ALBERT

Description: This paper presents recent advances in the design of an underactuated hand for applications in prosthetics. First, the design of the fingers is addressed. Based on previous experiments with prototypes developed in the past, new tendon routings are proposed that lead to a more effective transmission of the forces. A novel elastic tendon routing is also proposed for the passive opening of the hand. A simplified static analysis of the fingers is proposed to support the results. Then, a new kinematic design of the thumb is presented. The thumb is designed to perform out-of-the-plane motions in order to broaden the variety of possible grasps. A mechanism for the implementation of underactuation between the fingers is proposed that alleviates the friction problems encountered in earlier hand designs. Finally, a prototype of the hand is briefly described and typical grasps are shown. This paper was presented at the IFToMM/ASME International Workshop on Underactuated Grasping (UG2010), 19 August 2010, Montréal, Canada.

Description: In this paper, a novel approach of grasp planning is applied to find out the appropriate grasp points for a reconfigurable parallel robot called PARAGRIP (Parallel Gripping). This new handling system is able to manipulate objects in the six-dimensional Cartesian space by several robotic arms using only six actuated joints. After grasping, the contact elements at the end of the underactuated arm mechanisms are connected to the object which forms a closed loop mechanism similar to the architecture of parallel manipulators. As the mounting and grasp points of the arms can easily be changed, the manipulator can be reconfigured to match the user's preferences and needs. This paper raises the question, how and where these grasp points are to be placed on the object to perform well for a certain manipulation task. This paper was presented at the IFToMM/ASME International Workshop on Underactuated Grasping (UG2010), 19 August 2010, Montréal, Canada.

Description: It is shown that core-strahl electron system in the solar wind plasma is unstable with respect to excitation of the lower hybrid waves at anomalous Doppler resonance due to anisotropy of the strahl electron velocity distribution. Dynamics of the strahl electron distribution due to interaction with excited waves is studied.

Description: In this lecture, I will review some basic aspects of the mechanism of stochastic resonance, first introduced as a possible mechanism to explain long term climatic variation. Since then, there have been many applications of stochastic resonance in physical and biological systems. I will show that in complex system, stochastic resonance can substantially change as a function of the "system complexity". Also, I will briefly mention how to apply stochastic resonance for the case of Brownian motors.

Description: An artificial neural network (ANN) was developed to predict the depth-integrated alongshore suspended sediment transport rate using 4 input variables (water depth, wave height and period, and alongshore velocity). The ANN was trained and validated using a dataset obtained on the intertidal beach of Egmond aan Zee, the Netherlands. Root-mean-square deviation between observations and predictions was calculated to show that, for this specific dataset, the ANN (εrms=0.43) outperforms the commonly used Bailard (1981) formula (εrms=1.63), even when this formula is calibrated (εrms=0.66). Because of correlations between input variables, the predictive quality of the ANN can be improved further by considering only 3 out of the 4 available input variables (εrms=0.39). Finally, we use the partial derivatives method to "open and lighten" the generated ANNs with the purpose of showing that, although specific to the dataset in question, they are not "black-box" type models and can be used to analyze the physical processes associated with alongshore sediment transport. In this case, the alongshore component of the velocity, by itself or in combination with other input variables, has the largest explanatory power. Moreover, the behaviour of the ANN indicates that predictions can be unphysical and therefore unreliable when the input lies outside the parameter space over which the ANN has been developed. Our approach of combining the strong predictive power of ANNs with "lightening" the black box and testing its sensitivity, demonstrates that the use of an ANN approach can result in the development of generalized models of suspended sediment transport.

Description: The modelling of baroclinic tides generated in the northern South China Sea is studied using a fully-nonlinear non-hydrostatic numerical model. The focus of the modelling efforts was on the vertical structure of internal waves in the vicinity of the Luzon Strait. The barotropic tidal flow interacting with a two-ridge bottom topography in the area of the Luzon Strait produces a complex baroclinic tidal signal. A multimodal baroclinic bore with counter-phase displacement of isopycnals generated over the ridges and propagating westward disintegrates into a series of large-amplitude solitary internal waves. The leading first-mode solitary wave of depression is followed by a second mode solitary wave coupled with a packet of short-scale internal waves riding it. Scrutiny of the characteristics of the both wave forms, i.e. the carrier second-mode solitary wave and the packet of short waves, revealed that the short-scale waves are basically concentrated in the upper 500 m layer and attenuate exponentially below it. The short waves exist only thanks to a specific structure of horizontal velocity produced by the second-mode solitary wave. Having equal phase speeds and propagating together for a long distance, this coupled system produces quite a remarkable signal at the free surface, which can be detected by means of remote sensing technique. It was found in a series of sensitivity experiments that the eastern ridge is responsible for the generation of progressive first-mode tidal waves disintegrated into packets of first-mode ISWs. The western ridge produces quite a strong higher-mode signal. The waves generated over the eastern and western ridges interfere in the near-field, and their nonlinear superposition enhances the multimodal signal in the whole domain.

Description: Precipitation during the monsoon season over the Indian subcontinent occurs in form of enormously complex spatiotemporal patterns due to the underlying dynamics of atmospheric circulation and varying topography. Employing methods from nonlinear time series analysis, we study spatial structures of the rainfall field during the summer monsoon and identify principle regions where the dynamics of monsoonal rainfall is more coherent or homogenous. Moreover, we estimate the time delay patterns of rain events. Here we present an analysis of two separate high resolution gridded data sets of daily rainfall covering the Indian subcontinent. Using the method of event synchronization (ES), we estimate regions where heavy rain events during monsoon happen in some lag synchronised form. Further using the delay behaviour of rainfall events, we estimate the directionalities related to the progress of such type of rainfall events. The Active (break) phase of a monsoon is characterised by an increase(decrease) of rainfall over certain regions of the Indian subcontinent. We show that our method is able to identify regions of such coherent rainfall activity.

Description: Borehole logs provide geological information about the rocks crossed by the wells. Several properties of rocks can be interpreted in terms of lithology, type and quantity of the fluid filling the pores and fractures. Here, the logs are assumed to be nonhomogeneous Brownian motions (nhBms) which are generalized fractional Brownian motions (fBms) indexed by depth-dependent Hurst parameters H(z). Three techniques, the local wavelet approach (LWA), the average-local wavelet approach (ALWA), and Peltier Algorithm (PA), are suggested to estimate the Hurst functions (or the regularity profiles) from the logs. First, two synthetic sonic logs with different parameters, shaped by the successive random additions (SRA) algorithm, are used to demonstrate the potential of the proposed methods. The obtained Hurst functions are close to the theoretical Hurst functions. Besides, the transitions between the modeled layers are marked by Hurst values discontinuities. It is also shown that PA leads to the best Hurst value estimations. Second, we investigate the multifractional property of sonic logs data recorded at two scientific deep boreholes: the pilot hole VB and the ultra deep main hole HB, drilled for the German Continental Deep Drilling Program (KTB). All the regularity profiles independently obtained for the logs provide a clear correlation with lithology, and from each regularity profile, we derive a similar segmentation in terms of lithological units. The lithological discontinuities (strata' bounds and faults contacts) are located at the local extrema of the Hurst functions. Moreover, the regularity profiles are compared with the KTB estimated porosity logs, showing a significant relation between the local extrema of the Hurst functions and the fluid-filled fractures. The Hurst function may then constitute a tool to characterize underground heterogeneities.

Description: This paper addresses the use of the methods of nonlinear dynamics and chaos theory for building a predictive chaotic model from time series. The chaotic model predictions are made by the adaptive local models based on the dynamical neighbors found in the reconstructed phase space of the observables. We implemented the univariate and multivariate chaotic models with direct and multi-steps prediction techniques and optimized these models using an exhaustive search method. The built models were tested for predicting storm surge dynamics for different stormy conditions in the North Sea, and are compared to neural network models. The results show that the chaotic models can generally provide reliable and accurate short-term storm surge predictions.

Description: In the present study, the latitudinal aspect of chaotic behaviour of ionosphere during quiet and storm periods are analyzed and compared by using GPS TEC time series measured at equatorial trough, crest and outside crest stations over Indian subcontinent, by employing the chaotic quantifiers like Lyapunov exponent (LE), correlation dimension (CD), entropy and nonlinear prediction error (NPE). It is observed that the values of LE are low for storm periods compared to those of quiet periods for all the stations considered here. The lowest value of LE is observed at the trough station, Agatti (2.38° N, Geomagnetically), and highest at crest station, Mumbai (10.09° N, Geomagnetically) for both quiet and storm periods. The values of correlation dimension computed for TEC time series are in the range 2.23–2.74 for quiet period, which indicate that equatorial ionosphere may be described with three variables during quiet period. But the crest station Mumbai shows a higher value of CD (3.373) during storm time, which asserts that four variables are necessary to describe the system during storm period. The values of non linear prediction error (NPE) are lower for Agatti (2.38° N, Geomagnetically) and Jodhpur (18.3° N, Geomagnetically), during storm period, compared to those of quiet period, mainly because of the predominance of non linear aspects during storm periods The surrogate data test is carried out and on the basis of the significance of difference of the original data and surrogates for various aspects, the surrogate data test rejects the null hypothesis that the time series of TEC during storm and quiet times represent a linear stochastic process. It is also observed that using state space model, detrended TEC can be predicted, which reasonably reproduces the observed data. Based on the values of the above quantifiers, the features of chaotic behaviour of equatorial trough crest and outside the crest regions of ionosphere during geomagnetically quiet and disturbed periods are briefly discussed.

Description: In this paper, spectral and detrended fluctuation analyses, as well as time reversibility and magnitude-sign decomposition, have been applied to the 10-year time-series data resulting from geochemical monitoring of gas emissions on the flanks of Mt. Etna, and gases from a CO2 exploitation well located tens of kilometers from the volcano. The analysis of the time series which showed main effects of fractionation between gases due to selective dissolution in aquifers (e.g., the CO2 concentration series), revealed the occurrence of random fluctuations in time, typical of systems where several processes combine linearly. In contrast, the series of He isotopic composition exhibited power-law behavior of the second-order fluctuation statistics, with values of the scaling exponent close to 0.9. When related to the spectral exponent, this value indicates that the isotopic series closely resemble fractal flicker-noise signals having persistent long-range correlations. The isotopic signals also displayed asymmetry under time reversal and long-range correlation of the associated magnitude series, therefore it was statistically proved the presence of nonlinearity. Both long-range correlation and nonlinearity in time series have been generally considered as distinctive features of dynamic systems where numerous processes interact by feedback mechanisms, in accordance with the paradigm of self-organized criticality (SOC). Thus, it is here proposed that the system that generated the isotope series worked under conditions of SOC. Since the fluctuations of the isotope series have been related to magma degassing, the previous results place constraints on the dynamics of such process, and suggest that nonequilibrium conditions must be dominant. It remains unclear whether the signature of SOC is directly due to volatile degassing from magma, or if it derives from the interaction between melt and the stress field, which certainly influences magma decompression. The strength of scaling appears to increase after 2002 (α values from 0.8 up to 1.2), focusing on transition of the Etnean system from typical SOC toward conditions of lower criticality. By comparing this transition with those of geophysical observables, it can be suggested that the drop in the rate of magma supply, subsequent to the paroxysms of 2001 and 2002–2003, was the main cause of the scaling change.

Description: In the framework of a unified formalism for Kolmogorov-Lorenz systems, predictions of times of regime transitions in the classical Lorenz model can be successfully achieved by considering orbits characterised by energy or Casimir maxima. However, little uncertainties in the starting energy usually lead to high uncertainties in the return energy, so precluding the chance of accurate multi-step forecasts. In this paper, the problem of obtaining good forecasts of maximum return energy is faced by means of a neural network model. The results of its application show promising results.

Description: The complexity in the tsunami phenomenon makes the available warning systems not much effective in the practical situations. The problem arises due to the time lapsed in the data transfer, processing and modeling. The modeling and simulation needs the input fault geometry and mechanism of the earthquake. The estimation of these parameters and other aprior information increases the utilized time for making any warning. Here, the wavelet analysis is used to identify the tsunamigenesis of an earthquake. The frequency content of the seismogram in time scale domain is examined using wavelet transform. The energy content in high frequencies is calculated and gives a threshold for tsunami warnings. Only first few minutes of the seismograms of the earthquake events are used for quick estimation. The results for the earthquake events of Andaman Sumatra region and other historic events are promising.

Description: Intraplate seismicity occurs in central and northern Canada, but the underlying origin and dynamics remain poorly understood. Here, we apply a graph theoretic approach to characterize the statistical structure of spatiotemporal clustering exhibited by intraplate seismicity, a direct consequence of the underlying nonlinear dynamics. Using a recently proposed definition of "recurrences" based on record breaking processes (Davidsen et al., 2006, 2008), we have constructed directed graphs using catalogue data for three selected regions (Region 1: 45°−48° N/74°−80° W; Region 2: 51°−55° N/77°−83° W; and Region 3: 56°−70° N/65°−95° W), with attributes drawn from the location, origin time and the magnitude of the events. Based on comparisons with a null model derived from Poisson distribution or Monte Carlo shuffling of the catalogue data, our results provide strong evidence in support of spatiotemporal correlations of seismicity in all three regions considered. Similar evidence for spatiotemporal clustering has been documented using seismicity catalogues for southern California, suggesting possible similarities in underlying earthquake dynamics of both regions despite huge differences in the variability of seismic activity.

Description: The complex spatial and temporal characteristics of European dry spell lengths, DSL, (sequences of consecutive days with rainfall amount below a certain threshold) and their randomness and predictive instability are analysed from daily pluviometric series recorded at 267 rain gauges along the second half of the 20th century. DSL are obtained by considering four thresholds, R0, of 0.1, 1.0, 5.0 and 10.0 mm/day. A proper quantification of the complexity, randomness and predictive instability of the different DSL regimes in Europe is achieved on the basis of fractal analyses and dynamic system theory, including the reconstruction theorem. First, the concept of lacunarity is applied to the series of daily rainfall, and the lacunarity curves are well fitted to Cantor and random Cantor sets. Second, the rescaled analysis reveals that randomness, persistence and anti-persistence are present on the European DSL series. Third, the complexity of the physical process governing the DSL series is quantified by the minimum number of nonlinear equations determined by the correlation dimension. And fourth, the loss of memory of the physical process, which is one of the reasons for the complex predictability, is characterized by the values of the Kolmogorov entropy, and the predictive instability is directly associated with positive Lyapunov exponents. In this way, new bases for a better prediction of DSLs in Europe, sometimes leading to drought episodes, are established. Concretely, three predictive strategies are proposed in Sect. 5. It is worth mentioning that the spatial distribution of all fractal parameters does not solely depend on latitude and longitude but also reflects the effects of orography, continental climate or vicinity to the Atlantic and Arctic Oceans and Mediterranean Sea.

Description: Four oceanographic moorings were deployed in the South China Sea from April 2005 to June 2006 along a transect extending from the Batanes Province, Philippines in the Luzon Strait to just north of Dong-Sha Island on the Chinese continental slope. The purpose of the array was to observe and track large-amplitude nonlinear internal waves (NIWs) from generation to shoaling over the course of one full year. The basin and slope moorings observed velocity, temperature (T) and salinity (S) at 1–3 min intervals to observe the waves without aliasing. The Luzon mooring observed velocity at 15 min and T and S at 3 min, primarily to resolve the tidal forcing in the strait. The observed waves travelled WNW towards 282–288 degrees with little variation. They were predominantly mode-1 waves with orbital velocities exceeding 100 cm s−1 and thermal displacements exceeding 100 m. Consistent with earlier authors, two types of waves were observed: the a-waves arrived diurnally and had a rank-ordered packet structure. The b-waves arrived in between, about an hour later each day similar to the pattern of the semi-diurnal tide. The b-waves were weaker than the a-waves, usually consisted of just one large wave, and were often absent in the deep basin, appearing as NIW only upon reaching the continental slope. The propagation speed of both types of waves was 323±31 cm s−1 in the deep basin and 222±18 cm s−1 over the continental slope. These speeds were 11–20% faster than the theoretical mode-1 wave speeds for the observed stratification, roughly consistent with the additional contribution from the nonlinear wave amplitude. The observed waves were clustered around the time of the spring tide at the presumed generation site in the Luzon Strait, and no waves were observed at neap tide. A remarkable feature was the distinct lack of waves during the winter months, December 2005 through February 2006. Most of the features of the wave arrivals can be explained by the tidal variability in the Luzon Strait. The near-bottom tidal currents in the Luzon Strait were characterized by a large fortnightly envelope, large diurnal inequality, and stronger ebb (towards the Pacific) than flood tides. Within about ±4 days of spring tide, when currents exceeded 71 cm s−1, the ebb tides generated high-frequency motions immediately that evolved into well-developed NIWs by the time they reached mooring B1 in the deep basin. These waves formed diurnally and correspond to the a-waves described by previous authors. Also near spring tide, the weaker flood tides formed NIWs which took longer/further to form, usually not until they reached mooring S7 on the upper continental slope. These waves tracked the semidiurnal tide and correspond to the b-waves described by previous authors. These patterns were consistent from March to November. During December–February, the structure of the barotropic tide was unchanged, so the lack of waves during this time is attributed to the deep surface mixed layer and weaker stratification along the propagation path in winter.

Description: The energetics of internal waves in the presence of a background sheared current is explored via numerical simulations for four different situations based on oceanographic conditions: the nonlinear interaction of two internal solitary waves; an internal solitary wave shoaling through a turning point; internal solitary wave reflection from a sloping boundary and a deep-water internal seiche trapped in a deep basin. In the simulations with variable water depth using the Boussinesq approximation the combination of a background sheared current, bathymetry and a rigid lid results in a change in the total energy of the system due to the work done by a pressure change that is established across the domain. A final simulation of the deep-water internal seiche in which the Boussinesq approximation is not invoked and a diffuse air-water interface is added to the system results in the energy remaining constant because the generation of surface waves prevents the establishment of a net pressure increase across the domain. The difference in the perturbation energy in the Boussinesq and non-Boussinesq simulations is accounted for by the surface waves.

Description: Oceanic observations from the Bay of Biscay, Portugal, Mozambique Channel and Mascarene Ridge have provided evidence of the generation of internal solitary waves due to an internal tidal beam impinging on the thermocline from below – a process referred to as "local generation". Here we present two-dimensional numerical simulations with a fully nonlinear nonhydrostatic model of situations that are relevant for the Bay of Biscay in summer. We show that a beam impinging on a thermocline initially at rest can induce a displacement of the isopycnals, large enough for internal solitary waves to be generated. These internal solitary waves however differ from those observed in the Bay of Biscay through their amplitude and distance between wave trains. We then show that the latter feature is recovered when the background flow around the thermocline as found in the Bay of Biscay is included in the forcing, thereby yielding a more accurate view on the local generation mechanism.

Description: In order to get valuable information about the scale invariance in the process of seismogeny of Lijiang M 7.0 earthquake, the scaling property of the interevent time series of the seismic sequences for Lijiang area in China were studied by using the method of the local scaling property, the generalised dimension spectrum, and the correlation dimension. It is found that there is a clear characteristic variation of local scaling property prior to Lijiang M 7.0 earthquake while there is no characteristic variation of the generalised dimension spectrum and the correlation dimension. The reason for producing this phenomenon is that the fractal seismic system is a complex hierarchical system. For such a system, searching for a relevant choice in application of the three methodologies is needed. Compared with the generalised dimension spectrum and mono-fractal dimension which focus on the global description of the scaling properties of fractal objects, the local scaling property emphasizes the local features, and can give the local information of the singularity of the fractal system, therefore, it is easier for us to get valuable information from complex hierarchical structure with this method.

Description: The generation and evolution of solitary waves by intrusive gravity currents in an approximate two-layer fluid with equal upper- and lower-layer depths is examined in a cylindrical geometry by way of theory and numerical simulations. The study is limited to vertically symmetric cases in which the density of the intruding fluid is equal to the average density of the ambient. We show that even though the head height of the intrusion decreases, it propagates at a constant speed well beyond 3 lock radii. This is because the strong stratification at the interface supports the formation of a mode-2 solitary wave that surrounds the intrusion head and carries it outwards at a constant speed. The wave and intrusion propagate faster than a linear long wave; therefore, there is strong supporting evidence that the wave is indeed nonlinear. Rectilinear Korteweg-de Vries theory is extended to allow the wave amplitude to decay as r-p with p=½ and the theory is compared to the observed waves to demonstrate that the width of the wave scales with its amplitude. After propagating beyond 7 lock radii the intrusion runs out of fluid. Thereafter, the wave continues to spread radially at a constant speed, however, the amplitude decreases sufficiently so that linear dispersion dominates and the amplitude decays with distance as r-1.

Description: Recent developments of multi-point measurements in space provide a means to analyze spacecraft data directly in the wave vector domain. For turbulence study this means that we are able to estimate energy, helicity, and higher order moments in the wave vector domain without assuming Taylor's hypothesis or axisymmetry around the mean magnetic field. The methods of the wave vector analysis are presented and applied to four-point data of Cluster in the solar wind.

Description: We discuss two different physical processes that create localized high β plasma regions. One is nonlinear wave-steepening, generating magnetic decreases (MDs) by a ponderomotive force. The other is the mirror instability generating alternating high and low β plasma regions. It is demonstrated that MDs and mirror modes are observationally quite different structures. MDs spatially occur in interplanetary space and mirror modes primarily in planetary magnetosheaths. MDs are characterized by: 1) variable (exponentially decreasing number with increasing) angular changes, 2) variable (exponentially decreasing) thicknesses, and 3) no characteristic inter-event spacings. In sharp contrast, mirror modes are characterized by: 1) little or no angular changes across the structures, 2) a characteristic scale size, and 3) are quasiperiodic in nature. Arguments are presented for the recently observed magnetic dips in the heliosheath being mirror mode structures. The sources of free energy for instability are discussed. Both structures are important for energetic particle transport in astrophysical and heliospheric plasmas.

Description: The energetics of large amplitude, high-frequency nonlinear internal waves (NLIWs) observed over the New Jersey continental shelf are summarized from ship and mooring data acquired in August 2006. NLIW energy was typically on the order of 105 Jm−1, and the wave dissipative loss was near 50 W m−1. However, wave energies (dissipations) were ~10 (~2) times greater than these values during a particular week-long period. In general, the leading waves in a packet grew in energy across the outer shelf, reached peak values near 40 km inshore of the shelf break, and then lost energy to turbulent mixing. Wave growth was attributed to the bore-like nature of the internal tide, as wave groups that exhibited larger long-term (lasting for a few hours) displacements of the pycnocline offshore typically had greater energy inshore. For ship-observed NLIWs, the average dissipative loss over the region of decay scaled with the peak energy in waves; extending this scaling to mooring data produces estimates of NLIW dissipative loss consistent with those made using the flux divergence of wave energy. The decay time scale of the NLIWs was approximately 12 h corresponding to a length scale of 35 km (O(100) wavelengths). Imposed on these larger scale energetic trends, were short, rapid exchanges associated with wave interactions and shoaling on a localized topographic rise. Both of these events resulted in the onset of shear instabilities and large energy loss to turbulent mixing.

Description: We give an overview of a novel lattice-based avalanche model that reproduces well a number of observed statistical properties of solar flares. The anisotropic lattice is defined as a network of vertically-connected nodes subjected to horizontal random displacements mimicking the kinks introduced by random motions of the photospheric footpoints of magnetic fieldlines forming a coronal loop. We focus here on asymmetrical driving displacements, which under our geometrical interpretation of the lattice correspond to a net direction of twist of the magnetic fieldlines about the loop axis. We show that a net vertical electrical current density does build up in our lattice, as one would expect from systematic twisting of a loop-like magnetic structure, and that the presence of this net current has a profound impact on avalanche dynamics. The presence of an additional energy reservoir tends to increase the mean energy released by avalanches, and yield a probability distribution of released energy in better agreement with observational inferences than in its absence. Symmetrical driving displacements are in better conceptual agreement with a random shuffling of photospheric footpoint, and yield a power-law distribution of energy release with exponent larger than 2, as required in Parker's nanoflare model of coronal heating. On the other hand, moderate asymmetrical driving generate energy distribution exponents that are similar to those obtained from SOHO EUV observations.

Description: The Thirulamai-Mountain (TM) metric was first developed to study ergodicity in fluids and glasses (Thirumalai and Mountain, 1993) using the concept of effective ergodicity, where a large but finite time interval is considered. Tiampo et al. (2007) employed the TM metric to earthquake systems to search for effective ergodic periods, which are considered to be metastable equilibrium states that are disrupted by large events. The physical meaning of the TM metric for seismicity is addressed here in terms of the clustering of earthquakes in both time and space for different sets of data. It is shown that the TM metric is highly dependent not only on spatial/temporal seismicity clustering, but on the past seismic activity of the region and the time intervals considered as well, and that saturation occurs over time, resulting in a lower sensitivity to local clustering. These results confirm that the TM metric can be used to quantify seismicity clustering from both spatial and temporal perspectives, in which the disruption of effective ergodic periods are caused by the agglomeration of events.

Description: The influence of multiple spatio-temporal scales on the error growth and predictability of atmospheric flows is analyzed throughout the paper. To this aim, we consider the two-scale Lorenz'96 model and study the interplay of the slow and fast variables on the error growth dynamics. It is shown that when the coupling between slow and fast variables is weak the slow variables dominate the evolution of fluctuations whereas in the case of strong coupling the fast variables impose a non-trivial complex error growth pattern on the slow variables with two different regimes, before and after saturation of fast variables. This complex behavior is analyzed using the recently introduced Mean-Variance Logarithmic (MVL) diagram.

Description: Current disruption (CD) and the related kinetic instabilities in the near-Earth magnetosphere represent physical mechanisms which can trigger multi-scale substorm activity including global reorganizations of the magnetosphere. Lui et al. (2008) proposed a CD scenario in which the kinetic scale linear modes grow and reach the typical dipolarization scales through an inverse cascade. The experimental verification of the inverse nonlinear cascade is based on wavelet analysis. In this paper the Hilbert-Huang transform is used which is suitable for nonlinear systems and allows to reconstruct the time-frequency representation of empirical decomposed modes in an adaptive manner. It was found that, in the Lui et al. (2008) event, the modes evolve globally from high-frequencies to low-frequencies. However, there are also local frequency evolution trends oriented towards high-frequencies, indicating that the underlying processes involve multi-scale physics and non-stationary fluctuations for which the simple inverse cascade scenario is not correct.

Description: Understanding and describing spatial arrangements of mineral particles and determining the mineral distribution structure are important to model the rock-forming process. Geometric properties of individual mineral particles can be estimated from thin sections, and different models have been proposed to quantify the spatial complexity of mineral arrangement. The Gejiu tin-polymetallic ore-forming district, located in Yunnan province, southwestern China, is chosen as the study area. The aim of this paper is to apply fractal and multifractal analysis to quantify distribution patterns of pyrrhotite particles from twenty-eight binary images obtained from seven basalt segments and then to discern the possible petrological formation environments of the basalts based on concentrations of trace elements. The areas and perimeters of pyrrhotite particles were measured for each image. Perimeter-area fractal analysis shows that the perimeter and area of pyrrhotite particles follow a power-law relationship, which implies the scale-invariance of the shapes of the pyrrhotites. Furthermore, the spatial variation of the pyrrhotite particles in space was characterized by multifractal analysis using the method of moments. The results show that the average values of the area-perimeter exponent (DAP), the width of the multifractal spectra (Δ(D(0)−D(2)) and Δ(D(qmin)−D(qmax))) and the multifractality index (τ"(1)) for the pyrrhotite particles reach their minimum in the second basalt segment, which implies that the spatial arrangement of pyrrhotite particles in Segment 2 is less heterogeneous. Geochemical trace element analysis results distinguish the second basalt segment sample from other basalt samples. In this aspect, the fractal and multifractal analysis may provide new insights into the quantitative assessment of mineral microstructures which may be closely associated with the petrogenesis as shown by the bulk-rock geochemical analysis.

Description: Nonlinear phenomena are essential ingredients in many oceanic and atmospheric processes, and successful understanding of them benefits from multidisciplinary collaboration between oceanographers, meteorologists, physicists and mathematicians. The present Special Issue on "Nonlinear Processes in Oceanic and Atmospheric Flows" contains selected contributions from attendants to the workshop which, in the above spirit, was held in Castro Urdiales, Spain, in July 2008. Here we summarize the Special Issue contributions, which include papers on the characterization of ocean transport in the Lagrangian and in the Eulerian frameworks, generation and variability of jets and waves, interactions of fluid flow with plankton dynamics or heavy drops, scaling in meteorological fields, and statistical properties of El Niño Southern Oscillation.

Description: Large-amplitude internal solitary waves in continuously stratified systems can be found by solution of the Dubreil-Jacotin-Long (DJL) equation. For finite ambient density gradients at the surface (bottom) for waves of depression (elevation) these solutions may develop recirculating cores for wave speeds above a critical value. As typically modeled, these recirculating cores contain densities outside the ambient range, may be statically unstable, and thus are physically questionable. To address these issues the problem for trapped-core solitary waves is reformulated. A finite core of homogeneous density and velocity, but unknown shape, is assumed. The core density is arbitrary, but generally set equal to the ambient density on the streamline bounding the core. The flow outside the core satisfies the DJL equation. The flow in the core is given by a vorticity-streamfunction relation that may be arbitrarily specified. For simplicity, the simplest choice of a stagnant, zero vorticity core in the frame of the wave is assumed. A pressure matching condition is imposed along the core boundary. Simultaneous numerical solution of the DJL equation and the core condition gives the exterior flow and the core shape. Numerical solutions of time-dependent non-hydrostatic equations initiated with the new stagnant-core DJL solutions show that for the ambient stratification considered, the waves are stable up to a critical amplitude above which shear instability destroys the initial wave. Steadily propagating trapped-core waves formed by lock-release initial conditions also agree well with the theoretical wave properties despite the presence of a "leaky" core region that contains vorticity of opposite sign from the ambient flow.

Description: A hybrid approach for forward and inverse geophysical modeling, based on Artificial Neural Networks (ANN) and Finite Element Method (FEM), is proposed in order to properly identify the parameters of volcanic pressure sources from geophysical observations at ground surface. The neural network is trained and tested with a set of patterns obtained by the solutions of numerical models based on FEM. The geophysical changes caused by magmatic pressure sources were computed developing a 3-D FEM model with the aim to include the effects of topography and medium heterogeneities at Etna volcano. ANNs are used to interpolate the complex non linear relation between geophysical observations and source parameters both for forward and inverse modeling. The results show that the combination of neural networks and FEM is a powerful tool for a straightforward and accurate estimation of source parameters in volcanic regions.

Description: For the purposes of this study, an interval is the elapsed time between two earthquakes in a designated region; the minimum magnitude for the earthquakes is prescribed. A record-breaking interval is one that is longer (or shorter) than preceding intervals; a starting time must be specified. We consider global earthquakes with magnitudes greater than 5.5 and show that the record-breaking intervals are well estimated by a Poissonian (random) theory. We also consider the aftershocks of the 2004 Parkfield earthquake and show that the record-breaking intervals are approximated by very different statistics. In both cases, we calculate the number of record-breaking intervals (nrb) and the record-breaking interval durations Δtrb as a function of "natural time", the number of elapsed events. We also calculate the ratio of record-breaking long intervals to record-breaking short intervals as a function of time, r(t), which is suggested to be sensitive to trends in noisy time series data. Our data indicate a possible precursory signal to large earthquakes that is consistent with accelerated moment release (AMR) theory.

Description: Recently, new cycles, associated with periods of 30 and 43 months, respectively, have been observed by the authors in surface air temperature time series, using a wavelet-based methodology. Although many evidences attest the validity of this method applied to climatic data, no systematic study of its efficiency has been carried out. Here, we estimate confidence levels for this approach and show that the observed cycles are significant. Taking these cycles into consideration should prove helpful in increasing the accuracy of the climate model projections of climate change and weather forecast.

Description: We propose an alternative approach for the embedding space reconstruction method for short time series. An m-dimensional embedding space is reconstructed with a set of time delays including the relevant time scales characterizing the dynamical properties of the system. By using a maximal predictability criterion a d-dimensional subspace is selected with its associated set of time delays, in which a local nonlinear blind forecasting prediction performs the best reconstruction of a particular event of a time series. An locally unfolded d-dimensional embedding space is then obtained. The efficiency of the methodology, which is mathematically consistent with the fundamental definitions of the local nonlinear long time-scale predictability, was tested with a chaotic time series of the Lorenz system. When applied to the Southern Oscillation Index (SOI) (observational data associated with the El Niño-Southern Oscillation phenomena (ENSO)) an optimal set of embedding parameters exists, that allows constructing the main characteristics of the El Niño 1982–1983 and 1997–1998 events, directly from measurements up to 3 to 4 years in advance.

Description: A system made of two sliding blocks coupled by a spring is employed to simulate the long-term behaviour of a fault with two asperities. An analytical solution is given for the motion of the system in the case of blocks having the same friction. An analysis of the phase space shows that orbits can reach a limit cycle only after entering a particular subset of the space. There is an infinite number of different limit cycles, characterized by the difference between the forces applied to the blocks or, as an alternative, by the recurrence pattern of block motions. These results suggest that the recurrence pattern of seismic events produced by the equivalent fault system is associated with a particular stress distribution which repeats periodically. Admissible stress distributions require a certain degree of inhomogeneity, which depends on the geometry of fault system. Aperiodicity may derive from stress transfers from neighboring faults.

Description: We consider a highly idealized model for El Niño/Southern Oscillation (ENSO) variability, as introduced in an earlier paper. The model is governed by a delay differential equation for sea-surface temperature T in the Tropical Pacific, and it combines two key mechanisms that participate in ENSO dynamics: delayed negative feedback and seasonal forcing. We perform a theoretical and numerical study of the model in the three-dimensional space of its physically relevant parameters: propagation period τ of oceanic waves across the Tropical Pacific, atmosphere-ocean coupling κ, and strength of seasonal forcing b. Phase locking of model solutions to the periodic forcing is prevalent: the local maxima and minima of the solutions tend to occur at the same position within the seasonal cycle. Such phase locking is a key feature of the observed El Niño (warm) and La Niña (cold) events. The phasing of the extrema within the seasonal cycle depends sensitively on model parameters when forcing is weak. We also study co-existence of multiple solutions for fixed model parameters and describe the basins of attraction of the stable solutions in a one-dimensional space of constant initial model histories.

Description: The problem of the linear instability of quasi-geostrophic Rossby waves to zonal flow perturbations is investigated on an infinite β-plane using a phase dynamics formalism. Equations governing the coupled evolutions of a zonal velocity perturbation and phase and amplitude perturbations of a finite-amplitude wave are obtained. The analysis is valid in the limit of infinitesimal, zonally invariant perturbation components, varying slowly in the meridional direction and with respect to time. In the case of a slow sinusoidal meridional variation of the perturbation components, analytical expressions for the perturbation growth rates are obtained, which are checked against numerical codes based on standard Floquet theory.

Description: The role played by wind-forced anticyclones in the vertical transport and mixing at the ocean mesoscale is investigated with a primitive-equation numerical model in an idealized configuration. The focus of this work is to determine how the stratification impacts such transport. The flows, forced only at the surface by an idealized wind forcing, are predominantly horizontal and, on average, quasigeostrophic. Inside vortex cores and intense filaments, however, the dynamics is strongly ageostrophic. Mesoscale anticyclones appear as "islands" of increased penetration of wind energy into the ocean interior and they represent the maxima of available potential energy. The amount of available potential energy is directly correlated with the degree of stratification. The wind energy injected at the surface is transferred at depth through the generation and subsequent straining effect of Vortex Rossby Waves (VRWs), and through near-inertial internal oscillations trapped inside anticyclonic vortices. Both these mechanisms are affected by stratification. Stronger transfer but larger confinement close to the surface is found when the stratification is stronger. For weaker stratification, vertical mixing close to the surface is less intense but below about 150 m attains substantially higher values due to an increased contribution of both VRWs, whose time scale is on the order of few days, and of near-inertial motions, with a time scale of few hours.

Description: Discrete multiplicative random cascade (MRC) models were extensively studied and applied to disaggregate rainfall data, thanks to their formal simplicity and the small number of involved parameters. Focusing on temporal disaggregation, the rationale of these models is based on multiplying the value assumed by a physical attribute (e.g., rainfall intensity) at a given time scale L, by a suitable number b of random weights, to obtain b attribute values corresponding to statistically plausible observations at a smaller L/b time resolution. In the original formulation of the MRC models, the random weights were assumed to be independent and identically distributed. However, for several studies this hypothesis did not appear to be realistic for the observed rainfall series as the distribution of the weights was shown to depend on the space-time scale and rainfall intensity. Since these findings contrast with the scale invariance assumption behind the MRC models and impact on the applicability of these models, it is worth studying their nature. This study explores the possible presence of dependence of the parameters of two discrete MRC models on rainfall intensity and time scale, by analyzing point rainfall series with 5-min time resolution. Taking into account a discrete microcanonical (MC) model based on beta distribution and a discrete canonical beta-logstable (BLS), the analysis points out that the relations between the parameters and rainfall intensity across the time scales are detectable and can be modeled by a set of simple functions accounting for the parameter-rainfall intensity relationship, and another set describing the link between the parameters and the time scale. Therefore, MC and BLS models were modified to explicitly account for these relationships and compared with the continuous in scale universal multifractal (CUM) model, which is used as a physically based benchmark model. Monte Carlo simulations point out that the dependence of MC and BLS parameters on rainfall intensity and cascade scales can be recognized also in CUM series, meaning that these relations cannot be considered as a definitive sign of departure from multifractality. Even though the modified MC model is not properly a scaling model (parameters depend on rainfall intensity and scale), it reproduces the empirical traces of the moments and moment exponent function as effective as the CUM model. Moreover, the MC model is able to reproduce some rainfall properties of hydrological interest, such as the distribution of event rainfall amount, wet/dry spell length, and the autocorrelation function, better than its competitors owing to its strong, albeit unrealistic, conservative nature. Therefore, even though the CUM model represents the most parsimonious and the only physically/theoretically consistent model, results provided by MC model motivate, to some extent, the interest recognized in the literature for this type of discrete models.

Description: Analysis of year-long drifter trajectories and records of simulated surface Lagrangian Coherent Structures (LCSs) have suggested the presence of a resilient Cross-Shelf Transport Barrier (CSTB) on the West Florida Shelf (WFS). The CSTB was conjectured to provide a large degree of isolation, which is consequential for the fueling of red tides on the southern WFS by nutrients possibly released by rivers and canals directly on the region. Here this conjecture is thoroughly tested by identifying LCSs as well as performing tracer advection calculations based on seven-year-long records of surface and subsurface currents produced by a HYbrid-Coordinate Ocean Model (HYCOM) simulation of the Gulf of Mexico (GoM). The identified LCSs suggest that the CSTB extends downward in the water column. The tracer calculations suggest that, while the majority of the nutrients possibly released by rivers and canals directly on the southern WFS are retained within the region for long times, only a small fraction of the nutrients possibly released by rivers outside the WFS reach the southern WFS, mainly accompanying shoreward excursions of the CSTB. These results add importance to the role played by the CSTB in controlling red tide development on the WFS. Implications of the results for the dispersal of pollutants, such as oil, in the GoM are discussed.

Description: In coastal seas and straits, the interaction of barotropic tidal currents with the continental shelf, seamounts or sills is often observed to generate large-amplitude, horizontally propagating internal solitary waves. Typically these waves occur in regions of variable bottom topography, with the consequence that they are often modeled by nonlinear evolution equations of the Korteweg-de Vries type with variable coefficients. We shall review how these models are used to describe the propagation, deformation and disintegration of internal solitary waves as they propagate over the continental shelf and slope.

Description: We present a novel method for regional climate classification that is based on coarse-grained categorical representations of multivariate climate anomalies and a subsequent Markov chain analysis. From the estimated transition matrix several descriptors, such as persistence, recurrence time and entropy, are derived. These descriptors characterise dynamic properties of regional climate anomalies and are connected with fundamental concepts from nonlinear physics like residence times, relaxation process and predictability. Such characteristics are useful for a comparative analysis of different climate regions and, in the context of global climate change, for a regime shift analysis. We apply the method to the bivariate set of water vapour and temperature anomalies of two regional climates, the Iberian Peninsula and the islands of Hawaii in the central Pacific Ocean. Through the Markov chain analysis and via the derived descriptors we find significant differences between the two climate regions. Since anomalies are departures from seasonal and long term components, these differences relate to differences in the short term stability of both regional climates.

Description: A review of non-diffusive transport in fluids and plasmas is presented. In the fluid context, non-diffusive chaotic transport by Rossby waves in zonal flows is studied following a Lagrangian approach. In the plasma physics context the problem of interest is test particle transport in pressure-gradient-driven plasma turbulence. In both systems the probability density function (PDF) of particle displacements is strongly non-Gaussian and the statistical moments exhibit super-diffusive anomalous scaling. Fractional diffusion models are proposed and tested in the quantitative description of the non-diffusive Lagrangian statistics of the fluid and plasma problems. Also, fractional diffusion operators are used to construct non-local transport models exhibiting up-hill transport, multivalued flux-gradient relations, fast pulse propagation phenomena, and "tunneling" of perturbations across transport barriers.

Description: In this paper, classical surrogate data methods for testing hypotheses concerning nonlinearity in time-series data are extended using a wavelet-based scheme. This gives a method for systematically exploring the properties of a signal relative to some metric or set of metrics. A signal continuum is defined from a linear variant of the original signal (same histogram and approximately the same Fourier spectrum) to the exact replication of the original signal. Surrogate data are generated along this continuum with the wavelet transform fixing in place an increasing proportion of the properties of the original signal. Eventually, chaotic or nonlinear behaviour will be preserved in the surrogates. The technique permits various research questions to be answered and examples covered in the paper include identifying a threshold level at which signals or models for those signals may be considered similar on some metric, analysing the complexity of the Lorenz attractor, characterising the differential sensitivity of metrics to the presence of multifractality for a turbulence time-series, and determining the amplitude of variability of the Hölder exponents in a multifractional Brownian motion that is detectable by a calculation method. Thus, a wide class of analyses of relevance to geophysics can be undertaken within this framework.

Description: We present a viscoelastic constitutive relation which describes transient creep of a modified second grade fluid enhanced with elastic properties of a solid. The material law describes a Rivlin-Ericksen material and is a generalization of existing material laws applied to study the viscoelastic properties of ice. The intention is to provide a formulation tailored to reproduce the viscoelastic behaviour of ice ranging from the instantaneous elastic response, to recoverable deformation, to viscous, stationary flow at the characteristic minimum creep rate associated with the deformation of polycrystalline ice. We numerically solve the problem of a slab of material shearing down a uniformly inclined plate. The equations are made dimensionless in a form in which elastic effects and/or the influence of higher order terms (i.e., strain accelerations) can be compared with viscous creep at the minimum creep rate by means of two dimensionless parameters. We discuss the resulting material behaviour and the features exhibited at different parameter combinations. Also, a viable range of the non-dimensional parameters is estimated in the scale analysis.

Description: Spectral analyses performed on records of cosmogenic nuclides reveal a group of dominant spectral components during the Holocene period. Only a few of them are related to known solar cycles, i.e., the De Vries/Suess, Gleissberg and Hallstatt cycles. The origin of the others remains uncertain. On the other hand, time series of North Atlantic atmospheric/sea surface temperatures during the last ice age display the existence of repeated large-scale warming events, called Dansgaard-Oeschger (DO) events, spaced around multiples of 1470 years. The De Vries/Suess and Gleissberg cycles with periods close to 1470/7 (~210) and 1470/17 (~86.5) years have been proposed to explain these observations. In this work we found that a conceptual bistable model forced with the De Vries/Suess and Gleissberg cycles plus noise displays a group of dominant frequencies similar to those obtained in the Fourier spectra from paleo-climate during the Holocene. Moreover, we show that simply changing the noise amplitude in the model we obtain similar power spectra to those corresponding to GISP2 δ18O (Greenland Ice Sheet Project 2) during the last ice age. These results give a general dynamical framework which allows us to interpret the main characteristic of paleoclimate records from the last 100 000 years.

Description: We revisit a recent claim that the Earth's climate system is characterized by sensitive dependence to parameters; in particular, that the system exhibits an asymmetric, large-amplitude response to normally distributed feedback forcing. Such a response would imply irreducible uncertainty in climate change predictions and thus have notable implications for climate science and climate-related policy making. We show that equilibrium climate sensitivity in all generality does not support such an intrinsic indeterminacy; the latter appears only in essentially linear systems. The main flaw in the analysis that led to this claim is inappropriate linearization of an intrinsically nonlinear model; there is no room for physical interpretations or policy conclusions based on this mathematical error. Sensitive dependence nonetheless does exist in the climate system, as well as in climate models – albeit in a very different sense from the one claimed in the linear work under scrutiny – and we illustrate it using a classical energy balance model (EBM) with nonlinear feedbacks. EBMs exhibit two saddle-node bifurcations, more recently called "tipping points," which give rise to three distinct steady-state climates, two of which are stable. Such bistable behavior is, furthermore, supported by results from more realistic, nonequilibrium climate models. In a truly nonlinear setting, indeterminacy in the size of the response is observed only in the vicinity of tipping points. We show, in fact, that small disturbances cannot result in a large-amplitude response, unless the system is at or near such a point. We discuss briefly how the distance to the bifurcation may be related to the strength of Earth's ice-albedo feedback.

Description: We devise a procedure in order to characterize the relative vulnerability of the Earth's surface to tectonic deformation using the geometrical characteristics of drainage systems. The present study focuses on the nonlinear analysis of drainage networks extracted from Digital Elevation Models in order to localize areas strongly influenced by tectonics. We test this approach on the Potwar Plateau in northern Pakistan. This area is regularly affected by damaging earthquakes. Conventional studies cannot pinpoint the zones at risk, as the whole region is characterized by a sparse and diffuse seismicity. Our approach is based on the fact that rivers tend to linearize under tectonic forcing. Thus, the low fractal dimensions of the Swan, Indus and Jehlum Rivers are attributed to neotectonic activity. A detailed textural analysis is carried out to investigate the linearization, heterogeneity and connectivity of the drainage patterns. These textural aspects are quantified using the fractal dimension, as well as lacunarity and succolarity analysis. These three methods are complimentary in nature, i.e. objects with similar fractal dimensions can be distinguished further with lacunarity and/or succolarity analysis. We generate maps of fractal dimensions, lacunarity and succolarity values using a sliding window of 2.5 arc minutes by 2.5 arc minutes (2.5'×2.5'). These maps are then interpreted in terms of land surface vulnerability to tectonics. This approach allowed us to localize several zones where the drainage system is highly structurally controlled on the Potwar Plateau. The region located between Muree and Muzaffarabad is found to be prone to destructive events whereas the area westward from the Indus seems relatively unaffected. We conclude that a nonlinear analysis of the drainage system is an efficient additional tool to locate areas likely to be affected by massive destructing events affecting the Earth's surface and therefore threaten human activities.

Description: The predictability of the monthly North Atlantic Oscillation, NAO, index is analysed from the point of view of different fractal concepts and dynamic system theory such as lacunarity, rescaled analysis (Hurst exponent) and reconstruction theorem (embedding and correlation dimensions, Kolmogorov entropy and Lyapunov exponents). The main results point out evident signs of randomness and the necessity of stochastic models to represent time evolution of the NAO index. The results also show that the monthly NAO index behaves as a white-noise Gaussian process. The high minimum number of nonlinear equations needed to describe the physical process governing the NAO index fluctuations is evidence of its complexity. A notable predictive instability is indicated by the positive Lyapunov exponents. Besides corroborating the complex time behaviour of the NAO index, present results suggest that random Cantor sets would be an interesting tool to model lacunarity and time evolution of the NAO index.

Description: The present behaviour of the geomagnetic field as expressed by the International Geomagnetic Reference Field (IGRF) deserves special attention when compared with that shown over the past few thousands of years by two paleomagnetic/archeomagnetic models, CALS3K and CALS7K. The application of the Information theory in terms of Shannon Information and K-entropy to these models shows characteristics of an instable geomagnetic field. Although the result is mitigated when we correct the CALS7K model for its typical spectral damping, the present geomagnetic field as represented by IGRF is still rather distinct, at least for the past 4000 years, a result that is further confirmed by the CALS3K model. This is consistent with a significant global critical state started at around 1750, and still present, characterised by significant decays of the geomagnetic dipole, energy and Shannon information and high K-entropy. The details of how these characteristics may develop are not clear, since the present state could move toward an excursion or a geomagnetic polarity reversal, but we cannot exclude the possibility that the "critical" behaviour will become again more "normal", stopping the apparent trend of the recent geomagnetic field decay.

Description: The Very Local Interstellar Medium (VLISM) contains clouds which consist of partially-ionized plasma. These clouds can be effectively diagnosed via high resolution optical and ultraviolet spectroscopy of the absorption lines they form in the spectra of nearby stars. Information provided by these spectroscopic measurements includes values for ξ, the root-mean-square velocity fluctuation due to turbulence in these clouds, and T, the ion temperature, which may be partially determined by dissipation of turbulence. We consider whether this turbulence resembles the extensively studied and well-diagnosed turbulence in the solar wind and solar corona. Published observations are used to determine if the velocity fluctuations are primarily transverse to a large-scale magnetic field, whether the temperature perpendicular to the large scale field is larger than that parallel to the field, and whether ions with larger Larmor radii have higher temperatures than smaller gyroradius ions. We ask if the spectroscopically-deduced parameters such as ξ and T depend on the direction on the sky. We also consider the degree to which a single temperature T and turbulence parameter ξ account for the spectral line widths of ions with a wide range of masses. A preliminary examination of the published data shows no evidence for anisotropy of the velocity fluctuations or temperature, nor Larmor radius-dependent heating. These results indicate differences between solar wind and Local Cloud turbulence. Possible physical reasons for these differences are discussed.

Description: We investigate the competition between two different functional groups of phytoplankton in the wake of an island close to a coastal upwelling region. We couple a simple biological model with three trophic levels and a hydrodynamic model of a von Kármán vortex street. The spatio-temporal abundance shows that the different phytoplankton groups dominate in different regions of the flow. The composition of the phytoplankton community varies e.g. for the different vortices. We study the mechanism leading to these inhomogeneous dominance patterns by investigating the nutrient transport in the flow and the interplay of hydrodynamic and biological time scales.

Description: A study of alpha particle acceleration at parallel shock due to an interaction with Alfvén waves self-consistently excited in both upstream and downstream regions was conducted using a scale-separation model (Galinsky and Shevchenko, 2000, 2007). The model uses conservation laws and resonance conditions to find where waves will be generated or damped and hence where particles will be pitch-angle scattered. It considers the total distribution function (for the bulk plasma and high energy tail), so no standard assumptions (e.g. seed populations, or some ad-hoc escape rate of accelerated particles) are required. The heavy ion scattering on hydromagnetic turbulence generated by both protons and ions themselves is considered. The contribution of alpha particles to turbulence generation is important because of their relatively large mass-loading parameter Pα=nαmα/npmp (mp, np and mα, nα are proton and alpha particle mass and density) that defines efficiency of wave excitation. The energy spectra of alpha particles are found and compared with those obtained in test particle approximation.

Description: Resonant interactions between relativistic charged particles and oblique whistler mode waves are explored in this work, and it is shown that nonlinear phase trapping could happen in a gyrophase averaged sense, consistent with previous studies of interactions between nonrelativistic electrons and oblique whistler mode waves. A dimensionless parameter χ is derived to represent the ratio of wave-induced motion to the adiabatic motion of the particle. We show that phase trapping is likely to occur when the wave-induced motion dominates the adiabatic motion, which is caused mainly by the background fields. A mapping of probable regions of nonlinear interactions is shown based on the parameter χ. We show that the nonlinear interactions might be important near the equatorial plane for even moderate wave amplitude, and the latitudinal range for nonlinear interactions to occur is largest for electrons with local pitch angles around 50 degrees, consistent with previous findings. The results are important for understanding the nonlinear dynamics of relativistic radiation belt electrons and the generation of chorus waves.

Description: Two types of second baroclinic mode (mode-2) internal solitary waves (ISWs) were found on the continental slope of the northern South China Sea. The convex waveform displaced the thermal structure upward in the upper layer and downward in the lower layer, causing a bulge in the thermocline. The concave waveform did the opposite, causing a constriction. A few concave waves were observed in the South China Sea, marking the first documentation of such waves. On the basis of the Korteweg-de Vries (K-dV) equation, an analytical three-layer ocean model was used to study the characteristics of the two mode-2 ISW types. The analytical solution was primarily a function of the thickness of each layer and the density difference between the layers. Middle-layer thickness plays a key role in the resulting mode-2 ISW. A convex wave was generated when the middle-layer thickness was relatively thinner than the upper and lower layers, whereas only a concave wave could be produced when the middle-layer thickness was greater than half the water depth. In accordance with the K-dV equation, a positive and negative quadratic nonlinearity coefficient, α2, which is primarily dominated by the middle-layer thickness, resulted in convex and concave waves, respectively. The analytical solution showed that the wave propagation of a convex (concave) wave has the same direction as the current velocity in the middle (upper or lower) layer. Analysis of the three-layer ocean model properly reproduced the characteristics of the observed mode-2 ISWs in the South China Sea and provided a criterion for the existence of convex or concave waves. Concave waves were seldom seen because of the rarity of a stratified ocean with a thick middle layer. This analytical result agreed well with the observations.

Description: Intermittent fluctuations are the consequence of the dynamic interactions of multiple coherent or pseudo-coherent structures of varied sizes in the stochastic media (Chang, 1999). We briefly review here a recently developed technique, the Rank-Ordered Multifractal Analysis (ROMA), which is both physically explicable and quantitatively accurate in deciphering the multifractal characteristics of such intermittent structures (Chang and Wu, 2008). The utility of the method is demonstrated using results obtained from large-scale 2-D MHD simulations as well as in-situ observations of magnetic field fluctuations from the interplanetary and magnetospheric cusp regions, and the broadband electric field oscillations from the auroral zone.

Description: Techniques such as tomographic reconstruction may be used to provide images of electron content in the ionosphere. Models are also available which attempt to describe the dominant physical processes operating in the ionosphere, or the statistical relationships between ionospheric variables. It is sensible to try and couple model output to tomographic images with the aim of inferring the values of driver variables which best replicate some description of electron content imaged in the ionosphere, according to some criterion. This is a challenging task. The following describes an attempt to couple an ionospheric model to a tomographic reconstruction of the geomagnetic storm of 20 November 2003, along a latitudal line segment above north America. A simple model was chosen to reduce the number of input drivers that were varied. The investigation illustrates some of the issues involved in image-model coupling. The ability to make scientific deductions depends on the accuracy of the assumptions in the ionospheric model and the accuracy of the tomographic reconstruction. An ensemble technique was used to help assess confidence in the reconstruction.

Description: In this work we discuss applications of Lagrangian techniques to study transport properties of flows generated by shallow water models of estuarine flows. We focus on the flow in the Chesapeake Bay generated by Quoddy (see Lynch and Werner, 1991), a finite-element (shallow water) model adopted to the bay by Gross et al. (2001). The main goal of this analysis is to outline the potential benefits of using Lagrangian tools for both understanding transport properties of such flows, and for validating the model output and identifying model deficiencies. We argue that the currently available 2-D Lagrangian tools, including the stable and unstable manifolds of hyperbolic trajectories and techniques exploiting 2-D finite-time Lyapunov exponent fields, are of limited use in the case of partially mixed estuarine flows. A further development and efficient implementation of three-dimensional Lagrangian techniques, as well as improvements in the shallow-water modelling of 3-D velocity fields, are required for reliable transport analysis in such flows. Some aspects of the 3-D trajectory structure in the Chesapeake Bay, based on the Quoddy output, are also discussed.

Description: In this article we explore the utility of dynamical systems tools for visualizing transport in oceanic flows described by data sets measured from satellites. In particular we have found the geometrical skeleton of some transport processes in the Kuroshio region. To this end we have computed the special hyperbolic trajectories, and identified them as distinguished hyperbolic trajectories, that act as organizing centres of the flow. We have computed their stable and unstable manifolds, and they reveal that the turnstile mechanism is at work during several spring months in the year 2003 across the Kuroshio current. We have found that near the hyperbolic trajectories takes place a filamentous transport front-cross the current that mixes waters from both sides.

Description: Horizontal mixing has been found to play a crucial role in the development of spatial plankton structures in the ocean. We study the influence of time and length scales of two different horizontal two-dimensional (2-D) flows on the growth of a single phytoplankton patch. To that end, we use a coupled model consisting of a standard three component ecological NPZ model and a flow model able to mimic the mesoscale structures observed in the ocean. Two hydrodynamic flow models are used: a flow based on Gaussian correlated noise, for which the Eulerian length and time scales can be easily controlled, and a multiscale velocity field derived from altimetry data in the North Atlantic ocean. We find the optimal time and length scales for the Gaussian flow model favouring the plankton spread. These results are used for an analysis of a more realistic altimetry flow. We discuss the findings in terms of the time scale of the NPZ model, the qualitative interaction of the flow with the reaction front and a Finite-Time Lyapunov Exponent analysis.

Description: The backpropagation (BP) artificial neural network (ANN) technique of optimization based on steepest descent algorithm is known to be inept for its poor performance and does not ensure global convergence. Nonlinear and complex DC resistivity data require efficient ANN model and more intensive optimization procedures for better results and interpretations. Improvements in the computational ANN modeling process are described with the goals of enhancing the optimization process and reducing ANN model complexity. Well-established optimization methods, such as Radial basis algorithm (RBA) and Levenberg-Marquardt algorithms (LMA) have frequently been used to deal with complexity and nonlinearity in such complex geophysical records. We examined here the efficiency of trained LMA and RB networks by using 2-D synthetic resistivity data and then finally applied to the actual field vertical electrical resistivity sounding (VES) data collected from the Puga Valley, Jammu and Kashmir, India. The resulting ANN reconstruction resistivity results are compared with the result of existing inversion approaches, which are in good agreement. The depths and resistivity structures obtained by the ANN methods also correlate well with the known drilling results and geologic boundaries. The application of the above ANN algorithms proves to be robust and could be used for fast estimation of resistive structures for other complex earth model also.

Description: Entrainment at the top of the convectively-driven boundary layer (CBL) is revisited using data from a high-resolution large-eddy simulation (LES). In the range of values of the bulk Richardson number RiB studied here (about 15–25), the entrainment process is mainly driven by the scouring of the interfacial layer (IL) by convective cells. We estimate the length and time scales associated with these convective cells by computing one-dimensional wavenumber and frequency kinetic energy spectra. Using a Taylor assumption, based upon transport by the convective cells, we show that the frequency and wavenumber spectra follow the Kolmogorov law in the inertial range, with the multiplicative constant being in good agreement with previous measurements in the atmosphere. We next focus on the heat flux at the top of the CBL, , which is parameterized in classical closure models for the entrainment rate we at the interface. We show that can be computed exactly using the method proposed by Winters et al. (1995), from which the values of a turbulent diffusivity across the IL can be inferred. These values are recovered by tracking particles within the IL using a Lagrangian stochastic model coupled with the LES. The relative difference between the Eulerian and Lagrangian values of is found to be lower than 10%. A simple expression of we as a function of is also proposed. Our results are finally used to assess the validity of the classical "first-order'' model for we. We find that, when RiB is varied, the values for we derived from the "first-order'' model with the exact computation of agree to better than 10% with those computed directly from the LES (using its definition). The simple expression we propose appears to provide a reliable estimate of we for the largest values of RiB only.

Description: It is known that some quiescence precedes the strong events in the Bak–Tang–Wiesenfeld sand-pile (Pepke and Carlson, 1994) We introduce dissipation depending on the propagation of the events into this model such that in the constructed model the growth of activity occurs before the strong events. This fact allows the prediction of them in advance with a certain efficiency. This efficiency is variable in time. The best predictability is observed during subcritical time ranges, while the efficiency is definitely worse in the supercritical state.

Description: We consider issues associated with the Lagrangian characterisation of flow structures arising in aperiodically time-dependent vector fields that are only known on a finite time interval. A major motivation for the consideration of this problem arises from the desire to study transport and mixing problems in geophysical flows where the flow is obtained from a numerical solution, on a finite space-time grid, of an appropriate partial differential equation model for the velocity field. Of particular interest is the characterisation, location, and evolution of transport barriers in the flow, i.e. material curves and surfaces. We argue that a general theory of Lagrangian transport has to account for the effects of transient flow phenomena which are not captured by the infinite-time notions of hyperbolicity even for flows defined for all time. Notions of finite-time hyperbolic trajectories, their finite time stable and unstable manifolds, as well as finite-time Lyapunov exponent (FTLE) fields and associated Lagrangian coherent structures have been the main tools for characterising transport barriers in the time-aperiodic situation. In this paper we consider a variety of examples, some with explicit solutions, that illustrate in a concrete manner the issues and phenomena that arise in the setting of finite-time dynamical systems. Of particular significance for geophysical applications is the notion of flow transition which occurs when finite-time hyperbolicity is lost or gained. The phenomena discovered and analysed in our examples point the way to a variety of directions for rigorous mathematical research in this rapidly developing and important area of dynamical systems theory.

Description: Many volcanic eruptions exhibit periodic behavior. For instance, periodic ground inflations and deflations in proximity to a volcano are the consequences of periodic overpressure variations in the magma conduit and periodic magma flow rate. The period varies from a few hours to many years, depending on the volcano parameters. On the other hand, volatile components exsolve from an ascending magma by forming bubbles. The strong dependence of the melt viscosity with the volatile concentration generates a positive feedback on the magma flow. We consider here the effect of the growth of volatile bubbles on the dynamics of a magmatic flow in a shallow volcanic system. Various expressions for the bubble growth rate are treated, thus generalizing previous work. In particular, a growth rate law derived from a recent many-bubble theory is considered. It is seen that, for a range of flow rate values at the base of the magma conduit, the system undergoes a Hopf bifurcation. Periodic solutions compatible with the observations are generated. This work shows that measurements of volcanic activity have the potential to test various bubble growth models in magmatic systems.

Description: The aim of this paper is to find a convenient and effective method of displaying some second order properties in a neighbourhood of a selected point of the process. The used techniques are based on very general high-dimensional nonparametric smoothing developed to define a more general version of the conditional intensity function introduced in earlier earthquake studies by Vere-Jones (1978).

Description: The approach of conditional nonlinear optimal perturbation (CNOP) was previously proposed to find the optimal initial perturbation (CNOP-I) in a given constraint. In this paper, we extend the CNOP approach to search for the optimal combined mode of initial perturbations and model parameter perturbations. This optimal combined mode, also named CNOP, has two special cases: one is CNOP-I that only links with initial perturbations and has the largest nonlinear evolution at a prediction time; while the other is merely related to the parameter perturbations and is called CNOP-P, which causes the largest departure from a given reference state at a prediction time. The CNOP approach allows us to explore not only the first kind of predictability related to initial errors, but also the second kind of predictability associated with model parameter errors, moreover, the predictability problems of the coexistence of initial errors and parameter errors. With the CNOP approach, we study the ENSO predictability by a theoretical ENSO model. The results demonstrate that the prediction errors caused by the CNOP errors are only slightly larger than those yielded by the CNOP-I errors and then the model parameter errors may play a minor role in producing significant uncertainties for ENSO predictions. Thus, it is clear that the CNOP errors and their resultant prediction errors illustrate the combined effect on predictability of initial errors and model parameter errors and can be used to explore the relative importance of initial errors and parameter errors in yielding considerable prediction errors, which helps identify the dominant source of the errors that cause prediction uncertainties. It is finally expected that more realistic models will be adopted to investigate this use of CNOP.

Description: Previous research regarding the solutions of Long's equation always presumed that the flow far upstream is without shear. In this paper we derive the proper form of this equation when shear is present. We then apply a sequence of transformations to this equation which make it possible to linearize it while preserving its physical contents. We then derive conditions under which the solutions of this linear equation admit the existence (or creation) of gravity waves. We present also a solution of this model equation when the presence of shear in the overall flow is "small".

Description: Lower-hybrid (LH) oscillitons reveal one aspect of geocomplexities. They have been observed by rockets and satellites in various regions in geospace. They are extraordinary solitary waves the envelop of which has a relatively longer period, while the amplitude is modulated violently by embedded oscillations of much shorter periods. We employ a two-fluid (electron-ion) slab model in a Cartesian geometry to expose the excitation of LH oscillitons. Relying on a set of self-similar equations, we first produce, as a reference, the well-known three shapes (sinusoidal, sawtooth, and spiky or bipolar) of parallel-propagating ion-acoustic (IA) solitary structures in the absence of electron inertia, along with their Fast Fourier Transform (FFT) power spectra. The study is then expanded to illustrate distorted structures of the IA modes by taking into account all the three components of variables. In this case, the ion-cyclotron (IC) mode comes into play. Furthermore, the electron inertia is incorporated in the equations. It is found that the inertia modulates the coupled IA/IC envelops to produce LH oscillitons. The newly excited structures are characterized by a normal low-frequency IC solitary envelop embedded by high-frequency, small-amplitude LH oscillations which are superimposed upon by higher-frequency but smaller-amplitude IA ingredients. The oscillitons are shown to be sensitive to several input parameters (e.g., the Mach number, the electron-ion mass/temperature ratios, and the electron thermal speed). Interestingly, whenever a LH oscilliton is triggered, there occurs a density cavity the depth of which can reach up to 20% of the background density, along with density humps on both sides of the cavity. Unexpectedly, a mode at much lower frequencies is also found beyond the IC band. Future studies are finally highlighted. The appendices give a general dispersion relation and specific ones of linear modes relevant to all the nonlinear modes encountered in the text.

Description: In this paper, the author first reviews the different terminologies used in underactuated grasping and illustrates the current increase of activity on this topic. Then, the (probably) oldest known self-adaptive mechanism is presented and its performance as an underactuated finger is discussed. Its original application, namely a flapping wing, is also shown. Finally, it is proposed that the mechanisms currently used in underactuated grasping have actually other applications similarly to the previously discussed architecture could be used for both an underactuated finger and a flapping wing. This paper was presented at the IFToMM/ASME International Workshop on Underactuated Grasping (UG2010), 19 August 2010, Montréal, Canada.

Description: There is a lack of agreement in the literature as to what exactly quantifies the performance of underactuated hands. This paper proposes two benchmark tests to measure the ability of underactuated hands to grasp different objects and the ability to hold the objects when force disturbances apply. The first test determines the smallest and largest cylindrical object which can be successfully grasped in an enveloping grasp or in a pinch grasp. The second test provides the maximal allowable force which can be applied to a grasped object without loosing it. A setup was constructed consisting of standard components. Exemplary tests were applied to the Delft Hand 2. The proposed benchmark tests are representative to quantify the performance of pick and place operations with underactuated hands. The results of the tests can be applied to evaluate, compare, and improve the performance of robotic hands. This paper was presented at the IFToMM/ASME International Workshop on Underactuated Grasping (UG2010), 19 August 2010, Montréal, Canada.

Description: The concept called gesture-changeable under-actuated (GCUA) function is utilized to improve the dexterities of traditional under-actuated hands and reduce the control difficulties of dexterous hands. Based on GCUA function, a novel mechanical finger by multiple tendons: GCUA-T finger, is designed. The finger uses tendon mechanisms to achieve GCUA function which includes traditional underactuated (UA) grasping motion and special pre-bending (PB, or pre-shaping) motion before UA grasping. Operation principles and force analyses of the fingers are given, and the effect of GCUA function on the movements of a hand is discussed. The finger can satisfy the requirements of grasping and operating with low dependence on control system and low cost on manufacturing expenses, which develops a new way between dexterous hand and traditional under-actuated hand. This paper was presented at the IFToMM/ASME International Workshop on Underactuated Grasping (UG2010), 19 August 2010, Montréal, Canada.

Description: Anhand von zwei Dünenprofilen wird die Art, Dauer und Intensität von spätglazialen und holozänen Flugsand- und Bodenbildungen innerhalb des Pommerschen Sandergebietes dargestellt. Hierfür wurde ein interdisziplinärer Ansatz aus Sedimentologie, Pedologie, Palynologie und Geochronologie verwendet. Während des Spätglazials kommen auf den Sanderhochflächen flache Flugsanddecken zur Ablagerung, unterbrochen durch die Bildung des Finowbodens. Durch die Ausbreitung einer geschlossenen Vegetationsdecke im Frühholozän, erfolgt eine Stabilisierung der Reliefoberfläche mit anschließender Bodenbildung. Nach intensiven mittelalterlichen Rodungen werden die Oberflächen erneut destabilisiert. Es kommt zur partiellen Aufarbeitung der Flugsande resultierend in Dünenbildungen und einem kuppigen Relief. Eine der untersuchten Dünen wurde dabei komplett im späten Subatlantikum gebildet. Diese Studie unterstreicht die zeitlich-räumliche Variabilität äolischer Aktivität, wobei Umlagerungen entsprechender Korngrößen während verschiedener Phasen nach der Deglaziation ermöglicht wurden.

Description: Dieser Beitrag präsentiert die ersten Ergebnisse zur Untersuchung von Herstellungsprozessen (Rohstoffauswahl, Aufarbeitung und Herkunft sowie Maltechniken) von Keramik der Lengyelkultur aus der Siedlung von Michelstetten, die im Zentralweinviertel des norddanubischen Niederösterreich liegt und nach der Radiokarbon-Methode zwischen 4600 und 4360 a cal. BC datiert wurde. Unter Anwendung verschiedener archäometrischer Verfahren konnte die mineralogische Zusammensetzung von Lengyelkeramik und ihre Malpigmente sowie von Ton- und Lehmmaterialien, die als Rohstoffproben gedient haben, bestimmt werden. Neben einer genauen Charakterisierung der Herstellungssubstanzen prähistorischer Keramik von Michelstetten wurden unterschiedliche Erzeugungsvorgänge, wie Rohstoffauswahl, Art und Qualität der Materialaufarbeitung, Brennverfahren und Maltechniken behandelt, genauso wie Herkunftsfragen diskutiert.

Description: In einem Aufschluss von Löss-Paläoboden-Sequenzen über Rehberger Amphibolit NW von Langenlois wurden sechs Bodenprofile (Lois 1 bis Lois 6) beprobt und pedologisch, mineralogisch und geochemisch analysiert. Am Profil Lois 7 wurden bodenmikromorphologische Untersuchungen durchgeführt. Zwei Bodenprofile (Lois 1 und 2) haben sich über Amphibolit entwickelt, zwei über einer Amphibolit/Marmor-Wechsellagerung (Lois 5 und 6) und drei Bodenprofile sind Sequenzen von polyzyklischen Paläoböden mit fossilen Bodenhorizonten ohne unterlagerndes kristallines Gestein (Lois 3, 4 und 7). In den Profilen Lois 1–4 und Lois 7 konnten intensive Karbonatanreicherungen beobachtet werden. Diese hohen Mengen an Karbonat können nicht Produkt einer rezenten Bodenbildung sein, sondern sprechen für eine Infiltration von ursprünglich das Profil überlagernden kalzitreichen Sedimenten (Löss), die erodiert wurden. Zudem wurde in Profil Lois 2 ein Kalksinter angetroffen. Dieser Kalksinter könnte aus der Verwitterung der im Profil Lois 6 aufgeschlossenen Marmorlagen stammen. Die Kalksinter-Schicht scheint die Stoffflüsse zwischen unterliegendem Gestein und Solum in den Profilen Lois 1 und 2 mehr oder weniger zu unterbinden, was auch durch die Ergebnisse der geochemischen Analytik unterstrichen wird. In den fossilen Horizonten wurden auch ältere Anzeichen von Tonverlagerung in Form von Tonkutanen über den Aggregaten und darüber hinaus leichte Pseudovergleyungserscheinungen angetroffen. Die mächtigen Profile ohne aufgeschlossenes Grundgebirge (Lois 3, 4 und 7) weisen mehrere polyzyklische Sedimentationsphasen und dadurch mehrere Generationen von fossilen Horizonten auf. Aufgrund der bodenmikromorphologischen Analyse können die Böden vom „Roten Aufschluss“ altersmäßig im unteren bis mittleren Pleistozän oder älter angesiedelt werden.

Description: Die an der südwestlichen Ostseeküste gelegene Halbinsel Bug/NW Rügen wurde untersucht, um die Entwicklung von Haken und Nehrungen unter dem Einfluss des holozänen Meeresspiegelanstiegs zu studieren. Als Datengrundlage dienten 25 Sedimentkerne, sowie sieben Georadar- und sechs Sedimentecholotprofile, aus denen sechs Lithofaziestypen abgeleitet wurden. Danach besteht die Nehrung aus einer durchschnittlich 10 m mächtigen holozänen Sedimentfolge, die auf pleistozäner Basis aus Geschiebemergel und (glazi-)fluviolimnischen Feinsanden lagert. Obwohl keine absoluten Altersdaten gewonnen wurden, kann die Sedimentabfolge mit der lokalen relativen Meeresspiegelkurve problemlos korreliert und eine Modellvorstellung für die Nehrungsentwicklung geschlussfolgert werden. Die marine Inundation des Untersuchungsgebietes erfolgte um 7.000 BC während der Littorina-Transgression. In diesem Stadium stieg der Meeresspiegel rapide an und generierte einen schnell wachsenden Akkumulationsraum, in dem feinklastisches Material an oder unter der Wellenbasis akkumulierte und zu einem Reliefausgleich beitrug. Akkumulative Küstenformen bildeten sich nur in geringem Maße, da der Akkumulationsraum schneller wuchs als er durch das aus der Küstenerosion stammende Material aufgefüllt werden konnte. In dem Maße, indem der Meeresspiegelanstieg sich verlangsamte, gewann die Akkumulation an Bedeutung und der Hauptteil der Nehrung wurde innerhalb von rund zweitausend Jahren landfest. Entsprechend dem Verlauf von Strandwällen auf seiner heutigen Oberfläche lassen sich zwei Entwicklungsphasen aushalten, die von unterschiedlichen wellenenergetischen, erosiven und overwash-Prozessen bestimmt werden. Gegenwärtig besitzt die Nehrung ein Volumen von 66,4 Mio m³, woraus sich auf einen Rückgang des benachbarten Kliffs von rund 2000 m schließen lässt. Obwohl die Nehrung entwicklungsmäßig in ihrem Reifestadium angelangt zu sein scheint, deuten einige Merkmale auf zunehmende Instabilität hin. Im nördlichen Bereich verhindern Küstenschutzmaßnahmen einen Nehrungsdurchbruch und beginnende Auflösung. Im Süden haben Fahrwasserbaggerungen eine weitere Längenzunahme und das Zusammenwachsen mit Haken von Hiddensee verhindert. Ohne diese Maßnahmen würde die Nehrung durch Seegattbildung und zunehmende Erosion im Norden und Seegattschließung und zunehmende Uferprogradation im Süden eine neue Gestalt annehmen.

Description: Seit einigen Jahren gibt es zunehmend Studien, die, basierend auf der Untersuchung von fossilen Holzkohlen und Schneckenschalen aus Löss-Paläoboden Sequenzen, die traditionelle Vorstellung von weitestgehend baumlosen Steppen im Karpaten-Becken während der letzten Kaltzeit in Frage stellen. Mit unseren Arbeiten versuchen wir anhand von Biomarkern einen Beitrag zu dieser Diskussion zu leisten und herauszufinden, welches Potenzial in der Untersuchung von Alkan Biomarkern für die Rekonstruktion der Vegetationsgeschichte während der letzten glazialen Zyklen steckt. Kürzlich veröffentlichte erste Ergebnisse weisen darauf hin, dass der Degradationsgrad der pflanzenbürtigen organischen Substanz einen starken Einfluss auf das Alkanmuster in Böden hat und dass der in der Literatur häufig verwendete Alkanquotient nC31/nC27 kein reiner Vegetations-Proxy ist, sondern auch maßgeblich die unterschiedliche Degradation widerspiegelt. In der vorliegenden Arbeit führen wir daher erstmals einen End Member Modellierungsansatz ein, bei dem der Degradationsgrad der organischen Bodensubstanz mit berücksichtig wird. Das Modell wird auf die Loess-Paläoboden Sequenz Crvenka auf dem Bačka Loess Plateau (Serbien) zwischen Donau und Theiss angewendet. Die so für den letzten Interglazial-Glazial-Zyklus rekonstruierte Vegetationsgeschichte bestätigt die Holzkohle- und Mollusken-Befunde und deutet auf Gras-Steppen während des letzten Interglazials und -stadials hin (Marine Isotopenstadien (MIS) 5 bzw. 3). Die Ergebnisse machen deutlich, dass Steppen während des gesamten letzten glazialen Zyklus vorgeherrscht haben. Für das letzte Interglazial und das Interstadial der Marinen Isotopen Stufe (MIS) 3 deuten die Biomarker Befunde auf reine Grassteppen hin. Dagegen prägten in den Glazialen vermutlich auch vereinzelte Bäume das Landschaftsbild einer ‚Taiga-Steppe’. Die so rekonstruierte Vegetationsgeschichte steht im Einklang mit den Holzkohle- und Schneckenfunden, wie auch mit Ergebnissen von Klima- und Biom-Modellierungen.

Description: The Model for Ozone and Related chemical Tracers-2 (MOZART-2) is used to examine the evolution of pollutant O3 in the upper troposphere over the Indian region. Vertical profiles of ozone mixing ratio retrieved from Microwave Limb Sounder (MLS) aboard Earth Observing System (EOS) AURA satellite for the period 2005–2009 and Tropospheric Emission Spectrometer (TES) aboard (EOS) AURA for the period 2006–2007 has been analyzed. The satellite observations reveal the evidence of downward propagation of ozone (100–200 ppb) due to stratospheric intrusion during the winter and pre-monsoon seasons. The regular feature of enhancement of ozone in the upper troposphere over India is presented. Results obtained by the MOZART-2 simulations (for years 2000–2005) confirm the observations and indicate stratospheric intrusion of O3 during winter and pre-monsoon seasons. Observed enhanced O3 mixing ratio in the upper troposphere is explained by, variation of Potential Vorticity (PV), tropopause pressure, relative humidity and CO-O3 correlation.

Description: We present a reconstruction technique to solve the steady resistive MHD equations in two dimensions with initial inputs of field and plasma data from a single spacecraft as it passes through a coherent structure in space. At least two components of directly measured electric fields (the spacecraft spin-plane components) are required for the reconstruction, to produce two-dimensional (2-D) field and plasma maps of the cross section of the structure. For convenience, the resistivity tensor η is assumed diagonal in the reconstruction coordinates, which allows its values to be estimated from Ohm's law, E+v×B=η·j. In the present paper, all three components of the electric field are used. We benchmark our numerical code by use of an exact, axi-symmetric solution of the resistive MHD equations and then apply it to synthetic data from a 3-D, resistive, MHD numerical simulation of reconnection in the geomagnetic tail, in a phase of the event where time dependence and deviations from 2-D are both weak. The resistivity used in the simulation is time-independent and localized around the reconnection site in an ellipsoidal region. For the magnetic field, plasma density, and pressure, we find very good agreement between the reconstruction results and the simulation, but the electric field and plasma velocity are not predicted with the same high accuracy.

Description: We describe the methodology used to set up and compute spatial derivatives of the electron moments using data acquired by the Plasma Electron And Current Experiment (PEACE) from the four Cluster spacecraft. The results are used to investigate electron vorticity in the foreshock. We find that much of the measured vorticity, under nominal conditions, appears to be caused by changes in the flow direction of the return (either reflected or leakage from the magnetosheath) and strahl electron populations as they couple to changes in the magnetic field orientation. This in turn results in deflections in the total bulk velocity producing the measured vorticity.

Description: From magnetic field observations by CHAMP we estimate F-region dynamo current densities near the sunset terminator during solar maximum years from 2001 to 2002. The dynamo currents are compared with the pre-reversal enhancement (PRE) of vertical plasma drift as observed by ROCSAT-1. The seasonal-longitudinal variation of PRE can be largely related to the F-region dynamo current density, with the correlation coefficient reaching 0.74. The correlation can be further improved if we consider a zonal gradient of the E-region Pedersen conductivity, which also depends on season and longitude. It is widely accepted that the F-region dynamo drives PRE near sunset. For the first time, our observations provide confirmation for the close relationship between the F-region dynamo current density and PRE.

Description: According to current understanding, adiabatic cooling and heating induced by the meridional circulation driven by gravity waves is the major process for the cold summer and warm winter polar upper mesosphere. However, our calculations show that the upward/downward motion needed for adiabatic cooling/heating of the summer/winter polar mesopause simultaneously induces a seasonal variation in both the O maximum density and the altitude of the [O] peak that is opposite to the observed variables generalized by the MSISE-90 model. It is usually accepted that eddy turbulence can produce the [O] seasonal variations. Using this approach, we can infer the eddy diffusion coefficient for the different seasons. Taking these results and experimental data on the eddy diffusion coefficient, we consider in detail and estimate the heating and cooling caused by eddy turbulence in the summer and winter polar upper mesosphere. The seasonal variations of these processes are similar to the seasonal variations of the temperature and mesopause. These results lead to the conclusion that heating/cooling by eddy turbulence is an important component in the energy budget and that adiabatic cooling/heating induced by upward/downward motion cannot dominate in the mesopause region. Our study shows that the impact of the dynamic process, induced by gravity waves, on [O] distributions must be included in models of thermal balance in the upper mesosphere and lower thermosphere (MLT) for a consistent description because (a) the [O] distribution is very sensitive to dynamic processes, and (b) atomic oxygen plays a very important role in chemical heating and infrared cooling in the MLT. To our knowledge, this is the first attempt to consider this aspect of the problem.

Description: The ionospheric and magnetospheric current systems are responsible of the daily magnetic field changes. Recently, the Natural Orthogonal Components (NOC) technique has been applied to model the physical system responsible of the daily variation of the geomagnetic field, efficiently and accurately (Xu and Kamide, 2004). Indeed, this approach guarantees that the number of parameters used to represent the physical process is small as much as possible, and consequently process control for such system becomes apparent. We focus our present study on the analysis of the hourly means of the magnetic elements H, D and Z recorded at L'Aquila observatory in Italy from 1993 to 2004. We apply to this dataset the NOC technique to reconstruct the 3-dimensional structures of the different ionospheric and magnetospheric current systems which contribute to the geomagnetic daily variations. To support our interpretation in terms of the different ionospheric and magnetospheric current systems, the spectral and statistical features of the time-dependent amplitudes associated to the set of natural orthogonal components are analyzed and compared to those of a set of descriptors of the magnetospheric dynamics and solar wind changes.

Description: High-resolution radiosondes and calibrated radars operating close to 50 MHz, are used to examine the relationship between the strength of radar scatter and refractive index gradient. Three radars are used, in Kiruna in Arctic Sweden, at Gadanki in southern India and at the Swedish/Finnish base Wasa/Aboa in Queen Maud Land, Antarctica. Calibration is accomplished using the daily variation of galactic noise measured at each site. Proportionality between radar scatter strength and the square of the mean gradient of potential refractive index, M2, is found in the upper troposphere and lower stratosphere at all three sites, confirming previously reported results from many VHF radars. If the radar scatter is interpreted as Fresnel scatter, the constant of proportionality between radar scatter and M2 is found to be the same, within the calibration uncertainties, for all three radars. The radiosondes show evidence of distinct layering with sharp gradients, extending over 10s of kilometers horizontally, but the scatter is found to be two orders of magnitude weaker than would be expected from true Fresnel scatter from such layers. Using radar reflectivities resolved to a few 100 ms, we show that this is due to strong temporal variability in the scattering conditions, possibly due to undulations of the scattering layers. The constancy of the radar scatter – M2 relationship between the different sites suggests an unexpected uniformity in these perturbations between very different regions of the globe.

Description: The paper deals with wind measurements, recorded since the 1950s, at twelve meteorological stations along a transect near the westernmost European border, between 64° and 44° N. Extreme wind speed tends to decrease sharply near the northern boundary (at Reykjavick), near the middle of the study area (at Shannon and Valentia) and near the southern boundary (at Brest and Cap Ferret), to increase at Thorshavn, with less significant trends at the other stations. Average wind speeds confirm the above tendencies, with an additional increasing speed at Lerwick, Kirkwall, Malin Head, Belle-Ile and Cap Ferret. To compare changes in wind activity, the data have been subdivided into three periods: until 1975, 1976–1992 and 1993–2008. Frequencies have been computed also for the "winter" (October to March) period, per quadrants, and for occurrences exceeding the speed of 15 m s−1. At Reykjavick a recent increase in the frequency of strong winds has occurred from various directions. Between 62° N (Thorshavn) and 59° N (Kirkwall) strong wind has been increasing since 1975. Minor changes can be observed at Stornoway, whereas at Malin Head the greatest increase for southerlies and westerlies is observed during the 1976–1992 period. At Belmullet, the frequency of strong southerlies has almost doubled since 1992, while at Shannon and Valentia it remains quite low. Finally at Brest and Belle-Ile, westerlies are predominant among winds 〉15 m s−1. Important changes in time and latitude appear in the correlation with the NAO (North Atlantic Oscillation) index. The highest correlation coefficients, calculated with monthly or seasonal means between the early 1950s and 1975, are observed from between 58° N (Stornoway) and Iceland, whereas low positive coefficients are reported more south. During the period 1976–1992, when increasing NAO index is predominant, positive correlation improves southwards as far as 54° (Belmullet) with some improvement also at Shannon and Valentia, while it remains low or even negative near the French Atlantic coast. Finally in the 1993–2008 period, correlation improves for all the stations south of 54° N (Belmullet), while it weakens more north.

Description: The Polar Cap (PC) index is a controversial topic within the IAGA scientific community. Since 1997 discussions of the validity of the index to be endorsed as an official IAGA index have ensued. There is no doubt as to the scientific merit of the index which is not discussed here. What is in doubt is the methodology of the derivation of the index by different groups. The Polar Cap index (PC: PCN, northern; PCS, southern) described in Troshichev et al. (2006) and Stauning et al. (2006), both termed the "unified PC index", and the PCN index routinely derived at DMI are inspected using only available published literature. They are found to contain different derivation procedures, thus are not unified. The descriptions of the derivation procedures are found to not be adequate to independently derive the PC indices.

Description: An analysis of tropospheric column ozone using the NASA Langley TOR data during 1979–2005 has been done to investigate the trend over major Indian cities Delhi, Hyderabad and Bangalore. India was under social democratic-based policies before 1990s. Economic Liberalization began in nineties which lead to a significant growth in industrial, energy and transport sectors in major cities. Our analysis shows that there is a systematic increase in the number of months with higher tropospheric ozone values after 1990. A comparison of TOR climatology before and after 1990 over these cities shows evidence of increase in the tropospheric ozone after 1990. Trend obtained from the model shows significant change during monsoon over Delhi and during pre-monsoon and post-monsoon over Hyderabad and Bangalore. The present analysis using TOR technique demonstrates the TOR potential to detect changes in tropospheric ozone over large cities which are impacted by large anthropogenic pollution.

Description: The Planetary Waves (PWs) are believed to have significant role in generating the wintertime warming over the polar stratosphere, known as Stratospheric Sudden Warming (SSW). However, the origin, characteristics and evolution of these waves are still speculative. The possibility that the PWs over the polar stratosphere, which play an important role in the generation of SSW, could also have contribution from the tropics has been indicated through many numerical simulations in the past, but due to the paucity of global measurements it could not be established unequivocally. The earlier numerical studies also indicated the presence of a zero-wind line (more general the critical layer, where the zonal wind amplitude becomes zero) whose real counterparts were not observed in the atmosphere. The present study based on the NCEP/NCAR reanalysis of stratospheric wind and temperatures of recent years clearly shows that (i) the zero-wind line appears over the tropics ~60 days prior to the major SSWs and progresses towards the Pole and (ii) an enhanced PW activity of quasi periodicity 16-days, which is also seen almost simultaneously with the zero-wind line, shows a propagation from equator to the Pole. This result is significant as it presents for the first time the connection between the tropics during the SSW events and the pole, through the quasi 16-day wave.

Description: A re-evaluation of the reconnection event reported by Volwerk et al. (2009) shows that the original interpretation of the magnetic field data as quadrupolar Hall-current signatures around a reconnection site was mistaken. It could be interpreted as the signature of reconnection in the presence of a guide field. The path of VEX through the active region in Venus's magnetotail is re-evaluated and the strongly energized ions associated to this event are now in agreement with the magnetic field data.

Description: It is known that under certain solar wind (SW)/interplanetary magnetic field (IMF) conditions (e.g. high SW speed, low cone angle) the occurrence of ground-level Pc3–4 pulsations is more likely. In this paper we demonstrate that in the event of anomalously low SW particle density, Pc3 activity is extremely low regardless of otherwise favourable SW speed and cone angle. We re-investigate the SW control of Pc3 pulsation activity through a statistical analysis and two empirical models with emphasis on the influence of SW density on Pc3 activity. We utilise SW and IMF measurements from the OMNI project and ground-based magnetometer measurements from the MM100 array to relate SW and IMF measurements to the occurrence of Pc3 activity. Multiple linear regression and artificial neural network models are used in iterative processes in order to identify sets of SW-based input parameters, which optimally reproduce a set of Pc3 activity data. The inclusion of SW density in the parameter set significantly improves the models. Not only the density itself, but other density related parameters, such as the dynamic pressure of the SW, or the standoff distance of the magnetopause work equally well in the model. The disappearance of Pc3s during low-density events can have at least four reasons according to the existing upstream wave theory: 1. Pausing the ion-cyclotron resonance that generates the upstream ultra low frequency waves in the absence of protons, 2. Weakening of the bow shock that implies less efficient reflection, 3. The SW becomes sub-Alfvénic and hence it is not able to sweep back the waves propagating upstream with the Alfvén-speed, and 4. The increase of the standoff distance of the magnetopause (and of the bow shock). Although the models cannot account for the lack of Pc3s during intervals when the SW density is extremely low, the resulting sets of optimal model inputs support the generation of mid latitude Pc3 activity predominantly through upstream waves.

Description: This paper presents measurement of daytime Sodium (Na) airglow emissions at 589.6 nm wavelength using a ground based 1-m scanning monochromator from Trivandrum (8.5° N, 77° E, 0.5° N dip latitude), a near-equatorial station in India. The Na emission intensity exhibits significant temporal variability within a day and from one day to another. The Na intensity has been compared with the daytime OH airglow intensity at 731.6 nm simultaneously measured using the unique Multiwavelength Dayglow Photometer (MWDPM). The temporal variabilities of the Na and OH intensities corroborate each other in most of the occasions without any appreciable time delay, although a small time delay up to ~10 min has been observed at times. It appears that the variability of daytime Na emissions is influenced too by the photo-chemical excitations. The observed similarities in the Na and OH intensities are believed to be due to the similar roles played by [O] and O3 (in their photo-chemical excitations) and the dynamics occurring at about the same altitude region (~90 km). It has also been found that the gravity waves play significant role in producing the short-scale oscillations in these emissions.

Description: On 12 May 2008 at 14:28 LT great earthquake (M=8.0) occurred at Wenchuan (31.00° N, 103.40° E), China. The hourly values of foF2 are analyzed over ten ionospheric observatories: Haikou (20.00° N, 110.33° E), Kunming (25.00° N, 102.70° E), Guangzhou (20.00° N, 113.70° E), Chongqing (29.50° N, 106.40° E), Lhasa (29.63° N, 91.17° E), Lanzhou (36.07° N, 103.87° E), Beijing (40.00° N, 116.30° E), Urumqi (43.75° N, 87.63° E), Chuangchun (43.83° N, 125.30° E) and Manzhouli (49.60° N, 117.45° E). With a new factor, effective sunspot number Reff, the results show that there were giant positive disturbances of foF2 around the epicentral zone on 9 May, 3 days prior to the earthquake. Our results indicate that the observed positive ionospheric disturbances were most possibly associated with the imminent earthquake and the new analytic method has good prospects in practice.

Description: On 17 July 2005, an earthward bound north-south oriented magnetic cloud and its sheath were observed by the ACE, SoHO, and Wind solar wind monitors. A steplike increase of the solar wind dynamic pressure during northward interplanetary magnetic field conditions was related to the leading edge of the sheath. A timing analysis between the three spacecraft revealed that this front was not aligned with the GSE y-axis, but had a normal (−0.58,0.82,0). Hence, the first contact with the magnetosphere occurred on the dawnside rather than at the subsolar point. Fortunately, Cluster, Double Star 1, and Geotail happened to be distributed close to the magnetopause in this region, which made it possible to closely monitor the motion of the magnetopause. After the pressure front had impacted the magnetosphere, the magnetopause was perceived first to move inward and then immediately to correct the overshoot by slightly expanding again such that it ended up between the Cluster constellation with Double Star 1 inside the magnetosphere and Geotail in the magnetosheath. Coinciding with the inward and subsequent outward motion, the ground-based magnetic field at low latitudes was observed to first strengthen and then weaken. As the magnetopause position stabilised, so did the ground-based magnetic field intensity, settling at a level slightly higher than before the pressure increase. Altogether the magnetopause was moving for about 15 min after its first contact with the front. The high latitude ionospheric signature consisted of two parts: a shorter (few minutes) and less intense preliminary part comprised a decrease of AL and a negative variation of PC. A longer (about ten minutes) and more intense main part of the signature comprised an increase of AU and a positive variation of PC. Measurements from several ground-based magnetometer networks (210 MM CPMN, CANMOS, CARISMA, GIMA, IMAGE, MACCS, SuperMAG, THEMIS, TGO) were used to obtain information on the ionospheric E×B drift. Before the pressure increase, a configuration typical for the prevailing northward IMF conditions was observed at high latitudes. The preliminary signature coincided with a pair of reverse convection vortices, whereas during the main signature, mainly westward convection was observed at all local time sectors. Afterwards, the configuration preceding the pressure increase was recovered, but with slightly enhanced convection. Based on the timing analysis, the existence of the preliminary signature coincided with the passage of the oblique pressure front, whereas during the main signature the front was already well past Earth. The main signature existed during the time the magnetopause was observed to move. As the position stabilised, also the signature disappeared.