. The study region was divided into two sections, greater than 37° N and less than 37° N, in order to answer the question of geographic variability. Fractal and spectral analyses methods were applied to the data. Fractal analysis of the Lagrangian trajectories showed a fractal dimension of 1.21 + 0.02 with a scaling range of 83 - 343 km. The fractal dimension of the temperature fronts of the composite imagery is similar for the two regions with D = 1.11 + 0.01 over a scaling range of 4 - 44 km. Spectral analysis also reports a fairly consistent value for the spectral slope and its scaling range. Therefore, we conclude there is no geographic variability in the data set. A suitable scaling range for this contemporaneous data set is 80 - 200 km which is consistent with the expected physical conditions in the region. Finally, we address the idea of using five-day composite imagery to infer the surface flow of the Gulf Stream. Close analyses of the composite thermal fronts and the Lagrangian drifter trajectories show that the former is not a good indicator of the latter.

Description: The nonlinear dynamics of cnoidal waves, within the context of the general N-cnoidal wave solutions of the periodic Korteweg-de Vries (KdV) and Kadomtsev-Petvishvilli (KP) equations, are considered. These equations are important for describing the propagation of small-but-finite amplitude waves in shallow water; the solutions to KdV are unidirectional while those of KP are directionally spread. Herein solutions are constructed from the 0-function representation of their appropriate inverse scattering transform formulations. To this end a general theorem is employed in the construction process: All solutions to the KdV and KP equations can be written as the linear superposition of cnoidal waves plus their nonlinear interactions. The approach presented here is viewed as significant because it allows the exact construction of N degree-of-freedom cnoidal wave trains under rather general conditions.

Description: This paper presents an analysis of WOCE/TOGA surface drifter paths and its interpretation in conjunction with the west Pacific warm pool water motion. Our interest here lies in the existence of scale invariance in the observed data sets. The analysis proceeds by detecting scale invariance in the drifter paths data, and interpreting the invariance in terms of the statistical second order moment. The range of constant scaling exponent was found to be between 5 days and 10 days, and this range corresponded with the "long tail" of the temporal correlation function in the zonal direction. Velocity covariances in both the zonal and meridional directions were computed, and corresponding diffusivities were 8100 m2/sec meridionally and 41000 m2/sec zonally. Considering the existence of large scale mean flow, it is thought that self-similar energy cascade processes associated with constant scaling exponent may be responsible for the anomalous zonal diffusivity, while the meridional diffusivity may be approximated by ordinary Brownian processes. We suggest that the scale invariance of the WOCE/TOGA surface drifter paths may be a manifestation of energy cascade processes from large scale mean flow to smaller scale irregular flow that is represented by fractional Brownian motion in the zonal direction.

Description: We present an overview and some new results on anomalous diffusion of passive scalar in turbulent flows (including those used by Richardson in his famous paper in 1926). The obtained results are based on the analysis of the properties of invariant quantities (energy, enstrophy, dissipation, enstrophy generation, helicity density, etc.) - i.e. independent of the choice of the system of reference as the most appropriate to describe physical processes - in three different turbulent laboratory flows (grid-flow, jet and boundary layer, see Tsinober et al. (1992) and Kit et al. (1993). The emphasis is made on the relations between the asymptotic properties of the intermittency exponents of higher order moments of different turbulent fields (energy, dissipation, helicity, spontaneous breaking of isotropy and reflexional symmetry) and the variability of turbulent diffusion in the atmospheric boundary layer, in the troposphere and in the stratosphere. It is argued that local spontaneous breaking of isotropy of turbulent flow results in anomalous scaling laws for turbulent diffusion (as compared to the scaling law of Richardson) which are observed, as a rule, in different atmospheric layers from the atmospheric boundary layer (ABL) to the stratosphere. Breaking of rotational symmetry is important in the ABL, whereas reflexional symmetry breaking is dominating in the troposphere locally and in the stratosphere globally. The results are of speculative nature and further analysis is necessary to validate or disprove the claims made, since the correspondence with the experimental results may occur for the wrong reasons as happens from time to time in the field of turbulence.

Description: 1. The conference The third conference on "Nonlinear VAriability in Geophysics: scaling and multifractal processes" (NVAG 3) was held in Cargese, Corsica, Sept. 10-17, 1993. NVAG3 was joint American Geophysical Union Chapman and European Geophysical Society Richardson Memorial conference, the first specialist conference jointly sponsored by the two organizations. It followed NVAG1 (Montreal, Aug. 1986), NVAG2 (Paris, June 1988; Schertzer and Lovejoy, 1991), five consecutive annual sessions at EGS general assemblies and two consecutive spring AGU meeting sessions. As with the other conferences and workshops mentioned above, the aim was to develop confrontation between theories and experiments on scaling/multifractal behaviour of geophysical fields. Subjects covered included climate, clouds, earthquakes, atmospheric and ocean dynamics, tectonics, precipitation, hydrology, the solar cycle and volcanoes. Areas of focus included new methods of data analysis (especially those used for the reliable estimation of multifractal and scaling exponents), as well as their application to rapidly growing data bases from in situ networks and remote sensing. The corresponding modelling, prediction and estimation techniques were also emphasized as were the current debates about stochastic and deterministic dynamics, fractal geometry and multifractals, self-organized criticality and multifractal fields, each of which was the subject of a specific general discussion. The conference started with a one day short course of multifractals featuring four lectures on a) Fundamentals of multifractals: dimension, codimensions, codimension formalism, b) Multifractal estimation techniques: (PDMS, DTM), c) Numerical simulations, Generalized Scale Invariance analysis, d) Advanced multifractals, singular statistics, phase transitions, self-organized criticality and Lie cascades (given by D. Schertzer and S. Lovejoy, detailed course notes were sent to participants shortly after the conference). This was followed by five days with 8 oral sessions and one poster session. Overall, there were 65 papers involving 74 authors. In general, the main topics covered are reflected in this special issue: geophysical turbulence, clouds and climate, hydrology and solid earth geophysics. In addition to AGU and EGS, the conference was supported by the International Science Foundation, the Centre Nationale de Recherche Scientifique, Meteo-France, the Department of Energy (US), the Commission of European Communities (DG XII), the Comite National Francais pour le Programme Hydrologique International, the Ministere de l'Enseignement Superieur et de la Recherche (France). We thank P. Hubert, Y. Kagan, Ph. Ladoy, A. Lazarev, S.S. Moiseev, R. Pierrehumbert, F. Schmitt and Y. Tessier, for help with the organization of the conference. However special thanks goes to A. Richter and the EGS office, B. Weaver and the AGU without whom this would have been impossible. We also thank the Institut d' Etudes Scientifiques de Cargese whose beautiful site was much appreciated, as well as the Bar des Amis whose ambiance stimulated so many discussions. 2. Tribute to L.F. Richardson With NVAG3, the European geophysical community paid tribute to Lewis Fry Richardson (1881-1953) on the 40th anniversary of his death. Richardson was one of the founding fathers of the idea of scaling and fractality, and his life reflects the European geophysical community and its history in many ways. Although many of Richardson's numerous, outstanding scientific contributions to geophysics have been recognized, perhaps his main contribution concerning the importance of scaling and cascades has still not received the attention it deserves. Richardson was the first not only to suggest numerical integration of the equations of motion of the atmosphere, but also to attempt to do so by hand, during the First World War. This work, as well as a presentation of a broad vision of future developments in the field, appeared in his famous, pioneering book "Weather prediction by numerical processes" (1922). As a consequence of his atmospheric studies, the nondimensional number associated with fluid convective stability has been called the "Richardson number". In addition, his book presents a study of the limitations of numerical integration of these equations, it was in this book that - through a celebrated poem - that the suggestion that turbulent cascades were the fundamental driving mechanism of the atmosphere was first made. In these cascades, large eddies break up into smaller eddies in a manner which involves no characteristic scales, all the way from the planetary scale down to the viscous scale. This led to the Richardson law of turbulent diffusion (1926) and tot he suggestion that particles trajectories might not be describable by smooth curves, but that such trajectories might instead require highly convoluted curves such as the Peano or Weierstrass (fractal) curves for their description. As a founder of the cascade and scaling theories of atmospheric dynamics, he more or less anticipated the Kolmogorov law (1941). He also used scaling ideas to invent the "Richardson dividers method" of successively increasing the resolution of fractal curves and tested out the method on geographical boundaries (as part of his wartime studies). In the latter work he anticipated recent efforts to study scale invariance in rivers and topography. His complex life typifies some of the hardships that the European scientific community has had to face. His educational career is unusual: he received a B.A. degree in physics, mathematics, chemistry, biology and zoology at Cambridge University, and he finally obtained his Ph.D. in mathematical psychology at the age of 47 from the University of London. As a conscientious objector he was compelled to quit the United Kingdom Meteorological Office in 1920 when the latter was militarized by integration into the Air Ministry. He subsequently became the head of a physics department and the principal of a college. In 1940, he retired to do research on war, which was published posthumously in book form (Richardson, 1963). This latter work is testimony to the trauma caused by the two World Wars and which led some scientists including Richardson to use their skills in rational attempts to eradicate the source of conflict. Unfortunately, this remains an open field of research. 3. The contributions in this special issue Perhaps the area of geophysics where scaling ideas have the longest history, and where they have made the largest impact in the last few years, is turbulence. The paper by Tsinober is an example where geometric fractal ideas are used to deduce corrections to standard dimensional analysis results for turbulence. Based on local spontaneous breaking of isotropy of turbulent flows, the fractal notion is used in order to deduce diffusion laws (anomalous with respect to the Richardson law). It is argued that his law is ubiquitous from the atmospheric boundary layer to the stratosphere. The asymptotic intermittency exponent i hypothesized to be not only finite but to be determined by the angular momentum flux. Schmitt et al., Chigirinskaya et al. and Lazarev et al. apply statistical multifractal notions to atmospheric turbulence. In the former, the formal analogy between multifractals and thermodynamics is exploited, in particular to confirm theoretical predictions that sample-size dependent multifractal phase transitions occur. While this quantitatively explains the behavior of the most extreme turbulent events, it suggests that - contrary to the type of multifractals most commonly discussed in the literature which are bounded - more violent (unbounded) multifractals are indeed present in the atmospheric wind field. Chigirinskaya et al. use a tropical rather than mid-latitude set to study the extreme fluctuations form yet another angle: That of coherent structures, which, in the multifractal framework, are identified with singularities of various orders. The existence of a critical order of singularity which distinguishes violent "self-organized critical structures" was theoretically predicted ten years ago; here it is directly estimated. The second of this two part series (Lazarev et al.) investigates yet another aspect of tropical atmospheric dynamics: the strong multiscaling anisotropy. Beyond the determination of universal multifractal indices and critical singularities in the vertical, this enables a comparison to be made with Chigirinskaya et al.'s horizontal results, requiring an extension of the unified scaling model of atmospheric dynamics. Other approaches to the problem of geophysical turbulence are followed in the papers by Pavlos et al., Vassiliadis et al., Voros et al. All of them share a common assumption that a very small number of degrees of freedom (deterministic chaos) might be sufficient for characterizing/modelling the systems under consideration. Pavlos et al. consider the magnetospheric response to solar wind, showing that scaling occurs both in real space (using spectra), and also in phase space; the latter being characterized by a correlation dimension. The paper by Vassiliadis et al. follows on directly by investigating the phase space properties of power-law filtered and rectified gaussian noise; the results further quantify how low phase space correlation dimensions can occur even with very large number of degrees of freedom (stochastic) processes. Voros et al. analyze time series of geomagnetic storms and magnetosphere pulsations, also estimating their correlation dimensions and Lyapounov exponents taking special care of the stability of the estimates. They discriminate low dimensional events from others, which are for instance attributed to incoherent waves. While clouds and climate were the subject of several talks at the conference (including several contributions on multifractal clouds), Cahalan's contribution is the only one in this special issue. Addressing the fundamental problem of the relationship of horizontal cloud heterogeneity and the related radiation fields, he first summarizes some recent numerical results showing that even for comparatively thin clouds that fractal heterogeneity will significantly reduce the albedo. The model used for the distribution of cloud liquid water is the monofractal "bounded cascade" model, whose properties are also outlined. The paper by Falkovich addresses another problem concerning the general circulation: the nonlinear interaction of waves. By assuming the existence of a peak (i.e. scale break) at the inertial oscillation frequency, it is argued that due to remarkable cancellations, the interactions between long inertio-gravity waves and Rossby waves are anomalously weak, producing a "wave condensate" of large amplitude so that wave breaking with front creation can occur. Kagan et al., Eneva and Hooge et al. consider fractal and multifractal behaviour in seismic events. Eneva estimates multifractal exponents of the density of micro-earthquakes induced by mining activity. The effects of sample limitations are discussed, especially in order to distinguish between genuine from spurious multifractal behaviour. With the help of an analysis of the CALNET catalogue, Hooge et al. points out, that the origin of the celebrated Gutenberg-Richter law could be related to a non-classical Self-Organized Criticality generated by a first order phase transition in a multifractal earthquake process. They also analyze multifractal seismic fields which are obtained by raising earthquake amplitudes to various powers and summing them on a grid. In contrast, Kagan, analyzing several earthquake catalogues discussed the various laws associated with earthquakes. Giving theoretical and empirical arguments, he proposes an additive (monofractal) model of earthquake stress, emphasizing the relevance of (asymmetric) stable Cauchy probability distributions to describe earthquake stress distributions. This would yield a linear model for self-organized critical earthquakes. References: Kolmogorov, A.N.: Local structure of turbulence in an incompressible liquid for very large Reynolds number, Proc. Acad. Sci. URSS Geochem. Sect., 30, 299-303, 1941. Perrin, J.: Les Atomes, NRF-Gallimard, Paris, 1913. Richardson, L.F.: Weather prediction by numerical process. Cambridge Univ. Press 1922 (republished by Dover, 1965). Richardson, L.F.: Atmospheric diffusion on a distance neighbour graph. Proc. Roy. of London A110, 709-737, 1923. Richardson, L.F.: The problem of contiguity: an appendix of deadly quarrels. General Systems Yearbook, 6, 139-187, 1963. Schertzer, D., Lovejoy, S.: Nonlinear Variability in Geophysics, Kluwer, 252 pp, 1991.

Description: We present exploratory analogies and speculations on the mechanisms underlying the organization of faulting and earthquake in the earth crust. The mechanical properties of the brittle lithosphere at scales of the order or larger than a few kilometers are proposed to be analogous to those of non-cohesive granular media, since both systems present stress amplitudes controlled by gravity, and shear band (faulting) localization is determined by a type of friction Mohr-Coulomb rupture criterion. here, we explore the implications of this correspondence with respect to the origin of tectonic and earthquake complexity, on the basis of the existing experimental data on granular media available in the mechanical literature. An important observation is that motions and deformations of non-cohesive granular media are characterized by important fluctuations both in time (sudden breaks, avalanches, which are analogous to earthquakes) and space (strain localizations, yield surfaces forming sometimes complex patterns). This is in apparent contradiction with the conventional wisdom in mechanics, based on the standard tendency to homogenize, which has led to dismiss fluctuations as experimental noise. On the basis of a second analogy with spinglasses and neural networks, based on the existence of block and grain packing disorder and block rotation "frustration", we suggest that these fluctuations observed both at large scales and at the block scale constitute an intrinsic signature of the mechanics of granular media. The space-time complexity observed in faulting and earthquake phenomenology is thus proposed to result form the special properties of the mechanics of granular media, dominated by the "frustration" of the kinematic deformations of its constitutive blocks.

Description: Input-output systems are characterized by applying time series analysis techniques developed for autonomous systems to the input and the output time series separately and using the results as nonlinear statistics of the time series distributions. Two examples are presented using the correlation integral as a nonlinear statistic: the first one examines the change in the statistic when several sample input time series are passed through a nonlinear filter. The rectifier is chosen as the filter because it models, at first approximation, the effect of dayside magnetospheric reconnection to the interplanetary magnetic field and solar wind input. The changes in the correlation integral are used to characterize the filter response. A second example compares a linear filter of the rectified solar wind input to the observed auroral geomagnetic activity in terms of their correlation integrals. Implications for models of the solar wind-magneto- sphere coupling are discussed.

Description: In this paper we test the Unified Mulifractal model of atmospheric dynamics in the tropics. In the first part, we empirically investigate the scaling behaviour along the horizontal, in the second part along the vertical. Here we concentrate on the presentation of basic multifractal notions and techniques and on how they give rise to self-organized critical structures. Indeed, we point out a rather simple and clear characterisation of these structures which may help to clarify both the nature of the oft-cited coherent structures and the generation of cyclones. Using 30 aircraft series of horizontal wind and temperature, we find rather remarkable constancy of the three universal multifractal indices H, C1 and α as well as the value of critical exponents qD, γD associated with multifractal phase transitions and self-organized critical structures. This constancy extends not only from wind tunnel and mid-latitude to the tropics, but also to multifractals generated by Navier-Stokes like equations.

Description: Seventy-eight ostracod species belonging to 38 genera are recognized from the late Miocene Fujikotogawa Formation (c. 7–8 Ma), 40 km NE of Akita City, northern Japan. Some 30–40% of the ostracod species belong to the cold water groups (circumpolar and cryophilic species) reported from Plio-Pleistocene formations yielding the Omma-Manganji Fauna, the name given by Otuka (1939) to the Pliocene Japanese cold water molluscan fauna. This study demonstrates that most ostracod species distinguished in deposits yielding the Omma-Manganji Fauna had already appeared in the late Miocene. At least 13 of the ostracod species have been reported from both the Arctic and northern Atlantic Oceans, implying migration from the Pacific to the northern Atlantic through the Arctic after the Bering Strait had been breached. The 13 circumpolar, nine cryophilic and four endemic cold water species are illustrated, with brief taxonomic notes.

Description: Dinoflagellate cysts (dinocysts) are abundant in the Eocene of the North Sea and provide a high-resolution biostratigraphic zonation. Twelve species are erected to accommodate zonal markers that have not been previously described. These are Areosphaeridium ebdonii, Areosphaeridium michoudii, Cerebrocysta magna, Diphyes brevispinum, Diphyes pseudoficusoides, Hystrichosphaeropsis costae, Hystrichostrogylon clausenii, Membranilarnacia compressa, Phthanoperidinium clithridium, Phthanoperidinium distinctum, Phthanoperidinium powellii and Phthanoperidinium regalis.

Description: The trochoid coiling mode is the most dominant amongst hyaline foraminifera. The parallels in shape with especially gastropods neatly explains the use of the same terms to describe the spiral coiling. Other terms came in use, at first well-defined, but gradually losing their precision. Because of growing demands of systematics and changes in stress of use and value of characters, the inadequacy of this terminology has become a stumbling block. The terms ventral/dorsal and spiral/umbilical denote different things and are therefore all useful: the latter pair should not be relinquished as suggested (Haynes, 1990: 512). Historically, the terms ventral/dorsal and upper and lower side have been used by most students of the foraminifera with only few exceptions (notably Reuss and Loeblich & Tappan). Despite the protist nature of foraminifera, dorsal and ventral continued to be used, analogous to terms used to describe, for example gastropods. Far fewer problems beset the terms spiral and umbilical, which arc generally defined (Oxford English Dictionary) as: spiral a.. n. & v. 1. a. Coiled; winding about a centre in an enlarging or decreasing circular motion, either on a flat plane or rising in a cone. spire n. Spiral, coil; single twist of this; upper part of spiral shell [F. f. Lf. Gk speira coil] umbilical a. 1. Of, situated near, affecting, the umbilicus 2. Centrally placed. umbilicus n. Navel; (Bot. & Zool.) navel-like formation; (Geom.) point in a surface through which all cross-sections have same curvature [I., rel. to Gk omphalos]ORIENTATION: A GEOMETRICAL . . .

Description: The Chagos Archipelago is a series of atolls situated in the centre of the Indian Ocean close to the equator. The area experiences small tides and periods of strong winds. The combined effects of these is to cause relatively high energy conditions to exist in the shallow waters around the reefs, therefore the bottom sediments are coarse grained and mobile. Although the coral faunas are diverse, seagrasses are rare. The total benthic foraminiferal assemblages have low to high species diversity and are dominated by hyaline taxa. On the oceanic side of the atoll reefs, the dominant foraminiferan is Amphistegina lessonii, with subsidiary miliolids. Planklonic tests form up to 20% of the combined benthic and planktonic component. In the lagoon, the assemblages are dominated by Calcarina calcar, with subsidiary miliolids. Planktonic tests are relatively uncommon. Some post-mortem transport and damage to tests has taken place but the distribution patterns are believed to be representative of the original living ones.

Description: The Journal of Micropalaeontology is now well-established as an international publication covering all aspects of microfossils and their applications both in applied studies and in basic research. This has been brought about through the unstinting efforts of the two previous editors, Lesley Sheppard (1982-87) and Mike Keen (1988-94), and their supporting Editorial Boards. Last autumn, the officers of the Society decided that with the appointment of a new editor, the journal should be published through the Geological Society Publishing House. Since becoming Editor in March, my first task has been to implement the arrangements with the Geological Society. The advantages to the BMS are several. First, there is now a clear separation of duties between the Editorial Board, who will handle all aspects of scientific content and quality control of manuscripts accepted for publication, and the Publishing House, who will be responsible for the entire process of publication and distribution. Second, we gain from professional advice over format and layout. Third, the competitive pricing includes advertising in Geological Society publication lists and reciprocal arrangements with other major geological societies throughout the world. The first obvious manifestation of these changes is in the newly designed cover which now includes a list of keywords, the ISSN number and a bar code to conform with modern publishing practice.Another major change of policy concerns the role of the Editorial Board. Previously, each Specialist Group nominated an editor who then handled manuscripts appropriate to his or her specialty. As the number of Groups has

Description: Taxonomic revision reveals that the beyrichiacean ostracode ‘Nodibeyrichia jurassica’ can no longer be regarded as an index species for the uppermost (late Přídolí) ostracode ‘zone’ of the Silurian of the Baltic region embracing Estonia, Latvia and Baltic-floor derived erratic boulders. The taxon Nodibeyrichia jurassica Sarv, 1968 (non Gailite 1967) is regarded as a junior subjective synonym of Beyrichia protuberans Boll, 1862. Moreover, the material hitherto assigned to ‘Nodibeyrichia jurassica’ is herein considered to belong to two species: Nodibeyrichia protuberans (Boll, 1862) and Nodibeyrichia verrucosa Shaw, 1969. N. verrucosa occurs in England and Estonia, in the basal part and upper part of the Přídolí Series respectively. N. protuberans, as herein restricted, can be used to recognize the late Přídolí, uppermost ostracode assemblage level (N. jurassica Zone of previous literature) of the Silurian only in the central East Baltic (Latvia) and in erratic boulder material found in southern Baltic areas.

Description: A restudy of the planktonic foraminifera at DSDP Leg 90, Site 594, has been made and consequently a revised scheme of late Neogene zones has been necessary. The Globorotalia sphericomiozea Zone (including G. conomiozea) is contracted to occupy a much smaller interval just below the Miocene/Pliocene boundary and the G. puncticulata, G. inflata and G. truncatulinoides Zones have been expanded. In the uppermost Miocene and Lower Pliocene, the standard regional planktonic foraminiferal datums provide a good correlation with DSDP Leg 29 Hole 284, DSDP Leg 90 Hole 593 and with New Zealand on-land palaeomagnetically-zoned sequences. They do not, however, correlate with the magnetochronology adopted in the Leg 90 Initial Reports for this interval in Hole 594 in which Chrons 4–6 are offset downwards against the foraminiferal datums. It is possible that there are unrecognized hiatuses in the Plio-Pleistocene.Higher in the Pliocene, very low species diversity of the cold-water faunas, scarcity of warm-water foraminiferal zonal species, and their much later appearance in Hole 594, contribute to a recognition that the Subtropical Convergence has been an effective barrier against the southwards penetration of most warmer water planktonic species.Neoacarinina blowi Thompson and Globorotalia crozetensis Thompson, are recorded from the New Zealand area for the first time

Description: Census data on benthic foraminiferal tests in 45 surface sediment samples from Pauatahanui Inlet, Wellington, New Zealand, are analysed by Correspondence Analysis and Non-Hierarchical classification techniques. The faunas are grouped into 7 associations: (A) Trochamminita irregularis/Miliammina fusca - at high tide level in a small tidal creek at the limits of salt water influence; (B) Trochammina inflata/Jadammina macrescens - in an extreme high tidal pool, close to the mouth of a small stream; (C) Miliammina fusca/Haplophragmoides wilberti/Trochammina inflata - intertidal and shallow subtidal (to 0.6 m depth), muddy sand over a large area in the upper reaches of the inlet, where most freshwater runoff enters; (D) Elphidium excavatum/Miliammina fusca - intertidal muddy sand associated with shelly beaches on the fringe of association C; (E) Ammonia beccarii/Haynesina depressula - in a wide variety of intertidal and shallow subtidal (to 3 m depth) sediments that form a belt between the more brackish associations (A–D) and the more normal salinity associations (F–G); (F) Bolivina cf. translucens/Textularia earlandi/Bolivina subexcavata - in mud to muddy, very fine sand in a shallow basin (1–2.5 m deep) in the middle of the inlet and in a small, sheltered backwater; (G) Elphidium charlottensis/Patellinella inconspicua/Quinqueloculina seminula - in sandy mud and muddy fine sand, intertidal to 10 m depth, in the mouth, entrance channel and adjacent outer and middle parts of the inlet, where a flush of normal salinity water enters during each tidal cycle.Using Canonical Correspondence Analysis, the factors most influential in determining the faunal distribution are, in decreasing importance: freshwater influence (salinity), exposure to the air during tidal cycles, proximity to the open sea, tidal current strength and percentage of mud in the substrate.

Description: The systematics and stratigraphic ranges (constrained by conodont dating) of abundant and well preserved foraminiferal faunas from six sections in the Lower and Middle Triassic Eros Limestone of central and western Hydra (Argolis Peninsula, Greece) are described. A joint analysis of the conodonts, foraminifera and bivalves has enabled the Scythian and Anisian stages to be recognized with some certainty within the Eros Limestone carbonate platform. The foraminifera have affinities with those of many other Tethyan localities, in particular the Dinarides, Balkans, Carpathians and the Southern Alps.

Description: Frierfjord is the innermost part of a fjord system which connects with the open sea via Grenlandsfjord. Sills between fjords restrict bottom water circulation and in Frierfjord (sill depth: 23 m, max. water depth: 100 m) efficient deep water renewals at depths greater than about 50 m occur once every one to three years (Rygg et al., 1987). For several centuries waste products (primarily bark and wood fibres), initially from saw mills and later from pulp and paper industries, have been deposited in Frierfjord. Additionally, the fjord has received substantial amounts of organic material and nutrients from domestic sewage. In summary, this led to more or less permanent anoxic deep bottom water conditions. However, slight improvements have occurred over the last decade in response to reduced pollution input (Alve, in prep.). Investigations of short sediment cores (50 m) show that Stainforthia fusiformis exhibits typical opportunistic features. The oxygen concentration of the bottom water immediately above the sediment–water interface was 〉 1 ml I1at all stations at the time of collection, but the surface sediments reflected recent anoxic conditions. This was especially evident at 〉70 m where the sediments had a soupy appearance and black colour, with brownish faecal pellets and sometimes light grey, fluffy sediment aggregates in the topmost veneer. The total organic carbon content of the surface sediments is typically between 4 and 6%.DISCUSSIONThe following features characterize Stainforthia fusiformis as an opportunistic r-strategist:Distribution. Stainforthia fusiformis is a . . .

Description: Associations of epizoic foraminifera and invertebrates are widespread and have been reported from polar to tropical and shallow to bathyal environments (Zumwalt & DeLaca, 1980). Their fossil record stretches far back into Palaeozoic times as documented by agglutinated foraminifera attached to crinoids in Silurian and Devonian reef deposits of Morocco and Gotland (Franzen, 1974). Strong preferences for filter-feeding hosts suggest that epizoic foraminifera benefit from increased nutritional resources accumulated in the immediate flow microhabitat (Langer & Long, 1994).In the course of a broader study on foraminifera/invertebrate associations, several hundred foraminifera attached to the outer wall of agglutinated tubes of various polychaetes (e.g. Sabella sp., Potamilla sp.) were collected from sediment samples dredged at 61 m depth off the University of California, Moss Landing Marine Laboratory (NW Pacific). Attached foraminifera display a remarkable mode to obtain and differentially cement grains from the host tube that previously has not been reported. Agglutinated polychaete tubes and fragments thereof may reach 2 cm or more in length and are composed of fine sand, silt and micas cemented together by secreted organic material (Fig. 1). Tubes are typically orientated vertically in the mud and project above the sediment surface into the water column.NEW OBSERVATIONSExamination of agglutinated polychaete tubes revealed that their outer walls were commonly colonized by one to three foraminiferans (Figs 1–3, tube diameter 1.5–2.0 mm). The epizoic foraminiferal fauna comprised exclusively agglutinated taxa and included the following species: Alveophragmium advenum (Cushman), Textularia abbreviata Lalicker & McCulloch, Textularia schencki . . .

Description: Approximately 60 species of benthonic foraminifera are recorded from 14 samples collected by the RRS Discovery from water depths of 200–4200 m on the Antarctic Peninsula Shelf and Slope and adjacent areas of the Western Antarctic Ocean. Discussion focuses firstly on benthonic foraminiferal abundance, diversity and assemblage composition and the effects of calcite dissolution and, secondly, on the characteristic assemblages of the study area and their relationships to water-masses.

Description: The Lower Pechelbronn Formation (?Upper Eocene/?Lower Oligocene) of Malsch (clay-pit ‘Am Viehweg’) yielded a moderately abundant charophyte assemblage. One new species, Chara rhenana sp. nov., is erected, two more species, Harrisichara lineata and Nitellopsis (Tectochara) cf. wonnacotti, are recorded in the Rhine Graben area for the first time. The Lower Pechelbronn Formation may be correlated to the Stephanochara vectensis zone (Riveline, 1986) and the mammalian level MP 20 (reference locality: St. Capraise; Schmidt-Kittler, 1987). The associated ostracod fauna clearly indicates a limnic depositional environment.

Description: Specimens of Cassigerinelloita amekiensis Stolk from the type collections and DSDP/ODP holes are found to possess a microperforate and pustulate wall and a triserial, pseudoplanispiral coiling mode. These characters prompt its affinity with the contemporaneous Guembelitria triseriata (Terquem). An amended description of Cassigerinelloita amekiensis is given, and the peculiar coiling mode discussed.

Description: Es wird ein am Kliff des Klein Klütz Höved aufgeschlossenes Profil, das Sedimente von der Saalevereisung bis in das Frühweichselglazial umfaßt, besprochen. Von besonderer Bedeutung sind limnische Sedimente des Fern, die durch sandige Ablagerungen mit marinen Fossilien innerhalb eines Würgebodenhorizontes überlagert werden. In den limnischen Ablagerungen konnten neben einer reichen Mikroflora auch Früchte, Samen, Mollusken und Ostrakoden nachgewiesen werden. Die- Entstehung des Würgebodens ist auf frühweichselzeitliche Periglazialvorgänge zurückzuführen. Der Transgressionskontakt mit dem Eemmeer wird im Gegensatz zu anderen Profilen aus dem Mecklenburger Raum für die ausgehende Zone 4 und/oder 5 nach Erd (1973) angenommen.

Description: Zahlreiche Buchten an der Nordwest-Küste Cornwalls werden von ausgedehnten Sandstränden aufgebaut, die durch ästuarin-marine sowie fluviatile Vorgänge entstanden sind. Die Sedimente sind Verwitterungsprodukte des umliegenden pelagisch-geosynklinalen devonischen Gesteins (Abb. 1). Die litoralen Ablagerungen dienen als Liefergebiet für die großen Dünengebiete an der Küste. Zu unterscheiden sind jüngere (rezente) und ältere (fossile) Dünenablagerungen, die teils in stratigraphischer Abfolge übereinander liegen; die fossilen Dünensande lagern deckenförmig. Während die jüngeren Walldünen noch wandern. Beide Ablagerungen zeigen die für Dünensande typischen Korngrößenzusammensetzungen (etwa 70 - 95 % Mittelsand: 0.63 - 0.2 mm). Aufgrund der Winddynamik im Küstenbereich sind vereinzelt Fein(st)kiese, die im Grenzbereich der 2-mm-Korngröße liegen, als Gesteinssplitter in den Sedimenten zu finden. Die älteren Dünensande beinhalten fossile Böden; der älteste Horizont H 2 (Abb. 2) hat ein 14C-Alter von 20.300 ± 900 a B. P.: dies entspricht dem Pleniglazial der Jung-Weichselkaltzeit. Der H 4-Horizont wurde mit 13.000 ± 400 a B. P. datiert und fällt damit zeitlich in die Älteste Dryaszeit. Mit diesen Befunden lassen sich - analog zu den Untersuchungen auf dem Kontinent - ein älterer unterer sowie ein älterer oberer Flugsand sedimentologisch-pedologisch gliedern. Vergleichende Untersuchungen an europäischen Küstendünen lassen den Schluß zu, daß solch alte Windsedimente für Küstenräume die Ausnahme sind. Der H 6-Horizont (Abb. 2 ) besitzt ein 14C-Alter von 4.410 ± 70 a B. P. Dies entspricht zeitlich der späten Wärmezeit des frühen Subboreals (Mittelholozän). Dieser Flugsandabschnitt findet bisher wenig parallele Ablagerungen im Küstenraum oder auf dem Festland. Das Profil wird im Hanngenden von dem rezenten Boden abgeschlossen.

Description: Bis zum Vereisungsbeginn der Elster-Kaltzeit folgte die Weser ihrem "angestammten" pleistozänen Lauf: Hameln - Springe Nordstemmen- Hannover - Meilendorf - (?)Nienburg. Bei Nordstemmen nahm sie die Leine auf. Reste ihrer Oberterrassen-Kiese ermöglichen diese Rekonstruktion. Erst seit der Mittelterrassen-Zeit (Älterer Teil der Saale-Kaltzeit, evtl. von einem jüngeren Teil der Elster-Kaltzeit an) verläuft die Weser in dem Talabschnitt Hameln-Porta Westfalica. Von hier aus hat sie - in einer Breite bis 25 km - Sedimentstränge nördlich parallel zum Wiehengebirge aufgebaut. Etwa von Hunteburg westlich des Stemmweder Berges verlief sie zumindest teilweise weiter in Richtung Damme - Vechta. Die Leine der Mittelterrassen-Zeit läßt sich von Nordstemmen über Pattensen, Gehrden, Wunstorf, Rehburg verfolgen; sie mündete etwa im Gebiet von Uchte in die Weser. Die in einer Karte zusammengefasste flussgeschichtliche Darstellung beruht weitgehend auf Geländearbeiten der Geologischen Landesaufnahme des Niedersächsischen Landesamtes für Bodenforschung.

Description: Unter Lößbedeckung liegen in den Iserlohner und Attendorn-Elsper Kalksenken oft großflächig pleistozäne Fließerden, in denen außer Terrae calcis-Relikten auch Verwitterungsmaterial der umgebenden Gesteinseinheiten eingearbeitet sein kann. Mit Hilfe von Terrassenrelikten lassen sich alt- und jungpleistozäne Terra fusca-Fließerden ausweisen, die sich in charakteristischer Weise unterscheiden. Örtlich begraben sie ältere Lösse mit fossiler Parabraunerdeentwicklung. Innerhalb des Weichsellösses erlauben Schwermineralanalysen stellenweise eine weitere Deckschichtengliederung und die Identifizierung der jungtundrenzeitlichen Hauptlage. Synthetische Eisen-Silikate weisen auf holozäne Umlagerungen und Verhüttungstätigkeiten bei Hemer hin.

Description: Am Beispiel eines im mitteldeutschen Braunkohlentagebau Schleenhain im Übergangsbereich Quartär/Tertiär aufgeschlossenen Profils weiden typische genetische Formen kryogen verursachter gravitativer Deformationen aus dem Anaglazial der Elstervereisung des mitteldeutschen Raumes beschrieben. Sie zeigen einen mehrfachen Wechsel von Dauergefrornis und Frostbodendegradation der periglaziären Sedimentunterlage im Vorfeld des herannahenden Inlandeises für diesen Zeitraum an.

Description: Die Umlagerungsdynamik auf den großen Dolomit-Schuttflächen des Wimbachgries (Berchtesgadener Alpen) ist in erster Linie an starke sommerliche Gewitterregen gebunden, durch welche die Aufnahmefähigkeit des mächtigen Schuttkörpers überschritten und somit oberflächlichen Abgang von Wasser und Lockermaterial, meist in Form von Muren, bewirkt wird. Durch Ausaperung werden jedoch regelmäßig gegen Ende des Winterhalbjahres Formen freigelegt, welche auch auf Schuttumlagerungsvorgänge in bzw. unter der Schneedecke hinweisen. Aufgrund deutlicher Parallelen zu den entsprechenden Großformen werden diese als subnivale Kleinoser angesprochen. Sie scheinen bevorzugt dort vorzukommen, wo aufgrund der topographischen Situation größere Schmelzwassermengen bei noch gefrorenem Untergrund anfallen; für ihre Bildung ist offensichtlich die relativ homogene und feinkörnige Natur des "Gries" Materials förderlich.

Description: In der vorliegenden Arbeit werden einige Unsicherheitsfaktoren bei der Rekonstruktion von Paläo-Umweltbedingungen diskutiert. In der Diskussion werden zwei Beispiele aus dem terrestrischen Bereich angeführt, nämlich Frosthügel und Brände; wobei der Schwerpunkt der Untersuchungen auf dem Gegensatz von lokalen zu regionalen Umweltveränderungen liegt, Es wird demonstriert, daß lokale Veränderungen, die keine klimatischen Ursachen haben, Ablagerungen entstehen lassen können, die den Eindruck erwecken, als seien sie das Ergebnis klimatischer Veränderungen. Es wird festgestellt, daß künftige Untersuchungen eine Fülle zusätzlicher Informationen über Paläo-Umweltentwicklungen und ihre komplexen Beziehungen hinsichtlich Ursache und Wirkung liefern können. Um aber schlüssige Rekonstruktionen machen zu können, ist es notwendig, mögliche Effekte sowohl klimatisch als auch nicht klimatisch induzierter Entwicklungen zu untersuchen

Description: In vier spanischen Hochgebirgen (Picos de Europa, Pena Prieta - kantabrisches Gebirge, Sierra de Urbión - Nördliches Iberisches Randgebirge, Hauptmassiv der Sierra Nevada - Betische Kordillere) wurden insgesamt 33 Meßfelder zur Ermittlung der Bewegungsgeschwindigkeit von Solifluktionschuttdecken angelegt und über einen Zeitraum von 3 bis 4 Jahren meistens einmal jährlich vermessen (Tab. 1). Vermessene Steinmarkierungen und Holzpflöcke lieferten z. T. aussagekräftige Ergebnisse, die durchaus im Rahmen der Ergebnisse anderer Autoren liegen (Tab. 2). Der Einfluß der absoluten Höhe, der Vegetationsbedeckung, der Hangneigung, der Exposition, der Durchleuchtung des Materials und der Dauer der Schneedecke wurden berücksichtigt.

Description: Die glazialen und glazifluviatilen Ablagerungen im Bereich der Osterseen südlich des Starnberger Sees belegen eine großflächige Verbreitung von Toteis am Ende der letzten Eiszeit. Der Rückzug des Gletschers erfolgte durch sukzessiven Zerfall der Gletscherzunge an subglazialen Hochgebieten. Durch die palynologische Auswertung zweier Bohrprofile kann der Gletscherzerfall datiert werden. In beiden Profilen wurden das ausgehende Hochglazial sowie das gesamte Spät- und Postglazial angetroffen. In den hochglazialen Sedimenten finden sich thermophile Elemente in guter Erhaltung, deren Einlagerung durch Ferntransport diskutiert wird. Das Spätglazial beginnt mit der bekannten Florenassoziation und enthalt zu dem umgelagerte Thermophile. Diese können frühestens in das Sediment gelangt sein, als der Gletscher den Alpennordrand erreicht hatte. Damit sind die Gletscherstände außerhalb des Gebirges vermutlich ins Hochglazial zu datieren, während das glazialgeologische Bühl-Stadium mit der palynologischen Hoch-/Spätglazialgrenze zusammenfallen dürfte. Letzte Toteisreste können sich möglicherweise bis ins Bölling/Alleröd erhalten haben.

Description: Anhand von 61 Proben wurden die Grenzen der Anwendbarkeit der Thermolumineszenz(TL)-Datierungsmethode für Lößdeckschichten des Tönchesberg-Schlackenkegels aus der Osteifel untersucht. Zur Bestimmung der akkumulierten Dosis kamen sowohl die Regenerierungs-Methode als auch die Additive Methode und für einige wenige Proben die R-Gamma-Methode zur Anwendung. Die geologisch-stratigraphische Verläßlichkeit von TL-Altern für die letzten 200 000 Jahre wurde anhand von 126 voneinander unabhängigen TL-Daten untersucht. Die TL-Datierungen an Lössen des Profils Tönchesberg sind bis zu einem Alter von etwa 90 ka in guter Übereinstimmung mit den geologisch erwarteten Altern. (40)Ar (39)Ar-Datierungen von Tephren mit einem physikalischen Alter von 238±20 ka und 243±65 ka unterstützen die Vorstellung, daß signifikante TL-Altersunterbestimmungen für die Proben unterhalb des letztinterglazialen Bodens vorliegen. Die lößstratigraphische Abfolge und malakozoologisehe Untersuchungen implizieren jedoch, dass die (40)Ar/ (39)Ar-Datierungen altersüberbestimmt sind. Die mit der Additiven Methode kalkulierten TL-Alter für vorletztglaziale Lösse sind größer als bei Verwendung der Regenerierungs-Methode. Jedoch nehmen die TL-Alter weder mit der einen noch mit der anderen Methode außerhalb der Mutungsintervalle zum Liegenden hin zu. Neben physikalischen Gründen kann eine rasche Lößakkumulation während der jüngeren Saale-Kaltzeit als Grund für die nicht erkennbare Zunahme der TL-Alter angenommen werden. TL-Daten von mehr als 100 000 Jahren werden im allgemeinen durch eine wissenschaftlich fragwürdige Auswahl von Meßdaten sowie Anpassung von Meßbedingungen und Meßparametern ermittelt, um geologischen Altersabschätzungen oder unabhängigen Datierungen zu genügen. Die Unabhängigkeit als Grundprinzip einer Datierungsmethode ist mithin für diesen Alteisbereich bei der TL nicht gegeben.

Description: Im Rheinischen Braunkohlentagebau werden seit dem 19. Jahrhundert große Flächen der landwirtschaftlichen Nutzung entzogen und nach der Auskohlung einer Wiedernutzbarmachung zugeführt. Aufgrund der reichen Lößvorkommen in der Niederrheinischen Bucht besteht die Möglichkeit, agrarische Nutzflächen mit guten bodenkundlichen Eigenschaften herzustellen. Die Untersuchung eines im Tagebau Garzweiler I anstehenden Lößprofils soll die bodenphysikalisch-chemischen Verhältnisse aufzeigen und zu einer differenzierten Beurteilung der Rekultivierungseignung der Lösse führen. Anhand der Ergebnisse lassen sich auch Rekultivierungs- und Bearbeitungseffekte in Neulandboden (Kultosolen) besser einschätzen.

Description: During 4 years, 200 melliferous species have been inventoried and examined phenologically in an area of the Swiss High Jura. On the basis of their spatio-temporal variations. the author distinguishes five melliferous seasons with their correspondmg resources. and makes a number of proposals how to manage the melliferous landscape.

Description: L'évolution du systéme urbain helvétique est en partie conditionnée par sa position au sein du réseau de polarités qui structurent le continent. Dans cette espace multipolaire, la globalisation de l'économie, l'innovation technologique, I'avénement d'une nouvelle culture individuallste, la crise de l'égitimité de l'Etat, la formation de regions métropolitaines, la dégradation de l'environnement dessinent déjà des figures possibles de l'avenir La Suisse n'est pas à l'abri de ces turbulences. L'incertitude qui pèse sur les resultats de la dynamique urbaine incite à la mise en oeuvre de politiques territoriales globales, actives et préventives.

Description: In the tradition of studies about central places theory in urban Systems, some contributions have emphasized the invariability of the concentration index in Systems of a certain size, that comply with one of the main organizing principles elucidated by W. Christaller. This research of the structural change is an empirical, longitudinal study of some Swiss representative regions(1850-1990), their transformation of agricultural land into industrial and urban-industrial territoriality, and a prevision of their future.Central places, hierarchical structure, Swiss urban System.

Description: Le paysage, compris comme l'ensemble des formes visibles de l'espace géographique et des écosystèmes, ainsi que leurs images mentales, peut s'analyser à diverses echelles. L'aménagement du paysage en Suisse révèle un écart considerable entre la valeur accordée au paysage-spectacle et la prise de conscience souvent tres limitée des mécanismes menant à sa dénaturation. On observe quatre attitudes principales face au paysage, qui révèlent des symboltques et des systèmes de valeurs distincts, attitudes qui peuvent se définir à travers un paysage typique: la ville à la campagne, le terroir villageois, le décor, le biopaysage. Selon l'emprise que ces diverses attitudes auront sur la société suisse du siècle prochain, les paysages évolueront de manière fort diffèrentes, en matière d'intensité de l'usage agricole, de dépérissement des forêts ou d'extension des aires construites.

Description: L'intégration européenne pose la question de la disparition des frontières, souvent présentées comme des archaïsmes historiques. Peu d'analyses ont été conduites pour comprendre l'mfluence des frontières sur le fonctionnement des agglomérations transfrontalières. Cet article vise à analyser la fonetion d'une frontière internationale dans les rapports politiques entre collectivités locales dans la région de Genève. Alors que les frontières sont généralement analysées comme des limites administratives des Etats, l'approche uti lisée dans ce travail tente d'appréhender le rôle d'une frontière dans le fonctionnement du pouvoir local. L'article insiste sur le processus de différenciation spatiale du politique. Audelà de sa définition juridique, la frontière est envisagée comme la limite spatiale de systèmes politiques et administratifs qui intègrent cet élément dans leur stratégie de pouvoir.

Description: Introduisant, à titre d'éditeur invité, les autres travaux de ce numéro consacré à une présentation de certains aspects des connaissances et pratiques de la géographie humaine en Suisse romande à travers une réflexion prospective sur les devenirs de la Suisse, l'auteur focalise son attention sur les sources du changement liées à la dynamique des structures urbaines, au triple plan de leurs dimensions économiques, sociales et culturelles et sous les deux facettes du développement des entités urbaines et métropohtaines et de la vie en leur sein. Les transformations actuelles, comme celles qui sont les plus probables à court et moyen terme, imposent une remise en question de notre idée de ville et des modéles traditionnels de la géographie urbaine comme aussi de la hiérarchie de ses préoccupations. A ces conditions la géographie pourra, peut-être. contribuer à la lutte. difficile, pour défendre ou refaire l'unité de la ville, serait-ce à une autre échelle

Description: Cet article étudie la répartition spatiale des personnes d'origine étrangère dans l'agglomération lausannoise. A l'aide des méthodes traditionnelles de l'écologie factorielle urbaine, il tente de repondre à la question de l'´wventuelle ségrégation spatiale de ces populations selon les nationalés. En conclusion, il met en évidence les limites de la méthode utilisée et la nécessité d'une prise en compte du caractère spatialement discontinu et socialement construit des phénomenes dintégration et de ségrégation.

Description: Große Bewasserungsproiekte in Trockengebieten sollen einen Beitrag zur wirtschaftlichen Entwicklung und zur Lösung der Probleme im Zusammenhang mit dem Bevölkerungswachstum leisten. In Marib wurde 1984 bis 1986 ein neuer Staudamm gebaut, der auf eine jahrtausendealte Bewässerungstradition aufbauen sollte. Das ursprüngliche Ziel, das Angebot von Oberflächenwasser auf das ganze Jahr gleichmäßig zu verteilen, wurde verfehlt. Das Staudammproiekt ist bisher gescheitert, weil die Widersprüche zur bestehenden Sozialstruktur zu groß sind. Nach wie vor findet eine große Übernutzung der Grundwasservorräte statt, so daß bei gleichbleibender Entwicklung die Lebensgrundlage der Region, das Wasser, allmählich ausgehen wird.

Description: Die Schweiz verweigert sich hartnackig jeder Zukunftsperspektive und hat sich so in eine Reihe von Widersprüchen verstrickt, die sie daran hindern, an der Moderne teilzuhaben. Wir können fünf solcher Widerspruche benennen: Der erste besteht in einer unterschiedlichen Sichtweise von Innen und Außen: Die Schweiz betrachtet die anderen in verkleinertem, sich selbst aber in vergrößertem Maßstab Der zweite Widerspruch druckt sich in der nostalgischen Sehnsucht nach Stabilität aus. welche die Anpassung an den Wandel verlangsamt oder gar unterbindet Der dritte offenbart sich im Vorzug, der dem Mythos vor der Geschichtsschreibung gegeben wird. Ein vierter Widerspruch ist die Unfähigkeit, unsere Bezugszentren klar zu identifizieren. Was den fünften Widerspruch anbelangt, so steht er im Zusammenhang mit der wirtschaftlichen Öffnung bei gleichzeitig politischer Abschottung gegen außen.

Description: Kluses and Related Forms in the Swiss Jura Mountains – It is shown that the usual theory of the genesis of the "kluses" (transverse gorges cutting across ndges) in the Jura mountains of Switzerland by fluvial erosion by antecedent rivers is untenable: 1 st. the erosive power of a river on its bed is by at least a factor 100 too small to abrade solid rock as found in the kluses 2nd. the orientation structure of the segments of the rivers flowing in the kluses is non-random which, by the tenets of the principle of antagonism in landscape development. is indicative of a non-exogenic origin of them. 3rd. the orientation structure of the klus-nvers agrees with that of the joints in the area. 4th, in view of the fact that the joints are known to have been caused by recent plate-tectonic processes, the same must be assumed for the kluses: the latter owe their genesis to complicated geologic lineaments, folds and shear faults. This fact has practical consequences: During the construction of tunnels underneath a klus one has to take into consideration that the disturbance in the landscape represented by a klus my well reach geologically far into the basement. 5th,the erosion of the kluses oecurred in parallel to the direction of the joints. In this instance, the debris produced by the tectonic processes and by frost action was removed by the mechanical and chemical action of the water. During the cold times and cold spells during warm times this water was mainly melt-water. 6th, special studies are necessary for the determination of the quantity of debris that was removed. The time-span available for this removal is much longer than commonly assumed: it begins with the first tectonic foldnig, in the Jura mountains already in mid-Miocene, 15 Ma ago.

Description: Methods of upper wind measurements used in operational meteorology have been reviewed to provide guidance to those developing wind profiler radar systems. The main limitations of the various methods of tracking weather balloons are identified using results from the WMO radiosonde comparisons and additional tests in the United Kingdom. Costs associated with operational balloon measurements are reviewed. The sampling and quality of operational aircraft wind observations are illustrated with examples from the ASDAR system. Measurement errors in horizontal winds are quantified wherever possible. When tracking equipment is functioning correctly, random errors in southerly and westerly wind component measurements from aircraft and weather balloons are usually in the range 0.5-2 m s-1.

Description: It is shown that such data that exist on auroral activity in the period between 1450 and 1550 do not provide conclusive evidence that some authors have claimed for the existence of the so-called "Spörer minimum" in solar activity during this interval.

Description: The Bransfield Strait is one the best-known areas of Antarctica's oceanic surroundings. In spite of this, the study of the mesoscale variability of its local circulation has been addressed only recently. This paper focuses on the mesoscale structure of local physical oceanographic conditions in the Bransfield Strait during the Austral summer as derived from the BIOANTAR 93 cruise and auxiliary remote sensing data. Moreover, data recovered from moored current meters allow identification of transient mesoscale phenomena.

Description: The geographical area covered by the Fine-Resolution Antarctic Model (FRAM) includes that part of the South Atlantic south of 24°S. A description of the dynamics and thermodynamics of this region of the model is presented. Both the mean and eddy fields in the model are in good agreement with reality, although the magnitude of the transients is somewhat reduced. The heat flux is northward and in broad agreement with many other estimates. Agulhas eddies are formed by the model and propagate westward into the Atlantic providing a mechanism for fluxing heat from the Indian Ocean. The confluence of the Brazil and Falkland currents produces a strong front and a large amount of mesoscale activity. In the less stratified regions to the south, topographic steering of the Antarctic circumpolar current is important.

Description: As an introduction to this special issue of Annales Geophysicae a review is given of the applicability and performance of wind profilers. In meteorology, wind profilers play an increasingly important role. They can provide upper-wind measurements with an accuracy comparable to radiosonde data, but with a significantly higher temporal resolution. Height coverage and vertical resolution depend on the operating frequency, which, depending on the application, is usually chosen to be around 50, 400 or 1000 MHz. Measurements from stand-alone profilers in sparse data areas as well as data from wind profiler networks - which have increased the spatial resolution of an existing radiosonde network - have shown a positive impact on numerical weather forecasting. Information from nearby profilers can help the individual meterologist to optimize local short-term weather forecasts. In atmospheric research, wind profilers have been used for various boundary layer studies. In several mesoscale monitoring experiments wind profilers have played an important role. In Europe the development and implementation of wind profiler networks have been supported since 1987 by the CEC-sponsored COST-74 project. A follow-up project will probably start in 1994. Several topics deserve attention. A further assessment of the quality of wind profiler measurements is important. Automatic quality control procedures should be refined. Improved data assimilation techniques in numerical models will enable a better use of the high temporal resolution of wind profiler data. For a cost-effective development and use of wind profilers, the realization of frequency allocations, as globally harmonized as possible, is essential. Finally, the integration of wind profilers with other complementary measuring techniques is important.

Description: Observations of high-resolution data on radio refractivity were obtained by the airborne microwave refractometer over the Indian sub-continent (a tropical country) from 1971 to 1988. Detailed vertical and horizontal distributions of radio refractivity on a near-real-time basis in the atmospheric boundary layer were determined . Radiosonde observations cannot detect the thin refractivity gradients which characterize the propagation environment in this low-altitude region. This knowledge is required to design reliable and efficient communication systems for strategic, tactical and operational needs. However, the results demonstrate the layer structures and the variability of the boundary layer in time and space. The radio refractive effects on electromagnetic propagation and the future direction of radio refractivity fine-structure measurements are discussed.

Description: Doppler measurements have been carried out during a variety of observational campaigns using the stationary and the mobile SOUSY-VHF-Radars. The general data reduction procedure is presented in some detail. Particular emphasis is placed upon possible problems arising from contaminated data and solutions are proposed. Some results from measurements at tropospheric and mesospheric heights are presented.

Description: The aspect sensitivity of SOUSY-VHF-radar oblique-beam echoes from the troposphere and lower stratosphere has been examined for a number of jet stream passages during the years 1990 - 1992. When the core of the jet is overhead or nearly so, vertical profiles of the aspect sensitivity display two notable features. First, the distinction between mainly isotropic and strongly aspect-sensitive echoes in the troposphere and the lower stratosphere, respectively, often reported for measurements made during calm conditions, does not necessarily prevail in the vicinity of the jet stream. Second, echoes obtained at altitudes near the height of the horizontal wind maximum are found to be more aspect sensitive for beams directed parallel to the horizontal flow or nearly so, than for other beam directions. It is demonstrated that time-averaged horizontal wind speeds estimated from the radar data, taking into account the reduced effective oblique-beam zenith angle resulting from aspect sensitivity, may exceed uncorrected wind speeds by as much as 10 m s-1 in these circumstances. Implications for wind profiling and for describing the backscattering process are discussed. Doppler spectral widths examined for one jet stream passage are found to be narrower in a beam aligned with the horizontal wind at heights near the wind speed maximum than corresponding widths measured in a beam projected at right angles to the jet. The narrowest spectra thus coincide with the most aspect-sensitive echoes, consistent with the hypothesis that such returns result from specular backscattering processes.

Description: In long-arc precise orbit determinations of altimetric satellites such as ERS-1, large errors may occur from mismodelling of aerodynamic drag and solar radiation pressure. Such surface forces for non-spherical satellites require accurate modelling of the effective area and particle-surface interactions, but the dominant source of error is neutral air density as derived from thermospheric models for aerodynamic drag. Several techniques can be employed to alleviate air-drag mismodelling but all require the solution of additional parameters from the tracking data. However, for ERS-1 the sparsity of laser range data limits the application of such empirical techniques. To overcome this, use can be made of the dense DORIS Doppler tracking for SPOT2 which is in a similar orbit to ERS-1. A recent investigation by CNES examined the use of drag scale factors from SPOT2 to constrain the ERS-1 orbit. An improvement to that methodology is to consider along-track mismodelling as observed by timing errors in the Doppler data for each pass of SPOT2. The along-track correction to the acceleration as derived from SPOT2 can then be applied to ERS-1 orbits, solving for a scale factor to absorb systematic errors - particularly that arising from the 50 km altitude difference. Results are presented of the associated improvement in ERS-1 orbits as derived from concurrent SPOT2 arcs. It will be seen that the procedure not only improves the laser range fit, but more importantly, leads to more precise radial positioning as evident in the altimeter and crossover residuals.

Description: 50-MHz type-II coherent echoes at geometrical aspect angles of 11.5° have been observed in the northern polar cap during pre-noon hours. The echoes had an unusually large Doppler width of 1200-1400 m s-1 and were well correlated with strong magnetic disturbances in the range 500-1000 nT. The dependence of intensity, spectral width and skewness versus radial velocity were similar to those known from previous experiments at lower latitudes and at small aspect angles. It is concluded that echo onset was due to the combination of several factors, including a highly conducting ionosphere, the presence of a very intense electric field, and strong radar wave refraction.

Description: Ground-based microwave measurements of the diurnal and seasonal variations of ozoneat 42±4.5 and 55±8 km are validated by comparing with results from a zero-dimensional photochemical model and a two-dimensional (2D) chemical/radiative/dynamical model, respectively. O3 diurnal amplitudes measured in Bordeaux are shown to be in agreement with theory to within 5%. For the seasonal analysis of O3 variation, at 42±4.5 km, the 2D model underestimates the yearly averaged ozone concentration compared with the measurements. A double maximum oscillation (~3.5%) is measured in Bordeaux with an extended maximum in September and a maximum in February, whilst the 2D model predicts only a single large maximum (17%) in August and a pronounced minimum in January. Evidence suggests that dynamical transport causes the winter O3 maximum by propagation of planetary waves, phenomena which are not explicitly reproduced by the 2D model. At 55±8 km, the modeled yearly averaged O3 concentration is in very good agreement with the measured yearly average. A strong annual oscillation is both measured and modeled with differences in the amplitude shown to be exclusively linked to temperature fields.

Description: This paper presents a mechanism to explain the observed formation of a surface temperature minimum at tidal fronts in shelf seas. Tidal fronts mark the boundary between water which is kept vertically mixed by fast tidal currents and water which stratifies in summer. The fronts are associated with strong horizontal surface gradients of several water properties, including temperature. In the early studies of tidal fronts, a minimum in surface temperature was occasionally observed between the cool surface waters on the mixed side of the front and the warm surface waters on the stratified side. It was suggested that this was caused by upwelling of deep water at the front. In this paper we describe an alternative and simpler explanation based on the local balance of heating and stirring. The net heat flux into the sea in spring and early summer is greater on the mixed side of the front than on the stratified side. This happens because the heat loss mechanism is dependent on sea surface temperature and stratified waters, having a higher surface temperature, lose more heat. The stratified water near the front therefore has lower heat content (and lower depth-mean temperature) than the mixed water. If some of the stratified water becomes mixed, for example with increased tidal stirring at spring tides, a zone of minimum surface temperature will be formed at the front. A numerical model for the study of this mechanism shows that the temperature minimum at tidal fronts can be explained by the process described above. The minimum appears most clearly at spring tides, but can still be present in a weaker form at neap tides. A further prediction of the model is an increase of the horizontal temperature gradient at spring tides, which is in agreement with observations. An unexpected outcome of the modelling is the prediction of the formation of a marked sea surface temperature minimum, not yet observed, occurring in the autumn and located at the summer position of the tidal front.

Description: Data on the South Atlantic monthly sea surface temperature anomalies (SSTA) are analysed using the maximum-entropy method. It is shown that the Markov first-order process can describe, to a first approximation, SSTA series. The region of maximum SSTA values coincides with the zone of maximum residual white noise values (sub-Antarctic hydrological front). The theory of dynamic-stochastic climate models is applied to estimate the variability of South Atlantic SSTA and air-sea interactions. The Adem model is used as a deterministic block of the dynamic-stochastic model. Experiments show satisfactorily the SSTA intensification in the sub-Antarctic front zone, with appropriate standard deviations, and demonstrate the leading role of the abnormal drift currents in these processes.

Description: Adopting an appropriate procedure suitable for processing the amplitude-time records based on the two-component spectral analysis technique, the statistical information on Ps6 and other longer periods are worked out on the geomagnetic field registrations in the Indian longitudinal regions at and away from the equatorial electrojet influence. The storm interval during 21 and 22 September 1982 has been chosen for the analysis, as violent and regular cyclic variations of the geomagnetic field were recorded in all the three components of the field at the Indian observatories. The procedure, when applied to two intervals of afternoon and night conditions of equatorial ionosphere, showed practically the same polarisation characteristics in the H-D plane at all the frequencies under the equatorial electrojet. At far away places from this influence, the ellipticities are found to be relatively to the west during the afternoon. These, along with the other results, are discussed.

Description: This paper discusses the preliminary results of a study on the vegetation pattern and its relationship with meteorological parameters in and around Istanbul. The study covers an area of over 6800 km2 consisting of urban and suburban centers, and uses the visible and near-infrared bands of Landsat. The spatial variation of the Normalized Difference Vegetation Index (NDVI) and meteorological parameters such as sensible heat flux, momentum flux, relative humidity, moist static energy, rainfall rate and temperature have been investigated based on observations in ten stations in the European (Thracian) and Anatolian parts of Istanbul. NDVI values have been evaluated from the Landsat data for a single day, viz. 24 October 1986, using ERDAS in ten different classes. The simultaneous spatial variations of sensible heat and momentum fluxes have been computed from the wind and temperature profiles using the Monin-Obukhov similarity theory. The static energy variations are based on the surface meteorological observations. There is very good correlation between NDVI and rainfall rate. Good correlation also exists between: NDVI and relative humidity; NDVI, sensible heat flux and relative humidity; NDVI, momentum flux and emissivity; and NDVI, sensible heat flux and emissivity. The study suggests that the momentum flux has only marginal impact on NDVI. Due to rapid urbanization,the coastal belt is characterized by reduced NDVI compared to the interior areas, suggesting that thermodynamic discontinuities considerably influence the vegetation pattern. This study is useful for the investigation of small-scale circulation models, especially in urban and suburban areas where differential heating leads to the formation of heat islands. In the long run, such studies on a global scale are vital to gain accurate, timely information on the distribution of vegetation on the earth's surface. This may lead to an understanding of how changes in land cover affect phenomena as diverse as the atmospheric CO2 concentrations, the hydrological cycle and the energy balance at the surface-atmosphere interface.

Description: A study on the variability of temperature in the tropical middle atmosphere over Thumba (8 32' N, 76 52' E), located at the southern part of India, has been carried out based on rocket observations for a period of 20 years, extending from 1970 to 1990. The rocketsonde-derived mean temperatures over Thumba are corrected prior to 1978 and then compared with the middle atmospheric reference model developed from satellite observations and Solar Mesosphere Explorer (SME) satellite data. Temperature variability at every 1 km interval in the 25-75 km region was analysed. The tropical stratosphere is found to be highly stable, whereas considerable variability is noted in the middle mesosphere. The effect of seasonal cycle is least in the lower stratosphere. Annual and semi-annual oscillations in temperature are the primary oscillations in the tropical middle atmosphere. Annual temperature oscillations are dominant in the mesosphere and semi-annual oscillations are strong in the stratosphere. The stratopause region is noted to be the part of the middle atmosphere least sensitive to the changes in solar activity and long-term variability.

Description: Recent discussions on high-speed civil transport (HSCT) systems have renewed the interest in the chemistry of supersonic-aircraft plumes. The engines of these aircraft emit large concentrations of radicals like O, H, OH, and NO. In order to study the effect of these species on the composition of the atmosphere, the detailed chemistry of an expanding and cooling plume is examined for different expansion models. For a representative flight at 26 km the computed trace gas concentrations do not differ significantly for different models of the expansion behaviour. However, it is shown that the distributions predicted by all these models differ significantly from those adopted in conventional meso-scale and global models in which the plume chemistry is not treated in detail. This applies in particular to the reservoir species HONO and H2O2.

Description: Efforts have been made to extend the MF radar tidal profiles to E-region heights. The totally reflected MF radar echoes from E-region heights during daytime are known to be group-retarded and the corresponding wind and tidal data will have associated height discrepancies. The estimation of the E-region real heights (Namboothiri et al., 1993), and the elimination of the data for which the group retardation is significant, are selected as the basic criteria to extend the tidal profiles to 100-125 km. The analysis of the quiet (Ap

Description: Median hourly, electron content-latitude profiles obtained in South East Asia under solar minimum and maximum conditions have been used to establish seasonal and solar differences in the diurnal variations of the ionospheric equatorial anomaly (EIA). The seasonal changes have been mainly accounted for from a consideration of the daytime meridional wind, affecting the EIA diffusion of ionization from the magnetic equator down the magnetic field lines towards the crests. Depending upon the seasonal location of the subsolar point in relation to the magnetic equator diffusion rates were increased or decreased. This led to crest asymmetries at the solstices with (1) the winter crest enhanced in the morning (increased diffusion rate) and (2) the same crest decaying most rapidly in the late afternoon (faster recombination rate at lower ionospheric levels). Such asymmetries were also observed, to a lesser extent, at the equinoxes since the magnetic equator (located at about 9°N lat) does not coincide with the geographic equator. Another factor affecting the magnitude of a particular electron content crest was the proximity of the subsolar point, since this increased the local ionization production rate. Enhancements of the EIA took place around sunset, mainly during the equinoxes and more frequently at solar maximum, and also there was evidence of apparent EIA crest resurgences around 0300 LST for all seasons at solar maximum. The latter are thought to be associated with the commonly observed, post-midnight, ionization enhancements at midlatitudes, ionization being transported to low latitudes by an equatorward wind. The ratio increases in crest peak electron contents from solar minimum to maximum of 2.7 at the equinoxes, 2.0 at the northern summer solstice and 1.7 at northern winter solstice can be explained, only partly, by increases in the magnitude of the eastward electric field E overhead the magnetic equator affecting the [E×B] vertical drifts. The most important factor is the corresponding increase in ionization production rate due to the increase in solar radiation flux. The EIA crest asymmetries observed at solar maximum were less significant, and this is probably due to the corresponding increase in ionization densities leading to an increase of the retarding effect of ion-drag on the daytime meridional winds.

Description: Effective energy loss per electron-ion pair produced, (E0), as a function of a particle's initial energy has been obtained for proton transport in the atmosphere. The influence of some transport parameters on the shape of (E0) has been studied. Comparisons with the case of electron transport and with other results were made. It has been shown that: 1. for E0〉1 keV, (E0) varies within the range 30-36 eV; 2. as E0 increases the value of (E0) tries to attain an asymptotic value that is the same as for electrons (≈35 eV); 3. (E0) strongly depends on the average energy of secondary electrons, but the energy distribution of secondary electrons is not as important. The range of possible changes in (E0) associated with discrepancies in cross sections has been obtained.

Description: A superposed epoch analysis of geomagnetic storms has been undertaken. The storms are categorised via their intensity (as defined by the Dst index). Storms have also been classified here as either storm sudden commencements (SSCs) or storm gradual commencements (SGCs, that is all storms which did not begin with a sudden commencement). The prevailing solar wind conditions defined by the parameters solar wind speed (vsw), density (ρsw) and pressure (Psw) and the total field and the components of the interplanetary magnetic field (IMF) during the storms in each category have been investigated by a superposed epoch analysis. The southward component of the IMF, appears to be the controlling parameter for the generation of small SGCs (-100 nT〈 minimum Dst ≤ -50 nT for ≥ 4 h), but for SSCs of the same intensity solar wind pressure is dominant. However, for large SSCs (minimum Dst ≤ -100 nT for ≥ 4 h) the solar wind speed is the controlling parameter. It is also demonstrated that for larger storms magnetic activity is not solely driven by the accumulation of substorm activity, but substantial energy is directly input via the dayside. Furthermore, there is evidence that SSCs are caused by the passage of a coronal mass ejection, whereas SGCs result from the passage of a high speed/ slow speed coronal stream interface. Storms are also grouped by the sign of Bz during the first hour epoch after the onset. The sign of Bz at t = +1 h is the dominant sign of the Bz for ~24 h before the onset. The total energy released during storms for which Bz was initially positive is, however, of the same order as for storms where Bz was initially negative.

Description: Following numerous model studies of the global impacts of sub- and supersonic aircraft on the atmosphere, this paper assesses the separate aircraft engine exhaust effects of the 45°N cruise flight and at the 10- and 18-km levels of the July atmosphere. A box diffusion photochemical model in the cross-section plane of the flight trajectory is used to compute the effects of gas-phase and heterogeneous reactions on the condensation trail particles in the troposphere, and on the sulphate aerosols in the stratosphere. The enhanced horizontal dispersion of the exhaust plume is considered in the model. A significant but short term depletion of ozone is predicted, which is 99% restored in about 1 h in the wide plume with enhanced horizontal dispersion, but requires more than 24 h in the narrow plume without it. The oxidation rate of NO and NO2 into the HNO3 depends on the OH content in the exhausts and varies in all the cases. The heterogeneous photochemistry has only a small influence on the initial evolution of N2O5 and HO2 in the plume.

Description: The formation of a neutral induced weak nonlinear shock structure in a weakly ionised magnetoplasma has been analytically investigated. Using the reductive perturbation method, basic dynamical equations of a three-component (electron, ion and neutral) plasma have been reduced to a well-known Burger equation which can support a weak shock solution. Its stationary and initial value solutions have been derived to describe the characteristics of the weak shock profile. Asymptotic behaviour of the Burger solution results in a saw-tooth structure which has a practical implication to predict the nonlinear steepened structure of the nighttime irregularity in the lower portion of the Earth's ionosphere. Accordingly, it is suggested that the observation of saw-tooth shape of nighttime irregularity at 92 km could be attributed to the nonlinear saturation of the NILF mode instability as proposed by Dwivedi and Das in 1992. However, exact experimental verification of this suggestion requires more data on nighttime irregularity in the mesosphere and lower thermosphere (80-95 km) for a wide range of scale sizes extending up to about 1 km and above.

Description: An artificial feed-forward neural network with one hidden layer and error back-propagation learning is used to predict the geomagnetic activity index (Dst) one hour in advance. The Bz-component and ΣBz, the density, and the velocity of the solar wind are used as input to the network. The network is trained on data covering a total of 8700 h, extracted from the 25-year period from 1963 to 1987, taken from the NSSDC data base. The performance of the network is examined with test data, not included in the training set, which covers 386 h and includes four different storms. Whilst the network predicts the initial and main phase well, the recovery phase is not modelled correctly, implying that a single hidden layer error back-propagation network is not enough, if the measured Dst is not available instantaneously. The performance of the network is independent of whether the raw parameters are used, or the electric field and square root of the dynamical pressure.

Description: The Hydrologic Atmospheric Pilot EXperiment in the Sahel (HAPEX-Sahel) was carried out in Niger, West Africa, during 1991 - 1992, with an intensive observation period (IOP) in August - October 1992. It aims at improving the parameterization of land surface atmosphere interactions at the Global Circulation Model (GCM) gridbox scale. The experiment combines remote sensing and ground based measurements with hydrological and meteorological modelling to develop aggregation techniques for use in large scale estimates of the hydrological and meteorological behaviour of large areas in the Sahel. The experimental strategy consisted of a period of intensive measurements during the transition period of the rainy to the dry season, backed up by a series of long term measurements in a 1° by 1° square in Niger. Three "supersites" were instrumented with a variety of hydrological and (micro) meteorological equipment to provide detailed information on the surface energy exchange at the local scale. Boundary layer measurements and aircraft measurements were used to provide information at scales of 100 - 500 km2. All relevant remote sensing images were obtained for this period. This programme of measurements is now being analyzed and an extensive modelling programme is under way to aggregate the information at all scales up to the GCM grid box scale. The experimental strategy and some preliminary results of the IOP are described.

Description: A three-dimensional off-line tracer transport model coupled to the ECMWF analyses has been used to study the transport of trace gases in the atmosphere. The model gives a reasonable description of their general transport in the atmosphere. The simulation of the transport of aircraft emissions (as NOx) has been studied as well as the transport of passive tracers injected at different altitudes in the North Atlantic flight corridor. A large zonal variation in the NOx concentrations as well as large seasonal and yearly variations was found. The altitude of the flight corridor influences the amount of tracers transported into the troposphere and stratosphere to a great extent.