Geophysical flows with anisotropic turbulence and dispersive waves: flows with a β-effect

Geostrophic turbulence is a key paradigm in the current understanding of the large-scale planetary circulations. It implies that a flow is turbulent, rotating, stably stratified, and in near-geostrophic balance. When a small-scale forcing is present, geostrophic turbulence features an inverse energy cascade. When the meridional variation of the Coriolis parameter (or a β-effect) is included, the horizontal flow symmetry breaks down giving rise to the emergence of jet flows. The presence of a large-scale drag ensures that the flow attains a steady state. Dependent on the governing parameters, four steady-state flow regimes are possible, two of which are considered in this study. In one of these regimes, a flow is dominated by the drag while in the other one, the recently discovered regime of zonostrophic turbulence, a flow becomes strongly anisotropic and features slowly evolving systems of alternating zonal jets. Zonostrophic turbulence is distinguished by anisotropic inverse energy cascade and emergence of a new class of nonlinear waves known as zonons. In addition, meridional scalar diffusion is strongly modified in this regime. This paper provides an overview of various regimes of turbulence with a β-effect, elaborates main characteristics of friction-dominated and zonostrophic turbulence, elucidates the physical nature of the zonons, discusses the meridional diffusion processes in different regimes, and relates these results to oceanic observations.     

Probabilistic predictive model with complex remembrance

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Magnetotelluric data inversion with seismic data constraint

Introduction The research on the structure and physical property of ancient hidden hill, igneous rocks and basement is relatively difficult by using seismic data only. If we combine seismic data, magneto-telluric (MT) data and geophysical data together, better results can be obtained for the above problem. A number of geophysicists at home and abroad, such as CHEN and WANG (1990), Siri-punvarapor and Egbert (2000) have tried many methods to solve the problem by the inversion of seismic da…     

1989 Datong-Yanggao Earthquake with Ms=6.1

In this paper,the basic conditions and characteristics of the Datong-Yanggao earthquake are described in detail.The type of the earthquake,the aftershock activity,the earthquake trend,the characteristics of damage are analyzed and discussed.This earthquake belongs to a sequence of earthquake swarm type and is of the concentratedly occurring characteristics of several main shocks in a time sequence,and the aftershock activity was normally attenuated.Because of the unreasonable design of buildings and repeated vibration by several destructive main shocks within a short period,the damage in the high intensity region was aggravated.The analysis and the prediction procedure of the 1991 Datong-Yanggao earthquake(Ms=5.8)are also briefly given.     

3D wavefield extrapolation with optimal separable approximation

An accurate and wide-angle one-way propagator for wavefield extrapolation is an important topic for research on wave-equation prestack depth migration in the presence of large and rapid velocity variations. Based on the optimal separable approximation presented in this paper, the mixed domain algorithm with forward and inverse Fourier transforms is used to construct the 3D one-way wavefield extrapolation operator. This operator separates variables in the wavenumber and spatial domains. The phase shift operation is implemented in the wavenumber domain while the time delay for lateral velocity variation is corrected in the spatial domain. The impulse responses of the one-way wave operator show that the numeric computation is consistent with the theoretical value for each velocity, revealing that the operator constructed with the optimal separable approximation can be applied to lateral velocity variations for the case of small steps. Imaging results of the SEG/EAGE model and field data indicate that the new method can be used to image complex structure.     

Construction of constant-Q viscoelastic mode with three parameters

The popularly used viscoelastic models have some shortcomings in describing relationship between quality factor （Q） and frequency, which is not consistent with the observation data. Based on the theory of viscoelasticity, a new approach to construct constant-Q viscoelastic model in given frequency band with three parameters is developed. The designed model describes the frequency-independence feature of quality factor very well, and the effect of viscoelasticity on seismic wave field can be studied relatively accurate in theory with this model. Furthermore, the number of required parameters in this model has been reduced fewer than that of other constant-Q models, this can simplify the solution of the viscoelastic problems to some extent. At last, the accuracy and application range have been analyzed through numerical tests. The effect of viscoelasticity on wave propagation has been briefly illustrated through the change of frequency spectra and waveform in several different viscoelastic models.     

Construction of constant-Q viscoelastic model with three parameters

The popularly used viscoelastic models have some shortcomings in describing relationship between quality factor (Q) and frequency, which is not consistent with the observation data. Based on the theory of viscoelasticity, a new approach to construct constant-Q viscoelastic model in given frequency band with three parameters is developed. The designed model describes the frequency-independence feature of quality factor very well, and the effect of viscoelasticity on seismic wave field can be studied relatively accurate in theory with this model. Furthermore, the number of required parameters in this model has been reduced fewer than that of other constant-Q models, this can simplify the solution of the viscoelastic problems to some extent. At last, the accuracy and application range have been analyzed through numerical tests. The effect of viscoelasticity on wave propagation has been briefly illus-trated through the change of frequency spectra and waveform in several different viscoelastic models.     

On MSDT inversion with multi-angle remote sensing data

With the wavelet transform, image of multi-angle remote sensing is decomposed into multi-resolution. With data of each resolution, we try target-based multi-stages inversion, taking the inversion result of coarse resolution as the prior information of the next inversion. The result gets finer and finer until the resolution of satellite observation. In this way, the target-based multi-stages inversion can be used in remote sensing inversion of large-scaled coverage. With MISR data, we inverse structure parameters of vegetation in semiarid grassland of the Inner Mongolia Autonomous Region. The result proves that this way is efficient.     

Quantifying flow–ecology relationships with functional linear models

Abstract

Hydrologic metrics have been used widely to quantify flow-ecology relationships; however, there are several challenges associated with their use, including the selection from a large number of available metrics and the limitation that metrics are a synthetic measure of a multi-dimensional flow regime. Using two case studies of fish species density and community composition, we illustrate the use of functional linear models to provide new insights into flow–ecology relationships and predict the expected impact of environmental flow scenarios, without relying on hydrologic metrics. The models identified statistically significant relationships to river flow over the 12 months prior to sampling (r² range 36–67%) and an environmental flow scenario that may enhance native species’ densities while controlling a non-native species. Hydrologic metrics continue to play an important role in ecohydrology and environmental flow management; however, functional linear models provide an approach that overcomes some of the limitations associated with their use.

Editor Z.W. Kundzewicz; Guest editor M. Acreman

Citation Stewart-Koster, B., Olden, J.D., and Gido, K.B., 2014. Quantifying flow–ecology relationships with functional linear models. Hydrological Sciences Journal, 59 (3–4), 629–644.     

Common-offset domain reflection–diffraction separation with deep learning

Separation of diffracted from reflected events in seismic data is still challenging due to the relatively low amplitude of the diffracted wavefield compared to the reflected wavefield as well as the overlap in the kinematics of reflection and diffraction events. A workflow based on deep learning can be a simple and fast alternative, but using training data made by physics-based modelling is expensive and lacks diversity in terms of noise, amplitude, frequency content and wavelet. This results in poor generalization beyond the training data without retraining and transfer learning. In this paper, we demonstrate successful applications of reflection–diffraction separation using a conventional U-net architecture. The novelty of our approach is that we do not use synthetic data created from physics-based modelling, but instead use only synthetic data built from basic geometric shapes. Our domain of application is the pre-migration common-offset domain where reflected events resemble local geology and the diffracted wavefield consists of downward convex hyperbolic diffraction patterns. Both patterns were randomly perturbed in many ways while maintaining their intrinsic features. This approach is inspired by the common practice of data augmentation in deep learning for machine vision applications. Since many of the standard data augmentation techniques lack a geophysical motivation, we have instead perturbed our synthetic training data in ways to make more sense from a signal processing perspective or given our ‘domain knowledge’ of the problem at hand. We did not have to retrain the network to show good results on the field data set. The large variety and diversity in examples enabled to trained neural networks to show encouraging results on synthetic and field data sets that were not used in training.     

3-D acoustic wave equation forward modeling with topography

In order to model the seismic wave field with surface topography, we present a method of transforming curved grids into rectangular grids in two different coordinate systems. Then the 3D wave equation in the transformed coordinate system is derived. The wave field is modeled using the finite-difference method in the transformed coordinate system. The model calculation shows that this method is able to model the seismic wave field with fluctuating surface topography and achieve good results. Finally, the energy curves of the direct and reflected waves are analyzed to show that surface topography has a great influence on the seismic wave＇s dynamic properties.     

Mean Field Dynamos with Algebraic and Dynamic α-Quenchings

Calculations for mean field dynamo models (in both full spheres and spherical shells), with both algebraic and dynamic -quenchings, show qualitative as well as quantitative differences and similarities in the dynamical behaviour of these models. We summarise and enhance recent results with extra examples. Overall, the effect of using a dynamic appears to be complicated and is affected by the region of parameter space examined.     

Ocean-generated microseismic noise located with the Gräfenberg array

The main cause for mid-period seismic ground distortions are ocean waves generated by atmospheric disturbances. These act upon the earth through different mechanisms. The microseismic wavefield can be divided into primary (T =12–18 s) and secondary (T = 6–9 s) noise. Classical theory tells that the origin of these induced ground distortions depends on the location and the intensity of the low pressure region. A considerable part of the microseismic wave field reaches the GRF-array in southern Germany with high coherency and almost constant amplitudes. Thus it is possible to locate the generating areas using frequency-wavenumber analysis. Five discrete generating areas for secondary microseisms and three generating areas for primary microseisms could be determined in the Atlantic Ocean, the Arctic Sea and the Mediterranean Sea by investigating broadband continuous recordings over four months in winter 1995/96. An essential result is the long-time constancy of the backazimuths of the coherent part of the microseismic wavefield with respect to the origin areas, independent of the location of the moving low pressure zone. Results from a triangulation using additionally broadband data from the NORSAR-array and an independent estimation of the distance of the source region with water wave dispersion data indicate an origin of the secondary microseismic wavefield near the north-Norwegian coast for the strongest source. The array analysis of a temporary network of ten three-component broadband stations in south-east Germany shows that the ratio of energy between coherent Love and Rayleigh waves is much higher for the primary than for the secondary microseismic noise wavefield. This indicates differences in the source mechanisms.     

Earthquake accelerogram simulation with statistical law of evolutionary power spectrum

By using the technique for evolutionary power spectrum proposed by Nakayama and with reference to the Kameda formula, an evolutionary spectrum prediction model for given earthquake magnitude and distance is established based on the 80 near-source acceleration records at rock surface with large magnitude from the ground motion database of western U.S.. Then a new iteration method is developed for generation of random accelerograms non-stationary both in amplitude and frequency which are compatible with target evolutionary spectrum. The phase spectra of those simulated accelerograms are also non-stationary in time and frequency domains since the interaction between amplitude and phase angle has been considered during the generation. Furthermore, the sign of the phase spectrum increment is identified to accelerate the iteration. With the proposed statistical model for predicting evolutionary power spectra and the new method for generating compatible time history, the artificial random earthquake accelerograms non-stationary both in amplitude and frequency for certain magnitude and distance can be provided.     

P wave onset time picking with the B-spline biorthogonal wavelet

The seismic wave consists of many seismic phases, which contain rich geophysical information from the hypocenter, medium of seismic wave passing through and so on. It is very important to detect and pick these seis-mic phases for understanding the mechanism of earthquake, the Earth structure and property of seismic waves. In order to reduce or avoid the loss resulted from the earthquake, one of the important goals of seismic event detect-ing is to obtain its related information before and afte…     

Seminar for hydrocarbon detection with composite geophysical／geo-chemical techniques

"Seminar for hydrocarbon detection with composite geophysical/geo-chemical techniques", jointly organized by China Petroleum Exploration & Production Company and Exploration Geophysical Committee of CGS and supported by the Composite Geophysical/geo-chemical Department of Oriental Geophysical Company and China Exploration & Development Research Institute, was conducted in Guiyang of Guizhou Province on 27 September 2003. More than 70 people from over 20 organizations attended this meeting characterized as follows.     

Solar System Collisions with Dense Interstellar Gas Clouds and Radiocarbon Traces of Periods with “Abnormally Low” Solar Modulation of Cosmic Rays

Geomagnetism and Aeronomy - The causes of a sharp increase in the radiocarbon content in the Earth’s atmosphere for periods with abnormally low solar modulation of galactic cosmic rays (GCRs)...