Nonlinear Processes in Geophysics

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Combined list of the recent articles of the journal Nonlinear Processes in Geophysics and the recent discussion forum Nonlinear Processes in Geophysics Discussions
Updated: 5 hours 49 min ago

Application of Levy Processes in Modelling (Geodetic) Time Series With Mixed Spectra

Mon, 10/21/2019 - 15:57
Application of Levy Processes in Modelling (Geodetic) Time Series With Mixed Spectra
Jean-Philippe Montillet, Xiaoxing He, and Kegen Yu
Nonlin. Processes Geophys. Discuss., https//doi.org/10.5194/npg-2019-48,2019
Manuscript under review for NPG (discussion: open, 0 comments)
Geodetic time series, series of observations measured from various satellites, must be modelled carefully to extract accurate information about geophysical processes. These models take into account the properties of the noise in these time series, which are generally a mixed of several kinds of noise. This work proposes a model based on the family of Levy processes (Gaussian, fractional and stable) as an alternative with real and simulated data.

Data-driven versus self-similar parameterizations for Stochastic Advection by Lie Transport and Location Uncertainty

Wed, 10/16/2019 - 15:57
Data-driven versus self-similar parameterizations for Stochastic Advection by Lie Transport and Location Uncertainty
Valentin Resseguier, Wei Pan, and Baylor Fox-Kemper
Nonlin. Processes Geophys. Discuss., https//doi.org/10.5194/npg-2019-54,2019
Manuscript under review for NPG (discussion: open, 0 comments)
Geophysical flows span a broader range of temporal and spatial scales than can be resolved numerically. One way to alleviate the ensuing numerical errors is to combine simulations with measurements, taking account of the accuracies of these two sources of information. Here we quantify the distribution of numerical simulation errors without relying on high-resolution numerical simulations. Specifically, small-scale random vortices are added to simulations while conserving energy or circulation.

Baroclinic and barotropic instabilities in planetary atmospheres - energetics, equilibration and adjustment

Tue, 10/15/2019 - 15:57
Baroclinic and barotropic instabilities in planetary atmospheres - energetics, equilibration and adjustment
Peter Read, Neil Lewis, Daniel Kennedy, Hélène Scolan, Fachreddin Tabataba-Vakili, Yixiong Wang, Susie Wright, and Roland Young
Nonlin. Processes Geophys. Discuss., https//doi.org/10.5194/npg-2019-53,2019
Manuscript under review for NPG (discussion: open, 0 comments)
Baroclinic and barotropic instabilities are well known as the processes responsible for the production of the most important energy-containing eddies in the atmospheres and oceans of the Earth and other planets. Linear and nonlinear instability theories provide insights into when such instabilities may occur, grow to large amplitude and saturate, with examples from the laboratory, simplified numerical models and planetary atmospheres. We conclude with a number of open issues for future research.

Residence Time of Energy in the Atmosphere

Mon, 10/14/2019 - 15:57
Residence Time of Energy in the Atmosphere
Carlos Osácar, Manuel Membrado, and Amalio Fernández-Pacheco
Nonlin. Processes Geophys. Discuss., https//doi.org/10.5194/npg-2019-52,2019
Manuscript under review for NPG (discussion: open, 0 comments)
We deduce that after a global thermal perturbation, the atmosphere would need about a couple of months to come back to equilibrium.

Seismic section image detail enhancement method based on wavelet transform

Fri, 10/11/2019 - 15:57
Seismic section image detail enhancement method based on wavelet transform
Xiang-Yu Jia and Chang-Lei DongYe
Nonlin. Processes Geophys. Discuss., https//doi.org/10.5194/npg-2019-46,2019
Manuscript under review for NPG (discussion: open, 0 comments)
We proposed a texture detail enhancement method for seismic section image. Wavelet transform can effectively separate structure information and detail information of image. High frequency noise in structural information can be estimated and removed effectively by using bilateral texture filter in low frequency subband. In the high frequency subband, adaptive enhancement transform can be used to enhance the image edge and texture information, and effectively remove the low frequency noise.

Seasonal statistical-dynamical prediction of the North Atlantic Oscillation by probabilistic post-processing

Thu, 10/10/2019 - 15:57
Seasonal statistical-dynamical prediction of the North Atlantic Oscillation by probabilistic post-processing
André Düsterhus
Nonlin. Processes Geophys. Discuss., https//doi.org/10.5194/npg-2019-50,2019
Manuscript under review for NPG (discussion: open, 2 comments)
Seasonal prediction of the of the North Atlantic Oscillation (NAO) has been improved in recent years by improving dynamical models and ensemble predictions. One step therein was the so called sub-sampling, which combines statistical with dynamical prediction. This study generalises this approach and makes it much more accessible. Furthermore, it presents a new verification approach for such predictions.

Application of local attractor dimension to reduced space strongly coupled data assimilation for chaotic multiscale systems

Thu, 10/10/2019 - 15:57
Application of local attractor dimension to reduced space strongly coupled data assimilation for chaotic multiscale systems
Courtney Quinn, Terence J. O'Kane, and Vassili Kitsios
Nonlin. Processes Geophys. Discuss., https//doi.org/10.5194/npg-2019-51,2019
Manuscript under review for NPG (discussion: open, 0 comments)
This study presents a novel method for reduced-rank data assimilation of multiscale highly nonlinear systems. Time-varying dynamical properties are used to determine the rank and projection of the system onto a reduced subspace. The variable reduced-rank method is shown to succeed over other fixed-rank methods. This work provides implications for performing strongly coupled data assimilation with a limited number of ensemble members on high dimensional coupled climate models.

Numerical bifurcation methods applied to climate models: analysis beyond simulation

Tue, 10/08/2019 - 15:57
Numerical bifurcation methods applied to climate models: analysis beyond simulation
Henk A. Dijkstra
Nonlin. Processes Geophys., 26, 359–369, https://doi.org/10.5194/npg-26-359-2019, 2019
I provide a personal view on the role of bifurcation analysis of climate models in the development of a theory of variability in the climate system. By outlining the state of the art of the methodology and by discussing what has been done and what has been learned from a hierarchy of models, I will argue that there are low-order phenomena of climate variability, such as El Niño and the Atlantic Multidecadal Oscillation.

Remember the past: A comparison of time-adaptive training schemes for non-homogeneous regression

Wed, 10/02/2019 - 15:57
Remember the past: A comparison of time-adaptive training schemes for non-homogeneous regression
Moritz N. Lang, Sebastian Lerch, Georg J. Mayr, Thorsten Simon, Reto Stauffer, and Achim Zeileis
Nonlin. Processes Geophys. Discuss., https//doi.org/10.5194/npg-2019-49,2019
Manuscript under review for NPG (discussion: open, 1 comment)
Statistical post-processing aims to increase the predictive skill of probabilistic ensemble weather forecasts by learning the statistical relation between historical pairs of observations and ensemble forecasts within a given training data set. This study compares four different training schemes and shows that including multiple years of data in the training set typically yields a more stable post-processing while it loses the ability to quickly adjust to temporal changes in the underlying data.

Statistical post-processing of ensemble forecasts of the height of new snow

Thu, 09/26/2019 - 15:57
Statistical post-processing of ensemble forecasts of the height of new snow
Jari-Pekka Nousu, Matthieu Lafaysse, Matthieu Vernay, Joseph Bellier, Guillaume Evin, and Bruno Joly
Nonlin. Processes Geophys., 26, 339–357, https://doi.org/10.5194/npg-26-339-2019, 2019
Forecasting the height of new snow is crucial for avalanche hazard, road viability, ski resorts and tourism. The numerical models suffer from systematic and significant errors which are misleading for the final users. Here, we applied for the first time a state-of-the-art statistical method to correct ensemble numerical forecasts of the height of new snow from their statistical link with measurements in French Alps and Pyrenees. Thus the realism of automatic forecasts can be quickly improved.

Study of the fractality in an MHD Shell model forced by solar wind fluctuations

Wed, 09/18/2019 - 15:57
Study of the fractality in an MHD Shell model forced by solar wind fluctuations
Macarena Domínguez, Giuseppina Nigro, Víctor Muñoz, Vincenzo Carbone, and Mario Riquelme
Nonlin. Processes Geophys. Discuss., https//doi.org/10.5194/npg-2019-31,2019
Manuscript under review for NPG (discussion: open, 1 comment)
We study a model for the relationship between space plasma and geomagnetic activity, by using an MHD shell model, where its forcing has been replaced by solar wind fluctuations data. We study the fractality of the forcing, its output and the activity of the model, which may represent the existence of geomagnetic storms. We find correlations between some of these metrics and the solar cycle, suggesting that the complexity of the solar wind may have influence on the level of geomagnetic activity.

Temperature profiles, plumes and spectra in the surface layers of convective atmospheric boundary layers

Wed, 09/18/2019 - 15:57
Temperature profiles, plumes and spectra in the surface layers of convective atmospheric boundary layers
Keith G. McNaughton and Subharthi Chowdhuri
Nonlin. Processes Geophys. Discuss., https//doi.org/10.5194/npg-2019-43,2019
Manuscript under review for NPG (discussion: open, 1 comment)

We survey temperature patterns and heat transport in convective boundary layers (CBLs) from the perspective that these are emergent properties of far-from-equilibrium, complex dynamical systems. We use the term 'plumes' to denote the temperature patterns, in much the same way that the term 'eddies' is used to describe patterns of motion in turbulent flows. We introduce a two-temperature (2T) toy model to connect the scaling properties of temperature gradients, temperature variance and heat transport to the geometric properties of plumes. We then examine temperature (T) probability density functions and w-T joint probability density functions, T spectra and wT cospectra observed both within and above the surface friction layer. Here w is vertical velocity. We interpret these in terms of the properties of the plumes that give rise to them. We focus first on the self-similarity property of the plumes above the SFL, and then introduce new scaling results from within the SFL, which show that T spectra and wT cospectra are not self-similar with height at small heights z/zs < 0.1, but increasingly display properties associated with random diffusion. The CBL similarity parameters defined by McNaughton et al (Non-linear Processes in Geophysics 14, 257–271, 2007) are used throughout. We conclude by contrasting our interpretation of the role of buoyancy in CBL flows with that of Richardson (proc. Roy. Soc. London A 87, 354–373, 1920), whose ideas inform the current interpretation of the statistical fluid mechanics model of boundary-layer flows.

Effects of upwelling duration and phytoplankton growth regime on dissolved oxygen levels in an idealized Iberian Peninsula upwelling system

Wed, 09/18/2019 - 15:57
Effects of upwelling duration and phytoplankton growth regime on dissolved oxygen levels in an idealized Iberian Peninsula upwelling system
João H. Bettencourt, Vincent Rossi, Lionel Renault, Peter Haynes, Yves Morel, and Véronique Garçon
Nonlin. Processes Geophys. Discuss., https//doi.org/10.5194/npg-2019-47,2019
Manuscript under review for NPG (discussion: open, 0 comments)
We used a oxygen model and an hydrodynamic model of the Iberian upwelling to study the interplay between upwelling wind duration and phytoplankton growth and its impact on oxygen levels. When wind duration increases, marine currents remove oxygen from the coast, that is replenished by a fast phytoplankton growth. When phytoplankton growth is slow, the oxygen removal dominates and the coastal region looses oxygen. This can increase the future risk of upwelling regions becoming oxygen poor.

Post-processing of seasonal predictions – Case studies using the EUROSIP hindcast data base

Wed, 09/18/2019 - 15:57
Post-processing of seasonal predictions – Case studies using the EUROSIP hindcast data base
Emmanuel Roulin and Stéphane Vannitsem
Nonlin. Processes Geophys. Discuss., https//doi.org/10.5194/npg-2019-45,2019
Manuscript under review for NPG (discussion: open, 1 comment)
We need seasonal predictions of temperature and precipitation to prepare hydrological outlooks. Since the skill is limited, statistical correction and combination of outputs from multiple models are necessary. We use the forecasts of past situations from the EUROSIP multi-model system for 6 case studies in Western Europe and the Mediterranean Region. We identify skill for spring temperature in most areas and winter precipitation in Sweden and Greece. Sample size for training appears crucial.

Revising the stochastic iterative ensemble smoother

Tue, 09/17/2019 - 15:57
Revising the stochastic iterative ensemble smoother
Patrick Nima Raanes, Andreas Størksen Stordal, and Geir Evensen
Nonlin. Processes Geophys., 26, 325–338, https://doi.org/10.5194/npg-26-325-2019, 2019
A popular variational ensemble smoother for data assimilation and history matching is simplified. An exact relationship between ensemble linearizations (linear regression) and adjoints (analytic derivatives) is established.

Particle clustering and subclustering as a proxy for mixing in geophysical flows

Mon, 09/16/2019 - 15:57
Particle clustering and subclustering as a proxy for mixing in geophysical flows
Rishiraj Chakraborty, Aaron Coutino, and Marek Stastna
Nonlin. Processes Geophys., 26, 307–324, https://doi.org/10.5194/npg-26-307-2019, 2019
In this paper, we highlight a specific example of large-scale flows. We discuss a graph-theory-based Lagrangian technique for identifying regions of strong mixing (in the sense of diffusion) in the flow and compare it to previous Lagrangian approaches used in this context.

Detecting dynamical anomalies in time series from different palaeoclimate proxy archives using windowed recurrence network analysis

Mon, 09/09/2019 - 15:57
Detecting dynamical anomalies in time series from different palaeoclimate proxy archives using windowed recurrence network analysis
Jaqueline Lekscha and Reik V. Donner
Nonlin. Processes Geophys. Discuss., https//doi.org/10.5194/npg-2019-41,2019
Manuscript under review for NPG (discussion: open, 1 comment)

Analysing palaeoclimate proxy time series using windowed recurrence network analysis (wRNA) has been shown to provide valuable information on past climate variability. In turn, it has also been found that the robustness of the obtained results differs among proxies from different palaeoclimate archives. To systematically test the suitability of wRNA for studying different types of palaeoclimate proxy time series, we use the framework of forward proxy modelling. For this, we create artificial input time series with different properties and, in a first step, compare the time series properties of the input and the model output time series. In a second step, we compare the areawise significant anomalies detected using wRNA. For proxies from tree and lake archives, we find that significant anomalies present in the input time series are sometimes missed in the input time series after the nonlinear filtering by the corresponding models. For proxies from speleothems, we observe falsely identified significant anomalies that are not present in the input time series. Finally, for proxies from ice cores, the wRNA results show the best correspondence with those for the input data. Our results contribute to improve the interpretation of windowed recurrence network analysis results obtained from real-world palaeoclimate time series.

In-depth analysis of a discrete p model

Mon, 09/02/2019 - 15:57
In-depth analysis of a discrete p model
Uwe Saint-Mont
Nonlin. Processes Geophys. Discuss., https//doi.org/10.5194/npg-2019-17,2019
Manuscript under review for NPG (discussion: open, 0 comments)
Every student of probability knows Pascal's triangle. Mandelbrot's fractals are also rather well known; more recently, cascades have come into focus. This article starts with 'local' cascades and shows that they are equivalent to a new 'global' operation (weaving). Thus, one obtains a multiplicative pattern that lies at the heart of a new discrete 'p model.' Since the technical machinery is simple, corresponding distributions can be analysed in detail, extending received results considerably.

Mahalanobis distance-based recognition of changes in the dynamics of a seismic process

Tue, 08/27/2019 - 15:57
Mahalanobis distance-based recognition of changes in the dynamics of a seismic process
Teimuraz Matcharashvili, Zbigniew Czechowski, and Natalia Zhukova
Nonlin. Processes Geophys., 26, 291–305, https://doi.org/10.5194/npg-26-291-2019, 2019

In the present work, we aim to analyse the regularity of a seismic process based on its spatial, temporal, and energetic characteristics. Increments of cumulative times, increments of cumulative distances, and increments of cumulative seismic energies are calculated from an earthquake catalogue for southern California from 1975 to 2017.

As the method of analysis, we use the multivariate Mahalanobis distance calculation, combined with a surrogate data testing procedure that is often used for the testing of non-linear structures in complex data sets. Before analysing the dynamical features of the seismic process, we tested the used approach for two different 3-D models in which the dynamical features were changed from more regular to more randomised conditions by adding a certain degree of noise.

An analysis of the variability in the extent of regularity of the seismic process was carried out for different completeness magnitude thresholds.

The results of our analysis show that in about a third of all the 50-data windows the original seismic process was indistinguishable from a random process based on its features of temporal, spatial, and energetic variability. It was shown that prior to the occurrence of strong earthquakes, mostly in periods of generation of relatively small earthquakes, the percentage of windows in which the seismic process is indistinguishable from a random process increases (to 60 %–80 %). During periods of aftershock activity, the process of small earthquake generation became regular in all of the windows considered, and thus was markedly different from the randomised catalogues.

In some periods within the catalogue, the seismic process appeared to be closer to randomness, while in other cases it became closer to a regular behaviour. More specifically, in periods of relatively decreased earthquake generation activity (with low energy release), the seismic process appears to be random, while during periods of occurrence of strong events, followed by series of aftershocks, significant deviation from randomness is shown, i.e. the extent of regularity markedly increases. The period for which such deviation from random behaviour lasts depends on the amount of seismic energy released by the strong earthquake.

Explosive instability due to flow over a rippled bottom

Wed, 08/21/2019 - 15:57
Explosive instability due to flow over a rippled bottom
Anirban Guha and Raunak Raj
Nonlin. Processes Geophys., 26, 283–290, https://doi.org/10.5194/npg-26-283-2019, 2019
Waves observed on the ocean surface often nonlinearly interact among themselves and undergo algebraic growth – a mechanism known as resonant triad interaction. Bragg resonance is a special resonant triad in which one of the constituent waves is the ocean's undulating bottom boundary. Here we show that, in the presence of an ocean current, two surface waves or a surface wave and an interfacial wave (wave existing at the ocean pycnocline) can undergo exponential growth.

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