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  • Articles  (48)
  • English  (48)
  • 2020-2024  (48)
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  • English  (48)
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  • 1
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    Detecting electrostatic activity of oxygen ions in the topside ionosphere using electric field measurements in the VLF band (2023)
    In:  XXVIII General Assembly of the International Union of Geodesy and Geophysics (IUGG)
    Details
    Publication Date: 2023-06-14
    Description: We investigate the spectral properties of the ionospheric electric field during a period of high geomagnetic activity, namely on August 11 2018 from 21:40 to 22:17. The purpose is to detect possible signatures of the characteristic frequencies of the ions populating the ionosphere. In particular, we exploit measurements taken in the VLF band by the Electric Field Detector (EFD) onboard the Chinese Seismo-Electromagnetic Satellite - 01 (CSES-01) spacecraft, orbiting at around 500km of altitude in a sun-synchronous orbit. In the temporal interval considered, a clear peak in the frequencies between 2.5 kHz and 5 kHz, with a well defined latitudinal pattern, is observed in the power spectral density of the electric field at equatorial latitudes between two density drops, consistent with the presence of two plasma bubbles. Such a pattern perfectly matches the latitudinal pattern of the O+ plasma frequency as calculated by density measurements taken concurrently by another CSES-01 payload, the Plasma Analyzer Package (PAP) suite. We discuss possible interpretations of the presence of this signature in terms of O+ electrostatic perturbations generated by the ionospheric dynamics during geomagnetically active periods.
    Language: English
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  • 2
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    Ambient noise tomography of El Hierro island (Canary Islands) (2023)
    In:  XXVIII General Assembly of the International Union of Geodesy and Geophysics (IUGG)
    Details
    Publication Date: 2023-05-22
    Description: To better understand the shallow structure of El Hierro island, we determined a 3D S-wave velocity model using Ambient Noise Tomography (ANT). We exploited a dataset recorded by 21 broadband seismic stations deployed at El Hierro island in two surveys realized in 2015 and 2021. This dataset allowed us to obtain empirical Green’s functions by cross-correlating seismic ambient noise signals and retrieving 105 dispersion curves using the frequency-time analysis (FTAN). Then we obtained 2-D Rayleigh wave group velocity maps for periods between 0.6 s and 2.6 s through a non-linear multiscale inversion (Cabrera-Pérez et al, 2021). Finally, we performed depth inversion through a Bayesian transdimensional approach to obtain a 3-D S-wave velocity model. The obtained ANT model is merged with a local earthquake tomography model (García-Yeguas et al, 2014). Our study highlights six relevant seismic velocity anomalies. We observed the presence of three high-velocity zones located in the eastern, western and northern parts of the island, which could be related to intrusive bodies possibly associated with the formation of El Hierro island. We also observed three low-velocity anomalies in the northern and southern parts. The anomaly in the North of the island could be related to loose deposits generated by the El Golfo valley megalandslide. The anomalies in the South could be related to porous and highly fractured materials produced during the more recent volcanic episodes.
    Language: English
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  • 3
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    Can Plate Bending Explain the Observed Faster Landward Motion of Lateral Regions of the Subduction Zone After Major Megathrust Earthquakes? (2023)
    In:  Journal of Geophysical Research: Solid Earth
    Details
    Publication Date: 2023-05-22
    Description: Greater landward velocities were recorded after six megathrust earthquakes in subduction zone regions adjacent to the ruptured portion. Previous explanations invoked either increased slip deficit accumulation or plate bending during postseismic relaxation, with different implications for seismic hazard. We investigate whether bending can be expected to reproduce this observed enhanced landward motion (ELM). We use 3D quasi-dynamic finite element models with periodic earthquakes. We find that afterslip downdip of the brittle megathrust exclusively produces enhanced trenchward surface motion in the overriding plate. Viscous relaxation produces ELM when a depth limit is imposed on afterslip. This landward motion results primarily from in-plane elastic bending of the overriding plate due to trenchward viscous flow in the mantle wedge near the rupture. Modeled ELM is, however, incompatible with the observations, which are an order of magnitude greater and last longer after the earthquake. This conclusion does not significantly change when varying mantle viscosity, plate elasticity, maximum afterslip depth, earthquake size, megathrust locking outside of the rupture, or nature and location of relevant model boundaries. The observed ELM consequently appears to reflect faster slip deficit accumulation, implying a greater seismic hazard in lateral segments of the subduction zone.
    Language: English
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  • 4
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    Tropical precipitation response to stratospheric volcanic forcing: A large ensemble approach (2023)
    In:  XXVIII General Assembly of the International Union of Geodesy and Geophysics (IUGG)
    Details
    Publication Date: 2023-05-19
    Description: Sufficient large-ensemble simulations with the same model and radiative forcing scenario but varying initial conditions have become a great tool in recent years to disentangle forced and internal variability. Here we use 100-member ensembles of the MPI-ESM-LR for idealized volcanic eruptions of different eruption strength and latitude to investigate whether there is a linear volcanic signal on tropical precipitation dependent on the eruption strength, and when does it emerge from tropical internal variability. Our results show that for idealized tropical eruptions global and large hemispheric mean precipitation anomalies seemed to be scalable with the sulfur emission strength in a certain size range. An emission of 10 Tg sulfur seems to be a threshold where the volcanic signal is discernible from internal variability. We find that seasonal and ensemble mean pattern correlation of precipitation anomalies are highly correlated, in particular for larger emission strengths in the tropics and strongly modulated by ENSO with an increasing tendency for a warm ENSO increase with eruption strength. While the emergence of cooling appears on a hemispheric scale, the precipitation response is more localized and mainly confined to the tropics and subtropics. In line with previous findings our modelling results suggesting that large NH extratropical volcanic eruptions migrate the ITCZ to the south, whereas SH extratropical eruptions move the ITCZ to the north. Large regional differences depend on how the local Hadley circulation responds to the volcanic forcing.
    Language: English
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  • 5
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    A global overview on the application of urban seismic networks (2023)
    In:  XXVIII General Assembly of the International Union of Geodesy and Geophysics (IUGG)
    Details
    Publication Date: 2023-06-20
    Description: Local-scale seismic networks within urbanized areas have been usually employed for short-living seismological experiments or studies. However the possibility, to install permanent (or long-term) earthquake monitoring networks within urban contexts began in the mid '90s.If, from one hand, this possibility was certainly boosted by the support coming from technological developments (digital devices for acquisition and transmission), from the other, the necessity was also driven by the recent global expansion of many urban centers into large metropolitan areas. Also the awareness of the seismic risk in urban center resulted in the increasing interest in the monitoring these areas, with particular focus the most exposed or the most vulnerable ones. Earthquake monitoring networks especially designed may reveal important tools for several tasks related to the seismic phenomena: from earthquake warnings, to emergency operational tasks during emergencies, or scientific studies. In this paper we refer to such earthquake networks as "Urban Seismic Networks" (USN).Because of the increasing resorting USNs for several applications, we consider useful to provide a comprehensive view of the state-of-the-art of the use of USNs, looking at their global distribution and objectives but, most of all, at their design and at their technical characteristics. We retrieved information about 71 USNs worldwide. The USN objectives, as well the other characteristics, have been classified into prearranged groups in order to provide to easily synthesize the various features of the USNs. This review will represent a reference and a guideline for future implementation of USNs.
    Language: English
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  • 6
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    New insights into solar wind origins and dynamics involving observations by the Solar Wind Analyser investigation on Solar Orbiter (2023)
    In:  XXVIII General Assembly of the International Union of Geodesy and Geophysics (IUGG)
    Details
    Publication Date: 2023-07-25
    Description: Solar Orbiter was launched in February 2020, and has now completed the first 3 perihelia of its nominal mission phase. Mission science goals include establishing and understanding the links between processes occurring at the Sun and their consequences for the nature of the inner heliosphere and solar wind, as well as furthering our knowledge of the physics of the solar wind and the solar atmosphere themselves. A significant volume of science data has been accumulated by the 10 payload instruments, including novel data recorded by the 3 separate sensors which, together with a central DPU, comprise the Solar Wind Analyser (SWA) suite. Between them, these sensors, the Electron Analyser System, the Proton-Alpha Sensor and the Heavy Ion Sensor, make measurements of 3D velocity distribution functions of solar wind electron, proton and alpha particle populations, together with abundant heavy ions such as O6+ and ion charge states such as Fe9+ or Fe10+. In this presentation we summarise recent key results of studies using data from one or more of the 3 SWA sensors, and illustrate the quality of the data and their contribution to achieving the mission science goals. These include the availability of high time cadence observations which offer unique possibilities for resolving plasma kinetic processes at small scales in the solar wind. Combining with observations from other instruments on the platform, and from other missions, we also report on work to establish the origin of the solar wind stream passing the spacecraft and the physical processes driving its release.
    Language: English
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  • 7
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    Investigating the fresh-water inflow through the eastern gate in the Ross Sea (2023)
    In:  XXVIII General Assembly of the International Union of Geodesy and Geophysics (IUGG)
    Details
    Publication Date: 2023-07-25
    Description: The production of Antarctic Bottom Water (AABW) is a crucial factor in determining the strength of the Meridional Overturning Circulation, and therefore plays a significant role in the ocean's contribution to the global climate. AABW is primarily formed in the Ross and Weddell Seas, with unique thermohaline characteristics. In recent years, a negative decadal salinity trend has been observed in the Southern Ocean's Pacific sector, related to AABW modification. Correspondingly in the Ross Sea, observations have indicated changes in the thermohaline characteristics of the shelf waters, precursors of the AABW, since 1995. The significant freshening in the western Ross Sea, where AABW is formed and spreads to fill the Pacific Ocean's deep basins, was attributed to the inflow of waters from West Antarctica where a dramatic melting of glaciers is occurring. To determine the freshwater inflow from West Antarctica and the role of these waters in the salinity field variability, a dedicated oceanographic cruise was carried out during austral summer 2020 in the eastern sector of the Ross Sea. Additionally, a section of the same CTD grid was repeated during January 2021. Using physical data from the CTD and LADCP casts, glider deployment and drifters, we estimated water mass characteristics and dynamical features. Eventually, discrete sea water sampling for chemical analyses (nutrients, carbonate system, trace metals, persistent organic compounds) has been carried out to provide new information about the biogeochemistry of the area and origin of the water masses.
    Language: English
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  • 8
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    Plasma bubbles in the top side ionosphere: From automatic detection to possible sources (2023)
    In:  XXVIII General Assembly of the International Union of Geodesy and Geophysics (IUGG)
    Details
    Publication Date: 2023-07-25
    Description: Equatorial Plasma Bubbles (EPBs) are plasma density depletions observed in the equatorial ionosphere at different spatial and temporal scales. Typically, they occur within a narrow band of ±20° latitude, at altitudes between the bottom side of the ionospheric F region and up to ~1000 km. Generically, they appear at local dusk where the pre-reversal enhancement of the eastward electric field can elevate the F layer to higher altitudes, thereby increasing the Rayleigh–Taylor instability growth rate. However, EPBs are also observed during geomagnetic storms when the Prompt Penetration Electric Fields (PPEFs) of magnetospheric origin and/or the ionospheric disturbance dynamo can generate electric field perturbations, which can either suppress or favour the development of such irregularities. Here, we present a new algorithm able to automatically detect EPBs, based on the in-situ electron density (Ne) observations by Langmuir Probes (LPs) on-board the first China Seismo-Electromagnetic Satellite (CSES-01). CSES-01 is a sun-synchronous satellite flying with an orbital inclination of 97.4°, at an altitude of ~500 km, and with descending and ascending nodes at ~14:00 local time (LT) and ~02:00 LT, respectively. A statistical comparison between the main characteristics of the EPBs observed by CSES-01 and Swarm B in the time frame from 2019 to 2021 will be also presented. In addition, in order to investigate the possible sources of EPBs, we will show the analysis of the relative solar wind parameters.
    Language: English
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  • 9
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    Influence of the atlantic meridional overturning circulation on future climate change impacts (2023)
    In:  XXVIII General Assembly of the International Union of Geodesy and Geophysics (IUGG)
    Details
    Publication Date: 2023-07-25
    Description: In climate model simulations of future climate change, the Atlantic Meridional Overturning Circulation (AMOC) is projected to decline. However, the impacts of this decline, relative to other changes, remain to be identified. Here we address this problem by analyzing 30 idealized abrupt-4xCO2 climate model simulations. We find that in models with larger AMOC decline, there is a minimum warming in the North Atlantic, a southward displacement of the Inter-tropical Convergence Zone, and a poleward shift of the mid-latitude jet. The changes in the models with smaller AMOC decline are drastically different: there is a relatively larger warming in the North Atlantic, the precipitation response exhibits a wet-get-wetter, dry-get- drier pattern, and there are smaller displacements of the mid-latitude jet. We further investigate the impacts of a weakened AMOC in ad-hoc model experiments using EC-Earth3, a state-of-the-art climate model participating in CMIP6. We compare two model experiments forced with abrupt-4xCO2: one in which the AMOC weakens, and another one in which we artificially force the AMOC to stay at the same strength as in the preindustrial control simulation. With these experiments we are able to further investigate mechanisms of AMOC induced climate change impacts, using a moisture budget framework and assessing daily impacts on weather regimes. Overall, our work indicates that the AMOC is a major source of inter-model uncertainty, and continued observational efforts are needed to constrain the impacts of an AMOC decline in future climate change.
    Language: English
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  • 10
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    Q-coda from ambient noise cross-correlation: A new volcano monitoring technique? (2023)
    In:  XXVIII General Assembly of the International Union of Geodesy and Geophysics (IUGG)
    Details
    Publication Date: 2023-07-25
    Description: Time-lapse monitoring of seismic velocity at a volcanic area can provide important information about the dynamics of the volcanic system and its temporal variability. One standard technique to monitor small changes in the medium is ambient noise interferometry. This technique is based on quantifying relative velocity variations (dv/v) by measuring changes in the ambient noise cross-correlation signal phase. In this study, we demonstrate that together with velocity variations, the study of changes in seismic attenuation (Qc) extracted from ambient noise cross-correlation could be relevant for volcano monitoring. The Qc is determined using the lapse-time dependence method (Calvet and Margerin, 2013), in which, Qc is measured as a function of the coda window length for different onsets of the ambient-noise cross-correlation coda. We apply this technique to the 2021 Cumbre Vieja eruption in La Palma (Canary Islands), which started on Sept. 19th and had a significant social and scientific impact. First, we determine a reference Qc model of the Cumbre Vieja volcano using data from Aug. 1st to 31st, 2021. Then, we analyze the spatio-temporal Qc variations during the nineteen days preceding the eruption, and we compare our results with previously obtained dv/v results. We observe an increase of Qc during the pre-eruptive phase, corresponding to a dv/v decrease. We hypothesize that the observed correlated Qc increase and dv/v drop could be explained by the ascent of hydrothermal fluids towards the surface before the eruption.
    Language: English
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