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
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From research to applications – examples of operational ensemble post-processing in France using machine learning

Fri, 05/29/2020 - 20:40
From research to applications – examples of operational ensemble post-processing in France using machine learning
Maxime Taillardat and Olivier Mestre
Nonlin. Processes Geophys., 27, 329–347, https://doi.org/10.5194/npg-27-329-2020, 2020
Statistical post-processing of ensemble forecasts is now a well-known procedure in order to correct biased and misdispersed ensemble weather predictions. But practical application in European national weather services is in its infancy. Different applications of ensemble post-processing using machine learning at an industrial scale are presented. Forecast quality and value are improved compared to the raw ensemble, but several facilities have to be made to adjust to operational constraints.

Detecting flow features in scarce trajectory data using networks derived from symbolic itineraries: an application to surface drifters in the North Atlantic

Fri, 05/29/2020 - 20:40
Detecting flow features in scarce trajectory data using networks derived from symbolic itineraries: an application to surface drifters in the North Atlantic
David Wichmann, Christian Kehl, Henk A. Dijkstra, and Erik van Sebille
Nonlin. Processes Geophys. Discuss., https//doi.org/10.5194/npg-2020-18,2020
Preprint under review for NPG (discussion: open, 0 comments)
The surface transport of heat, nutrients and plastic in the North Atlantic Ocean is organized into large scale flow structures. We propose a new and simple method to detect such features in ocean drifter data sets, by identifying groups of trajectories with similar dynamical behaviour using network theory. We successfull detect well-known regions such as the Subpolar and Subtropical Gyres, the Western Boundary Current region and the Carribean Sea.

Correcting for model changes in statistical postprocessing – an approach based on response theory

Wed, 05/27/2020 - 20:40
Correcting for model changes in statistical postprocessing – an approach based on response theory
Jonathan Demaeyer and Stéphane Vannitsem
Nonlin. Processes Geophys., 27, 307–327, https://doi.org/10.5194/npg-27-307-2020, 2020
Postprocessing schemes used to correct weather forecasts are no longer efficient when the model generating the forecasts changes. An approach based on response theory to take the change into account without having to recompute the parameters based on past forecasts is presented. It is tested on an analytical model and a simple model of atmospheric variability. We show that this approach is effective and discuss its potential application for an operational environment.

Nonlinear vortex solution for perturbations in the Earth's ionosphere

Mon, 05/25/2020 - 20:40
Nonlinear vortex solution for perturbations in the Earth's ionosphere
Miroslava Vukcevic and Luka Č. Popović
Nonlin. Processes Geophys., 27, 295–306, https://doi.org/10.5194/npg-27-295-2020, 2020
The soliton vortex two-dimensional solution has been derived for the ionosphere. Why are solitons so important? The advantage of an analytical soliton solution is its localization in space and time as a consequence of balance between nonlinearity and dispersion. One very good example of the balance between nonlinear and dispersive effects is tsunami, a surface gravity one-dimensional wave that can propagate with constant velocity and constant amplitude when it is assured by a parameter regime.

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

Tue, 05/19/2020 - 20:40
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., 27, 277–294, https://doi.org/10.5194/npg-27-277-2020, 2020
The oceans are losing oxygen, and future changes may worsen this problem. We performed computer simulations of an idealized Iberian Peninsula upwelling system to identify the main fine-scale processes driving dissolved oxygen variability as well as study the response of oxygen levels to changes in wind patterns and phytoplankton species. Our results suggest that oxygen levels would decrease if the wind blows for long periods of time or if phytoplankton is dominated by species that grow slowly.

South Atlantic Anomalyduring ascending and maximum phase of solar cycle 24

Mon, 05/18/2020 - 20:40
South Atlantic Anomalyduring ascending and maximum phase of solar cycle 24
Khairul Afifi Nasuddin, Mardina Abdullah, and Nurul Shazana Abdul Hamid
Nonlin. Processes Geophys. Discuss., https//doi.org/10.5194/npg-2020-15,2020
Preprint under review for NPG (discussion: open, 0 comments)
Research on South Atlantic Anomaly (SAA) is conducted during active and normal period in certain phase of solar cycle 24. The result reveal SAA region has a tendency to be persistent during both period compare to other regions during the phase studied. Other regions in the research experience a tendency to be persistent and antipersistent. Based on the observation, the Earth magnetic field strength and the year the solar cycle phase occur may have an influence on the characteristic of a region.

Hilbert problems for the geosciences in the 21st century – 20 years later

Mon, 05/11/2020 - 20:40
Hilbert problems for the geosciences in the 21st century – 20 years later
Michael Ghil
Nonlin. Processes Geophys. Discuss., https//doi.org/10.5194/npg-2020-13,2020
Preprint under review for NPG (discussion: open, 0 comments)
This review paper covers progress in the climate sciences in the past two decades, through the perspective of ten major problems for the geosciences in the 21st century. It concentrates on the last of these ten, Can we achieve enlightened climate control of our planet by the end of the century? Coupled climate-economy modeling is described as a main tool in achieving such control, while emphasizing the role of nonlinear, intrinsic variability and of the uncertainties in the two subsystems.

A methodology to obtain model-error covariances due to the discretization scheme from the parametric Kalman filter perspective

Fri, 05/08/2020 - 20:40
A methodology to obtain model-error covariances due to the discretization scheme from the parametric Kalman filter perspective
Olivier Pannekoucke, Richard Ménard, Mohammad El Aabaribaoune, and Matthieu Plu
Nonlin. Processes Geophys. Discuss., https//doi.org/10.5194/npg-2020-14,2020
Preprint under review for NPG (discussion: open, 1 comment)
Numerical weather prediction involves numerically solving the mathematical equations, which describe the geophysical flow, by transforming them so that they can be computed. Through this transformation, it appears that the equations actually solved by the machine are then a modified version of the original equations, introducing an error that contributes to the model error. This work helps to characterize the covariance of the model error that is due to this modification of the equations.

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

Mon, 04/27/2020 - 20:40
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., 27, 261–275, https://doi.org/10.5194/npg-27-261-2020, 2020

Seismic section image detail enhancement method based on bilateral texture filtering and adaptive enhancement of texture details

Fri, 04/24/2020 - 20:40
Seismic section image detail enhancement method based on bilateral texture filtering and adaptive enhancement of texture details
Xiang-Yu Jia and Chang-Lei DongYe
Nonlin. Processes Geophys., 27, 253–260, https://doi.org/10.5194/npg-27-253-2020, 2020
We proposed a texture detail enhancement method for seismic section image. Wavelet transform can effectively separate structure information and detail information of an image. High-frequency noise in structural information can be estimated and removed effectively by using bilateral texture filter in a low-frequency sub-band. In the high-frequency sub-band, adaptive enhancement transform can be used to enhance the image edge and texture information and effectively remove the low-frequency noise.

Vertical profiles of wind gust statistics from a regional reanalysis using multivariate extreme value theory

Thu, 04/23/2020 - 20:40
Vertical profiles of wind gust statistics from a regional reanalysis using multivariate extreme value theory
Julian Steinheuer and Petra Friederichs
Nonlin. Processes Geophys., 27, 239–252, https://doi.org/10.5194/npg-27-239-2020, 2020
Many applications require wind gust estimates at very different atmospheric altitudes, such as in the wind energy sector. However, numerical weather prediction models usually only derive estimates for gusts at 10 m above the land surface. We present a statistical model that gives the hourly peak wind speed. The model is trained based on a weather reanalysis and observations from the Hamburg Weather Mast. Reliable predictions are derived at up to 250 m, even at unobserved intermediate levels.

Brief communication: Residence time of energy in the atmosphere

Fri, 04/17/2020 - 20:40
Brief communication: Residence time of energy in the atmosphere
Carlos Osácar, Manuel Membrado, and Amalio Fernández-Pacheco
Nonlin. Processes Geophys., 27, 235–237, https://doi.org/10.5194/npg-27-235-2020, 2020
We deduce that after a global thermal perturbation, the Earth's atmosphere would need about a couple of months to come back to equilibrium.

Behavior of the iterative ensemble-based variational method in nonlinear problems

Fri, 04/17/2020 - 20:40
Behavior of the iterative ensemble-based variational method in nonlinear problems
Shin'ya Nakano
Nonlin. Processes Geophys. Discuss., https//doi.org/10.5194/npg-2020-9,2020
Preprint under review for NPG (discussion: open, 1 comment)
The ensemble-based variational method is a method to solve nonlinear data assimilation problem by using an ensemble of multiple simulation results. Although this method is derived based on a linear approximation, highly uncertain problems, where system nonlinearity is significant, can also be solved by applying this method iteratively. This paper reformulated this iterative algorithm to closely analyze its behavior, and clarified the conditions for monotonic convergence in nonlinear context.

Simulating model uncertainty of subgrid-scale processes by sampling model errors at convective scales

Thu, 04/16/2020 - 20:40
Simulating model uncertainty of subgrid-scale processes by sampling model errors at convective scales
Michiel Van Ginderachter, Daan Degrauwe, Stéphane Vannitsem, and Piet Termonia
Nonlin. Processes Geophys., 27, 187–207, https://doi.org/10.5194/npg-27-187-2020, 2020
A generic methodology is developed to estimate the model error and simulate the model uncertainty related to a specific physical process. The method estimates the model error by comparing two different representations of the physical process in otherwise identical models. The found model error can then be used to perturb the model and simulate the model uncertainty. When applying this methodology to deep convection an improvement in the probabilistic skill of the ensemble forecast is found.

Data-driven versus self-similar parameterizations for stochastic advection by Lie transport and location uncertainty

Thu, 04/16/2020 - 20:40
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., 27, 209–234, https://doi.org/10.5194/npg-27-209-2020, 2020
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.

Study of the fractality in a magnetohydrodynamic shell model forced by solar wind fluctuations

Wed, 04/08/2020 - 20:40
Study of the fractality in a magnetohydrodynamic shell model forced by solar wind fluctuations
Macarena Domínguez, Giuseppina Nigro, Víctor Muñoz, Vincenzo Carbone, and Mario Riquelme
Nonlin. Processes Geophys., 27, 175–185, https://doi.org/10.5194/npg-27-175-2020, 2020
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 fluctuation 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.

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

Fri, 04/03/2020 - 20:40
Baroclinic and barotropic instabilities in planetary atmospheres: energetics, equilibration and adjustment
Peter Read, Daniel Kennedy, Neil Lewis, Hélène Scolan, Fachreddin Tabataba-Vakili, Yixiong Wang, Susie Wright, and Roland Young
Nonlin. Processes Geophys., 27, 147–173, https://doi.org/10.5194/npg-27-147-2020, 2020
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 Earth and other planets. Linear and nonlinear instability theories provide insights into when such instabilities may occur, grow to a 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.

Application of Gamma functions to the determination of unit hydrographs

Wed, 04/01/2020 - 20:40
Application of Gamma functions to the determination of unit hydrographs
Hongyan Li and Yangzong Cidan
Nonlin. Processes Geophys. Discuss., https//doi.org/10.5194/npg-2020-1,2020
Preprint under review for NPG (discussion: open, 1 comment)
Based on the theory of composition, a hydrological system was viewed as a generalized collection and Gamma functions were used to simulate the basin convergence process. At the same time, the Gamma function is parameterized and the parameters of Gamma function are optimized by genetic algorithm,before deriving the unit hydrograph. The Collins iteration method was used to compute the unit hydrograph. This method is more precise and illustrate the law of runoff.

Applications of matrix factorization methods to climate data

Wed, 03/25/2020 - 21:40
Applications of matrix factorization methods to climate data
Dylan Harries and Terence J. O'Kane
Nonlin. Processes Geophys. Discuss., https//doi.org/10.5194/npg-2020-7,2020
Preprint under review for NPG (discussion: open, 0 comments)
Different dimension reduction methods may produce profoundly different low-dimensional representations of multiscale systems. We perform a set of case-studies to investigate these differences. When a clear scale separation is present, similar bases are obtained using all methods, but when this is not the case some methods may produce representations that are poorly suited for describing features of interest, highlighting the importance of a careful choice of method when designing analyses.

Approximate multifractal correlation and products of universal multifractal fields, with application to rainfall data

Thu, 03/19/2020 - 21:40
Approximate multifractal correlation and products of universal multifractal fields, with application to rainfall data
Auguste Gires, Ioulia Tchiguirinskaia, and Daniel Schertzer
Nonlin. Processes Geophys., 27, 133–145, https://doi.org/10.5194/npg-27-133-2020, 2020
This paper aims to analyse and simulate correlations between two fields in a scale-invariant framework. It starts by theoretically assessing and numerically confirming the behaviour of renormalized multiplicative power law combinations of two fields with known scale-invariant properties. Then a new indicator of correlation is suggested and tested on rainfall data to study the correlation between the common rain rate and drop size distribution features.

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