Olivier De Viron

La Rochelle Université · LIttoral ENvironnement et Sociétés (LIENSs)

The motions of the liquid within the Earth's outer core lead to magnetic field variations together with mass distribution changes. As the core is not accessible for direct observation, our knowledge of the Earth’s liquid core dynamics only relies on indirect information sources. Mainly generated by the core dynamics, the surface geomagnetic field p...

The motions of the liquid within the Earth's outer core lead to magnetic field variations together with mass distribution changes. As the core is not accessible to direct observation, our knowledge of the Earth’s liquid core dynamics only relies on indirect information sources. Mainly generated by the core dynamics, the surface geomagnetic field pr...

Plain Language Summary The coastal science community currently lacks insights into the morphological evolution of sandy beaches, including rapid changes that occur during storms. This is, to a large extent, explained by the difficulty to monitor the seabed elevation under such conditions in a region of the nearshore where high‐energy waves break. I...

Remote-sensing technology, combined with depth-inversion algorithms, presents a promising opportunity to quantify the morphological evolution of sandy beaches during storms. Current depth-inversion algorithms such as cBathy rely on the linear wave dispersion relation to invert depth from remotely-sensed dispersion properties. In the surf zone, howe...

This study provides a quantitative approach to search for mantle plumes in global seismic tomography models without any preconceived notions about the associated mantle velocity anomalies, other than the assumption that the plumes are not significantly deflected horizontally by more than 6○, anywhere in the mantle. We design identification tests wi...

Accurately mapping the evolving bathymetry under energetic wave breaking is challenging, yet critical for improving our understanding of sandy beach morphodynamics. Though remote sensing is one of the most promising opportunities for reaching this goal, existing depth-inversion algorithms using linear approaches face major theoretical and/or techni...

Understanding and modelling the properties of the stochastic variations in geodetic time series is crucial to obtain realistic uncertainties for deterministic parameters, e.g., long-term velocities, and helpful in characterizing non-modelled processes. With the increasing span of geodetic time series, it is expected that additional observations wou...

Understanding and modelling the properties of the stochastic variability -- often referred to as noise -- in geodetic time series is crucial to obtain realistic uncertainties for deterministic parameters, e.g., long-term velocities, and helpful in characterizing non-modelled processes. With the ever-increasing span of geodetic time series, it is ex...

We investigate the potential of causal inference methods (CIMs) to reveal hydrological connections from time series. Four CIMs are selected from two criteria, linear or nonlinear and bivariate or multivariate. A priori, multivariate, and nonlinear CIMs are best suited for revealing hydrological connections because they fit nonlinear processes and d...

Extreme events will become more common due to global change, requiring enhanced monitoring and pushing conventional observation networks to their limits. This encourages us to combine all the possible sources of information to obtain a complete picture of extreme events and their evolution. This commentary builds on an example of the July 2021 cata...

We decompose the monthly global ocean bottom pressure (OBP) from GRACE(-FO) mass concentration solutions, with trends and seasonal harmonics removed from the signal, to extract 23 significant regional modes of variability. The 23 modes are analyzed and discussed considering sea-level anomalies (SLA), wind stress curl (WSC), and major climate indice...

We decompose the monthly global Ocean Bottom Pressure (OBP) from GRACE(-FO) mass concentration solutions, with trends and seasonal harmonics removed from the signal, to extract 23 significant regional modes of variability. The 23 modes are analyzed and discussed considering Sea-Level Anomalies (SLA), Wind Stress Curl (WSC), and major climate indice...

Monitoring vertical land motions (VLMs) at the level of 0.1 mm/yr remains one of the most challenging scientific applications of global navigation satellite systems (GNSS). Such small rates of change can result from climatic and tectonic phenomena, and their detection is important to many solid Earth‐related studies, including the prediction of coa...

We investigate the potential of causal inference methods (CIMs) to reveal hydrological connections from time-series. Four CIMs are selected from two criteria, linear or nonlinear, and bivariate or multivariate. A priori, multivariate and nonlinear CIMs are best suited for revealing hydrological connections because they suit nonlinear processes and...

Global seismic tomography has greatly progressed in the past decades, with many global Earth models being produced by different research groups. Objective, statistical methods are crucial for the quantitative interpretation of the large amount of information encapsulated by the models and for unbiased model comparisons. Here we propose using a rota...

Strong large-scale winds can relay their energy to the ocean bottom and elicit an almost immediate intraseasonal barotropic (depth independent) response in the ocean. The intense winds associated with the Madden-Julian Oscillation over the Maritime Continent generate significant intraseasonal basin-wide barotropic sea level variability in the tropi...

Over the past two decades, numerous studies demonstrated that the stochastic variability in GNSS position time series – often referred to as noise – is both temporally and spatially correlated. The time correlation of this stochastic variability can be well approximated by a linear combination of white noise and power-law stochastic processes with...

Global seismic tomography has greatly progressed in the past decades, with many global Earth models being produced by different research groups. Objective, statistical methods are crucial for the quantitative interpretation of the large amount of information encapsulated by the models as well as for unbiased model comparisons. We propose here to us...

Strong large-scale winds can relay their energy to the ocean bottom and elicit an almost immediate intraseasonal barotropic (depth independent) response in the ocean. The intense winds associated with the Madden-Julian Oscillation (MJO), over the tropical interface between the Indian Ocean and the Pacific Ocean (popularly known as Maritime Continen...

This study presents unpublished field observations of infragravity waves, collected at the dissipative beach of Saint‐Trojan (Oléron Island, France) during the storm Kurt (3 February 2017), characterized by incident short waves of significant heights reaching 9.5 m and peak periods reaching 22 s. Data analysis reveals the development of exceptional...

This study proposes a method for the cross calibration of tide gauges. Based on the combination of at least three collocated sea level time series, it takes advantage of the least squares variance component estimation (LS-VCE) method to assess both sea level biases and uncertainties in real conditions. The method was applied to a multi-instrument e...

Coastal populations are impacted by relative sea level variations, which consist both of absolute sea level variations and of vertical land motions. This paper focuses on the Southwest and Central Pacific region, a recognized vulnerable region to sea level rise and where a large range of vertical land motion dynamics is observed. We analyse vertica...

Unlike the other lakes, the Caspian Sea has regular water level fluctuations caused by variation in temperature and salinity, which is known as thermohaline fluctuations. Vertically variable temperature and salinity data are needed in order to monitor thermohaline fluctuations. These data are regularly recorded for the open seas by remote sensing a...

On Friday November 16, 2018, the kilogram will join its fellow metric units with a definition based on fundamental physical constants, but these units maintain links to their roots in the geosciences.

This article investigated the principal reason for water circulations in the Caspian Sea. Unlike other inland water bodies, and similar to the open seas, the Caspian Sea shows regular water circulations which are not explained by the wind. The Steric contribution of water level fluctuations was studied in this article by two approaches: one from re...

Studies about sea level change at the coast require high quality sea level time series. The main source of sea level measurements is presently provided by digital coastal tide gauges. Calibration campaigns are regularly carried out to ensure their precisions & accuracies. Several types of sea level sensors exist – tide pole, probe, radar tide gauge...

El Niño–Southern Oscillation (ENSO) events are classically associated with a significant increase in the length of day (LOD), with positive mountain torques arising from an east–west pressure dipole in the Pacific driving a rise of atmospheric angular momentum (AAM) and consequent slowing of the Earth's rotation. The large 1982–1983 event produced...

A recent article in Reviews of Geophysics examined terrestrial techniques for measuring changes in gravity over time and their application to the geosciences.

In a context of global change and increasing anthropic pressure on the environment, monitoring the Earth system and its evolution has become one of the key missions of geosciences. Geodesy is the geoscience that measures the geometric shape of the Earth, its orientation in space, and gravity field.Time-variable gravity, because of its high accuracy...

El Niño/Southern Oscillation (ENSO) events are classically associated with a significant increase in the length of day (LOD), with positive mountain torques arising from an east-west pressure dipole in the Pacific driving a rise of atmospheric angular momentum (AAM) and consequent slowing of the Earth's rotation. The large 1982–83 event produced a...

Evapotranspiration (ET) controls the flux between the land surface and the atmosphere. Assessing the ET ecosystems remains a key challenge in hydrology. We have found that the ET water mass loss can be directly inferred from continuous gravity measurements: as water evaporates and transpires from terrestrial ecosystems, the mass distribution of wat...

How and why does gravity vary? Why do we measure it? How do we measure gravity?

We estimate the signature of the climate-induced mass transfers in repeated absolute gravity measurements based on satellite gravimetric measurements from the GRACE mission. We show results at the globe scale, and compare them with repeated absolute gravity (AG) time behavior in three zones where AG surveys have been published: Northwestern Europe,...

Source separation is a key issue of gravimetric data interpretation because contributions from many sources such as crutal signal, mantle mass distribution,… are mixed together in every dataset. If one wants to use geoid data in order to infer information about one of the source, it requires to be able to isolate the relevant contribution. Ideally...

Testing different methods of interferometry in order to measure seasonal and inter-annual land deformations due to water loading.

This paper reports on different sources of errors that occur in the calibration process of a superconducting gravimeter (SG), determined by comparison with a ballistic absolute gravimeter (AG); some of them have never been discussed in the literature. We then provide methods to mitigate the impact of those errors, to achieve a robust calibration es...

From space gravity and station position data over southern Europe from 2002 to 2010, this study investigates the interannual mass redistributions using principal component analysis. The dominant mode, which appears both in gravity and positioning, results from the North Atlantic Oscillation (NAO). This analysis allows us to isolate and characterize...

The very coarse network of SG stations does not allow sampling enough the regional scale so that anything can really be learned out of the SG that can be useful for GRACE study. There are no reasons why they should look alike, and, actually, they do not: nothing is strange about that result. We deeply regret that the comment by Crossley et al. (201...

Moderate-Resolution Imaging Spectroradiometer (MODIS) optical and infrared data are used to monitor changes in the Caspian Sea coastline. The information extracted from MODIS images is converted into total water volume and mean lake level by combining a digital elevation model (DEM) with remote-sensing data. The elevation estimates were enhanced by...

At the interannual to decadal timescale, the changes in the Earth rotation rate are linked with the El-Niño Southern Oscillation phenomena through changes in the Atmospheric Angular Momentum. As climatic studies demonstrate that there were two types of El-Niño events, namely Eastern Pacific (EP) and Central Pacific (CP) events, we investigate how e...

[The definitive version is available at www.blackwell-synergy.com, http://dx.doi.org/10.1093/gji/ggt524] Recent studies show that terrestrial and space based observations of gravity agree over Europe. In this paper, we compare time series of terrestrial gravity (including the contribution due to surface displacement) as measured by superconducting...

Comparative analysis of coseismic and postseismic variations of the Earth’s gravity field is carried for the regions of three giant earthquakes (Andaman-Sumatra, December 26, 2004, magnitude M w = 9.1; Maule-Chile, February 27, 2010, M w = 8.8, and Tohoku-Oki, March 11, 2011, M w = 9.0) with the use of GRACE satellite data. Within the resolution of...

This paper investigates the precision of the estimation of geophysical fluid load deformation computed from GRACE space gravity, GPS vertical displacement and geophysical fluids models [Global Circulation Models (GCMs) for ocean, atmosphere and hydrology], using the three-cornered hat method. This method allows the estimation of the variance of the...

Geodetic measurements above subduction zones have revealed a range of transient deformations. The mechanism by which slow slips occur remains uncertain. In particular, does surface deformation represents the integrated deformation from a large number of discrete seismic slip events? Moreover, little is known about displacements of materials having...

The level of the Victoria Lake is analysed using space gravity and altimetry data, together with the output of the large-scale land LaD water model. The good agreement between the space gravity and altimetry proves the robustness of the results. Comparing these geodetic observations with the LaD land water model allows one to better estimate the re...

Variations in Earth's rotation (defined in terms of length of day) arise from external tidal torques, or from an exchange of angular momentum between the solid Earth and its fluid components. On short timescales (annual or shorter) the non-tidal component is dominated by the atmosphere, with small contributions from the ocean and hydrological syste...

We propose a method to evaluate the stress generated at the local scale by the spatial variations of the Gravitational Potential Energy (GPE), which is related to inhomogeneous topography and mass distribution in the lithosphere. We show that it is possible to infer these local stress sources from the second spatial derivatives of a geoid height gr...

The atmosphere, hydrosphere, and cryosphere form a fully coupled climate system. This system exhibits a number of large‒scale phenomena, such as the El Niño-Southern Oscillation, the Asian Monsoon, the North Atlantic Oscillation, and the Madden‒Julian Oscillation. While these modes of variability are not exactly periodic, they are oscillatory in ch...

This paper evaluates different data-processing methods to determine the gravity rate of change, using repeated absolute gravimeter (AG) measurements and continuous monitoring by a superconducting gravimeter (SG). Based on synthetic data representative of signals observed by SGs at various station locations, we demonstrate that the addition of SG in...

Measuring ground deformation underwater is essential for understanding Earth processes at many scales. One important example is subduction zones, which can generate devastating earthquakes and tsunamis, and where the most important deformation signal related to plate locking is usually offshore. We present an improved method for making offshore ver...

To understand the dynamics of the Earth’s fluid, iron-rich outer core, only indirect observations are available. The Earth’s magnetic field, originating mainly within the core, and its temporal variations can be used to infer the fluid motion at the top of the core, on a decadal and subdecadal time-scale. Gravity variations resulting from changes i...

At seasonal and shorter periods the solid Earth and its overlying geophysical fluids form a closed dynamical system, which (except for the effect of tides) conserves its total angular momentum. While atmospheric effects dominate changes in the Earth's rate of rotation and hence length-of-day (LOD) on these time scales, the addition of oceanic angul...

Over the last decade high-resolution, high-accuracy gravity and magnetic satellite data have been obtained from GRACE and Ørsted and CHAMP satellite missions, respectively. On one hand the gravity field, and on the other hand the core magnetic field, its secular variation and acceleration are now better than ever described. Dedicated gravity models...

Previous experiments on ground gravity gradiometry data have demonstrated that it was possible to significantly lower the noise in the gradients, using physical relationships between pairs of those components in addition to the traditional Laplace equation. We present here the extension of the method to GOCE gravity gradient data. In comparison wit...

At seasonal and shorter periods the solid Earth and its overlying geophysical fluids form a closed dynamical system, which (except for tidal forcing) conserves its total angular momentum. While atmospheric effects dominate changes in the Earth's rate of rotation and hence length-of-day (LOD) on these time scales, the addition of oceanic angular mom...

The monitoring of the global change, which have consequences on the climate system dynamics, has become a major challenge nowadays. The major climate parameters impact the gravity field and the shape of the Earth. These geodetic parameters are being continuously monitored by several techniques, such as the GRACE mission (Gravity Recovery and Climat...

At seasonal and shorter periods the solid Earth and its overlying atmosphere and ocean form a closed dynamical system, which (except for the effect of tides) conserves its total angular momentum. While atmospheric effects dominate changes in the Earth's rate of rotation and hence length-of-day (LOD) on these time scales, the addition of oceanic ang...

For nearly 10 years, GRACE has been orbiting the Earth, providing unprecedented information about the mass transfer in the Earth system. In particular, GRACE is very sensitive to the water mass distribution, in relation to the large climate modes. We investigate the largescale exchange in the climate system, and emphasize a few important modes asso...

The GRACE satellite has been monitoring the change in the mass distribution at the Earth surface for nearly 10 years. This becomes enough to study long-term mass change, and to separate interannual variations from trends. Up to now, many studies have shown a fast (and non-linear) loss of mass in many glaciers and ice sheets. They all have been attr...

Most often, vertical ground movements are at the limit of the noise level and close to or below the accuracy of current geodetic techniques. Absolute gravity measurements are valuable to quantify slow vertical movements, as this instrument is drift free and, unlike GPS, independent of the terrestrial reference frame. On the other hand, for logistic...

An absolute gravimeter allows us to determine the local value of gravity, which makes its accuracy assessment challenging. The instrumental offsets are classically estimated by performing comparisons of the results obtained by a set of instruments measuring at the same location but at different epochs (measuring at the same place and epoch is physi...

In continental plate interiors, ground surface movements are at the limit of the noise level and close to or below the accuracy of current geodetic techniques. Absolute gravity measurements are valuable to quantify slow vertical movements, as this instrument is drift free and, unlike GPS, independent of the terrestrial reference frame. Repeated abs...

Atmospheric angular momentum variations of a planet are associated with the global atmospheric mass redistribution and the wind variability. The exchange of angular momentum between the fluid layers and the solid planet is the main cause for the variations of the planetary rotation at seasonal time scales. In the present study, we investigate the a...

The geoid low over French Polynesia has been previously interpreted as the signature of an upper mantle upwelling associated with a low-viscosity zone located immediately below the lithosphere. We propose here an alternative explanation using new high-quality satellite gravity data and fluid mechanics constraints. We thus discuss the origin of the...

We propose a new estimation of the atmospheric contributions to Earth's nutations based on three reanalyses of atmospheric global circulation models (GCM), namely the two reanalyses of the National Center for Environmental Prediction (NCEP) and the ERA-40 reanalysis of the European Center for Medium-Ra