NPG - recent papershttp://www.nonlin-processes-geophys.net/2017-03-25T02:33:38+01:00Copernicus Publicationshttp://dx.doi.org/10.5194/npg-2017-9Extracting real-crack properties from nonlinear elastic behavior of rocks: abundance of cracks with dominating normal compliance and rocks with negative Poisson's ratio
<b>Extracting real-crack properties from nonlinear elastic behavior of rocks: abundance of cracks with dominating normal compliance and rocks with negative Poisson's ratio</b><br>
Vladimir Y. Zaitsev, Andrey V. Radostin, Elena Pasternak, and Arcady Dyskin<br>
Nonlin. Processes Geophys. Discuss., doi:10.5194/npg-2017-9,2017<br>
<b>Manuscript under review for NPG</b> (discussion: open, 0 comments)<br>
A new method of analysing pressure wave dependences is presented and tested against the published experimental data. Upon the results of examination of more than 90 rock samples it was found that a significant portion of rocks (~ 45 %) exhibiting negative Poisson's ratios at lower pressures. Such a significant number of naturally auxetic rocks suggest that the occurrence of negative Poisson's ratio is not as exotic as assumed previously.
<b>Extracting real-crack properties from nonlinear elastic behavior of rocks: abundance of cracks with dominating normal compliance and rocks with negative Poisson's ratio</b><br>
Vladimir Y. Zaitsev, Andrey V. Radostin, Elena Pasternak, and Arcady Dyskin<br>
Nonlin. Processes Geophys. Discuss., doi:10.5194/npg-2017-9,2017<br>
<b>Manuscript under review for NPG</b> (discussion: open, 0 comments)<br>
Results of examination of experimental data on nonlinear elasticity of rocks using experimental pressure-dependences of P- and S-wave velocities from various literature sources are presented. Overall, over 90 rock samples are considered. Interpretation of the data is performed using an effective-medium description in which cracks are considered as compliant defects (cracks) with independent shear and normal compliances without specifying a particular crack model with an <i>a priori</i> given ratio of the compliances. Comparison with the experimental data indicated abundance of cracks (~ 80 %) with the normal-to-shear compliance ratios significantly exceeding the values typical of conventionally used crack models (such as penny-shape cuts or thin ellipsoidal cracks). Correspondingly, rocks with such cracks demonstrate strongly decreased Poisson's ratio including a significant portion of rocks (~ 45 %) exhibiting negative Poisson's ratios at lower pressures, for which the concentration of not yet closed cracks is maximal. The obtained results indicate the necessity of further development of crack models to account the revealed numerous examples of cracks with strong domination of normal compliance. Discovering such a significant number of naturally auxetic rocks is in contrast with the conventional viewpoint that occurrence of negative Poisson's ratio is an exotic fact that is mostly associated with specially engineered structures.
Copernicus Electronic Production Support Office2017-03-17T02:33:38+01:002017-03-17T02:33:38+01:00http://dx.doi.org/10.5194/npg-24-141-2017Spatial and radiometric characterization of multi-spectrum satellite images through multi-fractal analysis
<b>Spatial and radiometric characterization of multi-spectrum satellite images through multi-fractal analysis</b><br>
Carmelo Alonso, Ana M. Tarquis, Ignacio Zúñiga, and Rosa M. Benito<br>
Nonlin. Processes Geophys., 24, 141-155, doi:10.5194/npg-24-141-2017, 2017<br>
NDVI and EVI vegetation indexes, estimated from satellite images, can been used to estimate root zone soil moisture. However, depending on the spatial and radiometric resolution of the sensors used, estimations could change. In this work, images taken by satellites IKONOS-2 and LANDSAT-7 of the same location are compared on the four bands involved in these vegetation indexes. The results show that spatial resolution has a similar scaling effect in the four bands, but not radiometric resolution.
<b>Spatial and radiometric characterization of multi-spectrum satellite images through multi-fractal analysis</b><br>
Carmelo Alonso, Ana M. Tarquis, Ignacio Zúñiga, and Rosa M. Benito<br>
Nonlin. Processes Geophys., 24, 141-155, doi:10.5194/npg-24-141-2017, 2017<br>
Several studies have shown that vegetation indexes can be used to
estimate root zone soil moisture. Earth surface images, obtained by high-resolution satellites, presently give a lot of information on these
indexes, based on the data of several wavelengths. Because of the potential capacity for
systematic observations at various scales, remote sensing technology extends
the possible data archives from the present time to several decades back.
Because of this advantage, enormous efforts have been made by researchers and
application specialists to delineate vegetation indexes from local scale to
global scale by applying remote sensing imagery.
<br><br>
In this work, four band images have been considered, which are involved in these
vegetation indexes, and were taken by satellites Ikonos-2 and Landsat-7 of the same
geographic location, to study the effect of both spatial (pixel size) and
radiometric (number of bits coding the image) resolution on these wavelength
bands as well as two vegetation indexes: the Normalized Difference
Vegetation Index (NDVI) and the Enhanced Vegetation Index (EVI).
<br><br>
In order to do so, a multi-fractal analysis of these multi-spectral images
was applied in each of these bands and the two indexes derived. The results
showed that spatial resolution has a similar scaling effect in the four
bands, but radiometric resolution has a larger influence in blue and green
bands than in red and near-infrared bands. The NDVI showed a higher
sensitivity to the radiometric resolution than EVI. Both were equally
affected by the spatial resolution.
<br><br>
From both factors, the spatial resolution has a major impact in the
multi-fractal spectrum for all the bands and the vegetation indexes. This
information should be taken in to account when vegetation indexes based on
different satellite sensors are obtained.
Copernicus Electronic Production Support Office2017-03-16T02:33:38+01:002017-03-16T02:33:38+01:00http://dx.doi.org/10.5194/npg-2017-14Retrieval and assimilation of velocities at the ocean surface
<b>Retrieval and assimilation of velocities at the ocean surface</b><br>
Jordi Isern-Fontanet, Joaquim Ballabrera-Poy, Antonio Turiel, and Emilio García-Ladona<br>
Nonlin. Processes Geophys. Discuss., doi:10.5194/npg-2017-14,2017<br>
<b>Manuscript under review for NPG</b> (discussion: open, 0 comments)<br>
Ocean currents play a key role in Earth’s climate, they are of major importance for navigation and human activities at sea, and impact almost all processes that take place in the ocean. Nevertheless, their observation and forecasting are still difficult. Here, we review the main techniques used to derive surface currents from satellite measurements and the existing approaches to assimilate this information into ocean models.
<b>Retrieval and assimilation of velocities at the ocean surface</b><br>
Jordi Isern-Fontanet, Joaquim Ballabrera-Poy, Antonio Turiel, and Emilio García-Ladona<br>
Nonlin. Processes Geophys. Discuss., doi:10.5194/npg-2017-14,2017<br>
<b>Manuscript under review for NPG</b> (discussion: open, 0 comments)<br>
Ocean currents play a key role in Earth’s climate, they are of major importance for navigation and human activities at sea, and impact almost all processes that take place in the ocean. Nevertheless, their observation and forecasting are still difficult. First, direct measurements of ocean currents are difficult to obtain synoptically at global scale. Consequently, it has been necessary to use Sea Surface Height and Sea Surface Temperature measurements and refer to dynamical frameworks to derive the velocity field. Second, the assimilation of the velocity field into numerical models of ocean circulation is difficult mainly due to lack of data. Recent experiments assimilating coastal-based radar data have shown that ocean currents will contribute to increase the forecast skill of surface currents, but require to be applied in multi-data assimilation approaches to allow better identification of the thermohaline structure of the ocean. In this paper we review the current knowledge on these fields and provide global and systematic view on the technologies to retrieve ocean velocities in the upper ocean and the available approaches to assimilate this information into ocean model.
Copernicus Electronic Production Support Office2017-03-09T02:33:38+01:002017-03-09T02:33:38+01:00http://dx.doi.org/10.5194/npg-24-125-2017Insights on the role of accurate state estimation in coupled model parameter estimation by a conceptual climate model study
<b>Insights on the role of accurate state estimation in coupled model parameter estimation by a conceptual climate model study</b><br>
Xiaolin Yu, Shaoqing Zhang, Xiaopei Lin, and Mingkui Li<br>
Nonlin. Processes Geophys., 24, 125-139, doi:10.5194/npg-24-125-2017, 2017<br>
Parameter estimation (PE) with a global coupled data assimilation (CDA) system can improve the runs, but the improvement remains in a limited range. We have to come back to simple models to sort out the sources of noises. Incomplete observations and the chaotic nature of the atmosphere have much stronger influences on the PE through the state estimation (SE) process. Here, we propose the guidelines of how to enhance the signal-to-noise ratio under partial SE status.
<b>Insights on the role of accurate state estimation in coupled model parameter estimation by a conceptual climate model study</b><br>
Xiaolin Yu, Shaoqing Zhang, Xiaopei Lin, and Mingkui Li<br>
Nonlin. Processes Geophys., 24, 125-139, doi:10.5194/npg-24-125-2017, 2017<br>
The uncertainties in values of coupled model parameters
are an important source of model bias that causes model climate drift. The
values can be calibrated by a parameter estimation procedure that projects
observational information onto model parameters. The signal-to-noise ratio
of error covariance between the model state and the parameter being estimated
directly determines whether the parameter estimation succeeds or not. With
a conceptual climate model that couples the stochastic atmosphere and
slow-varying ocean, this study examines the sensitivity of state–parameter
covariance on the accuracy of estimated model states in different model
components of a coupled system. Due to the interaction of multiple timescales,
the fast-varying <q>atmosphere</q> with a chaotic nature is the major
source of the inaccuracy of estimated state–parameter covariance. Thus,
enhancing the estimation accuracy of atmospheric states is very important
for the success of coupled model parameter estimation, especially for the
parameters in the air–sea interaction processes. The impact of
chaotic-to-periodic ratio in state variability on parameter estimation is
also discussed. This simple model study provides a guideline when real
observations are used to optimize model parameters in a coupled general
circulation model for improving climate analysis and predictions.
Copernicus Electronic Production Support Office2017-03-06T02:33:38+01:002017-03-06T02:33:38+01:00http://dx.doi.org/10.5194/npg-2017-11Multiscaled Solitary Waves
<b>Multiscaled Solitary Waves</b><br>
Oleg G. Derzho<br>
Nonlin. Processes Geophys. Discuss., doi:10.5194/npg-2017-11,2017<br>
<b>Manuscript under review for NPG</b> (discussion: open, 1 comment)<br>
It is analytically shown how competing nonlinearities yield new multiscaled (multi humped) structures for internal solitary waves in shallow fluids. These solitary waves only exist for large amplitudes beyond the limit of applicability of the KdV equation or its usual extensions. Multiscaling phenomenon exists or do not exist for almost identical density profiles. Trapped core inside the wave prevents appearance of such multiple scales within the core area.
<b>Multiscaled Solitary Waves</b><br>
Oleg G. Derzho<br>
Nonlin. Processes Geophys. Discuss., doi:10.5194/npg-2017-11,2017<br>
<b>Manuscript under review for NPG</b> (discussion: open, 1 comment)<br>
It is analytically shown how competing nonlinearities yield new multiscaled (multi humped) structures for internal solitary waves in shallow fluids. These solitary waves only exist for large amplitudes beyond the limit of applicability of the KdV equation or its usual extensions. Multiscaling phenomenon exists or do not exist for almost identical density profiles. Trapped core inside the wave prevents appearance of such multiple scales within the core area. It is anticipated that multiscaling phenomena exist for solitary waves in various physical origins.
Copernicus Electronic Production Support Office2017-03-06T02:33:38+01:002017-03-06T02:33:38+01:00http://dx.doi.org/10.5194/npg-24-113-2017A matrix clustering method to explore patterns of land-cover transitions in satellite-derived maps of the Brazilian Amazon
<b>A matrix clustering method to explore patterns of land-cover transitions in satellite-derived maps of the Brazilian Amazon</b><br>
Finn Müller-Hansen, Manoel F. Cardoso, Eloi L. Dalla-Nora, Jonathan F. Donges, Jobst Heitzig, Jürgen Kurths, and Kirsten Thonicke<br>
Nonlin. Processes Geophys., 24, 113-123, doi:10.5194/npg-24-113-2017, 2017<br>
Deforestation and subsequent land uses in the Brazilian Amazon have huge impacts on greenhouse gas emissions, local climate and biodiversity. To better understand these land-cover changes, we apply complex systems methods uncovering spatial patterns in regional transition probabilities between land-cover types, which we estimate using maps derived from satellite imagery. The results show clusters of similar land-cover dynamics and thus complement studies at the local scale.
<b>A matrix clustering method to explore patterns of land-cover transitions in satellite-derived maps of the Brazilian Amazon</b><br>
Finn Müller-Hansen, Manoel F. Cardoso, Eloi L. Dalla-Nora, Jonathan F. Donges, Jobst Heitzig, Jürgen Kurths, and Kirsten Thonicke<br>
Nonlin. Processes Geophys., 24, 113-123, doi:10.5194/npg-24-113-2017, 2017<br>
Changes in land-use systems in tropical regions, including deforestation, are
a key challenge for global sustainability because of their huge impacts on
green-house gas emissions, local climate and biodiversity. However, the
dynamics of land-use and land-cover change in regions of frontier expansion
such as the Brazilian Amazon are not yet well understood because of the
complex interplay of ecological and socioeconomic drivers. In this paper, we
combine Markov chain analysis and complex network methods to identify regimes
of land-cover dynamics from land-cover maps (TerraClass) derived from
high-resolution (30 m) satellite imagery. We estimate regional transition
probabilities between different land-cover types and use clustering analysis
and community detection algorithms on similarity networks to explore patterns
of dominant land-cover transitions. We find that land-cover transition
probabilities in the Brazilian Amazon are heterogeneous in space, and adjacent
subregions tend to be assigned to the same clusters. When focusing on
transitions from single land-cover types, we uncover patterns that reflect
major regional differences in land-cover dynamics. Our method is able to
summarize regional patterns and thus complements studies performed at the
local scale.
Copernicus Electronic Production Support Office2017-02-28T02:33:38+01:002017-02-28T02:33:38+01:00http://dx.doi.org/10.5194/npg-24-101-2017Conditional nonlinear optimal perturbations based on the particle swarm optimization and their applications to the predictability problems
<b>Conditional nonlinear optimal perturbations based on the particle swarm optimization and their applications to the predictability problems</b><br>
Qin Zheng, Zubin Yang, Jianxin Sha, and Jun Yan<br>
Nonlin. Processes Geophys., 24, 101-112, doi:10.5194/npg-24-101-2017, 2017<br>
When the initial perturbation is large or the prediction time is long, the strong nonlinearity of the dynamical model on the prediction variable will lead to failure of the ADJ-CNOP method; when the objective function has multiple extreme values, ADJ-CNOP has a large probability of producing local CNOPs, hence making false estimations of the lower bound of maximum predictable time.
<b>Conditional nonlinear optimal perturbations based on the particle swarm optimization and their applications to the predictability problems</b><br>
Qin Zheng, Zubin Yang, Jianxin Sha, and Jun Yan<br>
Nonlin. Processes Geophys., 24, 101-112, doi:10.5194/npg-24-101-2017, 2017<br>
In predictability problem research, the conditional nonlinear
optimal perturbation (CNOP) describes the initial perturbation that satisfies
a certain constraint condition and causes the largest prediction error at the
prediction time. The CNOP has been successfully applied in estimation of the
lower bound of maximum predictable time (LBMPT). Generally, CNOPs are
calculated by a gradient descent algorithm based on the adjoint model, which
is called ADJ-CNOP. This study, through the two-dimensional Ikeda model,
investigates the impacts of the nonlinearity on ADJ-CNOP and the
corresponding precision problems when using ADJ-CNOP to estimate the LBMPT.
Our conclusions are that (1) when the initial perturbation is large
or the prediction time is long, the strong nonlinearity of the dynamical
model in the prediction variable will lead to failure of the ADJ-CNOP method,
and (2) when the objective function has multiple extreme values, ADJ-CNOP has
a large probability of producing local CNOPs, hence making a false estimation
of the LBMPT. Furthermore, the particle swarm optimization (PSO) algorithm,
one kind of intelligent algorithm, is introduced to solve this problem. The
method using PSO to compute CNOP is called PSO-CNOP. The results of numerical
experiments show that even with a large initial perturbation and long
prediction time, or when the objective function has multiple extreme values,
PSO-CNOP can always obtain the global CNOP. Since the PSO algorithm is a
heuristic search algorithm based on the population, it can overcome the
impact of nonlinearity and the disturbance from multiple extremes of the
objective function. In addition, to check the estimation accuracy of the
LBMPT presented by PSO-CNOP and ADJ-CNOP, we partition the constraint domain
of initial perturbations into sufficiently fine grid meshes and take the
LBMPT obtained by the filtering method as a benchmark. The result shows that
the estimation presented by PSO-CNOP is closer to the true value than the one
by ADJ-CNOP with the forecast time increasing.
Copernicus Electronic Production Support Office2017-02-22T02:33:38+01:002017-02-22T02:33:38+01:00http://dx.doi.org/10.5194/npg-2017-5Detecting Changes in Forced Climate Attractors with Wasserstein Distance
<b>Detecting Changes in Forced Climate Attractors with Wasserstein Distance</b><br>
Yoann Robin, Pascal Yiou, and Philippe Naveau<br>
Nonlin. Processes Geophys. Discuss., doi:10.5194/npg-2017-5,2017<br>
<b>Manuscript under review for NPG</b> (discussion: open, 1 comment)<br>
If climate is viewed as a chaotic dynamical system, its trajectories yielding on an object called attractor. Being perturbed by an external forcing, this attractor could be modified. With Wasserstein distance, we estimate on a derived Lorenz model the impact of a forcing similar to climate change. Our approach appears to work with small data sizes. We have obtained a methodology quantifying the deformation of well known attractors, coherent with the size of data available.
<b>Detecting Changes in Forced Climate Attractors with Wasserstein Distance</b><br>
Yoann Robin, Pascal Yiou, and Philippe Naveau<br>
Nonlin. Processes Geophys. Discuss., doi:10.5194/npg-2017-5,2017<br>
<b>Manuscript under review for NPG</b> (discussion: open, 1 comment)<br>
The climate system can been described by a dynamical system and its associated attractor. The
dynamics of this attractor depends on the external forcings that influence the climate. Such
forcings can affect the mean values or variances, but regions of the attractor that are seldom visited
can also be affected. It is an important challenge to measure how the climate attractor responds to
different forcings. Currently, the Euclidean distance or similar measures like the Mahalanobis
distance have been favoured to measure discrepancies between two climatic situations. Those
distances do not have a natural building mechanism to take into account the attractor dynamics. In
this paper, we argue that a Wasserstein distance, stemming from optimal transport theory, offers an
efficient and practical way to discriminate between dynamical systems. After treating a toy
example, we explore how the Wasserstein distance can be applied and interpreted to detect
non-autonomous dynamics from a Lorenz system driven by seasonal cycles and a warming trend.
Copernicus Electronic Production Support Office2017-02-20T02:33:38+01:002017-02-20T02:33:38+01:00http://dx.doi.org/10.5194/npg-2017-7Ensemble Kalman filter for the reconstruction of the Earth's mantle
circulation
<b>Ensemble Kalman filter for the reconstruction of the Earth's mantle
circulation</b><br>
Marie Bocher, Alexandre Fournier, and Nicolas Coltice<br>
Nonlin. Processes Geophys. Discuss., doi:10.5194/npg-2017-7,2017<br>
<b>Manuscript under review for NPG</b> (discussion: open, 1 comment)<br>
We propose a new method to reconstruct the circulation in the Earth's Mantle for the last 300 Myrs. This method is based on the sequential assimilation of plate layouts obtained from plate tectonic reconstructions into mantle convection models. This method allows us to take into account uncertainties on plate tectonic reconstructions, and provides an estimation of the uncertainties on the final result. We test and validate this method in a controlled environment by using synthetic experiments.
<b>Ensemble Kalman filter for the reconstruction of the Earth's mantle
circulation</b><br>
Marie Bocher, Alexandre Fournier, and Nicolas Coltice<br>
Nonlin. Processes Geophys. Discuss., doi:10.5194/npg-2017-7,2017<br>
<b>Manuscript under review for NPG</b> (discussion: open, 1 comment)<br>
Recent advances in mantle convection modelling led to the release of a new generation of convection codes, able to generate self-consistently plate-like tectonics at their surface. Those models physically link mantle dynamics to surface tectonics. Combined with plate tectonic reconstructions, they have the potential to produce a new generation of mantle circulation models that use data assimilation methods and where uncertainties on plate tectonic reconstructions are taken into account. We recently provided a proof of this concept by applying a suboptimal Kalman Filter to the reconstruction of mantle circulation (Bocher et al., 2016). Here, we propose to go one step further and apply the ensemble Kalman filter (EnKF) to this problem. The EnKF is a sequential Monte Carlo method particularly adapted to solve high dimensional data assimilation problems with nonlinear dynamics. We tested the EnKF using synthetic observations consisting of surface velocity and heat flow measurements, on a 2D-spherical annulus model and compared it with the method developed previously. The EnKF performs on average better and is more stable than the former method. Less than 300 ensemble members are sufficient to reconstruct an evolution. We use covariance adaptive inflation and localization to correct for sampling errors. We show that the EnKF results are robust over a wide range of covariance localization parameters. The reconstruction is associated with an estimation of the error, and provides valuable information on where the reconstruction is to be trusted or not.
Copernicus Electronic Production Support Office2017-02-20T02:33:38+01:002017-02-20T02:33:38+01:00http://dx.doi.org/10.5194/npg-2017-4Network-based study of Lagrangian transport and mixing
<b>Network-based study of Lagrangian transport and mixing</b><br>
Kathrin Padberg-Gehle and Christiane Schneide<br>
Nonlin. Processes Geophys. Discuss., doi:10.5194/npg-2017-4,2017<br>
<b>Manuscript under review for NPG</b> (discussion: open, 2 comments)<br>
Transport and mixing processes in fluid flows are crucially influenced by coherent structures, such as eddies, gyres, or jets in geophysical flows.
We propose a very simple and computationally efficient approach for analyzing coherent behavior in fluid flows. The central object is a flow network constructed directly from particle trajectories. The network's local and spectral properties are shown to give a very good indication of coherent as well as mixing regions in the underlying flow.
<b>Network-based study of Lagrangian transport and mixing</b><br>
Kathrin Padberg-Gehle and Christiane Schneide<br>
Nonlin. Processes Geophys. Discuss., doi:10.5194/npg-2017-4,2017<br>
<b>Manuscript under review for NPG</b> (discussion: open, 2 comments)<br>
Transport and mixing processes in fluid flows are crucially influenced by coherent structures and the characterization of these Lagrangian objects is a topic of intense current research. While established mathematical approaches such as variational or transfer operator based schemes require full knowledge of the flow field or at least high resolution trajectory data, this information may not be available in applications. Recently, different computational methods have been proposed to identify coherent behavior in flows directly from Lagrangian trajectory data. In this context, spatio-temporal clustering algorithms have been proven to be very effective for the extraction of coherent sets from sparse and possibly incomplete trajectory data. Inspired by these recent approaches, we consider an unweighted, undirected network, where Lagrangian particle trajectories serve as network nodes. A link is established between two nodes if the respective trajectories come close to each other at least once in the course of time. Classical graph concepts are then employed to analyze the resulting network. In particular, local network measures such as the node degree serve as indicators of highly mixing regions, whereas spectral graph partitioning schemes allow us to extract coherent sets. The proposed methodology is very fast to run and we demonstrate its applicability in two geophysical flows – the Bickley jet as well as the antarctic stratospheric polar vortex.
Copernicus Electronic Production Support Office2017-02-17T02:33:38+01:002017-02-17T02:33:38+01:00http://dx.doi.org/10.5194/npg-24-89-2017Statistical analysis of Lagrangian transport of subtropical waters in the Japan Sea based on AVISO altimetry data
<b>Statistical analysis of Lagrangian transport of subtropical waters in the Japan Sea based on AVISO altimetry data</b><br>
Sergey V. Prants, Maxim V. Budyansky, and Michael Yu. Uleysky<br>
Nonlin. Processes Geophys., 24, 89-99, doi:10.5194/npg-24-89-2017, 2017<br>
Transport of subtropical waters in the Japan Sea is simulated based on altimeter data. Preferred transport pathways across the Subpolar Front are found.
The cross-frontal transport is shown to be inhomogeneous with gates and barriers whose locations are determined by a local velocity field. The gates open due to suitable dispositions of mesoscale eddies facilitating propagation of subtropical waters to the north. There are forbidden zones where the northward transport has not been observed.
<b>Statistical analysis of Lagrangian transport of subtropical waters in the Japan Sea based on AVISO altimetry data</b><br>
Sergey V. Prants, Maxim V. Budyansky, and Michael Yu. Uleysky<br>
Nonlin. Processes Geophys., 24, 89-99, doi:10.5194/npg-24-89-2017, 2017<br>
Northward near-surface Lagrangian transport of subtropical waters in the
Japan Sea frontal zone is simulated and analysed based on altimeter data for
the period from 2 January 1993 to 15 June 2015. Computing different
Lagrangian indicators for a large number of synthetic tracers launched weekly
for 21 years in the southern part of the Sea, we find preferred transport
pathways across the Subpolar Front. This cross-frontal transport is
statistically shown to be meridionally inhomogeneous with <q>gates</q> and
<q>barriers</q> whose locations are determined by the local advection velocity
field. The gates <q>open</q> due to suitable dispositions of mesoscale eddies
facilitating propagation of subtropical waters to the north. It is documented
for the western, central and eastern gates with the help of different kinds
of Lagrangian maps and verified by some tracks of available drifters. The
transport through the gates occurs by a portion-like manner, i.e.
subtropical tracers pass the gates in specific places and during specific
time intervals. There are some <q>forbidden</q> zones in the frontal area where
the northward transport has not been observed during all the observation
period. They exist due to long-term peculiarities of the advection velocity
field.
Copernicus Electronic Production Support Office2017-02-16T02:33:38+01:002017-02-16T02:33:38+01:00http://dx.doi.org/10.5194/npg-2017-8Insights on the three-dimensional Lagrangian geometry of the Antarctic Polar Vortex
<b>Insights on the three-dimensional Lagrangian geometry of the Antarctic Polar Vortex</b><br>
Jezabel Curbelo, Victor J. García-Garrido, Carlos R. Mechoso, Ana M. Mancho, Stephen Wiggins, and Coumba Niang<br>
Nonlin. Processes Geophys. Discuss., doi:10.5194/npg-2017-8,2017<br>
<b>Manuscript under review for NPG</b> (discussion: open, 2 comments)<br>
The present paper introduces an algorithm for the visualization, analysis and verification of transport and mixing processes in three-dimensional atmospheric flows. This algorithm is based on the methodology of Lagrangian descriptors (LDs), a technique from Dynamical Systems Theory. The algorithm is applied to reanalysis data in order to illustrate the evolution of the flow above Antarctica during a period of rapid changes in the southern spring of 1979. The evolution of Lagrangian coherent structures is discussed and connections with the stratosphere is examined. The results suggest that the cyclonic stratospheric polar vortex during late winter appears to extend down to the troposphere. The results are also indicative of features related to invariante manifolds that can act as deep vertical barriers to transport between vortices.
Copernicus Electronic Production Support Office2017-02-16T02:33:38+01:002017-02-16T02:33:38+01:00http://dx.doi.org/10.5194/npg-2017-3Continuum model of wave propagation in fragmented media: linear damping approximation
<b>Continuum model of wave propagation in fragmented media: linear damping approximation</b><br>
Maxim Khudyakov, Arcady V. Dyskin, and Elena Pasternak<br>
Nonlin. Processes Geophys. Discuss., doi:10.5194/npg-2017-3,2017<br>
<b>Manuscript under review for NPG</b> (discussion: open, 2 comments)<br>
In order to assess energy loss during wave propagation in fragmented media, an impact model is proposed. The proposed model can be expressed by or used together with other linear damping models, which is important for the determination of mechanical characteristics of such media and mineral exploration.
<b>Continuum model of wave propagation in fragmented media: linear damping approximation</b><br>
Maxim Khudyakov, Arcady V. Dyskin, and Elena Pasternak<br>
Nonlin. Processes Geophys. Discuss., doi:10.5194/npg-2017-3,2017<br>
<b>Manuscript under review for NPG</b> (discussion: open, 2 comments)<br>
Energy dissipation during wave propagation in fragmented geomaterials can be caused by independent movement of fragments leading to energy loss on their impact. By considering a pair of impacting fragments at times much greater than the period of their oscillations we show that at large time scale, the dynamics of the pair can be described by a linear viscous model with damping coefficient expressed through the restitution coefficient representing energy loss on impact. Wave propagation in fragmented geomaterials is also considered at the large time scale assuming that the wavelengths are much larger than the fragment sizes such that the attenuation associated with wave scattering on the fragment interfaces can be neglected. These assumptions lead to Kelvin-Voigt model of wave propagation, which allows the determination of dispersion relationship. As the attenuation and dispersion are not related to the rate dependence of rock deformation, but rather to the interaction of fragments the increasing damping and dispersion at low frequencies can be seen as an indication of fragmented nature of the geomaterial and the capacity of the fragments for independent movement.
Copernicus Electronic Production Support Office2017-02-08T02:33:38+01:002017-02-08T02:33:38+01:00http://dx.doi.org/10.5194/npg-24-77-2017Scale and space dependencies of soil nitrogen variability
<b>Scale and space dependencies of soil nitrogen variability</b><br>
Ana M. Tarquis, María Teresa Castellanos, Maria Carmen Cartagena, Augusto Arce, Francisco Ribas, María Jesús Cabello, Juan López de Herrera, and Nigel R. A. Bird<br>
Nonlin. Processes Geophys., 24, 77-87, doi:10.5194/npg-24-77-2017, 2017<br>
Melon crop got different levels of N that constituted a contribution to the variation of soil N at mainly larger scales. During its development a proportion of the N was taken up, adding a second factor of variability at smaller scales. After the melon harvest, the wheat was sown across the plots and harvested at the end of the season. Wheat was used as a N sink crop and allowed us to evaluate the soil N residual. Multiscale and relative entropy were applied to study N scale dependencies.
<b>Scale and space dependencies of soil nitrogen variability</b><br>
Ana M. Tarquis, María Teresa Castellanos, Maria Carmen Cartagena, Augusto Arce, Francisco Ribas, María Jesús Cabello, Juan López de Herrera, and Nigel R. A. Bird<br>
Nonlin. Processes Geophys., 24, 77-87, doi:10.5194/npg-24-77-2017, 2017<br>
In this study, we use multifractal analysis, through generalized
dimensions (<i>D</i><sub>q</sub>) and the relative entropy (<i>E</i>(<i>δ</i>)), to investigate
the residual effects of fertigation treatments applied to a previous crop on
wheat and grain biomass and nitrogen content. The wheat crop covered nine
subplots from a previous experiment on melon responses to fertigation. Each
subplot had previously received a different level of applied nitrogen
(N<sub>app</sub>), and the plants from the previous melon crop had already taken up
part of it. Many factors affect these variables, causing them to vary at
different scales and creating a non-uniform distribution along a transect.
Correlations between the four variables and N<sub>app</sub> showed high volatility,
although the relationships between grain weight and wheat weight versus
wheat nitrogen content presented a statistically significant logarithmic
trend.
<br><br>
The <i>D</i><sub>q</sub> values were used to study the relation between scales and
<i>E</i>(<i>δ</i>) values, and their increments between scales were used to
identify the scale at which the variable had the maximum structure and were
compared with the scaling behaviour of the N<sub>app</sub>. <i>E</i>(<i>δ</i>) is particularly
appropriate for this purpose because it does not require any prior
assumptions regarding the structure of the data and is easy to calculate.
<br><br>
The four variables studied presented a weak multifractal character with a
low variation in <i>D</i><sub>q</sub> values, although there was a distinction between
variables related to nitrogen content and weight. On the other hand, the
<i>E</i>(<i>δ</i>) and the increments in <i>E</i>(<i>δ</i>) help us to detect changes in
the scaling behaviour of all the variables studied. In this respect, the
results showed that the N<sub>app</sub> through fertigation dominated the wheat and
grain biomass response, as well as the nitrogen content of the whole plant;
surprisingly, the grain nitrogen content did not show the same structure as
N<sub>app</sub>. At the same time, there was a noticeable structure variation in all
the variables, except wheat nitrogen content, at smaller scales that could
correspond to the previous cropping root arrangement due to uptake of the
N<sub>app</sub>.
Copernicus Electronic Production Support Office2017-02-06T02:33:38+01:002017-02-06T02:33:38+01:00http://dx.doi.org/10.5194/npg-2016-80Analysis of Wave Propagation in a Discrete Chain of Bilinear
Oscillators
<b>Analysis of Wave Propagation in a Discrete Chain of Bilinear
Oscillators</b><br>
Maria S. Kuznetsova, Elena Pasternak, and Arcady V. Dyskin<br>
Nonlin. Processes Geophys. Discuss., doi:10.5194/npg-2016-80,2017<br>
<b>Manuscript under review for NPG</b> (discussion: open, 2 comments)<br>
The process of wave propagation in the discrete chain of bilinear oscillators subjected to several types of external harmonic excitation has been analysed. The phenomenon of sign inversion of the displacement is observed for tension-compression excitation. The solution for wave propagation in a continuous 1D bimodular rod is developed and the numerical results are compared showing good agreement.
<b>Analysis of Wave Propagation in a Discrete Chain of Bilinear
Oscillators</b><br>
Maria S. Kuznetsova, Elena Pasternak, and Arcady V. Dyskin<br>
Nonlin. Processes Geophys. Discuss., doi:10.5194/npg-2016-80,2017<br>
<b>Manuscript under review for NPG</b> (discussion: open, 2 comments)<br>
The process of wave propagation in the discrete chain of bilinear oscillators subjected to several types of external harmonic excitation has been analysed. The phenomenon of sign inversion of the displacement is observed for tension-compression excitation. The solution for wave propagation in a continuous 1D bimodular rod is developed and the numerical results are compared.
Copernicus Electronic Production Support Office2017-02-01T02:33:38+01:002017-02-01T02:33:38+01:00http://dx.doi.org/10.5194/npg-24-61-2017The fully nonlinear stratified geostrophic adjustment problem
<b>The fully nonlinear stratified geostrophic adjustment problem</b><br>
Aaron Coutino and Marek Stastna<br>
Nonlin. Processes Geophys., 24, 61-75, doi:10.5194/npg-24-61-2017, 2017<br>
We have re-examined the classical geostrophic adjustment problem, where a disturbance of a density stratification is released from rest in a rotating frame of reference, from a numerical point of view. This has enabled us to consider the governing equations without approximations. We show that both the waves generated and the remaining state exhibit nonlinear effects. Due to advances in available computational power, we can now revisit classical problems and solve them completely.
<b>The fully nonlinear stratified geostrophic adjustment problem</b><br>
Aaron Coutino and Marek Stastna<br>
Nonlin. Processes Geophys., 24, 61-75, doi:10.5194/npg-24-61-2017, 2017<br>
The study of the adjustment to equilibrium by a stratified fluid
in a rotating reference frame is a classical problem in geophysical fluid
dynamics. We consider the fully nonlinear, stratified adjustment problem from
a numerical point of view. We present results of smoothed dam break
simulations based on experiments in the published literature, with a focus on
both the wave trains that propagate away from the nascent geostrophic state
and the geostrophic state itself. We demonstrate that for Rossby numbers in
excess of roughly 2 the wave train cannot be interpreted in terms of linear
theory. This wave train consists of a leading solitary-like packet and a
trailing tail of dispersive waves. However, it is found that the leading wave
packet never completely separates from the trailing tail. Somewhat
surprisingly, the inertial oscillations associated with the geostrophic state
exhibit evidence of nonlinearity even when the Rossby number falls below 1.
We vary the width of the initial disturbance and the rotation rate so as to
keep the Rossby number fixed, and find that while the qualitative response
remains consistent, the Froude number varies, and these variations are
manifested in the form of the emanating wave train. For wider initial
disturbances we find clear evidence of a wave train that initially propagates
toward the near wall, reflects, and propagates away from the geostrophic
state behind the leading wave train. We compare kinetic energy inside and
outside of the geostrophic state, finding that for long times a Rossby number
of around one-quarter yields an equal split between the two, with lower
(higher) Rossby numbers yielding more energy in the geostrophic state (wave
train). Finally we compare the energetics of the geostrophic state as the
Rossby number varies, finding long-lived inertial oscillations in the
majority of the cases and a general agreement with the past literature that
employed either hydrostatic, shallow-water equation-based theory or
stratified Navier–Stokes equations with a linear stratification.
Copernicus Electronic Production Support Office2017-01-30T02:33:38+01:002017-01-30T02:33:38+01:00http://dx.doi.org/10.5194/npg-24-43-2017Variational modelling of extreme waves through oblique interaction of solitary waves: application to Mach reflection
<b>Variational modelling of extreme waves through oblique interaction of solitary waves: application to Mach reflection</b><br>
Floriane Gidel, Onno Bokhove, and Anna Kalogirou<br>
Nonlin. Processes Geophys., 24, 43-60, doi:10.5194/npg-24-43-2017, 2017<br>
Extreme water waves impacting ships and offshore structures can not only cause severe structural damage, but also threaten the safety of passengers and crew. Accordingly, the motivation for the present work is to better understand the dynamics of extreme waves in two cases: the case of "green water" and the case of "freak waves". Our methodology can simulate those two events in order to estimate the forces of such extreme waves and thus aid engineers in the design of safer maritime structures.
<b>Variational modelling of extreme waves through oblique interaction of solitary waves: application to Mach reflection</b><br>
Floriane Gidel, Onno Bokhove, and Anna Kalogirou<br>
Nonlin. Processes Geophys., 24, 43-60, doi:10.5194/npg-24-43-2017, 2017<br>
In this work, we model extreme waves that occur due to Mach
reflection through the intersection of two obliquely incident solitary waves.
For a given range of incident angles and amplitudes, the Mach stem wave grows
linearly in length and amplitude, reaching up to 4 times the amplitude of the
incident waves. A variational approach is used to derive the bidirectional
Benney–Luke equations, an asymptotic equivalent of the three-dimensional
potential-flow equations modelling water waves. This nonlinear and weakly
dispersive model has the advantage of allowing wave propagation in two
horizontal directions, which is not the case with the unidirectional
Kadomtsev–Petviashvili (KP) equation used in most previous studies. A
variational Galerkin finite-element method is applied to solve the system
numerically in Firedrake with a second-order Störmer–Verlet temporal
integration scheme, in order to obtain stable simulations that conserve the
overall mass and energy of the system. Using this approach, we are able to
get close to the 4-fold amplitude amplification predicted by Miles.
Copernicus Electronic Production Support Office2017-01-27T02:33:38+01:002017-01-27T02:33:38+01:00http://dx.doi.org/10.5194/npg-24-23-2017Laboratory experimental investigation of heat transport in fractured media
<b>Laboratory experimental investigation of heat transport in fractured media</b><br>
Claudia Cherubini, Nicola Pastore, Concetta I. Giasi, and Nicoletta Maria Allegretti<br>
Nonlin. Processes Geophys., 24, 23-42, doi:10.5194/npg-24-23-2017, 2017<br>
Aquifers offer the possibility of exploiting geothermal energy. Especially in fractured aquifers, in order to increase the optimal efficiency of installations which use groundwater as a geothermal resource, flow and heat transport dynamics need to be well understood. This study is aimed at deepening the understanding of this topic through heat transport experiments in fractured networks and their interpretation.
<b>Laboratory experimental investigation of heat transport in fractured media</b><br>
Claudia Cherubini, Nicola Pastore, Concetta I. Giasi, and Nicoletta Maria Allegretti<br>
Nonlin. Processes Geophys., 24, 23-42, doi:10.5194/npg-24-23-2017, 2017<br>
Low enthalpy geothermal energy is a renewable resource that is still
underexploited nowadays in relation to its potential for development in
society worldwide. Most of its applications have already been investigated,
such as heating and cooling of private and public buildings, road defrosting,
cooling of industrial processes, food drying systems or desalination.
<br><br>
Geothermal power development is a long, risky and expensive process. It
basically consists of successive development stages aimed at locating the
resources (exploration), confirming the power generating capacity of the
reservoir (confirmation) and building the power plant and associated
structures (site development). Different factors intervene in influencing the
length, difficulty and materials required for these phases, thereby affecting
their cost.
<br><br>
One of the major limitations related to the installation of low enthalpy
geothermal power plants regards the initial development steps that are risky
and the upfront capital costs that are huge.
<br><br>
Most of the total cost of geothermal power is related to the reimbursement of
invested capital and associated returns.
<br><br>
In order to increase the optimal efficiency of installations which use
groundwater as a geothermal resource, flow and heat transport dynamics in
aquifers need to be well characterized. Especially in fractured rock aquifers
these processes represent critical elements that are not well known.
Therefore there is a tendency to oversize geothermal plants.
<br><br>
In the literature there are very few studies on heat transport, especially on
fractured media.
<br><br>
This study is aimed at deepening the understanding of this topic through heat
transport experiments in fractured networks and their interpretation.
<br><br>
Heat transfer tests have been carried out on the experimental apparatus
previously employed to perform flow and tracer transport experiments, which
has been modified in order to analyze heat transport dynamics in a network of
fractures. In order to model the obtained thermal breakthrough curves, the
Explicit Network Model (ENM) has been used, which is based on an adaptation
of Tang's solution for the transport of the solutes in a semi-infinite single
fracture embedded in a porous matrix.
<br><br>
Parameter estimation, time moment analysis, tailing character and other
dimensionless parameters have permitted a better understanding of the
dynamics of heat transport and the efficiency of heat exchange between the
fractures and the matrix. The results have been compared with the previous
experimental studies on solute transport.
Copernicus Electronic Production Support Office2017-01-26T02:33:38+01:002017-01-26T02:33:38+01:00http://dx.doi.org/10.5194/npg-2016-76Quantifying the changes of soil surface microroughness due to rainfall-induced erosion on a smooth surface
<b>Quantifying the changes of soil surface microroughness due to rainfall-induced erosion on a smooth surface</b><br>
Benjamin K. B. Abban, A. N. Thanos Papanicolaou, Christos P. Giannopoulos, Dimitrios C. Dermisis, Kenneth M. Wacha, Christopher G. Wilson, and Mohamed Elhakeem<br>
Nonlin. Processes Geophys. Discuss., doi:10.5194/npg-2016-76,2017<br>
<b>Revised manuscript under review for NPG</b> (discussion: final response, 6 comments)<br>
We examine rainfall-induced change in soil microroughness of bare soil surfaces in agricultural landscapes with initial microroughness length scales of 2 mm or less. Past studies have focused on scales between 5–50 mm. A rainfall simulator is used. Microroughness measurements are obtained via a laser scanner. Findings show a consistent increase in roughness under rainfall action for initial length scales of 2 mm. This contradicts existing literature where a monotonic decay of roughness is recorded.
<b>Quantifying the changes of soil surface microroughness due to rainfall-induced erosion on a smooth surface</b><br>
Benjamin K. B. Abban, A. N. Thanos Papanicolaou, Christos P. Giannopoulos, Dimitrios C. Dermisis, Kenneth M. Wacha, Christopher G. Wilson, and Mohamed Elhakeem<br>
Nonlin. Processes Geophys. Discuss., doi:10.5194/npg-2016-76,2017<br>
<b>Revised manuscript under review for NPG</b> (discussion: final response, 6 comments)<br>
This study examines the rainfall induced change in soil microroughness of a bare soil surface in agricultural landscapes. The focus is on the quantification of roughness length under the action of rainfall for initial microroughness length scales of 2 mm or less, defined here as initial smooth surface conditions. These conditions have not been extensively examined in the literature as most studies have focused on initial disturbed surface conditions (bed surface conditions with initial length scales greater than 2 mm and varying between 5–50 mm). Three representative intensities namely 30 mm/h, 60 mm/h and 75 mm/h were applied over a smoothened bed surface at a field plot via a rainfall simulator. Soil surface microroughness measurements were obtained via a surface-profile laser scanner. Two indices were utilized to quantify soil surface microroughness, namely the Random Roughness (RR) index and the crossover length. Findings show a consistent increase in roughness under the action of rainfall for initial microroughness length scales of 2 mm. This contradicts existing literature where a monotonic decay of roughness of soil surfaces with rainfall is recorded for disturbed surfaces. Analysis shows that on an average the RR and the crossover length post run increase by a multiple of 3.15 and 1.9, respectively from their corresponding values apriori the runs.
Copernicus Electronic Production Support Office2017-01-23T02:33:38+01:002017-01-23T02:33:38+01:00http://dx.doi.org/10.5194/npg-24-9-2017Estimating the state of a geophysical system with sparse observations: time delay methods to achieve accurate initial states for prediction
<b>Estimating the state of a geophysical system with sparse observations: time delay methods to achieve accurate initial states for prediction</b><br>
Zhe An, Daniel Rey, Jingxin Ye, and Henry D. I. Abarbanel<br>
Nonlin. Processes Geophys., 24, 9-22, doi:10.5194/npg-24-9-2017, 2017<br>
The problem of forecasting the behavior of a complex dynamical system through
analysis of observational time-series data becomes difficult when the system
expresses chaotic behavior and the measurements are sparse, in both space
and/or time. Despite the fact that this situation is quite typical across
many fields, including numerical weather prediction, the issue of whether the
available observations are "sufficient" for generating successful forecasts
is still not well understood. An analysis by Whartenby et al. (2013) found that in the context of the nonlinear shallow water equations on a <i>β</i> plane, standard nudging techniques require observing approximately 70 % of the full set
of state variables. Here we examine the same system using a method introduced
by Rey et al. (2014a), which generalizes standard nudging methods to utilize time delayed measurements. We show that in certain circumstances, it provides a
sizable reduction in the number of observations required to construct
accurate estimates and high-quality predictions. In particular, we find that
this estimate of 70 % can be reduced to about 33 % using time delays,
and even further if Lagrangian drifter locations are also used as
measurements.
Copernicus Electronic Production Support Office2017-01-16T02:33:38+01:002017-01-16T02:33:38+01:00